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Ferroelectric Tungsten Bronze Bulk Crystals and Epitaxial Thin Films for Electro-Optic Device Applications
Semi-annual technical rept. no. 4, 1 Apr-30 Sep 1984
ROCKWELL INTERNATIONAL CORP THOUSAND OAKS CA SCIENCE CENTER
Pagination or Media Count:
Several doped and undoped SBN60 single crystals have been grown by the Czochralski technique, and crystals as large as 2-2.5 cm in diameter have been successfully developed. The crystal quality and striations seem to depend strongly on the type of dopant incorporated. For example, Ce-doped SBN60 crystals exhibit no striations with excellent optical quality, while Fe-doped SBN60 crystals are heavily striated. The Ce-doped crystals seem to have promising device applications and, hence further work on this crystal is in progress to optimize its photorefractive properties. Since the crystals have been grown in an oxygen atmosphere, it is difficult to predict whether both valance states are present. Therefore, future work will include the determination of dopant valance states and their effect on photorefractive sensitivity and speed. Measurements on the photorefractive effect in undoped and Ce-doped SBN60 crystals have shown a 5.5 increase in the two-beam coupling coefficient for Ce-doped material, but with a similar response time 0.12 s. A band construction transport model is presented which indicates that response time may be reduced to 0.01 s or less by a decrease of the number of empty acceptor traps, NA, perhaps by means of crystal annealing in a partially reducing atmosphere. Additional keywords tungsten bronzes, impurities.
APPROVED FOR PUBLIC RELEASE