X-ray and TEM studies of CdTeMoO6 and CoTeMoO6: A new superstructure of fluorite type with cation and anion deficiencies (square CoTeMo)(square O-2(6))

The crystal structures of two telluromolybdates CdTeMoO6 and CoTeMoO6 have been solved ab initio. CdTeMoO6 crystallizes in a tetragonal cell (space gr oup No. 113, P42(1)m, Z = 2) with a = 5.2840(1) Angstrom, c = 9.0595(2) Ang strom whereas CoTeMoO6 crystallizes in orthorhombic space group P2(1)2(1)2 (No. 18) with two formula units in the unit cell of dimensions a = 5.2545(1 ) Angstrom, b = 5.0653(1) Angstrom, and c = 8.8589(2) Angstrom. The X-ray p owder diffraction pattern data were refined by the Rietveld profile techniq ue and led respectively to R-Bragg = 0.07 for CdTeMoO6 and R-Bragg = 0.07 f or CoTeMoO6 The crystal structure of CdTeMoO6 is built up from corner-shari ng distorted CdO4 tetrahedra which build a layer in the a,b plane, while in CoTeMoO6 cobalt atoms exhibited an octahedral distorted surrounding. Both compounds are simultaneously cation- and anion-deficient 1.1.2 superstructu res of fluorite in which the electron lone pairs of tellurium are stereo-ch emically active. High-resolution electron microscopy images of CdTeMoO6 sho wed well-ordered crystals fragments, but in some crystals defects have also been detected. (C) 2001 Academic Press.