Yttria is an electroceramic material that has a negative temperature coefficient of resistivity (i.e. it is an NTC type semiconductor). This property, along with its high melting point and good stability, makes yttria a potential sensor material (thermistor) for measuring temperature differences in demanding applications. Recently there has been increasing interesting in studying this ceramic material. How-ever, there is very limited published information on the microstructural characteristics of pure yttria processed under various conditions. Furthermore, reported evidence on the effect of processing conditions on the electrical response of the material is still lacking. Studies within our Center have revealed a correlation between aging time and electrical behaviour in pure yttria samples. The present study examines the evolution of the microstructure of sintered yttria powder during different annealing treatments.

Yttria pellets (6mm diameter, 2mm height) were cold pressed and then sintered at 1550°C for 24h in air. The sintered pellets were then annealed at 1100°C for different times. Specimens for SEM examination were prepared by grinding the surface of the pellets (using grit paper up to 400) and subsequently polishing them using l μm alumina powders.