Phase relations in the system K{sub 2}MoO{sub 4}-KPO{sub 3}-MoO{sub 3}-Bi{sub 2}O{sub 3}: A new phosphate K{sub 3}Bi{sub 5}(PO{sub 4}){sub 6}

Phase equilibrium in the pseudo-quaternary system K{sub 2}O-MoO{sub 3}-P{sub 2}O{sub 5}-Bi{sub 2}O{sub 3} was studied as three-component solvent K{sub 2}MoO{sub 4}-KPO{sub 3}-MoO{sub 3} containing 15 mol% Bi{sub 2}O{sub 3} during slow cooling and spontaneous crystallization. The results of the investigation were shown on a composition diagram, which indicates the crystallization fields of K{sub 2}Bi(PO{sub 4})(MoO{sub 4}), K{sub 5}Bi(MoO{sub 4}){sub 4}, BiPO{sub 4} and K{sub 3}Bi{sub 5}(PO{sub 4}){sub 6}. New phosphate K{sub 3}Bi{sub 5}(PO{sub 4}){sub 6} was characterized by single-crystal X-ray diffraction (space group C2/c, a=17.680(4), b=6.9370(14), c=18.700(4) A, {beta}=113.79(3){sup o}) and FTIR spectroscopy. The possibility of lone electron pair stereoactivity of bismuth was suggested using the calculations of characteristics of the Voronoi-Dirichlet polyhedra for K{sub 3}Bi{sub 5}(PO{sub 4}){sub 6} and K{sub 2}Bi(PO{sub 4})(MoO{sub 4}). - Graphical abstract: Composition diagram of the K{sub 2}MoO{sub 4}-KPO{sub 3}-MoO{sub 3} system containing 15 mol% Bi{sub 2}O{sub 3} with approximate fields of phase formation bismuth phosphates, molybdate and phosphate-molybdate.