Effect of absorbed power and dopant content on densification during rapid microwave sintering of Bi2O3-doped ZnO

ZnO samples with an addition of 0, 0.035, 0.1, and 0.35 mol.% Bi2O3 were microwave sintered at heating rates 10 and 50 degrees C/min to a maximum temperature of 1200 degrees C with zero hold time. The densification curves obtained by optical dilatometry have been studied in their dependence on the dopant concentration and the heating rate. Direct volumetric absorption of microwave radiation resulted in a 50-60 degrees C shift of the densification curves toward low temperatures compared to susceptor-assisted heating. An analysis of the effect of the volumetrically absorbed microwave power on the formation of grain-boundary phases that facilitate densification is presented.