pyrochlore phase structure without impurity phase such as CaZrO3, implying
that the maximum Ca-doping content may be greater than0.10. However, the second phase CaZrO3might have appeared atxless 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.