Interaction in the molten system Rb₂O‐P₂O₅‐TiO₂‐NiO. Crystal structure of the langbeinite‐related Rb₂Ni_0.5Ti_1.5(PO₄)₃

Abstract

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.

Phase formation in molten system (Na/K)2O‐TiO2‐P2O5. Crystal structures of NASICON and langbeinite‐related phosphates (K/Na)1+xTi2(PO4)3 (x = 0 and 0.357)

“…In the case of phosphate K 0.10 Na 0.90 Ti 2 (PO 4 ) 3 such blocks are connected along axes c that is characteristic for sodium‐containing compounds with NASICON‐type structure (figure a). In the structure of K 0.877 Na 0.48 Ti ІІІ 0.357 Ti ІV 1.643 (PO 4 ) 3 the fragments [Ti 2 (PO 4 ) 3 ] run in four directions parallel to the cube diagonals (figure b) that is characteristic for complex substituted potassium or rubidium‐containing langbeinites .…”