Anharmonic Interaction in Negative Thermal Expansion Material CaTiF6

Lei Wang; Ying Chen; Jun Ni; Feng Ye; Cong Wang

doi:10.1021/acs.inorgchem.2c03263

Anharmonic Interaction in Negative Thermal Expansion Material CaTiF₆

Inorg Chem. 2022 Oct 31;61(43):17378-17386. doi: 10.1021/acs.inorgchem.2c03263. Epub 2022 Oct 19.

Authors

Lei Wang¹, Ying Chen², Jun Ni³, Feng Ye⁴, Cong Wang⁵

Affiliations

¹ Department of Physics, University of Science and Technology Beijing, Beijing100083, China.
² Fracture and Reliability Research Institute, School of Engineering, Tohoku University, Sendai980-8579, Japan.
³ State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing100084, China.
⁴ State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing100083, China.
⁵ School of Integrated Circuit Science and Engineering, Beihang University, Beijing100191, China.

PMID: 36261410
DOI: 10.1021/acs.inorgchem.2c03263

Abstract

Although the quasi-harmonic approximation (QHA) method applies to many materials, it is necessary to study the anharmonic interaction for extremely anharmonic materials. In this work, the unusual negative thermal expansion (NTE) property of CaTiF₆ is studied by combing QHA and anharmonic interaction. The improved self-consistent phonon approximation (ISCPA), which treats anharmonic effects in solids nonperturbatively, is employed. The agreement of NTE behavior between the calculation and the experiment can be further promoted from qualitative consistency by QHA to quantitative consistency by the ISCPA. From mode Grüneisen parameters, it is found that the low-frequency phonons, especially acoustic phonons, contribute greatly to the NTE behavior of CaTiF₆. The rigid unit modes (RUMs) of low-frequency optical phonons can be identified. The phonon lifetime of CaTiF₆ is calculated from three-phonon interactions; thereby, the NTE mechanism can be further explored by phonon lifetimes of phonons with different frequencies on heating. The anomalous lattice thermal conductivity (LTC) is predicted using the Boltzmann transport equation within the relaxation time approximation. The glasslike LTC can occur in crystal CaTiF₆.