See our new website: https://feng.mech.utah.edu/ 

Overview

• Thermal management

• Thermoelectrics

• Thermal insulation

• Thermal protection

• Thermal energy storage

• Batteries

• Machine Learning

Theoretical methods:

• Density functional theory (DFT) packages: (phase stability, phase transition/ transformation, mechanical/ electrical/ thermodynamical/ thermal/ thermoelectical properties, atomic vibration, ion migration, ab-initio molecular dynamics (AIMD)) -- VASP, Abinit, ELK, Quantum Espresso

• Classical molecular dynamics (MD) simulations, e.g., LAMMPS

• Tight-binding molecular dynamics (TBMD) -- DFTB

• Harmonic lattice dynamics (LD) calculations, e.g., (my own code, GULP, Phonopy)

• Phonon normal mode analysis (NMA), i.e., spectral energy density (SED) analysis (my own code & my tool)

• First principles calculations of three- and four-phonon scattering rates (my own developed method & code, Thirdorder, ShengBTE)

• Spectral phonon temperature (SPT) method (my own developed method & code)

• Exact solution to linearized Boltzmann transport equation (BTE) including three- and four-phonon scattering (my own developed method & code)

• Finite difference and finite volume methods (FDM, FVM) in heat, mass, and momentum transfer (my own code)

• Gray BTE -- FVM solver

Experimental methods:

• 3-Omega Thermal Conductivity Measurement

• Laser Flash Thermal Conductivity measurement

• Electron microscopy

Ultra-high thermal conductivity materials

• Diamond, BAs, SiC, etc.

Semiconductors

• C, Si, Ge, BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, CdTe, etc.

• impurity, defects, alloy, nanostructures (nanowires, nanomeshes, superlattices, etc.)

Ultra-high temperature materials

• HfB2, ZrB2, HfC, ZrC, HfN, ZrN, etc.

Thermoelectric materials & nanostructures

• SnSe, GeTe, SnS, PbS, PbTe, Bi2Te3, Sb2Te3, Bi2Se3, Bi2S3, etc.

• PbTe-Bi2Te3, PbTe-Bi2-xSbxTe3, Bi2Te3-xSex, Bi13S18I2 heterostructures & nanocomposites

• Cage-structure materials: skutterudites, clathrates

Emerging 1D/2D layered materials

• III, IV, V groups: Graphene, boron nitride, carbon nanotube (CNT), black phosphorus, phosphorene, silicene, germanene, borophene, etc.

• Transition-metal chalcogenide (MoS2, MoSe2, VS2, VSe2, WS2, WSe2, PdSe2, ZrTe5, etc.)

• Their nanostructures: graphene nanomesh & nanoribbon, graphene/substrate & sandwich, graphene/BN superlattice & heterostructure, etc.

Complex oxides, thin films, surfaces, heterostructures

• Thermal, electrical: LaCoO3, LaxSr1-xCoO3-d, etc. Magnetic, electrical: SrTiO3, LaxSr1-xMnO3, etc.

• Rutile: RuO2, CrO2, PdO2, ReO2, RhO2, OSO2, IrO2, etc.

Lithium ion related

• Batteries: LiCoO2, LiFePO4, Li10GeP2S12, LiNiO2, MgV2O5, CaV2O5, etc.

• LiNbO2 Memristors

Molecules, amorphous, organic materials

• polymers (polyethylene, polystyrene, polypropylene, EVOH, etc.), SiO2

Highlight: Four-Phonon Processes

Phonon is the microscopic heat carrier in solids, and the phonon-phonon scattering is the main thermal resistance mechanism that determines the thermal transport in solids.

Four-phonon scattering is a multi-phonon process, and its evaluation has been a long-standing challenge for decades. 

We solved this problem and found the four-phonon scattering to be of great importance in: 

1. Low-thermal-conductivity anharmonic materials, such as all ionic crystals, thermoelectric materials, salts, complex oxides, etc.

2. Simple crystals with acoustic-optical phonon band gaps

3. Most materials at high temperatures

4. Optical phonons of most materials

5. Materials with reflection symmetry (such as single-layer grahpene, BN, CNT)

References:

• T. Feng, X. Ruan*, "Quantum mechanical prediction of four-phonon scattering rates and reduced thermal conductivity of solids", Physical Review B 93, 045202 (2016). [Link] [PDF] 

• T. Feng, L. Lindsay, X. Ruan*, "Four-phonon scattering significantly reduces intrinsic thermal conductivity of solids", Physical Review B: Rapid Communications 96 (16), 161201 (2017). [Link] [PDF+SI]  (This work is highlighted by several academic news: see our News)  (This work is intensively cited by three Science reports: see our News)

• T. Feng, Xiulin Ruan*, "Four-phonon scattering reduces intrinsic thermal conductivity of graphene and the contributions from flexural phonons", Physical Review B 97, 045202 (2018). [Link] [PDF] 

• T. Feng*, X. Yang, X. Ruan*, "Phonon anharmonic frequency shift induced by four-phonon scattering calculated from first principles", Journal of Applied Physics 124, 145101 (2018). [Link] [PDF] 

• X. Yang, T. Feng, J. Li, X. Ruan, "Stronger role of four-phonon scattering than three-phonon scattering in thermal conductivity of III-V semiconductors at room temperature", Physical Review B 100, 245203, (2019). [Link] 

• X. Yang#, T. Feng#, J. S. Kang, Y. Hu, J. Li, X. Ruan*, Observation of strong higher-order lattice anharmonicity in Raman and infrared response, Physical Review B 101, 161202(R) (2020). [Link] (# these authors contributed equally) 

• Z. Tong, X. Yang, T. Feng, H. Bao, X. Ruan, First-principles predictions of temperature-dependent infrared dielectric function of polar materials by including four-phonon scattering and phonon frequency shift, Phys. Rev. B 101, 125416 (2020). [Link] 

• (Book Chapter) T. Feng*, X. Ruan*, Higher-order phonon scattering: advancing the quantum theory of phonon linewidth, thermal conductivity and thermal radiative properties. in Nanoscale Energy Transport 2-1-2–44 (IOP Publishing, 2020). https://doi.org/10.1088/978-0-7503-1738-2ch2 (invited book) [Link] 

• T. Feng*,  A. O'Hara, S. T. Pantelides*, "Quantum Prediction of Ultra-Low Thermal Conductivity in Lithium Intercalation Materials", Nano Energy, 104916 , 2020. https://doi.org/10.1016/j.nanoen.2020.104916   [PDF] [SI]