Publication list with abstracts

Published Journal Articles

57. “Impact of anharmonicity on the vibrational entropy and specific heat of UO₂”, M.S. Bryan, J.W.L. Pang, B.C. Larson, A. Chernatynskiy, D.L. Abernathy, K. Gofryk, and M.E. Manley, Phys. Rev. Materials 3, 065405 (2019). doi:10.1103/PhysRevMaterials.3.065405

• Abstract: The impact of anharmonicity on the vibrational entropy and heat capacity of UO₂ has been investigated from 10 to 1200 K using inelastic neutron-scattering measurements of the phonon density of states (PDOS). Small changes in the PDOS are observed from 10 to 295 K, with more noticeable changes appearing in the 750- and 1200-K data. The specific heat determined from the PDOS measurements is in agreement with macroscopic specific heat measurements, and the overall impact of nondilation anharmonicity on the specific heat has been shown to be less than 2%. An analysis of the phonon measurements shows that the softening of acoustic phonons with temperature is consistent with the quasiharmonic approximation. The optical phonons deviate from the quasiharmonic prediction, with the low-energy optical phonons between approximately 20 and 50 meV softening more than expected, while the higher-energy optical phonons between approximately 50 and 80 meV have no appreciable softening over the temperature range measured. The observation of a small anharmonic specific heat contribution has been shown to be the result of relatively large energy-dependent anharmonic effects which have opposite sign, leading to a total contribution near zero.

56. “Energetics and kinetics of metal impurities in the low-temperature ordered phase of V₂C from first-principles calculations”, B.J. Demaske, A. Chernatynskiy and S.R. Phillpot, J. Nucl. Mat. 513, 185 (2019). doi: 10.1016/j.jnucmat.2018.11.007

• Abstract: The site preference of Fe, Ni, Ce, Nd and U impurities and their migration behaviors in the low-temperature ordered orthorhombic phase of V₂C are calculated using density functional theory. It is found that all impurities prefer the substitutional vanadium site over the octahedral interstitial site. The energy required to incorporate an impurity into the lattice increases with increasing impurity size. Binding between an impurity at the substitutional vanadium site and a neighboring vanadium vacancy is shown to be much stronger for large impurities, U, Ce and Nd, than for small impurities, Fe and Ni. The strong binding can be attributed to the openness of the V2C structure, which allows large impurity atoms to relax by shifting towards neighboring empty octahedral sites. The proximity of each impurity-vacancy pair to nearby carbon interstitial atoms leads to a high degree of anisotropy in binding strength with binding energies differing by > 2 eV for the same impurity type. Small impurities, Fe and Ni, have negative impurity volumes at the substitutional vanadium site, so binding with neighboring vanadium vacancies is much weaker. Migration barriers for direct exchange of an impurity with a vanadium vacancy are calculated for Fe and Ni. On average migration barriers for Ni are lower than those for Fe.

55. “First-principles investigation of intrinsic defects and self-diffusion in ordered phases of V₃C ”, B.J. Demaske, A. Chernatynskiy, S.R. Phillpot , J. Phys.: Cond. Matter 29, 245403 (2017). doi:10.1088/1361-648X/aa7031

• Abstract: The self-diffusion behavior of vanadium subcarbide (V₂C) is investigated using density functional theory calculations, owing to its potential application as a diffusion barrier in nuclear applications. Three ordered V₂C structures, two of which correspond to experimentally observed phases, are characterized in terms of their equilibrium structural, electronic and elastic properties. Our model for self-diffusion in V₂C considers diffusion of carbon and vanadium to occur separately on each sublattice. Two sets of self-diffusion coefficients are calculated for each structure: one for vacancy-mediated diffusion of vanadium and the other for interstitial diffusion of carbon. Calculated activation energies and diffusion prefactors are compared to experimental data for the cubic transition metal carbides as there is no experimental self-diffusion data for any of the hexagonal subcarbides.

54. “Nanoindentation of ZrO₂ and ZrO₂/Zr Systems by Molecular Dynamics Simulation”, Z. Lu, A. Chernatynskiy, M. Noordhoek, S.B. Sinnott, and S.R. Phillpot, JNM 486, 250 (2017). doi:10.1016/j.jnucmat.2017.01.022

• Abstract: The deformation behaviors of cubic zirconia and a cubic zirconia thin film on top of an hcp zirconium substrate are investigated using molecular dynamics nanoindentation simulation. Interatomic interactions are described by the previously developed Charge Optimized Many Body (COMB) potential for the Zr-ZrO₂-O₂ system. The load-displacement curves, deformation processes and hardnesses of zirconia and the zirconia/zirconium systems are characterized. In addition, by comparing with a previous nanoindentation simulation on zirconium, the effects of the zirconia layer on top on the mechanical properties of the zirconium substrate are determined.

53. “Seeing the invisible plasma with transient phonons in cuprous oxide”, L. Frazer, R. D. Schaller, K. B. Chang, A. Chernatynskiy, K. R. Poeppelmeier, Phys. Chem. Chem. Phys. 19, 1151 (2017). doi: 10.1039/C6CP06532E

• Abstract: The emission of phonons from electron–hole plasma is the primary limit on the efficiency of photovoltaic devices operating above the bandgap. In cuprous oxide (Cu₂O) there is no luminescence from electron–hole plasma. Therefore, we searched for optical phonons emitted by energetic charge carriers using phonon-to-exciton upconversion transitions. We found 14 meV phonons with a lifetime of 0.916 ± 0.008 ps and 79 meV phonons that are longer lived and overrepresented. It is surprising that the higher energy phonon has a longer lifetime.

52. “Spin-exchange interaction between transition metals and metalloids in soft-ferromagnetic metallic glasses”, S. Das, K. Choudhary, A. Chernatynskiy, H.C. Yim, A.K. Bandyopadhyay, and S. Mukherjee, J. Phys.: Cond. Matter., 28, 216003 (2016). doi:10.1088/0953-8984/28/21/216003

• Abstract: High-performance magnetic materials have immense industrial and scientific importance in wide-ranging electronic, electromechanical, and medical device technologies. Metallic glasses with a fully amorphous structure are particularly suited for advanced soft-magnetic applications. However, fundamental scientific understanding is lacking for the spin-exchange interaction between metal and metalloid atoms, which typically constitute a metallic glass. Using an integrated experimental and molecular dynamics approach, we demonstrate the mechanism of electron interaction between transition metals and metalloids. Spin-exchange interactions were investigated for a Fe–Co metallic glass system of composition [(Co_1-xFe_x)_0.75B_0.2Si_0.05]₉₆Cr₄. The saturation magnetization increased with higher Fe concentration, but the trend significantly deviated from simple rule of mixtures. Ab initio molecular dynamics simulation was used to identify the ferromagnetic/anti-ferromagnetic interaction between the transition metals and metalloids. The overlapping band-structure and density of states represent 'Stoner type' magnetization for the amorphous alloys in contrast to 'Heisenberg type' in crystalline iron. The enhancement of magnetization by increasing iron was attributed to the interaction between Fe 3d and B 2p bands, which was further validated by valence-band study.

51. “Role of composition and structure on the properties of metal/multifunctional ceramic interfaces”, F.-Y. Lin, A. Chernatynskiy, J. C. Nino, J. L. Jones, R. Hennig, S. B. Sinnott, J. Appl. Phys., 120, 045310 (2016). doi:10.1063/1.4959074

• Abstract; The formation of intermetallic secondary phases, such as Pt₃Pb, has been observed experimentally at PbTiO₃/Pt and Pb(Zr,Ti)O₃/Pt, or PZT/Pt, interfaces. Density functional theory calculations are used here to calculate the work of adhesion of these interfacial systems with and without the secondary intermetallic phase. The charge density maps of the interfaces reveal the electronic interactions at the interface and the impact of the secondary phase. In addition, Bader charge analysis provides a quantitative assessment of electron transfer from the perovskites to the Pt. Analysis of the band diagrams indicates an increase of the potential barrier associated with electron transfer due to the formation of the Pt₃Pb at PZT/Pt interfaces.

50. “Thermal transport at (001) twist grain boundaries in UO₂”, B. Deng, A. Chernatynskiy, S.B. Sinnott, and S.R. Phillpot, J. Nucl. Mater., 479, 167 (2016) doi: 10.1016/j.jnucmat.2016.06.054

• Abstract: We use phonon wave-packet dynamics to study the phonon transmission at UO₂ twist grain boundariesas a function of phonon frequency, mode and incident angle. We find that grain boundaries with more disordered structures show stronger phonon transmission than more ordered grain boundaries. The transmission coefficients are used to calculate the grain boundary thermal conductance at elevated temperature.

49. “Phase equilibria in the U-Si system from first-principles calculations”, M. Noordhoek, T.M. Besmann, D.Andersson, S.C. Middleburgh, and A. Chernatynskiy, J. Nucl. Mater., 479, 216 (2016). doi:10.1016/j.jnucmat.2016.07.006

• Abstract: Density functional theory calculations have been used with spin-orbit coupling and on-site Coulomb correction (GGA + U) methods to investigate the U-Si system. Structural prediction methods were employed to identify alternate stable structures. Convex hulls of the U-Si system were constructed for each of the methods to highlight the competing energetics of various phases. For GGA calculations, new structures are predicted to be dynamically stable, but these have not been experimentally observed. When the GGA + U (Ueff > 1.3 eV) method is considered, the experimentally observed structures are predicted to be energetically preferred. Phonon calculations were used to investigate the energy predictions and showed that the use of the GGA + U method removes the significant imaginary frequencies observed for U₃Si₂ when the correction is not considered. Total and partial electron density of states calculations were also performed to understand the role of GGA + U methods and orbitals on the bonding and stability of U-Si compounds.

48. “Elastic and thermal properties of hexagonal perovskites”, A. Chernatynskiy, A. Auguste, B. Steele, J.E. Phillpot, R.W. Grimes, and S. R. Phillpot, Comp. Mater. Sci., 122, 139 (2016). doi:10.1016/j.commatsci.2016.05.015

• Abstract: We systematically investigate the mechanical and thermal properties of the P63cm hexagonal perovskites with composition A³⁺B³⁺O_x for potential use in thermal barrier coatings. In spite of the structural anisotropy, the elastic constants are essentially isotropic. The thermal expansion is, however, strongly anisotropic, while the thermal conductivity is relatively isotropic. The thermal conductivities of the hexagonal perovskites are much larger than those of the orthorhombic perovskites.

47. “Lattice expansion by intrinsic defects in uranium by molecular dynamics simulation”, T.-Y. Li, A. Chernatynskiy, J.R. Kennedy, S. B. Sinnott and S. R. Phillpot, J. Nucl. Mater., 475, 6 (2016). doi:10.1016/j.jnucmat.2016.03.018

• Abstract: A re-formulated and re-parameterized interatomic potential for uranium metal in the Charge-Optimized Many-Body (COMB) formalism is presented. Most physical properties of the orthorhombic α and bcc γ phases are accurately reproduced. In particular, this potential can reproduce the negative thermal expansion of the b axis in α-U while keeping this phase as the most stable phase at low temperatures, in accord with experiment. Most of the volume expansion in α-U by intrinsic defects is shown to come from the b axis, due to the formation of prismatic loops normal to this direction. Glide dislocation loops forming stacking faults are also observed. Structures of both loop types are analyzed. An expansion simulation is conducted and the results are verified by using the Norgett-Robinson-Torrens model. Rather than forming extended defect structures as in α-U, the γ phase forms only isolated defects and thus results in a much smaller and isotropic expansion.

46. “Systematic Investigation of the Misorientation- and Temperature-Dependent Kapitza Resistance in CeO₂”, A. Chernatynskiy, X.-M. Bai, J. Gan, Int. J. Heat Mass Transfer 99, 461 (2016). doi: 10.1016/j.ijheatmasstransfer.2016.03.105

• Abstract: The misorientation- and temperature-dependent grain boundary thermal (Kapitza) resistance in CeO₂ is investigated using molecular dynamics simulations. A few empirical potentials for molecular dynamics simulations are evaluated for their predicted properties such as the phonon dispersion curves, bulk thermal conductivity, and grain boundary structures. Through the comparison of these properties with experimental results, the most reasonable potential (Gotte2007) is selected. The Kapitza resistances of tilt and twist grain boundaries with misorientation angles ranging from 3° to 87° are calculated and a clear transition angle at about 16° is observed. The Kapitza resistance is found to increase almost linearly with misorientation angle in the low-angle regime but remain nearly constant at the high-angle regime, a behavior very similar to the grain boundary energy. A nearly linear correlation between Kapitza resistance and grain boundary energy is thus obtained. Similar to the grain boundary energy, the Read–Shockley model can well describe the misorientation-dependent Kapitza resistance at low-angle regime. The Kapitza conductance (the inverse of Kapitza resistance) is found to increase almost linearly with temperature in our simulations.

45. “Potential Optimization Software for Materials (POSMat)”, J.A. Martinez, A. Chernatynskiy, D.E. Yilmaz, T. Liang, S.B. Sinnott, S.R. Phillpot, Comp. Phys. Comm., 203, 201 (2016). doi: 10.1016/j.cpc.2016.01.015

• Abstract: The Potential Optimization Software for Materials package (POSMat) is presented. POSMat is a powerful tool for the optimization of classical empirical interatomic potentials for use in atomic scale simulations, of which molecular dynamics is the most ubiquitous. Descriptions of the empirical formalisms and targetable properties available are given. POSMat includes multiple tools, including schemes and strategies to aid in the optimization process. Samples of the inputs and outputs are given as well as an example for fitting an MgO Buckingham potential, which illustrates how the targeted properties can influence the results of a developed potential. Approaches and tools for the expansion of POSMat to other interatomic descriptions and optimization algorithms are described.

44. “Dynamical properties of AlN nanostructures and heterogeneous interfaces predicted using COMB potentials”, K. Choudhary, T. Liang, K. Mathew, B. Revard, A. Chernatynskiy, S.R. Phillpot, R.G. Hennig, S.B. Sinnott, Comp. Mater. Sci., 113, 80 (2016). doi:10.1016/j.commatsci.2015.11.025.

• Abstract: A new empirical variable charge potential has been developed for AlN within the third-generation charge optimized many-body (COMB3) potential framework. The potential is able to reproduce the fundamental physical properties of AlN, including cohesive energy, elastic constants, defect formation energies, surface energies and phonon properties of AlN obtained from experiments and first-principles calculations. The thermodynamic properties of the Al(1 1 1)-AlN and Al₂O₃(0 0 0 1)-AlN interfaces and the tensile response of AlN nanowires and nanotubes are investigated in classical molecular dynamical (MD) simulations using this COMB3 potential. The results demonstrate that the potential is well suited to model heterogeneous materials in the Al–O–N system. Most importantly, the fully transferrable potential parameters can be seamlessly coupled with existing COMB3 parameters of other elements to enable MD simulations for an even wider range of heterogeneous materials systems.

43. “Development of a multiscale thermal conductivity model for fission gas in UO₂”, M.R. Tonks, X.Y. Liu, D. Andersson, D. Perez, A. Chernatynskiy, G. Pastore, C.R. Stanek, R. Williamson, J. Nucl. Mater., 469, 89 (2016). doi:10.1016/j.jnucmat.2015.11.042.

• Abstract: Accurately predicting changes in the thermal conductivity of light water reactor UO₂ fuel throughout its lifetime in reactor is an essential part of fuel performance modeling. However, typical thermal conductivity models from the literature are empirical. In this work, we begin to develop a mechanistic thermal conductivity model by focusing on the impact of gaseous fission products, which is coupled to swelling and fission gas release. The impact of additional defects and fission products will be added in future work. The model is developed using a combination of atomistic and mesoscale simulation, as well as analytical models. The impact of dispersed fission gas atoms is quantified using molecular dynamics simulations corrected to account for phonon-spin scattering. The impact of intragranular bubbles is accounted for using an analytical model that considers phonon scattering. The impact of grain boundary bubbles is determined using a simple model with five thermal resistors that are parameterized by comparing to 3D mesoscale heat conduction results. When used in the BISON fuel performance code to model four reactor experiments, it produces reasonable predictions without having been fit to fuel thermocouple data.

42. “First-principles investigation of ferroelectricity in LaBGeO₅”, B.J. Demaske, A. Chernatynskiy, and S. R. Phillpot, J. Phys.: Cond. Mater., 28, 165901 (2016). doi: 10.1088/0953-8984/28/16/165901.

• Abstract: Density functional theory calculations are performed to characterize the structural, electronic and vibrational properties of both the low-temperature ferroelectric and high-temperature paraelectric phases of LaBGeO₅. Phonon dispersion calculations for the high-temperature phase reveal an unstable mode whose zone-center eigenvector corresponds to a rigid rotation of the BO₄ tetrahedra, in agreement with previous calculations based on a short-range model potential. A possible switching path between two symmetry-equivalent ferroelectric phases that goes through the high-temperature paraelectric phase is identified and used to calculate the spontaneous polarization. The theoretical value for the spontaneous polarization calculated using the modern theory of polarization is 4.9 mC cm^-1 for the PBEsol+U functional, which lies within the experimental range.

41. “Nanoindentation of Gold and Gold Alloys by Molecular Dynamics Simulation”, Y. Li, A. Goyal, A. Chernatynskiy, J. S. Jayashankar, M. C. Kautzky, S. B. Sinnott, and S. R. Phillpot, Mater. Sci. Eng.: A, 651, 346 (2016). doi:10.1016/j.msea.2015.10.081.

• Abstract: The nanoindentation hardnesses and stacking fault energies (SFE) for pure and alloyed Au are determined from classical molecular dynamics simulations. Rather than a traditional force–displacement dependence that is examined in many previous nanoindentation works, we analyze the hardness vs. force in this study, which shows features that allow us to distinguish defect nucleation processes from hardening processes. During nanoindentation, homogeneously nucleated defects interact to form V-shape lock structures, and finally form four-sided dislocations that are continuously released into the bulk, in a manner similar to the heterogeneous Frank-Read dislocation generation mechanism. Hardness in the alloy system is predicted to be critically controlled by the ease and frequency of nucleation of new defects. Consistent with previous simulation results, the difference of the unstable and stable SFE, rather than the stable SFE along, is found to be closely related to this nucleation process, and thus to hardness.

40. “Diffusion Across M/Pb(Zr,Ti)O₃ Interfaces (M=Pt₃Pb or Pt) as a Function of Pb Chemical Potential”, F.-Y. Lin, A. Chernatynskiy, J. Nikkel, R. Bulanadi, J. L. Jones, J. C. Nino, S. B. Sinnott, J. Am. Cer. Soc., 99, 356 (2016). doi:10.1111/jace.13966.

• Abstract: Interfaces between functional ceramics, such as Pb(Zr_0.5Ti_0.5)O₃ or PZT, and metal electrodes, such as Pt, are important for many devices. Maintaining an interface that is free of secondary phases is necessary for the efficient transfer of electrons and device function. However, there are instances where unstable transient phases form at the interface due to atomic diffusion, such as Pt₃Pb. Here, we investigate the migration barriers for the diffusion of Pb across the PZT/Pt and PZT/Pb₃Pb interfaces using density functional theory (DFT) and the climbing image nudge elastic band (c‐NEB) method. Our calculation models take into account the influence of atmospheric conditions on Pb diffusion through the preferential stabilization of defects near the interface as a result of changes to the Pb and O chemical potentials. In addition, the PZT structures that are stable above and below the Curie temperature are considered. The migration barriers are predicted to be strongly dependent on atmospheric conditions and the phase of the PZT, tetragonal or cubic. In particular, an inversion of the Pb diffusion direction at the PZT/Pt interface is predicted to take place as the oxygen partial pressure increases. This prediction is confirmed by experimental in situ X‐ray diffraction measurements of a PZT/Pt interface.

39. “Nanoindentation of Zr by Molecular Dynamics Simulation”, Z. Lu, A. Chernatynskiy, J. M. J. Noordhoek, S. B. Sinnott, and S. R. Phillpot, J. Nucl. Mater., 467, 742 (2015), doi:10.1016/j.jnucmat.2015.10.042.

• Abstract: Molecular dynamics simulations of nanoindentation are used to study the deformation behaviors of single crystal Zr for four different surface orientations. The comparison of results for two different potentials, an embedded atom method potential and a charged optimized many body potential, reveals the influence of stable and unstable stacking fault energy on dislocation behaviors under nanoindentation. The load–displacement curve, hardness and deformation behaviors of the various surface orientations Zr are compared and the elastic and plastic deformation behaviors are analyzed.

38. "Computational Discovery of Lanthanide Doped and Co-doped Y₃Al₅O₁₂ for Optoelectronic Applications", K. Choudhary, A. Chernatynskiy, K. Mathew, E. W. Bucholz , S. R. Phillpot, S. B. Sinnott, R. G. Hennig, Appl. Phys. Lett., 107, 112109 (2015), doi:10.1063/1.4929434.

• Abstract: We systematically elucidate the optoelectronic properties of rare-earth dopedand Ce co-doped yttrium aluminum garnet (YAG) using hybrid exchange-correlation functional based density functional theory. The predicted optical transitions agree with the experimental observations for single doped Ce:YAG, Pr:YAG, and co-doped Er,Ce:YAG. We find that co-doping of Ce-doped YAG with any lanthanide except Eu and Lu lowers the transition energies; we attribute this behavior to the lanthanide-induced change in bonding environment of the dopant atoms. Furthermore, we find infrared transitions only in case of the Er, Tb, and Tm co-doped Ce:YAG and suggest Tm,Ce:YAG and Tb,Ce:YAG as possible functional materials for efficient spectral up-conversion devices.

37. “A coherent phonon pulse model for transient phonon thermal transport”, X. Chen, A. Chernatynskiy, L. Xiong, Y. Chen, Comp. Phys. Comm., 195, 116 (2015). doi: 10.1016/j.cpc.2015.05.008.

• Abstract: In this work, we present a novel heat source model, the coherent phonon pulse (CPP), composed of spatiotemporal Gaussian wave packets to mimic the coherent excitation of a non-equilibrium phonon population by ultrashort laser techniques, for the study of transient phonon thermal transport. Through molecular dynamic simulations of phonon transport in bicrystalline silicon-nanowires containing 3 and 19 grain-boundaries (GBs), we demonstrate that the new model facilitates not only a quantitative measurement of phonon-interface scattering, but also a mechanistic understanding of the highly non-equilibrium process of phonon transport with the coherent wave nature being preserved.

36. “Charge optimized many-body (COMB) potential for dynamical simulation of Ni–Al phases”, A. Kumar, A. Chernatynskiy, T. Liang, K. Choudhary, M.J. Noordhoek, Y.-T. Cheng, S.R. Phillpot and S.B. Sinnott, J. Phys.: Cond. Matter. 27, 336302 (2015), doi:10.1088/0953-8984/27/33/336302.

• Abstrat: An interatomic potential for the Ni–Al system is presented within the third-generation charge optimized many-body (COMB3) formalism. The potential has been optimized for Ni₃Al, or the γ' phase in Ni-based superalloys. The formation energies predicted for other Ni–Al phases are in reasonable agreement with first-principles results. The potential further predicts good mechanical properties for Ni₃Al, which includes the values of the complex stacking fault (CSF) and the anti-phase boundary (APB) energies for the (1 1 1) and (1 0 0) planes. It is also used to investigate dislocation propagation across the Ni₃Al (1 1 0)–Ni (1 1 0) interface, and the results are consistent with simulation results reported in the literature. The potential is further used in combination with a recent COMB3 potential for Al₂O₃ to investigate the Ni₃Al (1 1 1)–Al₂O₃ (0 0 01) interface, which has not been modeled previously at the classical atomistic level due to the lack of a reactive potential to describe both Ni₃Al and Al₂O₃ as well as interactions between them. The calculated work of adhesion for this interface is predicted to be 1.85 J m^-2, which is in agreement with available experimental data. The predicted interlayer distance is further consistent with the available first-principles results for Ni (1 1 1)–Al₂O₃ (0 0 0 1).

35. "Combined Experimental and Computational Methods Reveal the Evolution of Buried Interfaces during Synthesis of Ferroelectric Thin Films”, J. L. Jones, J. M. LeBeau, J. Nikkel, A. A. Oni, J. H. Dycus, C. Cozzan, F.-Y. Lin, A. Chernatynskiy, J. C. Nino, S. B. Sinnott, S. Mhin, G. L. Brennecka, and J. Ihlefeld, Adv. Mater. Interfaces. 2, 1500181 (2015), doi: 10.1002/admi.201500181. (Featured on the front cover of the Volume)

• Abstract: Understanding interfaces between dissimilar materials is crucial to the development of modern technologies, for example, semiconductor–dielectric and thermoelectric–semiconductor interfaces in emerging electronic devices. However, the structural characterization of buried interfaces is challenging because many measurement techniques are surface sensitive by design. When interested in interface evolution during synthesis, the experimental challenges multiply and often necessitate in situ techniques. For solution‐derived lead zirconate titanate (PZT) ferroelectric thin films, the evolution of buried interfaces during synthesis (including dielectric–metal and metal–metal) is thought to dramatically influence the resultant dielectric and ferroelectric properties. In the present work, multiple experimental and computational methods are combined to characterize interface evolution during synthesis of ferroelectric PZT films on platinized Si wafers—including in situ X‐ray diffraction during thermal treatment, aberration‐corrected scanning transmission electron microscopy of samples quenched from various synthesis states, and calculations using density functional theory. Substantial interactions at buried interfaces in the PZT/Pt/Ti/SiO x /Si heterostructure are observed and discussed relative to their role(s) in the synthesis process. The results prove that perovskite PZT nucleates directly from the platinum (111)‐oriented bottom electrode and reveal the roles of Pb and O diffusion and intermetallic Pt₃Pb and Pt₃Ti phases.

34. “Anharmonic properties in Mg₂X (X=C, Si, Ge, Sn, Pb) from first-principles calculations”, A. Chernatynskiy and S. R. Phillpot, Phys. Rev. B 92, 064303 (2015), doi:10.1103/PhysRevB.92.064303.

• Abstract: Thermal conductivity reduction is one of the potential routes to improve the performance of thermoelectric materials. However, detailed understanding of the thermal transport of many promising materials is still missing. In this paper, we employ electronic-structure calculations at the level of density functional theory to elucidate thermal transport properties of the Mg₂X (X=C, Si, Ge, Sn, and Pb) family of compounds, which includes Mg₂Si, , a material already identified as a potential thermoelectric. All these materials crystallize into the same antifluorite structure. Systematic trends in the anharmonic properties of these materials are presented and examined. Our calculations indicate that the reduction in the group velocity is the main driver of the thermal conductivity trend in these materials, as the phonon lifetimes in these compounds are very similar. We also examine the limits of the applicability of perturbation theory to study the effect of point defects on thermal transport and find that it is in good agreement with experiment in a wide range of scattering parameter values. The thermal conductivity of the recently synthesized Mg₂C is computed and predicted to be 34 W/mK at 300 °C.

33. “Charge Optimized Many-Body (COMB) Potential for Al₂O­₃ Materials, Interfaces, and Nanostructures", K. Choudhary, T. Liang, A.Chernatynskiy, S. R. Phillpot and S. Sinnott, J. Phys.: Cond. Matter. 27, 305004 (2015), doi:10.1088/0953-8984/27/30/305004.

• Abstract: This work presents the development and applications of a new empirical, variable charge potential for Al₂O₃ systems within the charge optimized many-body (COMB) potential framework. The potential can describe the fundamental physical properties of Al₂O₃, including cohesive energy, elastic constants, defect formation energies, surface energies and phonon properties of α-Al₂O₃ comparable to that obtained from experiments and first-principles calculations. The potential is further employed in classical molecular dynamics (MD) simulations to validate and predict the properties of the Al (1 1 1)–Al₂O₃ (0 0 0 1) interface, tensile properties of Al nanowires, Al2O3 nanowires, Al2O3-covered Al nanowires, and defective Al₂O₃ nanowires. The results demonstrate that the potential is well-suited to model heterogeneous material systems involving Al and Al₂O₃. Most importantly, the parameters can be seamlessly coupled with COMB3 parameters for other materials to enable MD simulations of a wide range of heterogeneous material systems.

32. “Phonon transport simulator (PhonTS)”, A. Chernatynskiy and S. R. Phillpot, Comp. Phys. Comm., 192, 196 (2015), doi:10.1016/j.cpc.2015.01.008.

• Abstract: Thermal conductivity prediction remains an important subject in many scientific and engineering areas. Only recently has such prediction become possible on the basis of the first principles calculations, thus ensuring high quality results. Implementation of the methodology, however, is technically challenging and requires a lengthy development process. We thus introduce the Phonon Transport Simulator (PhonTS), a Fortran90, fully parallel code to perform such calculations. PhonTS possesses a large array of options and returns the thermal conductivity tensor together with related quantities, such as spectral thermal conductivity, phonon lifetimes, mean free paths and Grüneisen parameters. First principles calculations are implemented via convenient interfaces to widely-used third-party codes, while many classical potentials are included in PhonTS itself. The code is carefully validated against data published in the literature from various thermal conductivity computational techniques and against experimental data.

31. “Deformation Processes in Nanocrystalline Zr by Molecular Dynamics Simulations” Z. Lu, M. J. Noordhoek, A. Chernatynskiy, S.B. Sinnott and S.R. Phillpot, J. Nucl. Mater., 462, 147 (2015), doi:10.1016/j.jnucmat.2015.03.048.

• Abstract: Molecular dynamics simulation is used to characterize the deformation behavior of polycrystalline Zr. The predictions of two different potentials, an embedded atom method potential and a charge optimized many body potential are compared. The experimentally observed prismatic dislocations, pyramidal dislocations and twinning behaviors are produced in the simulations of and [0 0 0 1] textured structures and in fully 3D structure simulations. The relationship between the generalized stacking fault energy and the mechanical properties is discussed. In particular we find that the different shapes of the generalized stacking-fault energy curve for the two different interatomic descriptions of Zr have a significant effect on the deformation mechanisms. The deformation behavior of Zr is compared with analogous simulations of deformation of polycrystalline Mg.

30. “An ab initio investigation of the effect of alloying elements on the elastic properties and magnetic behavior of Ni₃Al” A. Kumar, A. Chernatynskiy, M. Hong, S.R. Phillpot and S.B. Sinnott, Comp. Mater. Sci. 101, 39 (2015), doi:10.1016/j.commatsci.2015.01.007.

• Abstract: First principles density functional theory calculations were performed on pure and doped Ni₃Al. The dopants investigated were Cr, Zr, La and Ce at concentrations of 3.13, 6.25 and 9.38 at.%, and B was considered at concentrations of 3.03, 5.88 and 8.57 at.%. The defect formation energies, doping site preferences, and elastic properties of pure and doped Ni₃Al were determined and compared to published theoretical and experimental results. The magnetic properties of Ni₃Al and, where appropriate, the dopants, were always taken into account, as the elastic constants predicted from spin-polarized and non-spin-polarized calculations were significantly different. The results were successfully correlated to the electronic structure through the electronic density using Miedema’s established model (Miedema et al., 1973). The calculations revealed that Cr doping increases the bulk modulus of Ni3Al and that all the other dopants considered decrease it.

29. “Charge Optimized Many-Body Potential for Aluminum" K. Choudhary, T. Liang, A. Chernatynskiy, Z. Lu, A. Goyal, S.R. Phillpot and S.B. Sinnott, J. Phys.: Condens. Matter. 27, 015003 (2015), doi:10.1088/0953-8984/27/1/015003.

• Abstract:An interatomic potential for Al is developed within the third generation of the charge optimized many-body (COMB3) formalism. The database used for the parameterization of the potential consists of experimental data and the results of first-principles and quantum chemical calculations. The potential exhibits reasonable agreement with cohesive energy, lattice parameters, elastic constants, bulk and shear modulus, surface energies, stacking fault energies, point defect formation energies, and the phase order of metallic Al from experiments and density functional theory. In addition, the predicted phonon dispersion is in good agreement with the experimental data and first-principles calculations. Importantly for the prediction of the mechanical behavior, the unstable stacking fault energetics along the <12-1> direction on the (1 1 1) plane are similar to those obtained from first-principles calculations. The polycrsytal when strained shows responses that are physical and the overall behavior is consistent with experimental observations.

28. “Anisotropy in Oxidation of Zirconium Surfaces from Density Functional Theory Calculations”, T.-W. Chiang, A. Chernatynskiy, M. J. Noordhoek, S. B. Sinnott and S. R. Phillpot, Comput. Mater. Sci. 98, 112 (2015), doi:10.1016/j.commatsci.2014.10.052.

• Abstract: This work uses density functional theory calculations to analyze the energy barriers for oxygen migration into the basal and prismatic surfaces of zirconium. Specifically, the migration energy barriers between each octahedral site and tetrahedral site in the basal surface, prism surface, and the bulk are determined. The possible oxygen migration paths in each system are also analyzed. Oxygen has higher energy barriers to penetrating the basal surface than the prism surface. It also has a lower energy barrier to escape from basal surface than from the prism surface. This is consistent with the experimental observation that the prism plane of zirconium oxidizes more quickly than the basal plane.

27. “Effect of Pores and He Bubbles on the Thermal Transport Properties of UO₂ by Molecular Dynamics Simulation”, C.-W. Lee, A. Chernatynskiy, P. Shukla, R. E. Stoller, S. B. Sinnott and S. R. Phillpot, J. Nucl. Mater. 456, 253 (2015) doi:10.1016/j.jnucmat.2014.09.052.

• Abstract: The thermal conductivities of UO₂ single crystals containing nanoscale size pores and He gas bubbles are calculated using non-equilibrium molecular dynamics as a function of pore size and gas density in the bubble. As expected, the thermal conductivity decreases as pore size increases, while the decrease in thermal conductivity is determined to be more substantial than the predictions of traditional analytical models by Loeb and Maxwell-Eucken. However, the recent model of Alvarez, which is applicable when the phonon mean-free path is comparable to the pore size, is able to quantitatively reproduce the simulation results. The thermal conductivity of UO₂ of the small pores considered here is reduced further when the pore is filled with He gas. This surprising result is due to the penetration of the helium atoms into the lattice where they act as phonon scattering centers.

26. “A molecular dynamics study of tilt grain boundary resistance to slip and heat transfer in nanocrystalline silicon”, X. Chen, L. Xiong, A. Chernatynskiy and Y. Chen, J. Appl. Phys. 116, 244309 (2014) doi:10.1063/1.4905248.

• Abstract: We present a molecular dynamics study of grain boundary (GB) resistance to dislocation-mediated slip transfer and phonon-mediated heat transfer in nanocrystalline silicon bicrystal. Three most stable ⟨110⟩ tilt GBs in silicon are investigated. Under mechanical loading, the nucleation and growth of hexagonal-shaped shuffle dislocation loops are reproduced. The resistances of different GBs to slip transfer are quantified through their constitutive responses. Results show that the Σ3 coherent twin boundary (CTB) in siliconexhibits significantly higher resistance to dislocation motion than the Σ9 GB in glide symmetry and the Σ19 GB in mirror symmetry. The distinct GB strengths are explained by the atomistic details of the dislocation-GB interaction. Under thermal loading, based on a thermostat-induced heat pulse model, the resistances of the GBs to transient heat conduction in ballistic-diffusive regime are characterized. In contrast to the trend found in the dislocation-GB interaction in bicrystal models with different GBs, the resistances of the same three GBs to heat transfer are strikingly different. The strongest dislocationbarrier Σ3 CTB is almost transparent to heat conduction, while the dislocation-permeable Σ9 and Σ19 GBs exhibit larger resistance to heat transfer. In addition, simulation results suggest that the GB thermal resistance not only depends on the GB energy but also on the detailed atomic structure along the GBs.

25. “Phonon thermal transport through tilt grain boundaries in strontium titanate” Z. Zheng, X. Chen, B. Deng, A. Chernatynskiy, S. Yang, L. Xiong and Y. Chen, J. Appl. Phys. 116, 073706 (2014) doi:10.1063/1.4893648.

• Abstract: In this work, we perform nonequilibrium molecular dynamics simulations to study phonon scattering at two tilt grain boundaries (GBs) in SrTiO₃. Mode-wise energy transmission coefficients are obtained based on phonon wave-packet dynamics simulations. The Kapitza conductance is then quantified using a lattice dynamics approach. The obtained results of the Kapitza conductance of both GBs compare well with those obtained by the direct method, except for the temperature dependence. Contrary to common belief, the results of this work show that the optical modes in SrTiO₃ contribute significantly to phonon thermal transport, accounting for over 50% of the Kapitza conductance. To understand the effect of the GB structural disorder on phonon transport, we compare the local phonon density of states of the atoms in the GB region with that in the single crystalline grain region. Our results show that the excess vibrational modes introduced by the structural disorder do not have a significant effect on phonon scattering at the GBs, but the absence of certain modes in the GB region appears to be responsible for phonon reflections at GBs. This work has also demonstrated phonon mode conversion and simultaneous generation of new modes. Some of the new modes have the same frequency as the initial wave packet, while some have the same wave vector but lower frequencies.

24. “Phonon Density of States and Anharmonicity of UO₂”, J.W.L. Pang, A. Chernatynskiy, B. C. Larson, W.J.L. Buyers, D.L. Abernathy, K.J. McClellan, S.R. Phillpot, Phys. Rev. B 89, 115132 (2014) doi:10.1103/PhysRevB.89.115132.

• Abstract: Phonon density of states (PDOS) measurements have been performed on polycrystalline UO₂ at 295 and 1200 K using time-of-flight inelastic neutron scattering to investigate the impact of anharmonicity on the vibrational spectra and to benchmark ab initio PDOS simulations performed on this strongly correlated Mott insulator. Time-of-flight PDOS measurements include anharmonic linewidth broadening, inherently, and the factor of ~7 enhancement of the oxygen spectrum relative to the uranium component by the increased neutron sensitivity to the oxygen-dominated optical phonon modes. The first-principles simulations of quasiharmonic PDOS spectra were neutron weighted and anharmonicity was introduced in an approximate way by convolution with wave-vector-weighted averages over our previously measured phonon linewidths for UO₂, which are provided in numerical form. Comparisons between the PDOS measurements and the simulations show reasonable agreement overall, but they also reveal important areas of disagreement for both high and low temperatures. The discrepancies stem largely from a ~10 meV compression in the overall bandwidth (energy range) of the oxygen-dominated optical phonons in the simulations. A similar linewidth-convoluted comparison performed with the PDOS spectrum of Dolling et al. obtained by shell-model fitting to their historical phonon dispersion measurements shows excellent agreement with the time-of-flight PDOS measurements reported here. In contrast, we show by comparisons of spectra in linewidth-convoluted form that recent first-principles simulations for UO₂ fail to account for the PDOS spectrum determined from the measurements of Dolling et al. These results demonstrate PDOS measurements to be stringent tests for ab inito simulations of phonon physics in UO₂ and they indicate further the need for advances in theory to address the lattice dynamics of UO₂.

23. “Kapitza resistance of Si/SiO₂ interface”, B. Deng, A. Chernatynskiy, M. Khafizov, D. Hurley and S. R. Phillpot, J. Appl. Phys. 115, 084910 (2014) doi:10.1063/1.4867047.

• Abstract: A phonon wave packet dynamics method is used to characterize the Kapitza resistance of a Si/SiO₂ interface in a Si/SiO₂/Si heterostructure. By varying the thickness of SiO₂ layer sandwiched between two Si layers, we determine the Kapitza resistance for the Si/SiO₂ interface from both wave packet dynamicsand a direct, non-equilibrium molecular dynamics approach. The good agreement between the two methods indicates that they have each captured the anharmonic phonon scatterings at the interface. Moreover, detailed analysis provides insights as to how individual phonon mode scatters at the interfaceand their contribution to the Kapitza resistance.

22. “Interaction between Voids and Grain Boundaries in UO₂ by Molecular-Dynamics Simulation”, T.-W. Chiang, A. Chernatynskiy, B. Deng, S. B. Sinnott and S. R. Phillpot, J. Nucl. Mater., 448, 53 (2014) doi:10.1016/j.jnucmat.2014.01.027.

• Abstract: This work uses atomic-level simulations to analyze the interactions of voids with a grain boundary (GB) in UO₂, the ubiquitous fuel material for light water reactors. Specifically, the high-temperature interactions of a (3 1 0) Σ5 tilt GB structure with voids of diameter 1.8 nm are analyzed. We find that the GB tends to move towards the void when they are within a few nm of each other. With increasing temperature, GB migration from greater distances toward to the void is predicted to take place. Both GB pinning to the void and void dissolution at the GB take place. The atomic-level mechanisms and the energetics associated with these processes are characterized.

21. “Thermal Conductivity in Nanocrystalline Ceria Thin Films” M. Khafizov, I.-W. Park, A. Chernatynskiy, L. He, J. Lin, J.J. Moore, D. Swank, T. Lillo, S.R. Phillpot, A. El-Azab, D.H. Hurley, J. Am. Ceram. Soc. 97, 562 (2014), doi: 10.1111/jace.12673.

• Abstract: The thermal conductivity of nanocrystalline ceria films grown by unbalanced magnetron sputtering is determined as a function of temperature using laser‐based modulated thermoreflectance. The films exhibit significantly reduced conductivity compared with stoichiometric bulk CeO₂. A variety of microstructure imaging techniques including X‐ray diffraction, scanning and transmission electron microscopy, X‐ray photoelectron analysis, and electron energy loss spectroscopy indicate that the thermal conductivity is influenced by grain boundaries, dislocations, and oxygen vacancies. The temperature dependence of the thermal conductivity is analyzed using an analytical solution of the Boltzmann transport equation. The conclusion of this study is that oxygen vacancies pose a smaller impediment to thermal transport when they segregate along grain boundaries.

20. “Thermal conductivity of argon at high pressure from first principles calculations” A. Chernatynskiy and S.R. Phillpot, J. App. Phys., 114, 064902 (2013), doi:10.1063/1.4817901.

• Abstract: We present calculations of the thermal conductivity of fcc Argon at high pressures (pressure range is 10–150 GPa, temperatures range is 400–1200 K) from first principles in the framework of density functional theory and solution of the Boltzmann Transport Equation. Local density approximation (LDA) and generalized gradient approximation (GGA) produce similar thermal conductivities, with differences accounted by the known overbinding and underbinding of the LDA and GGA, correspondingly. Thermal conductivities at all considered pressures and temperatures are found to be consistent with the results of previous molecular dynamics simulations based on classical 2-body potentials. However, they are not consistent with recent experimental findings. Possible reasons for this disagreement are discussed. In addition, in light of our calculations, we critically examine analytically tractable approximations for thermal conductivity as applied to solid argon.

19. “Uncertainty Quantification in Multiscale Simulation of Materials: A Prospective”, A. Chernatynskiy, S. R. Phillpot and R. A. LeSar, Ann. Rev. Mater. Res., 43, 157 (2013), doi:10.1146/annurev-matsci-071312-121708.

• Abstract: Simulation has long since joined experiment and theory as a valuable tool to address materials problems. Analysis of errors and uncertainties in experiment and theory is well developed; such analysis for simulations, particularly for simulations linked across length scales and timescales, is much less advanced. In this prospective, we discuss salient issues concerning uncertainty quantification (UQ) from a variety of fields and review the sparse literature on UQ in materials simulations. As specific examples, we examine the development of atomistic potentials and multiscale simulations of crystal plasticity. We identify needs for conceptual advances, needs for the development of best practices, and needs for specific implementations.

18. “Phonon Lifetime Limited Thermal Conductivity of UO₂ by Neutron Scattering and Theory” J. W.L. Pang, W. J.L. Buyers, A. Chernatynskiy, M. D. Lumsden, B. C. Larson and Simon R. Phillpot, Phys. Rev. Lett., 110, 157401 (2013), doi:10.1103/PhysRevLett.110.157401.

• Abstract: Inelastic neutron scattering measurements of individual phonon lifetimes and dispersion at 295 and 1200 K have been used to probe anharmonicity and thermal conductivity in UO₂. They show that longitudinal optic phonon modes carry the largest amount of heat, in contrast to past simulations and that the total conductivity demonstrates a quantitative correspondence between microscopic and macroscopic phonon physics. We have further performed first-principles simulations for UO₂ showing semiquantitative agreement with phonon lifetimes at 295 K, but larger anharmonicity than measured at 1200 K.

17. “Phonon-mediated Thermal Transport: Confronting Theory and Microscopic Simulation with Experiment” A. Chernatynskiy and S. R. Phillpot, Curr. Opin. Solid State Mater. Sci, 17, 1 (2013), doi:10.1016/j.cossms.2012.11.001.

• Abstract: We discuss recent advances in the microscopic simulations of thermal conductivity through the prism of comparisons with experimental measurements. By dissecting the thermal conductivity into its constituent properties, heat capacity, phonon structure and anharmonic phonon properties, we show that the reliable prediction of the thermal transport properties over a range of conditions requires each to be described correctly. However, it is sometimes possible to obtain thermal conductivity values in overall good agreement with experiment through a cancellation of errors in the constituent properties. Major advances in the prediction of thermal transport properties in the last few years have come through increases in computational power and through development of numerical algorithms for the essentially exact solution of the linearized Boltzmann Transport Equation, with interatomic interactions described by first-principles electronic-structure calculations. This approach enables consistent ab initio determination of the thermal conductivity in the pure crystals. We also discuss the effects of various defects on thermal conductivity and compare results from the atomistic simulations, classical theories from the 1950s, and experimental measurements.

16. “Atomistic structure of (Ba,Sr)TiO₃: Comparing molecular-dynamics simulations with structural measurements” M. J. Noordhoek, V. Krayzman, A. Chernatynskiy, S. R. Phillpot, and I. Levin, Appl. Phys. Lett., 103, 022909 (2013), doi:10.1063/1.4813273.

• Abstract: Atomistic structures of Ba_1-xSr_1-xTiO₃ (x ≤ 0.5) determined by molecular-dynamics simulations are compared with five types of experimental structural data and with the results of multiple-technique Reverse Monte Carlo refinements. The simulations and experimental studies agree on many fundamental aspects of the local atomic displacements; in some cases, this agreement is quantitative, in others only semi-quantitative. Key local-structure characteristics of the solid solutions are identified along with a possible mechanism of dielectric relaxation.

15. “Segregation of Ru to edge dislocations in UO₂” A. Goyal, T. Rudzik, B. Deng, M. Hong, A. Chernatynskiy, S. B. Sinnott and S. R. Phillpot, J. Nucl. Mater., 441, 96 (2013), doi:10.1016/j.jnucmat.2013.05.031.

• Abstract: Atomic-level simulation methods are used to determine the interaction of a metallic fission product, Ru⁴⁺, with the core of ao/2〈1 1 0〉{1 1 0} and ao/2〈1 1 0〉{0 0 1} edge dislocations in UO₂, experimentally the most active slip systems. Specifically, the segregation behavior of Ru⁴⁺ is examined at the cationic substitution site; comparisons are made with both continuum-elastic results and with the results of atomistic simulations on strained single crystals. The results on strained single crystals suggest that segregation behavior is a strong function of the elastic strain field around the detailed atomic structure at the dislocation core. Furthermore, the segregation is affected by the orientation of the dislocation and electrostatic interactions at the atomic defect site.

14. “Effects of Edge Dislocations on the Thermal Conductivity of UO₂” B. Deng, A. Chernatynskiy, P. Shukla, S. Sinnott and S. R. Phillpot, J. Nucl. Mater., 434, 203 (2013), doi:10.1016/j.jnucmat.2012.11.043.

• Abstract: Molecular-dynamics simulations are used to characterize the effects of dislocations on the thermal transport properties of UO₂. Microstructures with various dislocation densities of the order of 10¹⁶ m^-2 are simulated at temperatures between 800 and 1600 K. The effects of dislocations on the thermal-transport properties are found to be independent on temperature, consistent with the classic Klemens–Callaway analysis. The effect of dislocation density is also quantified. The simulation results are also fit to the pertinent part of the empirical formula for the thermal conductivity used in the FRAPCON fuel-performance code, which gives the overall effects of temperature and dislocation effects on thermal conductivity. The fitted results can be well-described within this formalism, indicating that the results of molecular-dynamics simulations can be used as a reliable source of parameters for models at longer length scales.

13. “Critical Assessment of Classical Potentials for MgSiO₃ Perovskite with Application to Thermal Conductivity Calculations” Y. Chen, A. Chernatynskiy, P.K. Shelling, E. Artacho and S.R. Phillpot, Phys. Earth Planet. Inter., 210, 75 (2012), doi:10.1016/j.pepi.2012.08.002.

• Abstract: Atomistic simulations using classical empirical potentials are an invaluable tool for studying minerals in lower-mantle conditions. Here we systematically survey literature potentials for MgSiO₃ perovskite. The value of the present work is two-fold: (i) a systematic data set for a large number of potentials is determined, reproducing previous results where they exist and filling in gaps where they do not, and (ii) the first predictions using these potentials for the thermal-transport properties critical to geothermal models is provided. We focus particularly on the thermal expansion and the thermal-transport properties, both of which probe the anharmonic structure of the potential. Simple two-body potentials with the partially-ionic charges are found to be the most successful representation of MgSiO₃ perovskite properties. The addition of a shell model or many-body interactions does not lead to any systematic improvement.

12. “Low Thermal Conductivity Oxides” W. Pan, S. R. Phillpot, C. Wan, A. Chernatynskiy and Z. Qu, MRS Bull., 37, 917 (2012), doi:10.1557/mrs.2012.234.

• Abstract: Oxides hold great promise as new and improved materials for thermal-barrier coating applications. The rich variety of structures and compositions of the materials in this class, and the ease with which they can be doped, allow the exploration of various mechanisms for lowering thermal conductivity. In this article, we review recent progress in identifying specific oxides with low thermal conductivity from both theoretical and experimental perspectives. We explore the mechanisms of lowering thermal conductivity, such as introducing structural/chemical disorder, increasing material density, increasing the number of atoms in the primitive cell, and exploiting the structural anisotropy. We conclude that further systematic exploration of oxide crystal structures and chemistries are likely to result in even further improved thermal-barrier coatings.

11. “Critical assessment of UO₂ classical potentials for thermal conductivity calculations” A. Chernatynskiy, C. Flint, S. Sinnott and S. R. Phillpot, J. Mater. Sci., 47, 7693 (2012), doi:10.1007/s10853-011-6230-0.

• Abstract: This article reviews the thermal transport properties as predicted by 26 classical interatomic potentials for uranium dioxide, an important nuclear fuel material, determined using a lattice dynamics-based method. The calculations reveal structural instabilities for multiple potentials, as well as the presence of lower energy structures even for potentials in which the fluorite structure is stable. Both rigid atom and shell model potentials are considered, and general trends in their representation of the thermal conductivity are identified. Reviewed classical potentials predict thermal conductivity in the range of ~5–22 W/mK, compared to the experimental value of 8.9 W/mK. The quality of the anharmonicity correction that is based on the correlation between thermal expansion and thermal conductivity is investigated, and it found to generally improve thermal conductivities results.

10. “Relativistic Tight-binding model: Application to Pt Surfaces” A. Tchernatinsky and J. W. Halley, Phys. Rev. B, 83, 205431 (2011), doi:10.1103/PhysRevB.83.205431.

• Abstract: We report a parametrization of a previous self-consistent tight-binding model, suitable for metals with a high atomic number in which nonscalar-relativistic effects are significant in the electron physics of condensed phases. The method is applied to platinum. The model is fitted to density functional theory band structures and cohesive energies and spectroscopic data on platinum atoms in five oxidation states, and is then shown without further parametrization to correctly reproduce several low index surface structures. We also predict reconstructions of some vicinal surfaces.

9. “Lattice Thermal Conductivity in Ionic Solids: Effects of Long Range Interactions” A. Chernatynskiy, J. Turney, A. McGaughey, C.H. Amon and S.R. Phillpot. J. Am. Ceram. Soc., 94, 3523 (2011), doi: 10.1111/j.1551-2916.2011.04743.x.

• Abstract: Phonon properties predicted from lattice dynamics calculations and the Boltzmann Transport Equation (BTE) are used to elucidate the thermal‐transport properties of ionic materials. It is found that a rigorous treatment of the Coulombic interactions within the harmonic analysis is needed for the analysis of the phonon structure of the solid, while a short‐range approximation is sufficient for the third‐order force constants. The effects on the thermal conductivity of the relaxation time approximation, the classical approximation to the phonon statistics, the direct summation method for the electrostatic interactions, and the quasi‐harmonic approximation to lattice dynamics are quantified. Quantitative agreement is found between predictions from molecular dynamics simulations (a method valid at temperatures above the Debye temperature) and the BTE result within quasi‐harmonic approximation over a wide temperature range.

8. “Thermal Conductivity of UO₂ Fuel: Predicting Fuel Performance from Simulation” S. R. Phillpot, A. El-Azab, A. Chernatynskiy and J. S. Tulenko, JOM, 63, 73-79 (2011), doi:10.1007/s11837-011-0143-x.

• Abstract: Recent progress in understanding the thermal-transport properties of UO₂ for fission reactors is reviewed from the perspective of computer simulations. A path to incorporating more accurate materials models into fuel performance codes is outlined. In particular, it is argued that a judiciously integrated program of atomic-level simulations and mesoscale simulations offers the possibility of both better predicting the thermal-transport properties of UO₂ in light-water reactors and enabling the assessment of the thermal performances of novel fuel systems for which extensive experimental databases are not available.

7. “Effect of Inversion on Thermoelastic and Thermal-Transport Properties of MgAl₂O₄ and Related Spinels by Molecular-Dynamics Simulation” P. Shukla, A. Chernatynskiy, J. C. Nino, S. B. Sinnott and S. R. Phillpot, J. Mater. Sci. 46, 55 (2011), doi:10.1007/s10853-010-4795-7.

• Abstract: MgAl₂O₄ is commonly found in the normal spinel structure with the Mg²⁺ ions located in tetrahedral sites and the AL³⁺ ions occupying octahedral sites. We use atomic-level simulation to characterize the effect of inversion on the elastic and thermal properties. Cation ordering and volumetric changes tend to affect the structure and properties in opposite ways, thereby compensating each other up for up to 50% inversion. For higher inversions, volumetric effects dominate. In the case of the thermal conductivity, the effects of changes in the elastic properties and thermal expansion essentially cancel over the entire range of inversion.

6. “Evaluation of Computational Techniques for Solving the Boltzmann Transport Equation for Lattice Thermal Conductivity Calculations” A. Chernatynskiy and S.R. Phillpot, Phys. Rev. B, 82 134301 (2010), doi:10.1103/PhysRevB.82.134301.

• Abstract: Three methods for computing thermal conductivity from lattice dynamics (the iterative method, the variational method, and the relaxation-time approximation) are compared for the prototypical case of solid argon. The iterative method is found to produce results in close agreement with Green-Kubo molecular-dynamics simulations, a formally correct method for computing thermal conductivity. The variational method and relaxation-time approximation are found to underestimate the thermal conductivity. The relationship among the methods is established; a combination of the iterative and variational methods is found to have a fastest convergence. Formal convergence of the iterative method is demonstrated and a simple mixing rule is shown to provide stability in practice. The ability to use these methods to provide detailed insight into the relationship between phonon properties and thermal conductivity is demonstrated.

5. “Stability and Charge Transfer Levels of Extrinsic Defects in LiNbO₃”, H. Xu, A. Chernatynskiy, D. Lee, S. B. Sinnott, V. Gopalan, V. Dierolf, and S. R. Phillpot, Phys. Rev. B 82, 184109 (2010), doi:10.1103/PhysRevB.82.184109.

• Abstract: The technologically important incorporation of extrinsic defects (Mg²⁺, Fe²⁺, Fe³⁺, Er³⁺, and Nd³⁺) in LiNbO₃ is investigated using density-functional theory combined with thermodynamic calculations. Defect energies, the charge compensation mechanisms, and charge transfer levels, are determined for congruent and stoichiometric compositions. In general, under congruent (Nb₂O₅-rich) conditions impurities occupy lithium sites, compensated by lithium vacancies. Under stoichiometric (Li₂O-rich) conditions, impurities occupy both lithium and niobium sites. The effects of the concentration of Mg on the dominant defect and site occupancy are analyzed. In addition, the thermal ionization energy and relative defect stability order for Fe²⁺ and Fe³⁺ are evaluated. The charge transfer levels of impurities with regard to the band structure, and their influences on the optical properties of the material are elucidated.

4. “Cross-over in Thermal Transport Properties of Natural, Perovskite-structured Superlattices”, A. Chernatynskiy, R. W. Grimes, M. A. Zurbuchen, D. R. Clarke, and S. R. Phillpot, Appl. Phys. Lett. 95 161906 (2009), doi:10.1063/1.3253421.

• Abstract: Atomic-level simulations are used to analyze the thermal-transport propertiesof a naturally layered material: the Ruddlesden–Popper phase, formed by interleaving perovskite layers of strontium titanate with strontium oxide rocksalt layers. The thermal conductivity parallel to the plane of structurallayering is found to be systematically greater than that perpendicular to the layering. With decreasing number of perovskite blocks in the structure, a transition is seen from the thermal-transport properties of a bulk solid containing interfaces to that of an anisotropic monolithic material. The exact transition point should be temperature dependent and might enable tuning of the thermal conductance properties of the material.

3. “Anisotropic Thermal Properties in Orthorhombic Perovskite”, B. Steele, A. D. Burns, A. Chernatynskiy, R. W. Grimes, and S. R. Phillpot, J. Mater. Sci., 45, 168-176 (2010), doi:10.1007/s10853-009-3912-y.

• Abstract: The structure, elastic properties, thermal expansion, and thermal conductivity of the orthorhombic-structured A³⁺B³⁺O₃ perovskites are determined using atomistic simulations with classical potentials. When considered as pseudo-cubic monoclinic systems, they show relatively small deviations in structure and properties from their cubic perovskite parent phase. The variations in properties are shown to be related to the magnitude of the tilting of the BO₆ octahedra, which in turn is related to the relative sizes of the A and B ions, as encapsulated in the tolerance factor.

2. “Adsorption of Oxygen Molecules on Individual Carbon Single-walled Nanotubes”, A. Tchernatinsky, B. Nagabhirava, S.Desai, G. Sumanasecera, B. Alphenaar, C.S. Jayanthi, and S.Y. Wu, J. Appl. Phys. 99, 034306 (2006), doi:10.1063/1.2163008.

• Abstract: Our study of the adsorption of oxygen molecules on individual semiconductiong single-walled carbon nanotubes at ambient conditions reveals that the adsorption is physisorption, the resistance without O₂ increases by approximately two orders of magnitude as compared to that with O₂, and the sensitive response is due to the pinning of the Fermi level near the top of the valence band of the tube, resulting from impurity states of O₂ appearing above the valence band.

1. “Spin System Radiofrequency Superradiation: a Phenomenological Study and comparison with Nimeric Simulation”, C. L. Davis, V.K. Henner, A. V. Tchernatinsky, and I.V. Kaganov, Phys. Rev. B, 72, 054406 (2005), doi:10.1103/PhysRevB.72.054406.

• Abstract: We discuss the coherent behavior of a polarized, nuclear or electron, spin system for which the magnetic dipole radiation emitted in the radio-frequency region, has approximately quadratic dependence on the number of spins. An effective method of describing these phenomena is provided by computer simulation of a microscopic model of the spin system. Important aspects of this numeric simulation are described, together with a comparison with the theoretical predictions. The behavior of the transverse component of the magnetic moment, M⁺(t), in super-radiant conditions is studied. In addition, the role of dipole-dipole interactions in super-radiation phenomena is investigated in detail. It is shown that some important features of super-radiation cannot be described with the Bloch equations.

Book Chapters and Reports

2. “Thermal Transport in Nanostructured Materials” A. Chernatynskiy, D. R. Clarke and S. R. Phillpot, book chapter in “Handbook of Nanoscience, Engineering and Technology”, 3^rd Edition, CRC Press (2012).

1. “Simulation of the Thermal Transport Properties of UO₂: Recent Progress and Current Challenges” A. Chernatynskiy, A. El-Azab, J. Tulenko, S.R. Phillpot, to appear in “IAEA Review Report on Nuclear Fuels”, 2014.