Redox Reaction of Praseodymium Oxide in the ZnO Sintered Ceramics

The reason why Pr2O3 remains stable in the ZnO sintered body in air through pure Pr2O3 is only stable at high temperature was investigated using high-temperature XRD and thermogravimetry. The Pr2O3 in the ZnO sintered body was not due to reduction by the metallic Zn in the intestitial site of ZnO as reported in the literature. The redox reaction of praseodymium oxide in the ZnO grains is strongly affected by the microstructure. The reduction temperature of PrOx with defect fluorite structure upon heating is increased with the decrease of PrOx composition due to the decrease of open pores. On cooling, the oxidation of Pr2O3 into PrOx is kinetically suppressed by the O2 diffusion. In this way, Pr2O3 remains stable in ZnO sintered ceramics.