Structural features and thermoelectric properties of Al-doped (ZnO)(5)In2O3 homologous phases

In this work, we investigated the influence of Al doping on the structure of the (ZnO)(5)In2O3 homologous phase and the thermoelectric characteristics of (ZnO)(5)(In1-xAlx)(2)O-3 ceramics for x=0, 0.01, 0.03, 0.05, 0.1, and 0.2, prepared using a classic ceramic procedure and sintering at 1500 degrees C for 2 hours. The Al substituted for In on both the primary sites in the Zn-5(In1-xAlx)(2)O-8 homologous phase, the octahedral sites in the basal-plane inversion boundaries and the trigonal bi-pyramidal sites in the zig-zag inversion boundaries, which resulted in a uniformly increased shrinkage of the unit cell with the additions of Al. The a and c parameters were reduced for x=0.2 by a maximum 0.8%. All the samples had similar microstructures, so the differences in the TE characteristics mainly resulted from the effects of the substitution of Al for In, decreasing the charge-carrier concentration and affecting their mobility. Slightly improved TE characteristics were only observed for Al additions with x=0.01-0.05, while larger additions of Al only resulted in a reduced electrical conductivity and decreased ZT values in comparison to the un-doped composition.