Ultrasound studies of phase transitions in tungsten bronze ferroelectric materials

Attenuation and velocity measurements at ultrasonic frequencies were perfor med in two ferroelectric solid solutions with tungsten bronze structure typ e, SBN and PBN, as a function of temperature (from 200 to 380 K). Both mate rials, in polycrystalline form, presented sensitive changes in the temperat ure dependence curves of attenuation and velocity. One of these anomalies ( at 350 K for SBN and 323 K for PEN) was associated with a second-order phas e transition, confirming the ferroelectric orthorhombic-ferroelectric tetra gonal phase transition suggested for both systems in this temperature range . (C) 2000 Elsevier Science S.A. All rights reserved.