Information storage with a barium-calcium titanate crystal

Barium-calcium titanate is a novel photorefractive crystal for optical storage applications. It is grown from a congruently melting composition from BaTiO3 and CaTiO3. In contrast to pure BaTiO3 the melting temperature is with 1592 degrees C nearly 30 degrees deeper, the crystal is cubic at the growth temperature and shows a phase transition to the tetragonal structure at 98 degrees C. It means that as in BaTiO3 a spontaneous poling appears. The lattice constants are smaller than in BaTiO3, a = b = 3.962 nm and c = 3.999 nm and decreace with increasing Ca content. Therefore, the crystal is an optical uniaxial one. A second phase transition like in BaTiO3 is not found /1/. The refractive indices are slightly smaller than those of BaTiO3 but the electrooptic coefficients r(13) = 36 pm/V and r(33) = 140 pm/V are larger (lambda = 514 nm) /2/. Therefore, the Ba1-xCaxTiO3-crystal is a very promising material for optical information storage. In our experiments we used a 1 cm * 1 cm * 1 cm large crystal, poled in an external electric field, therfore obtaining a single domain sample. All sides are polished to optical quality. The sample shows in ordinarily polarized Light extremly high fanning effects. We have studied the two wave mixing (TWM) for ordinary and extraordinary polarized light (lambda = 514 nm).