Calcia-doped yttria-stabilized zirconia for thermal barrier coatings: synthesis and characterization

Doping with other oxides has been a stabilization method of ZrO2 for thermal barrier coating applications. Such a stabilized system is 7–8 mol% YO1.5-doped zirconia (7YSZ), which has been in use for around 20 years. In this study, calcia (CaO) and yttria (Y2O3) have been used for doping ZrO2 to produce a stable single-phase cubic calcia-doped yttria-stabilized zirconia (CaYSZ). This has been synthesized using wet chemical synthesis as well as by solid-state synthesis. Unlike partially stabilized zirconia where 5 mol% CaO is doped into ZrO2, CaYSZ has been found to be stable up to 1600 °C. Detailed CaYSZ synthesis steps and phase characterization are presented. Wet chemical synthesis resulted in a stable single-phase CaYSZ just after 4 h treatment at 1400 °C, whereas a 36 h annealing at 1600 °C is required for CaYSZ synthesis during solid-state processing. The CaYSZ has been found stable even for 600 h at 1250 °C. Coefficient of thermal expansion and sintering temperature of CaYSZ was found to be 11 × 10−6 K−1 and 1220 °C, respectively, which are comparable to 7YSZ. An increase in sintering rate with increasing dopant concentration has also been observed.