Synthesis, Structural Change upon Heating, and Electronic Structure of Ramsdellite-Type TiO2

Abstract

Polycrystalline samples of TiO2(R) with the ramsdellite-type structure were synthesized by a soft chemical technique using ramsdellite-type Li0.5TiO2 as a parent compound. The structural stability and phase transition of TiO2(R) upon heating were investigated by XRD and DSC measurements. In the heating process between 423 and 723 K, a novel intergrowth form of TiO2 between the rutile and ramsdellite-type structures, similar to the γ-MnO2 structure, has been found for the first time. From the results of the UV−vis absorption measurements, we found that the band gap energy (3.34 eV) for TiO2(R) was revealed experimentally to be the largest among those for the known TiO2 compounds; the gap energy changed abruptly to 3.04 eV in the intergrowth phase of the ramsdellite and rutile domains after introduction of the rutile character. These findings were very consistent with those obtained by the FLAPW calculations.