EXAFS studies of ruthenium based double perovskite ALaMnRuO6 (A= Ca, Sr, Ba)

Room and liquid nitrogen temperatures Mn K - edge extended X-ray fine structure (EXAFS) studies were carried out on powder samples of ALaMnRuO/sub 6/ (A= Ca, Sr, Ba) perovskites. The EXAFS analysis of Mn K-edge spectra showed that MnO/sub 6/ octahedra were distorted. Among the three perovskites, the polyhedral distortion was highest for SrLaMnRuO/sub 6/ ( delta =1.4 X 10/sup -3/). For CaLaMnRuO/sub 6/ (delta = 0.5 X 10/sup -3/) and BaLaMnRuO/sub 6/, (delta = 0.7 X 10/sup -3/), the smaller values of distortion parameters indicated that the MnO/sub 6/ octahedra were relatively regular and undistorted in the latter two systems. In SrLaMnRuO/sub 6/, MnO/sub 6/ distortion appeared to be of orthorhombic (Q/sub 2/) type whereas for CaLaMnRuO/sub 6/ and BaLaMnRuO/sub 6/, the distortion was of tetragonal or Q/sub 3/ type. The Mn - O distances as determined from the EXAFS measurements, increased with the increase in the size of the divalent cation. No structural changes occurred in the local environment around Mn atom when the temperature was lowered from room to liquid nitrogen temperature. (Orig./A.B.)