Phase formation, crystal structure, and electrical conductivity of triple phosphates of alkali metals and titanium

For triple phosphates of composition A′0.5A0.5 Ti2(PO4)3 (A−A′=Li−Na, Na−K, K−Rb), phase formation is studied, the crystal structure is refined, and the electrical conductivity is measured. The compounds are classified with the NaZr2(PO4)3 structure type (NZP, space group R 3 c). The phosphate frameworks are built of TiO6 octahedra and PO4 tetrahedra. Extraframework positions M1 are fully occupied by randomly distributed alkali cations. Positions M2 are vacant. Correlations are found between the structural distortion and electrical conductivity of the phosphates, on one hand, and the alkali cation size, on the other.