Results and discussion
As shown in Fig. 1, all the samples of La2xCaxZr2O77δ
(x¼0, 0.06, 0.07, 0.08, 0.09, 0.10) exhibits 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.
Fig. 2 shows the calculated intensity ratio of reflections
(662) and (331) for La2xCaxZr2O7. It can be seen clearly that
the intensity ratio increases with increasing Ca-doping value x.
With the increase of x from 0 to 0.10, the intensity ratio
increases by 15% from 8.14 to 9.37. The lanthanum zirconate
normally exhibits oxygen nonstoichiometry as represented by
formula La2Zr2O77δ. The effect of oxygen nonstoichiometry