Utilizing of high-pressure high-temperature synthesis to enhance the thermoelectric properties of Zn_0.98Al_0.02O with excellent electrical properties

The temperature in the high-pressure high-temperature (HPHT) synthesis is optimized to enhance the thermoelectric properties of high-density ZnO ceramic, Zn_0.98Al_0.02O. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy show that HPHT can be utilized to control the crystal structure and relative density of the material. High pressure can be utilized to change the energy band structure of the samples via changing the lattice constant of samples, which decreases the thermal conductivity due to the formation of a multi-scale hierarchical structure and defects. The electrical conductivity of the material reaches 6× 10⁴ S/m at 373 K, and all doped samples behave as n-type semiconductors. The highest power factor (6.42 μ W cm ^{- 1}K ^-2) and dimensionless figure of merit (zT=0.09) are obtained when Zn_0.98Al_0.02O is produced at 973 K using HPHT, which is superior to previously reported power factors for similar materials at the same temperature. Hall measurements indicate a high carrier concentration, which is the reason for the enhanced electrical performance.