Lattice vibration fundamentals of nanocrystalline anatase: Temperature-dependent study using micro-Raman scattering spectroscopy

A detailed temperature-dependent Raman scattering study was carried out from 83 to 723 K for nanocrystalline anatase with nanocrystal size of 19.4 nm. All six Raman-active modes, including the hardly observed E-g(2) mode, were observed, and each had its own unique temperature-dependent characteristic. The softest and the second softest modes, namely the E-g(1) and E-g(2), each showed hardening with increasing temperatures. The B-1g(1) mode, which is between the E-g(1) and E-g(3), showed weak hardening from 83 to similar to 330 K, and then its frequency decreased with increasing temperatures. Very good fittings were obtained for both the Raman frequencies and peak linewidths by using the Klemens model. The fitting results show that for the E-g(1) and E-g(2) modes, the hardening behavior came mostly from three-phonon processes, while for the A(1g) and E-g(3) modes, both three- and four-phonon processes contributed to the Raman softening. (c) 2007 American Institute of Physics.