SYNTHESIS BY CHIMIE-DOUCE AND PROPERTIES OF CHROMIUM(III) VANADATES(V)

The Cr2O3-V2O5 system has been thoroughly investigated using boiling s olutions of xerogel (V2O5.1.6H(2)O) or of vanadic acid mixed with solu tions of chromium(el) nitrate. In general, hydrated amorphous phases, CrVO4.4H(2)O and Cr2V4O13.13H(2)O, were obtained and led, via heating, to two crystalline anhydrous phases, which were characterized by thei r indexed powder diagram. A new form of CrVO4, CrVO4-I, was found: mon oclinic system, a=9.791(6) Angstrom, b= 8.848(5) Angstrom, c=6.834(6) Angstrom and beta=107.8(1)degrees; D-x=3.98 with Z=8; and space group C2/m. It is antiferromagnetic under 11 K while the known form of CrVO4 , CrVO4-III (orthorhombic) is antiferromagnetic under 63 K. The second vanadate was Cr2V4O13, which crystallizes in a monoclinic system with a=8.277(3) Angstrom, b=9.291(5) Angstrom, c=7.527(5) Angstrom and bet a=109.26(6)degrees; Dx=3.21 with Z=2. Upon heating CrVO4-I leads to Cr VO4-III and Cr2V4O13 decomposes to a mixture of CrVO4-III and V2O5.