Synthesis and Structure of New Layered Oxides, M II La 2 Ti 3 O 10 (M = Co, Cu, and Zn)

New layered perovskite compounds, M II [La 2 Ti 3 O 10 ] (M = Co, Cu, and Zn) were synthesized by the ion-exchange reaction of the parent Na 2 La 2 Ti 3 O 10 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) Å and c = 27.568(1), 26.329(1), and 27.5129(9) Å with an I 4/ 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 °C under an Ar atmosphere. Such a contraction is likely to result from the flattening of the CuO 4 unit toward a quasi-square planar coordination.