HIGH-PRESSURE SYNTHESIS AND CRYSTAL-STRUCTURE OF CAFETI2O6, A NEW PEROVSKITE STRUCTURE TYPE

Single-crystal and powder samples of a new calcium iron (II) titanate, CaFeTi2O6, have been synthesized at 12-15 GPa and 1200-1400 degrees C , and studied by X-ray diffraction. This compound is a variant of the perovskite structure and crystallizes in the tetragonal space group P4 (2)/nmc, a = 7.5157(2) Angstrom, c = 7.5548(2) Angstrom, and Z = 4. Ca lcium and two iron atoms are ordered on three different A sites, with calcium in approximately 10-fold coordination, with one iron atom in t etrahedral coordination (Fe-O = 2.084(2) Angstrom), and the other iron atom in square-planar coordination (Fe-O = 2.097(2) Angstrom). The sy stem of octahedral tilts which this compound adopts has not been obser ved previously in a perovskite. The tilt system was described in a the oretical treatment of perovskites (a(+)a(+)c(-) in the notation of A. M. Glazer (Acta Crystallogr. Sect. B 28, 3384, 1972) and was (incorrec tly) assigned to space group Pmmn. (C) 1995 Academic Press, Inc.