TOPOTACTIC OXIDATION OF RAMSDELLITE-TYPE LI0.5TIO2, A NEW POLYMORPH OF TITANIUM-DIOXIDE - TIO2(R)

The topotactic oxidation in air at room temperature of the lithium tit anate bronze LixTiO2 (x = 0.5) crystals with the ramsdellite-type stru cture leads to lower x values and decreased unit-cell volumes. The cry stal structures of the three specimens, Li0.41TiO2, Li0.16TiO2, and Li 0.14TiO2, have been determined by the single-crystal X-ray diffraction method. The deintercalation of lithium in LixTiO2 with 0 less-than-or -equal-to x less-than-or-equal-to 0.5 has been investigated by differe nce-Fourier maps at z = 1/4 sections. The complete oxidation of parent bronze crystals using an acidic solution obtained colorless crystals of a new polymorph of titanium dioxide, TiO2(R). It crystallizes in th e orthorhombic ramsdellite-type structure, in the same space group Pbn m with a = 4.9022(14) angstrom, b = 9.4590(12) angstrom, c = 2.9585(14 ) angstrom, V = 137.18(7) angstrom3, D(x) = 3.87 g/cm3. D(m) = 3.80 g/ cm3, and Z = 4. The TiO2(R) structure was also refined from the single -crystal X-ray study to the conventional values R = 0.049 and wR = 0.0 44 for 596 independent reflections. When heated above 640 K, TiO2(R) t ransforms into brookite-type TiO2. DTA and IR data of TiO2(R) are meas ured. (C) 1994 Academic Press, Inc.