STRUCTURAL STUDY ON NEW ORDERED POTASSIUM-NICKEL FLUORIDE-TYPE OXIDES, STRONTIUM LANTHANUM MAGNESIUM MANGANESE OXIDE AND STRONTIUM LANTHANUM ZINC MANGANESE OXIDE

The crystal structure of two new K2NiF4-type oxides, SrLaMg0.5Mn0.5O4 and SrLaZn0.5Mn0.5O4, have been determined with space group both I4/mm m and P422 using Rietveld refinement profile. An improvement in reliab ility factor on the basis of space group P422 suggested that they have ordered structure and unit cell parameters be a is-approximately-equa l-to a0 square-root 2 = 5.4428(1) angstrom, c is-almost-equal-to c0 = 12.6084(2) angstrom for SrLaMg0.5Mn0.5O4 and a is-approximately-equal- to a0 square-root 2 = 5.4588(1) angstrom, c is-almost-equal-to c0 = 12 .6247(3) angstrom for SrLaZn0.5Mn0.5O4. Comparing lengths of (Mn-O) bo nds calculated with space group P422, the local symmetry of (MnO6) oct ahedron is strongly dependent on competing Mg and Zn ions in the perov skite-type plane.