The topmost structure of annealed single crystal of LiNbO3

The effects of heat treatments in a vacuum chamber for a (001) single crystal of LiNbO3 have been examined with XPS, TPD and CAICISS. The single crystal of an as-received LiNbO3 lost lithium from its surface, and the lower valence niobium ion (Nb4+) was observed in the XPS spectrum for the Nb 3d level. The atomic ratios of Li/Nb and Nb4+/Nb changed very little, even after annealing at 600 degrees C for 1 h in a vacuum chamber from those for an as-received sample, but a TPD spectrum showed the desorption of Li2O from the surface in the region of over 400 degrees C. The loss of Li and O, induced by annealing, was compensated to a certain extent by the out-diffusion of these elements from the bulk. The crystal structure of the topmost layer of an as-received LiNbO3 and its annealed one was detected as LiNbO3 from its threefold symmetry on the azimuthal angle dependence of Nb signal intensities by CAICISS even after 600 degrees C annealing for 1 h. (C) 1998 Elsevier Science B.V. All rights reserved.