Photorefractive effect of BaTiO_3 single crystals grown in inert atmospheres

BaTiO3 single crystals were grown by the top-seeded solution growth technique in inert atmospheres of nitrogen gas and of argon gas and in air. They were then annealed at 1200°C in air. These crystals, prepared from a mixture of 99.999% pure BaCO3 powder and 99.99% pure TiO2 powder, contained virtually equal amounts of transition-metal impurities (Fe, Co, Ni, etc.). The maximum beam-coupling gain of the two crystals grown in inert atmospheres was 6 cm−1, and that of the crystal grown in air was 3 cm−1; the sign of the beam-coupling gain of the crystals was positive. We found that the crystals grown in inert atmospheres exhibited high gains without having been doped with any transition-metal elements.