A comparison of acidic and acidic-to-basic impurity introduction on the thermophototropic behavior of the alkaline earth titanates is presented. The latter is a new method of introducing impurities into alkaline earth titanates which will be described here. It involves the synthesis of a photoactive titanate from a previously synthesized titanate or titanyl oxalate. This method gave a considerably enhanced absorptivity change for barium titan ate, but proved to be much less effective for the titanates of calcium and strontium. In all cases the slurries were made alkaline with alkali metal hydroxides. For barium titanate the optimum alakalinity was obtained with 10 mole percent sodium hydroxide, which led to the conclusion that the phenomenon is a surface one in which the alkali metal oxide corticates the surfaces of the host crystals.
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