Local structural studies of the cubic Cd1–xCaxO system through Cd K‐edge extended X‐ray absorption spectroscopic studies

Cd K-edge extended X-ray absorption fine-structure spectroscopic studies were carried out on Cd1–xCaxO (0 ≤ x ≤0.9) solid solutions and the first and second nearest neighbour (NN) distances and their mean square relative displacement σ2 were estimated. The first NN distance, dCd–O(x), was found to be smaller than its expected value, a(x)/2, obtained from the X-ray diffraction measurements. It increases monotonically and non-linearly with a negative curvature, comparable with that of the a(x) value variation. The variation σ2 of the 1NN with x is consistent with a disordered solid solution model. The 2NN distances dCd–Cd(x) and dCd–Ca(x) are found to follow the average values obtained by X-ray diffraction with dCd–Ca(x) > dCd–Cd(x). From detailed analysis it is argued that the solid solution exhibits a bimodal distribution of the 1NN distances, dCd–O(x) and dCa–O(x), and that the system belongs to a persistent type.