Effect of sintering temperature on composition, microstructure and electrical properties of K0.5Na0.5NbO3 ceramics

Lead free potassium sodium niobate (K0.5Na0.5NbO3) ceramic powders were synthesized by colloidal coating method. The calcined powders (800 °C) were sintered conventionally at three different temperatures (1050 °C, 1100 °C and 1150 °C) and the effect of sintering temperature on density, microstructure, composition and electrical properties was investigated. All the samples showed a single phase perovskite structure with orthorhombic symmetry similar to KNbO3 ceramics. Microstructure examined under FEG-SEM revealed an optimum microstructure, in terms of grain size, porosity and uniformity, at the sintering temperature of 1100 °C, which also showed density of 92% of ρTh. As the sintering temperature increased the X-ray diffraction peaks shifted to lower 2θ values indicating excess volatilization of Na at higher temperature as compared to K. This was further confirmed through elemental Probe X-ray microanalysis and ICP-AES studies. Dielectric constant (εr), dielectric loss (tanδ), ferroelectric (P-E loop) and piezoelectric (d33) properties showed considerable improvement and leakage current decreased with increasing sintering temperature. The sample sintered at 1100 °C showed marked improvement in maximum dielectric constant (573) at RT at 1 kHz, minimum tangent loss (0.04) at RT at 1 kHz, maximum remnant polarization (13.5 μC/cm2), lower leakage current (7.6×10−7 A/cm2) and maximum d33 value (100 pC/N).