Current Research

We aim to discover new materials and engineer existing materials for extreme applications for ultra-high temperatures (1000-3000 °C), ultra-low temperatures (-270 °C), ultra-high thermal conductivity (2000 W/mK), ultra-low thermal conductivity (<0.01 W/mK), ultra-high power density, and ultra-fast energy transfer rate, from the atomic level to human scale.

To realize these targets, we conduct both advanced simulations and experiments. We develop novel, accurate, and multiscale simulation models and methods based on first principles, molecular dynamics, finite element analysis, and machine learning. Guided by the predictive simulations, we design novel materials and systems and examine them through experiments.

We are interested in both fundamental problems of energy carriers including phonons, electrons, photons, and ions, and cutting-edge technologies including ultra-high-temperature thermal barrier coatings, thermal protections of hypersonic vehicles, nuclear materials, thermal management of electronic devices, thermoelectric energy harvesting, building energy efficiency, lithium-ion batteries, etc.

Our research areas include:

  • Ultra-high-temperature thermal transport
  • Thermal barrier coatings
  • Thermal management of hypersonic vehicles
  • Nuclear Materials
  • Thermal insulation materials & building energy efficiency
  • Thermal management of power electronics
  • Thermoelectric energy harvesting

Highlight: Four-Phonon Processes

Video credit: Linqing Peng, Tianli Feng, Xiulin Ruan

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

Four-phonon scattering is a multi-phonon process, and its prediction has been a long-standing challenge for decades. We have solved this problem and found the four-phonon scattering to be of great importance in:

  • Low-thermal-conductivity anharmonic materials, such as all ionic crystals, thermoelectric materials, salts, complex oxides, etc.
  • Simple crystals with acoustic-optical phonon band gaps
  • Most materials at high temperatures
  • Optical phonons of most materials
  • Materials with reflection symmetry (such as single-layer graphene, 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]

Research Methods:

Theoretical:

  • 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:

  • Laser Flash Thermal Conductivity measurement
  • Electron microscopy (TEM, SEM, STEM)
  • Fourier-transform infrared spectroscopy (FTIR)
  • Spark plasma sintering (SPS)

Materials:

  • 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

Past Projects at ORNL

  • DOE, BTO, “A New Approach to Encapsulate Salt Hydrate PCM”, (2020 - 2021).
  • DOE, BTO, “Facer barriers for aged foam boards with >R8/in”, $300,000 (2021).
  • DOE, BTO, “Active insulation systems, simulations and prototype development”, $300,000 (2021).
  • DOE, BTO, “Developing the Metrology for Accurately Assessing the R-value of Super Insulation”, $975,000(2018 - 2021).
  • DOE, BTO, “Models to Evaluate and Guide the Development of Low Thermal Conductivity Materials for Building Envelopes”, $850,000 (2018 - 2021).
  • DOE, BES, “Physics of Complex Materials Systems Through Theory and Microscopy/EELS”, $500,000 (2017- 2019).

Past Projects at Purdue

  • DARPA, “First Principles-Based Prediction and Design of Thermoelectric Materials and Interfaces under Large Temperature Gradients”, $1,000,000 (2015 - 2017).
  • NSF, “First Principles-Enabled Prediction of Thermal Conductivity and Radiative Properties of Solids”, $400,000(2012 - 2017).