Structure and dielectric properties of potassium niobate nano glass-ceramics

Abstract

Glasses in the composition of 25K₂O-25Nb₂O₅-50SiO₂ (mol %) have been prepared by melt quenching technique and isothermally heat-treated at 800 °C for different duration (0-200 h). The formed nanocrystalline KNbO₃ phase, crystallite size and morphology are examined by X-ray diffraction, Fourier transform infrared reflection spectroscopy, field emission scanning and transmission electron microscopes. The frequency and temperature dependent dielectric constant and loss tangent are measured in the frequency and temperature ranges 0.1-1000 kHz and 200-500 °C respectively. The dielectric constant and loss tangent are found to decrease with increasing frequency and increase with increasing temperature. The dielectric constant and loss tangent versus temperature curve at different frequency revealed the phase transition of KNbO₃ from paraelectric cubic to ferroelectric tetragonal around 425 and 397 °C (Curie temperature) for nano glass-ceramics obtained after 1 and 200 h heat-treatment respectively.