Synthesis by Chimie douce and properties of chromium (III) vanadates(V)

Abstract

The Cr₂O₃–V₂O₅ system has been thoroughly investigated using boiling solutions of xerogel (V₂O₅·1.6H₂O) or of vanadic acid mixed with solutions of chromium(III) nitrate. In general, hydrated amorphous phases, CrVO₄·4H₂O and Cr₂V₄O₁₃·13H₂O, were obtained and led, via heating, to two crystalline anhydrous phases, which were characterized by their indexed powder diagram. A new form of CrVO₄, CrVO₄-I, was found: monoclinic system, a= 9.791(6)Å, b= 8.848(5)Å, c= 6.834(6)Å and β= 107.8(1)°; 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)Å, b= 9.291(5)Å, c= 7.527(5)Å and β= 109.26(6)°; D_x= 3.21 with Z= 2. Upon heating CrVO₄-I leads to CrVO₄-III and Cr₂V₄O₁₃ decomposes to a mixture of CrVO₄-III and V₂O₅.