Low-frequency zone boundary phonons in Li doped ZnO ceramics

Room temperature Raman spectra of Li doped ZnO (Zn1-xLixO) ceramics with varying Li concentrations (x=0.0, 0.05, 0.10, and 0.15) are investigated in this study. Four peaks were identified at 96.6, 127, 157, and 194 cm(-1) in the Li doped samples. The peaks at 127, 157, and 194 cm(-1) are assigned to zone boundary phonons in ZnO [J. M. Calleja and M. Cardona, Phys. Rev. B 16, 3753 (1977)], and appear due to disorder in ZnO lattice with Li incorporation. Lithium, owing to its smaller radius, adjusts itself anywhere in the ZnO lattice and breaks the crystal translational symmetry to a large extent, compared to other dopants. Disorder in the lattice is seen to be finely modulated with varying Li content. The peak at 96.6 cm(-1) is hypothesized to be a projection of the vibrational motion of Li atoms at lower frequencies, which contributes in a major fashion at higher frequencies, due to its lighter mass than Zn or O atoms. (C) 2008 American Institute of Physics.