Thermoelectric properties and phase transition of (ZnxCu2-x)V2O7

The phase stability and thermoelectric properties of the layered structure of (ZnxCu2-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 (ZnxCu2-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 (ZnxCu2-x)V2O7 solid solution was formed. The Seebeck coefficients of the low-temperature (ZnxCu2-x)V2O7 solid solution exhibited large negative values in the range of approximately -520 to -700 mu V/K, and the electrical resistivity increased with Zn addition. The maximum power factor of 1.99 x 10(-7) W/ m K-2 was obtained at 823 K for the low-temperature form of the (Zn0.2Ca1.8)V2O7 solid solution.