A temperature-dependent powder diffraction study of chromium lanthanum nitrate, LaCr(NO3)6.12H2O

The new phase LaCr(NO3)6 .12H2O was synthesized from a nitric acid solution. The symmetry is trigonal with the parameters a= 10.9564(4) A and c= 16.835(1) A [V= 1750.2(2) A^3 space group R - 3]. The thermal decomposition, studied by temperature-dependent X-ray powder diffraction and thermogravimetry, gave successively the cubic phase LaCr(NO3)6. 6H2O [a= 12.301(1) A, space group P2 1 3] and the chromate(V) LaCrO4 The reduction of LaCrO4 to LaCrO3 occurred at a temperature depending on the oxygen pressure in the reaction atmosphere.