Thermoelectric Properties and Phase Transition of (Zn_xCu_2−x)V₂O₇

Abstract

The phase stability and thermoelectric properties of the layered structure of (Zn_xCu_2−x)V₂O₇ solid solutions were studied for x≥0.2. X-ray diffraction measurements, compositional studies, and thermal analysis verified that the low-temperature form of the (Zn_xCu_2−x)V₂O₇ solid solution (monoclinic structure, C2/c) was stable for 0.2≤x≤2 when heated below 863 K in air. On heating, phase transformation occurred at least at 0.2≤x≤2 at a nearly constant temperature of approximately 873 K; above this temperature, a high-temperature form of the (Zn_xCu_2−x)V₂O₇ solid solution was formed.
The Seebeck coefficients of the low-temperature (Zn_xCu_2−x)V₂O₇ solid solution exhibited large negative values in the range of approximately −520 to −700 μV/K, and the electrical resistivity increased with Zn addition. The maximum power factor of 1.99×10⁻⁷ W/m K² was obtained at 823 K for the low-temperature form of the (Zn_0.2Cu_1.8)V₂O₇ solid solution.