Research on the Crystal Growth and Dielectric Properties of High Permittivity Ferroelectric Materials. Annual Report March 1, 1984 - February 28, 1985

摘要

Millimeter wave measurements on tungsten bronze Sr0.6Ba0.4Nb2O6 (SBN:60) and Ba2-xSrxK1-yNayNb5O15(BSKNN) have shown a strong temperature dependence for permittivity and dielectric loss, with both decreasing at low temperature down to 77K for the electric field parallel to the polar axis. The observed changes in and perpendicular to the polar axis are much less, being only 30-40%. A temperature sensitive peak in the polar has been observed for some samples. First experimental determination of the millimeter wave dn/dE for SBN:60 single crystal has been demonstrated successfully at cryogenic temperature. These results are encouraging both for basic understanding of the mechanisms controlling millimeter wave susceptibilities in ferroelectric tungsten bronze as well as for practical device applications. It has been shown for SBN:60 that the large millimeter wave nonlinear response is retained at cryogenic temperature (dn3/dE3 = .0000005m/V at 77K) while the absorption is reduced by an order of magnitude. The experimental database has allowed, for the time, the construction of a modeling work based on coupling of the microwave field to acoustic phonons which is consistent with the observations.