Dielectric properties of ferroelectric tungsten bronze Ba2-xSrxK1-yNayNb5O15crystals at RF and millimeter wave frequencies

Permittivity and dielectric loss have been measured for a number of single crystal samples of barium strontium potassium sodium niobate (BSKNN) in three frequency ranges: 0–1 MHz, 30–40 GHz, and 90–100 GHz. This work is part of an ongoing study of millimeter wave properties of ferroelectrics with potential applications in active components such as phase shifters, modulators, and switches. BSKNN has been selected as typifying one extreme in the tungsten bronze family, where all 15- and 12-fold coordinated cation sites are occupied. Measurements on these crystals show significantly lower millimeter wave absorption than is found in strontium barium niobate (SBN) crystals grown by the same techniques. The permittivities along the principal crystal axes showed a substantial decrease with increasing frequencies over the range of observations, which may be indicative of a relaxation mechanism occurring in the GHz frequency region.