Concentration dependence of optical phonons in the TiO2-SnO2 system

The concentration dependence of optical phonons in the TiO2-SnO2 system whose phase diagram exhibits a miscibility gap, has been studied by Raman scattering and Fourier-transform infrared spectroscopy. X-ray diffraction confirmed that the mixed oxides Ti1-xSnxO2 with intervals x=0.1 are a single uniform phase (tetragonal) except some x's; no phase separation by spinodal decomposition could be avoided for x=0.3, 0.4, 0.5, and 0.6, characterizing x-ray-diffraction profiles by sidebands. The 449 cm(-1) A(1g) and 610 cm(-1) E(g) Raman modes for TiO2 never changed linearly in frequency and linewidth with x. It is stressed that the x dependence of optical phonons is predominated by the octahedral distortion in Ti1-xSnxO2, where different/anisotropic compressibilities and thermal expansivities of each end member play a crucial role. Infrared-reflectance spectra consisting of the infrared-active A(2u) and E(u) modes between 50-900 cm(-1), also changed systematically with x in Ti1-xSnxO2. The concentration dependence of optical phonons in Ti1-xSnxO2 is discussed, from the viewpoint of the mode behavior of mixed crystals.