Photorefractive Properties of Two Series of BaTiO₃ Crystals Annealed in Temperatures of 900°C and 1000°C

Two series of nominally undoped BaTiO₃ crystals are fabricated and then systematically investigated by processing in a varying oxygen partial pressure atmosphere at 900°C and 1000°C. The photorefractive properties are sequentially controlled by the factors of dark decay, deep/shallow traps, deep/shallow traps with hole/electron competition, and then dark conductivity as the oxygen partial pressure is reduced. The properties of these two sample series show a similar trend, although the compensation point for 900°C samples occurs at an oxygen partial pressure of 10^-10 atm and that for 1000°C samples at 10^-7 atm. The two-beam coupling gains, effective trap densities, speeds, and dark conductivities for the two samples series are all at their smallest values around the compensation point. The range between the compensation point and the dark conductivity controlling regime decreases on the P side as the processing temperature increases, although it does not change on the N side.