Growth of lead barium niobate (Pb_1-xBa_xNb₂O₆) crystals by the vertical Bridgman method I. Self-seeded growth

Pb_1-xBa_xNb₂O₆ (PBN) single crystals were grown by the vertical Bridgman method without the loss of PbO during the growth process, which has been a serious problem in the Czochralski growth method. A self-seeded technique using sealed Pt crucibles containing the ceramic charges produced stoichiometric and transparent single-crystal grains of millimeter sizes. The preferred growth direction was found to be [0 0 1] which is the same as in Sr_1-xBa_xNb₂O₆ (SBN). The grain size increased as the grains propagated, but normal grain selection was not sufficient to produce individual single grains with centimeter size cross sections. The ferroelectric domain structures of tetragonal PBN could be revealed either by etching in hydrofluoric acid or polishing with colloidal silica. The typical domain size on the surface perpendicular to the polar axis was 10-50 μm. The measured spontaneous polarization, P_s, was 0.40-0.70 μC/mm² depending on the composition. As-grown crystals contained a high concentration of protons (H⁺) on the order of 10¹⁷/cm³, which is important for the holographic data storage applications. In addition, the concentration of protons could be increased or decreased by post-growth heat-treatment processing.