A synchrotron X-ray diffraction analysis of near-stoichiometric LiNbO3

Single-crystal diffraction data was collected at 120 and 294 K for an appro ximately spherical LiNbO3 crystal, 16 mum in diameter, using focused lambda = 0.7516(1) Angstrom wavelength synchrotron X-radiation and a fast avalanc he photodiode (APD) detector. Extinction was significantly less than that r ecorded for previous single-crystal X-ray diffraction experiments. Anharmon ic atomic displacements of Nb and Li were refined using a Gram-Charlier exp ansion to the fourth order. There was no significant change in the topograp hy of the difference electron density (Ak)) map after anharmonic refinement . An accumulation of electrons present at the vacant site in the 294 K Delt a rho map was not evident in the 120 K Delta rho map, indicating a migratio n of Li atoms to the vacant site as the temperature increased. The orientat ion of the electron density around Nb flipped by 90 degrees going from 120 to 294 K.