STRUCTURAL AND DIELECTRIC STUDIES ON THE NEW SERIES OF LAYERED COMPOUNDS, STRONTIUM LANTHANUM SCANDIUM OXIDES

A new series of K2NiF4 related layered compounds SrLaScO4 and SrLa2SC2O7 have been synthesized. Structural parameters were determined by X-ray powder Rietveld analysis. The results showed both compounds have orthorhombic lattice symmetry with the constants a = 5.7657(5) angstrom, b = 5.7513(4) angstrom and c = 12.467(1) angstrom for SrLaScO4 and a = 5.7818(5), b = 5.7367(5) and b = 20.534(2) angstrom for SrLa2Sc2O7. Although pure phases were not obtained for compounds BaLaScO4 and BaLa2Sc2O7, their X-ray diffraction patterns could be indexed as a tetragonal lattice symmetry, respectively. The orthorhombic nature of crystal distortion in Sr-compounds at room temperature was attributed to be the tilting of ScO6 octahedra in perovskite layer. Two types of reorientation of the octahedra occurred with increasing temperature for both SrLaScO4 and SrLa2Sc2O7, along the sequence of symmetry O' --> O --> T. During these transitions dielectric anomalies were observed. The anomalies are considered to be accompanied by a zone-boundary phase transition attributed to the ScO6 octahedra rotation.