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

Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de Investigaciones Científicas (CSIC), Sor Juana Inés de la Cruz 3, 28049 Madrid, Spain

Departamento de Física de Materiales, Universidad Complutense de Madrid, E-28040 Madrid, Spain

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)

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Abstract

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

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MDPI and ACS Style

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. https://doi.org/10.3390/met10010048

AMA Style

Gainza J, Serrano-Sánchez F, Nemes NM, Martínez JL, Fernández-Díaz MT, Alonso JA. Features of the High-Temperature Structural Evolution of GeTe Thermoelectric Probed by Neutron and Synchrotron Powder Diffraction. Metals. 2020; 10(1):48. https://doi.org/10.3390/met10010048

Chicago/Turabian Style

Gainza, Javier, Federico Serrano-Sánchez, Norbert M. Nemes, José L. Martínez, María T. Fernández-Díaz, and José A. Alonso. 2020. "Features of the High-Temperature Structural Evolution of GeTe Thermoelectric Probed by Neutron and Synchrotron Powder Diffraction" Metals 10, no. 1: 48. https://doi.org/10.3390/met10010048

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

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