Ferroelectric Tungsten Bronze Crystals for Far Infrared Electro-Optic Device Applications

摘要

The primary objective of this research program is to develop for electro-optic and nonlinear optical applications high quality, striation-free crystals of a number of interesting tungsten bronze compositions such as Ba(2-x)Sr(x)K(1-y)Na(y)Nb5O15 (BSKNN), Ba6Ti2Nb8O30 (BTN), and a few compositions which are close to a morphotropic phase boundary, using the Czochralski and edge defined crystal growth techniques. The large transverse and longitudinal electro-optic response obtainable near morphotropic phase boundaries are studied in particular detail for optical device applications. A second objective is to improve material photorefractive performance using selected dopants. Several undoped and doped tungsten bronze BSKNN-1 and BSKNN-2 single crystals have been grown by the Czochralski technique. Optical evaluation shows that both the crystals show minimum striations, and are useful for optical studies. Current growth results suggest that the existence of striations depends on the type of dopant and the purity of starting materials. Both BSKNN-1 and BSKNN-2 crystals show excellent ferroelectric and optical properties which are similar to perovskite BaTiO3 rather than to tungsten bronze SBN:60 single crystals. The unit cells for BSKNN-1 and BSKNN-2 are slightly bigger than SBN:60 crystal and for these small changes their entire ferroelectric properties are different. For example, epsilon sub 11, d sub 15 and r sub 51 are larger for BSKNN crystals while the epsilon sub 33, d sub 33 and r sub 33 are larger for smaller unit cell SBN:60 single crystals. Further work is in progress to identify the differences in these bronze crystals.