pyrochlore phase structure without impurity phase such as CaZrO3, implying that the maximum Ca-doping content may be greater than 0.10. However, the second phase CaZrO3 might have appeared at x less than 0.10 and could not be found while its quantity is below the detection limit of the XRD method. Thus, the precise value of the maximum Ca-doping content needs be determined by other methods.