NaNbO 3 crystals dispersed in a B 2O 3 glass matrix – Structural characteristics versus electrical and dielectrical properties

Abstract

Sodium niobate (NaNbO 3) is a crystal with a perovskite structure that exhibits, at room temperature, an antiferroelectric behaviour. It is a very interesting material due to the several phase transitions that it presents as a function of the temperature (ferroelectric–antiferroelectric–paraelectric). Thus, the preparation of glass-ceramics containing NaNbO 3 crystals is scientifically and technologically important. Besides, there is actually few works available about the preparation of NaNbO 3 crystals embedded in a glass matrix. The present work reports the preparation process and the study of glass and glass-ceramics in the B 2O 3–NaNbO 3 system. The glass with the molar composition 60B 2O 3–30Na 2O–10Nb 2O 5 (mol%) was prepared by the melt-quenching method. Sodium niobate (NaNbO 3) crystallites were precipitated through a controlled heat-treatment (HT) process. NaNbO 3 crystallites were detected by X-ray diffraction (XRD) in the samples treated above 500 °C. The treatments above 600 °C favour also the formation of Na 2B 4O 7 and Nb 2O 5 crystalline phases. Scanning electron microscopy (SEM) reveals that the crystallization occurs in volume and that the number of particles increases with the rise in HT temperature. The number of network modifier ions (Na + and Nb 5+) in the glass network is the main factor in the dc and ac conductivity behaviours. The dielectric constant ( ɛ′) value increases with the increase of the volume ratio between the particles and the glass matrix. The sample heat-treated at 550 °C shows two thermally stimulated depolarization current (TSDC) peaks. The high temperature peak can be related to the presence of NaNbO 3 particles.