Synthesis and structure of new layered oxides, MIILa2Ti3O10 (M = Co, Cu, and Zn)

New layered perovskite compounds, M-II[La2Ti3O10] (M = Co, Cu, and Zn) were synthesized by the ion-exchange reaction of the parent Na2La2Ti3O10 in molten salts. The crystal structure of the as-synthesized phases was determined by the Rietveld refinement for the powder X-ray diffraction patterns. The unit cells are tetragonal with a = 3.8128(1), 3.8248(2), and 3,8127(1) Angstrom and c = 27.568(1), 26.329(1), and 27.5129(9) Angstrom with an I4/mmm (Z = 2) space group for the Co, Cu, and Zn phases, respectively. The transition-metal atoms occupy strongly flattened tetrahedral sites with 50% probability between the perovskite slabs. These oxides represent the first example of layered perovskite whose interlayer spaces are occupied by small transition-metal cations. Particularly for the Cu oxide, remarkable shortening of the c-axis was observed upon heating up to 700 degrees C under an Ar atmosphere. Such a contraction is likely to result from the flattening of the CuO4 unit toward a quasi-square planar coordination.