Microstructure and thermoelectric properties of α-and γ-Al2O3 doped ZnO under high pressure

Abstract

Using high pressure and high temperature (HPHT) technology to improve the thermoelectric properties of oxides is a feasible solution. To further understand the micro-physical mechanism improving the thermoelectric performance of ZnO in a higher pressure environment, the effects of α and γ lattice structure Al2O3 (α-Al2O3, γ-Al2O3) on doped ZnO were systematically studied. ZnO samples with different Al doping ratios (α-x, γ-x; x = 0.02, 0.04, 0.06, 0.08) were prepared by HPHT. Test results show that the high pressure and high temperature synthesis method effectively improves the solid solubility of α-Al2O3 and γ-Al2O3 in ZnO, among which γ-Al2O3 is more easily dissolved into the zinc oxide crystal lattice. Under the same doping ratio, the electronic conductivity of the sample synthesized with γ-Al2O3 is higher than that of the sample synthesized with α-Al2O3. In addition, the ZnAl2O4 phase precipitated out of the sample with increased Al doping. Although the ZnAl2O4 phase decreases the electrical properties of the sample, a small amount of ZnAl2O4 is uniformly dispersed in the ZnO sample, which can inhibit the growth of crystal grains, and assist grain refinement. The optimized high pressure sintering temperature was 1123 K, and the zT value of γ-0.04 was 0.17 at 973 K.