Preparation and structural characterization of two new titanium phosphates NaCa0,5Ti(PO4)3 and Ni0,5TiOPO4

The titanium phosphate Na4Ca0.5Ti(PO4)(3) crystallizes in the trigonal space group R32 (a(h)=9.008+/-0.002 Angstrom, c(h)=21.814+/-0.003 Angstrom and Z = 6). Irs structure belongs to the Nasicon type family. The titanyl phosphate Ni0.5TiOPO4 crystallizes in a monoclinic unit cell, P2(1)/c, (a = 7.383 +/- 0.001 Angstrom, b = 7.323 +/- 0.001 Angstrom, c = 7.344 +/- 0.001 Angstrom, beta = 120.23 +/- 0.01 degrees and Z = 4). The structure of these two compounds is based on a three-dimensional framework built of TiO6 octahedra acid PO4 tetrahedra. The PO4 tetrahedra are isolated in both Na4Ca0.5Ti(PO4)(3) and Ni0.5TiOPO4. The TiO6 octahedra are isolated in the former and linked together by "titanyl" oxygen atoms to form -Ti-O-Ti-O- infinite chains in the latter. These structural data are confirmed by the Raman spectroscopy study.