A temperature-dependent powder diffraction study of chromium lanthanum nitrate, LaCr(NO3)(6)center dot 12H(2)O

The new phase LaCr(NO3)(6). 12H(2)O was synthesized from a nitric acid solu tion. The symmetry is trigonal with the parameters a=10.9564(4) Angstrom an d c=16.835(1)Angstrom [V=1750.2(2)Angstrom(3), space group R-3]. The therma l decomposition, studied by temperature-dependent X-ray powder diffraction and thermogravimetry, gave successively the cubic phase LaCr(NO3)(6). 6H(2) O [a = 12.301(1) Angstrom, space group P2(1)3] and the chromate(V) LaCrO4. The reduction of LaCrO4 to LaCrO3 occurred at a temperature depending on th e oxygen pressure in the reaction atmosphere. (C) 2000 International Centre for Diffraction Data. [S0885-7156(99)01003-9].