Thermoelectric properties of textured Zn1−xAlxO ceramics prepared by spark plasma sintering of hydrothermally synthesized rod-shaped powders

Textured Zn1−xAlxO (x=0, 0.01, 0.02, 0.04) ceramics were prepared by spark plasma sintering (SPS) using rod-shaped powders synthesized by hydrothermal synthesis. An orientation degree of up to 0.6 was obtained after SPS because the precursor powders are dominantly grown along the [0001] direction. Along with a low Al3+ solution level, no trace of ZnAl2O4 was detected in both the powders and sintered bulks due to a high pH value of 8.5–9.0 during hydrothermal synthesis. The textured structure of the resultant Zn1−xAlxO bulks possesses high carrier mobility, leading to enhanced electrical conductivity, which increased from 68.2 S cm−1 to 749.2 S cm−1 for the Zn0.96Al0.04O composition as the temperature is increased from 373 K to 573 K. As a result, the textured Zn0.96Al0.04O ceramic exhibited an enhanced power factor of up to 4.7 W m−1 K−2 at 573 K.