Interaction in the molten system Rb2O-P2O5-TiO2-NiO. Crystal structure of the langbeinite-related Rb2Ni0.5Ti1.5(PO4)3.

The interaction in the molten system Rb2O-P2O5-TiO2-NiO was investigated at different molar ratios Rb/P = 0.5-1.3, fixed Ti/P = 0.15, Ti/Ni = 1.0 at temperature range 1073-953 K. The conditions of formation of complex phosphates RbTi2(PO4)3, Rb2Ni0.5Ti1.5(PO4)3 and RbNiPO4 have been determined. The new phosphate Rb2Ni0.5Ti1.5(PO4)3 (space group P213, a = 9.9386(2) Å) has been obtained and investigated by the single crystal X-ray diffraction and FTIR-spectroscopy. It has langbeinite-like structure, that is built up from mixed (Ni/Ti)O6-octahedra and РО4-tetrahedra. Rubidium atoms are located in closed cavities of 3D-framework. [ABSTRACT FROM AUTHOR]