Coupling between acoustic and soft transverse optical phonons leads to negative thermal expansion of GeTe near the ferroelectric phase transition
File(s)
Accepted version
OA Location
Author(s)
Dangić, Đorđe
Murray, ED
Murphy, Aoife R
Fahy, Stephen
Savić, Ivana
Type
Journal Article
Abstract
GeTe is a well-known ferroelectric and thermoelectric material that undergoes a structural phase transition from a rhombohedral to the rocksalt structure at ∼600–700 K. We present a first-principles approach to calculate the thermal expansion of GeTe in the rhombohedral phase up to the Curie temperature. We find the minimum of the Helmholtz free energy with respect to the structural parameters, including the internal atomic displacement, in a manner similar to the traditional Grüneisen theory, explicitly accounting for the variation of the static elastic energy with respect to all structural parameters. We obtain the temperature dependence of the structural parameters of rhombohedral GeTe in very good agreement with experiments. In particular, we correctly reproduce a negative volumetric thermal expansion of GeTe near the phase transition. We show that the negative thermal expansion is induced by the coupling between acoustic and soft transverse optical phonons, which is also responsible for the low lattice thermal conductivity of GeTe.
Date Issued
2018-06-26
Date Acceptance
2018-06-19
Citation
Physical review B: Condensed matter and materials physics, 2018, 97
ISSN
1098-0121
Publisher
American Physical Society
Journal / Book Title
Physical review B: Condensed matter and materials physics
Volume
97
Copyright Statement
©2018 American Physical Society
Subjects
Science & Technology
Technology
Physical Sciences
Materials Science, Multidisciplinary
Physics, Applied
Physics, Condensed Matter
Materials Science
Physics
HIGH THERMOELECTRIC PERFORMANCE
PBTE
TEMPERATURE
1ST-PRINCIPLES
Publication Status
Published
Article Number
224106