Measurements of Photorefractive Properties in BaTiO3:Co

In the past, the photorefractive properties of BaTiO3 crystals doped with chromium [1] and iron [2, 3] have been described. Iron impurities, present in nominally undoped .crystals at levels between 40 and 150 ppm, have been identified as the microscopic centers correlated with the photorefractive effect [4]. The observed photorefractive effect in high purity crystals, however, with an iron level claimed to be smaller than 0.3 ppm [3], has been interpreted as evidence for another photorefractive species in these samples. The exact role of transition metal dopants in photorefractive BaTiO3 is still unclear.