Optical properties of lead barium niobate (Pb_1-xBa_xNb₂O₆) crystals

PBN (Pb_1-xBa_xNb₂O₆) polycrystals have been grown by the vertical Bridgman method. Transparent, stoichiometric, striation-free single-crystal specimens of millimeter size were obtained. The ordinary and extraordinary refractive indices, n_o and n_e, of crystals with compositions Pb_0.50Ba_0.50Nb₂O₆ and Pb_0.57Ba_0.43Nb₂O₆ were measured by the minimum deviation method using optically polished prisms. Neither n_o nor n_e was found to be strongly dependent on crystal composition, in contrast to the case of SBN (Sr_1-xBa_xNb₂O₆), in which n_e is strongly dependent on composition. Optical transmission spectra showed PBN to be transparent in the range from 0.4 to 5 μm except for the OH^- absorption bands around 2.87 μm The dependence of the integrated OH^- absorption intensity on polarization showed that all of the O-H bonds lie either in the a-b plane or along the c axis, with a greater density of O-H bonds in the a-b plane than along the c axis.