Low and high frequency dielectric properties of ferroelectric tungsten bronze Sr2KNb5O15 crystals

Single crystals of Sr2KNb5O15 (SKN), approximately 5-8 mm in diameter and 10-20 mm long, have successfully been grown by the Czochralski technique. The crystal has a ferroelectric tetragonal tungsten bronze structure with a Curie temperature of about 150°C. The dielectric and electromechanical coupling constants for this crystal have been established: the polar axis dielectric constant, K33, exceeds 20,000 at the Curie temperature while the coupling constants are K33 = 0.52 and K31 = 0.19, respectively. High frequency dielectric properties of SKN samples were also determined between 90-100 GHz. These measurements indicate that the bulk of the polar axis permittivity has relaxed below 90 GHz, implying that the low frequency dielectric response is not soft-mode controlled.