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 ALaMnRuO6 (A = Ca, Sr, Ba) perovskites. The EXAFS analysis of Mn K-edge spectra showed MnO6 octahedra are distorted. Among the three perovskites, the polyhedral distortion is highest for SrLaMnRuO6 ( = 1.4 × 10). For CaLaMnRuO6 ( = 0.5 × 10) and BaLaMnRuO6, ( = 0.7  10), the smaller values of distortion parameters indicate that the MnO6 octahedra are relatively regular and undistorted in the latter two systems. In SrLaMnRuO6, MnO6 distortion appears to be of orthorhombic (Q2) type whereas for CaLaMnRuO6 and BaLaMnRuO6, the distortion is of tetragonal or Q3 type. The Mn-O distances as determined from the EXAFS measurements, increases 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.