Temperature-dependent thermal expansion of cast and hot-pressed LAST (Pb–Sb–Ag–Te) thermoelectric materials

Abstract

The thermal expansion for two compositions of cast and hot-pressed LAST (Pb–Sb–Ag–Te) n-type thermoelectric materials has been measured between room temperature and 673 K via thermomechanical analysis (TMA). In addition, using high-temperature X-ray diffraction (HT-XRD), the thermal expansion for both cast and hot-pressed LAST materials was determined from the temperature-dependent lattice parameters measured between room temperature and 623 K. The TMA and HT-XRD determined values of the coefficient of thermal expansion (CTE) for the LAST compositions ranged between 20 × 10⁻⁶ K⁻¹ and 24 × 10⁻⁶ K⁻¹, which is comparable to the CTE values for other thermoelectric materials including PbTe and Bi₂Te₃. The CTE of the LAST specimens with a higher Ag content (Ag_0.86Pb₁₉Sb_1.0Te₂₀) exhibited a higher CTE value than that of the LAST material with a lower Ag content (Ag_0.43Pb₁₈Sb_1.2Te₂₀). In addition, a peak in the temperature-dependent CTE was observed between room temperature and approximately 450 K for both the cast and hot-pressed LAST with the Ag_0.86Pb₁₉Sb_1.0Te₂₀ composition, whereas the CTE of the Ag_0.43Pb₁₈Sb_1.2Te₂₀ specimen increased monotonically with temperature.

Keywords:

• semiconductor
• thermomechanical analysis
• powder diffraction
• thermal expansion

Acknowledgements

The authors acknowledge the financial assistance of the U.S. Department of Energy Grant DE-FC26-04NT42281 and Office of Naval Research MURI Grant number N000140310789. The research work at the High Temperature Materials Laboratory was sponsored by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Freedom CAR and Vehicle Technologies, as part of the High Temperature Materials Laboratory User Program, Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract number DE-AC05-00OR22725. One of the authors (F. Ren) would like to acknowledge the financial support from the Higher Education Research Experience program sponsored by the Oak Ridge National Laboratory during his tenure at the High Temperature Materials Laboratory.

The authors would like to thank Dr. Andrew Payzant at the Materials Science and Technology Division of the Oak Ridge National Laboratory for his technical assistance and helpful discussion with respect to the high temperature x-ray experiments. One of the authors (F. Ren) would like to acknowledge the help from Mr. Takayuki Kobayashi (Visiting scholar, Department of Chemical Engineering and Materials Science, Michigan State University) for his assistance in translating ref. 24 to English.