Neutron and X-ray study of stoichiometric and doped LiNbO 3 :Zn 0.08

LiNbO3 (LN) crystals possess useful optical prop- erties, which are strongly dependent on both the crystal sto- ichiometry and the content of dopants such as Mg 2+ ,Z n 2+ , In 3+ ,a nd Sc 3+ . Such elements drastically reduce photore- fraction at a sufficiently high threshold concentration, which for Zn is in the range of 7-8 at. % and was supposed to be connected with the change of dopant-atom localisation in the lattice. We report the results of a single-crystal neutron study of stoichiometric, congruent, and doped (with 8. 2a t. %Z n) LiNbO3 at T = 78 K and 298 K and also a multi-pattern pow- der neutron and X-ray Rietveld refinement of the doped ma- terial. Zn ions occupy both Li and Nb sites and there is no residual Nb on Li sites. LN single crystals are very perfect, and extinction problems are discussed.