EXAFS study of double perovskite (Sr2-xCax)FeMoO6 (0 ≤ x ≤ 2.0) and Sr2CrMO6 (M = Mo, W) systems

The local structure of the double perovskite (Sr2-xCax)FeMoO6 (0 ≤ x ≤ 2.0) and Sr2CrMO6 (M = Mo, W) systems have been probed by extended X-ray absorption fine structure (EXAFS) spectroscopy at the Fe and Cr K-edges. It was found that the Fe-O distance decreases from 1.999(7) A (x = 0) to 1.991(1) A (x = 1.0) in (Sr2-xCax)FeMoO6 with a tetragonal phase (I4/m). When the x value is further increased from 1.5 to 2.0, the Fe-O bond distance decreases from 2.034(5) to 2.012(4) A with a monoclinic phase (P21/n). On the other hand, Cr-O, Cr-Sr and Cr-W bond distances in Sr2CrWO6 are all slightly longer than the corresponding bond distances in Sr2CrMoO6, which is attributable to the larger ionic radius of W5+ (0.62 A) than Mo5+ (0.61 A).