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 si ngle crystal of an as-received LiNbO3 lost lithium from its surface, a nd the lower valence niobium ion (Nb4+) was observed in the XPS spectr um 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 vacuu m chamber from those for an as-received sample, but a TPD spectrum sho wed 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 b ulk. The crystal structure of the topmost layer of an as-received LiNb O3 and its annealed one was detected as LiNbO3 from its threefold symm etry on the azimuthal angle dependence of Nb signal intensities by CAI CISS even after 600 degrees C annealing for 1 h. (C) 1998 Elsevier Sci ence B.V. All rights reserved.