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Open AccessArticle

Features of the High-Temperature Structural Evolution of GeTe Thermoelectric Probed by Neutron and Synchrotron Powder Diffraction

1
Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de Investigaciones Científicas (CSIC), Sor Juana Inés de la Cruz 3, 28049 Madrid, Spain
2
Departamento de Física de Materiales, Universidad Complutense de Madrid, E-28040 Madrid, Spain
3
Institut Laue Langevin, BP 156X, Grenoble F-38042, France
*
Authors to whom correspondence should be addressed.
Metals 2020, 10(1), 48; https://doi.org/10.3390/met10010048
Received: 26 November 2019 / Revised: 20 December 2019 / Accepted: 24 December 2019 / Published: 25 December 2019
(This article belongs to the Special Issue Thermoelectric Compounds: Processing, Properties and Applications)
Among other chalcogenide thermoelectric materials, GeTe and derivative alloys are good candidates for intermediate temperature applications, as a replacement for toxic PbTe. We have prepared pure polycrystalline GeTe by using arc-melting, and investigated its structural evolution by using neutron powder diffraction (NPD) and synchrotron X-ray diffraction (SXRD), as well as its correlation with the thermal variation of the Seebeck coefficient. Besides a significant Ge deficiency (~7% Ge vacancies), the thermal evolution of the unit-cell volume and Ge-Te bond lengths in the rhombohedral phase (space group R3m), below 700 K, show unexpected anomalies involving the abrupt Ge-Te bond lengthening accompanied by increased Te thermal displacements. Above 700 K, the sample is cubic (space group Fm-3m) and shows considerably larger displacement parameters for Ge than for Te, as a consequence of the random distribution of the lone pair lobes of Ge2+. The Seebeck coefficient, reaching 120 μV K−1 at 775 K, shows a shoulder in the 500–570 K region that can be correlated to the structural anomaly, modifying the electron-phonon scattering in this temperature range. View Full-Text
Keywords: thermoelectrics; neutron powder diffraction; Ge deficiency; structural phase transition thermoelectrics; neutron powder diffraction; Ge deficiency; structural phase transition
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Gainza, J.; Serrano-Sánchez, F.; Nemes, N.M.; Martínez, J.L.; Fernández-Díaz, M.T.; Alonso, J.A. Features of the High-Temperature Structural Evolution of GeTe Thermoelectric Probed by Neutron and Synchrotron Powder Diffraction. Metals 2020, 10, 48.

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