Subsolidus Phase Relations in the Systems M2+O–M2+O–V2O5(M+= Li, Na, K, Rb, Cs; M2+= Mg, Ca)

Abstract

Subsolidus phase relations in the M2O(M2CO3)–MgO–V2O5 and M2O(M2CO3)–CaO–V2O5 (M = Li, Na, K, Rb, Cs) systems are studied. Twenty mixed vanadates are obtained, of which Rb2CaV2O7 , Cs2CaV2O7 , LiMg4(VO4)3 , RbCaVO4 , and CsCaVO4 are identified for the first time. Structural data are summarized for all of the mixed vanadates: the space group and lattice parameters are indicated for 14 compounds (for 6 compounds, such data are obtained for the first time), and I and d data are presented for 8 compounds. Partial series of Ca3(VO4)2-based solid solutions with the general formula Ca3 – x M2x (VO4)2 (M = Na, K, Rb, Cs) are identified in the range 0 < x ≤ 0.14. Six phase diagrams (M+ = Li, Rb, Cs; M2+ = Mg, Ca) are investigated and are compared with the phase diagrams of the other ternary systems in question. The key features of the ternary phase diagrams and, hence, the reactivity of the constituent oxides are shown to vary systematically in going from Li2O to Cs2O and from MgO to SrO, which is interpreted in terms of the variation in the ionic radius of the alkali and alkaline-earth metals.