SUBSOLIDUS-PHASE EQUILIBRIA IN THE SYSTEM MGO-V2O5-MOO3

The phase relations in the system MgO-V2O5-MoO3 were studied and the s ubsolidus region of the phase diagram was constructed. The new compoun d Mg2.5VMoO8 was discovered on the join of MgMoO4-Mg3V2O8. Mg2.5VMoO8 crystallizes in the orthorhombic space group Pnma (No. 62) with cell d imensions a = 5.0515(1) angstrom, b = 10.3455(2) angstrom, c = 17.4683 (4) angstrom, and Z = 6. The structure is a framework of MoO4 and VO4 tetrahedra with linking octahedral and trigonal prismatic MgO6 groups. The molybdenum and vanadium cations preserve their highest oxidation state, and the electrical neutrality of the crystalline lattice is mai ntained by partial occupancy of magnesium sites. Simple quasi-binary e quilibria were established between MgMoO4 and MoV2O8, V2-xMo2xO5, MgV2 O6, and Mg2V2O7. (C) 1994 Academic Press, Inc.