SYNTHESIS AND CRYSTAL-STRUCTURE OF NATI8O13

A new member of the Ti3+ Ti4+ mixed-valence sodium titanate family, NaTi8O13, was synthesized by the reaction of sodium metal and titanium oxides at high temperatures. It crystallizes in the trigonal system, space group R3 with hexagonal lattice constants a = 7.7544(7) Å, c = 14.073(3) Å, V = 732.9(2) Åm, and Z = 3. The structure was determined from a single-crystal X-ray diffraction study and refined to the conventional values of R = 0.033 and Rw = 0.031 for 869 observed reflections. The structure can be described as a cubic closest packing of oxygen atoms, in which the defects of oxygen packing are occupied by sodium ions, and some of the octahedral O6 interstices are occupied by two types of Ti cations. Sodium ion is surrounded by twelve oxygen ions in a cuboctahedron. © 1991.