Phase transformation behavior of Ca-doped zirconia sintered at different temperatures

The phase evolution studies of 16 mol% calcium-doped zirconia have been carried out after sintering the samples at 800 °C, 1000 °C, 1200 °C, and 1400 °C. The X-ray diffraction (XRD), Raman spectroscopic along FTIR studies confirmed that the pure zirconia exists only in the monoclinic phase. However, the XRD analysis of calcium-doped zirconia and its Rietveld refinement studies revealed the stabilization of zirconia in the monoclinic and cubic phases both. With increasing sintering temperature, the development of cubic phase in zirconia is seen and at 1400 °C, an almost fully stabilized cubic phase of zirconia is achieved. The traces of CaZrO3 (perovskite phase) are observed in XRD and Raman studies when samples are sintered at 800 °C and 1000 °C. The results of FESEM suggest that grains are uniformly distributed and closely packed. Further, EDS mapping suggests that the calcium is uniformly distributed in samples. The thermal stability analysis confirms that calcium-stabilized zirconia is stable at high temperatures and analysis of the Vickers hardness test confirms that it is harder as compared to pure zirconia. Results reported here indicate that the sintering of 16 mol% calcium-doped zirconia at 1400 °C leads to the complete transformation of m-ZrO2 to c-ZrO2.