I: Material Design and Growth


Shanyuan aims to develop novel semiconductors for infrared photonic and optoelectronic applications, and renewable energy applications. This includes constructing and examining databases of existing materials, and ranking candidates based on a combination of empirical rules, preliminary DFT calculations, and simple machine learning approaches. The major material platforms for such targeted functionality is based on complex oxides and chalcogenides, particularly the transition metal perovskite chalcogenides (TMPCs), with a general chemical formula of ABX3, where A is an alkali, alkaline, or rare earth metal; B is a transition metal; and X is a chalcogen. Shanyuan makes these materials in polycrystalline powder form with solid state reaction in sealed quartz ampoules. Shanyuan also grows single crystals using chemical vapor transport and salt flux methods.
Synthesis of new materials is of course followed by extensive material characterizations. A set of characterization routines for bulk, surface, or local studies with different sensitivities was developed, including thin film and powder XRD, Rietveld analysis, Raman spectroscopy, AFM, SEM, TEM, EDS, XPS, XRF, etc. Advanced beamline facility based measurements were also carried out. Through user experiments/proposals, various synchrotron and neutron scattering/spectroscopy techniques were performed in collaboration with SLAC SSRL, NIST NCNR, LBL ALS, Brookhaven, Oak Ridge National Laboratories.
Relavent works: S. Niu et al. Nat, Photon. 2018, 12, 392. [doi]; S. Niu, et al. Adv. Mater. 2017, 29, 1604733 [doi]; S. Niu, et al. Chem. Mater. 2018, 30, 4882. [doi]; S. Niu et al. Chem. Mater. 2018, 30, 4897. [doi]

II: Quasi-1D Materials For Mid-IR Photonics and Optoelectronics


The goal is to identify Mid-wave IR and Long-wave IR optical materials for high performance, low cost infrared optics and photodetectors. The techniques to study these materials include UV-Vis-IR spectrophotometry, variable angle spectroscopic ellipsometry, polarization-resolved Fourier-transform IR spectroscopy, photocurrent, Raman analysis, etc.



III: 3D and Quasi-2D Materials for Solar Energy Conversion and Lighting


Photovoltaics with high performance inorganic chalcogenide perovskites without toxic or rare elements. Relevant studies include static, quantitative, and time-resolved photoluminescence to extract the optical properties of the materials.

IV: Materials for Thermoelectrics


TMPCs share a lot of exciting features with the well-studied oxide counterparts, including rich, tunable chemistry, high stability, and environmentally friendly and earth abundant composition. Similar to the perovskite oxides, the valence band and the conduction band of TMPC are primarily composed of chalcogen p orbitals and transition metal d orbitals, respectively. High density of states (DOS) is thus expected from the combination of highly symmetric structure and degenerate transition metal d orbitals. These features are desirable attributes for high temperature thermoelectric candidates. In fact, perovskite oxides have been extensively studied for thermoelectrics due to this advantage. However, the high lattice thermal conductivity and large band gaps limit their thermoelectric performance. With the replacement of oxygen with larger, heavier, and less electronegative chalcogen elements, TMPCs are expected to possess lower thermal conductivity and lower band gaps spanning IR to visible spectrum, thereby mitigating those issues in the oxide counterparts for both thermoelectric and opto-electronic applications. Ongoing experimental studies include electrical and thermal transport coefficient measurements, and chemical and thermal stability tests of TMPCs. Exceptionally low thermal conductivity of grown TMPC crystals has been experimentally discovered. Good thermal stability of polycrystalline samples are also reported. Doping study to tune the electrical conductivity is under way.

Materials under Extreme Conditions

Diamond Anvil Cells are compact devices that enable compression of materials up to hundreds of GPa.