Nd-Doping Induced Lattice Distortion in TiO₂ Nanoparticles

Nd-doping effects are investigated in TiO₂ nanoparticles with various annealing temperatures T from 70 °C to 1100 °C by means of x−ray diffraction (XRD) and Raman scattering spectroscopy. XRD results indicate that the sample shows a rutile phase at 1100 °C, which changes to anatase phase at 900 °C. With decreasing T down to 300 °C, a significant lattice shrink is found, that is, the lattice parameter c is significantly suppressed while the a value shows a gradual decrease. With further decrease of T, the c−value shows an unexpected increase while the a−value keeps a gradual decrease. Thus, a lattice distortion takes place with changing the annealing temperature. In Raman investigation, all the Raman modes for the anatase phase show hardening behaviors with decreasing T in the range 900–300 °C, and then the E_g and A_1g modes show softening behaviors below 300 °C, suggesting the variation of the lattice distortion. The variation of the lattice distortion at different annealing temperatures is ascribed to different depositions of Nd ions on the surface of TiO₂ nanoparticles.