Inherent Anharmonicity of Harmonic Solids  

作　　者：Matthias T.Agne Shashwat Anand G.Jeffrey Snyder 

机构地区：[1]Department Materials Science and Engineering,Northwestern University,Evanston,IL,USA

出　　处：《Research》2022年第3期409-419,共11页研究（英文）

基　　金：the U.S.Department of Energy,Office of Energy Efficiency and Renewable Energy(EERE)program“Accelerated Discovery of Compositionally Complex Alloys for Direct Thermal Energy Conversion”(DOE Award DE-AC02-76SF00515).

摘　　要：Atomic vibrations,in the form of phonons,are foundational in describing the thermal behavior of materials.The possible frequencies of phonons in materials are governed by the complex bonding between atoms,which is physically represented by a spring-mass model that can account for interactions(spring forces)between the atoms(masses).The lowest-order,harmonic,approximation only considers linear forces between atoms and is thought incapable of explaining phenomena like thermal expansion and thermal conductivity,which are attributed to nonlinear,anharmonic,interactions.Here,we show that the kinetic energy of atoms in a solid produces a pressure much like the kinetic energy of atoms in a gas does.This vibrational or phonon pressure naturally increases with temperature,as it does in a gas and therefore results in a thermal expansion.Because thermal expansion thermodynamically defines a Grüneisen parameterγ,which is a typical metric of anharmonicity,we show that even a harmonic solid will necessarily have some anharmonicity.A consequence of this phonon pressure model is a harmonic estimation of the Grüneisen parameter asγ≈(3/2)(3−4x^(2))/(1+2x^(2)),where x=vt/vl is the ratio of the transverse and longitudinal speeds of sound.We demonstrate the immediate utility of this model by developing a high-throughput harmonic estimate of lattice thermal conductivity that is comparable to other state-of-the-art estimations.By linking harmonic and anharmonic properties explicitly,this study provokes new ideas about the fundamental nature of anharmonicity,while also providing a basis for new material engineering design metrics.

关 键 词：HARMONIC PHONON LINKING 

分 类 号：O562[理学—原子与分子物理]