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

摘要

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 ～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.