Anharmonicity of optical phonon modes in copper doped rutile TiO2 nanorod composed microflowers

Abstract

Anharmonicity and impurities have a significant impact on the dynamic and optical properties of crystalline solids. In this report, we have performed temperature-dependent Raman spectroscopy in the range of 300–800 K for hydrothermally synthesized titanium dioxide (TiO2) nanorod composed microflowers doped with Cu. X-ray diffraction and high resolution transmission electron microscopy confirm the pure rutile phase of both pristine and Cu doped TiO2. The most intense Eg and A1g modes exhibit a frequency redshift, and the linewidth increases with temperature, which leads to Fano line shape type asymmetry. The anharmonicity induced phonon frequency shift as a function of temperature was well fitted using the Klemens model by combining three and four-phonon coupling processes. The Raman modes soften with the increasing concentration of Cu doping. The Cu dopant acts as an impurity, which manifests defect states to tune the bandgap and shorten the phonon lifetime and anharmonicity. Such an anharmonic effect can lead to applications in the sensing devices with suitable thermal and electrical conductivities.