Properties of new and useful tungsten-bronze niobates

It is experimentally shown that the electrooptic properties of the ferroelectric phase of the new tungsten-bronze compositions can be treated as a biased quadratic electrooptic effect . This is done by directly measuring the electrooptic behavior above the transition temperature in KSr2Nb5O15. A term linear in electric field is not found. Thus the crystal has a center of inversion. We find m⁴/C². This value is very similar to that obtained for a number of compounds containing NbO6and similar octahedra. This value is also in good agreement with the effective room-temperature linear electrooptic coefficient rc, if it is assumed that rccan be considered to arise from a biased quadratic effect. Then we use these considerations systematically on other tungsten-bronze ferroelectrics, KSr2Nb5O15, NaBa2Nb5O15, Sr0.25Ba0.75Nb2O6, and Sr0.5Ba0.5Nb2O6. We calculate g33and g13separately and also find m⁴/C²for all of these materials. Thus all these ferroelectrics give similar values to those found elsewhere for oxygen octahedra compounds. We also calculate values for the spontaneous polarization or the induced change in the indices of refraction.