Effects of reduction treatment on the photorefractive properties of Pb0.5Ba0.5Nb2O6

Abstract Lead barium niobate is a new photorefractive material of high interest for a variety of applications including holographic storage. Pb0.5Ba0.5Nb2O6 crystals have been grown by the Bridgman method, and the effects of heat treatments on their photorefractive properties were investigated using Ar ion laser at λ=514.5 nm. The color and absorption spectrum of the crystals varied depending on the oxygen partial pressure during heat treatment. The oxygen diffusivity was estimated to be in the order of 10−6 and 10−5 cm2/h at 425 and 550 °C, respectively. Reduction treatment at an oxygen pressure of 215 mTorr increased the effective density of photorefractive charges about three times from 8.0×1015 to 2.2×1016 cm−3 and made the charge transport more electron-dominant. As a result, the maximum gain coefficient improved from 5.5 to 13.8 cm−1. A diffraction efficiency as high as 70% was achieved in a reduced crystal.