Studies on annealing and quenching of strontium barium niobate (SBN) single crystals: A-site cation ordering-disordering effect

Abstract

Quenching and annealing studies have been carried out to investigate the effects of the A-site occupancy in the tungsten bronze structure on the polarization, pyroelectric coefficient, dielectric permittivity, and phase transition (Curie temperature range) behavior of ferroelectric relaxor Sr_1−xBa _x Nb₂O₆ (1−x = 0.75, 0.60, 0.50) single crystals. Quenching possibly generates a random distribution of vacancies between A1 and A2 sites and enhances the ordering of the cations in A-site. As a consequence of that, a T_c increase of as much as about 30°C above the T_c of non-quenched state has been observed. Quenching at a higher temperature, i.e., approximately about 1000°C results in reducing the ordering of the A-site because of random distribution of Sr²⁺, Ba²⁺, as well as vacancies. A continuous T_c increase accompanied by a decrease in dielectric permittivity and a broadened phase transition is reported and is believed to be due to strain built up because of energetically unfavored distribution of Ba²⁺ in A1. By suitable annealing, the original T_c and dielectric property are essentially reproduced. However, quenching at around 1000°C generates a new anomaly related to T_c , which is detected by both Raman measurement and Byer and Roundy pyroelectric measurement. This new anomaly still exists even after carefully annealing. It is suggested that both vacancy and cation distribution, as well as associated strain built-up, play the major role in the phase transition behavior.