The effect of processing conditions on phase and microstructure of CaGeO3 ceramics

The present study illustrates the effects of processing conditions on phase and microstructure of CaGeO3 ceramics. It is shown that the fabrication of single phase, high density and crack-free CaGeO3 ceramics is particularly challenging using conventional sintering or spark plasma sintering. The main difficulties in achieving single phase are predominantly related to the segregation of an additional phase identified as Ca5Ge3O11, most likely driven by the volatilization of GeO2 during processing at high temperature. This can be mainly suppressed by adding an appropriate excess amount of GeO2. High density can be achieved by conventional sintering and spark plasma sintering (SPS), but in the temperature ranges that lead to the formation of Ca5Ge3O11. The presence of cracks observed in the ceramics is attributed to the development of local residual stresses caused by the anisotropy of the thermal expansion and elastic properties, and it can be avoided under certain SPS conditions.