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 Cd(1-x)Ca(x)O (0 ≤ x ≤0.9) solid solutions and the first and second nearest neighbour (NN) distances and their mean square relative displacement σ(2) were estimated. The first NN distance, d(Cd-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 σ(2) of the 1NN with x is consistent with a disordered solid solution model. The 2NN distances d(Cd-Cd)(x) and d(Cd-Ca)(x) are found to follow the average values obtained by X-ray diffraction with d(Cd-Ca)(x) > d(Cd-Cd)(x). From detailed analysis it is argued that the solid solution exhibits a bimodal distribution of the 1NN distances, d(Cd-O)(x) and d(Ca-O)(x), and that the system belongs to a persistent type.