Synthesis and Characterizations of Lead Free KNN Ceramics Near Morphotropic Phase Boundaries

Abstract

Ferroelectric oxides are a group of advanced electronic materials with a wide variety of properties useful in applications such as capacitors, memory devices,resonators and filters, infrared sensors, microelectromechanical systems, optical waveguides and modulators. Among the oxide based perovskite-structured ferroelectric system lead zirconate titanate (PZT) emerged as one of the useful material in various applications. But due to the toxicity of lead and serious environmental concerns there is an urgent need to develop lead free alternatives to replace the currently dominant lead based piezoelectric such as PZT.Among non lead based ferroelectric systems Sodium Potassium Niobate( KXNa1-XNbO3 / KNN) based ferroelectric ceramics has recently emerged as a promising materials in radio frequency (rf) and microwave applications due to high dielectric tunability , low dielectric loss , relatively high curie temperature and piezoelectric coefficient. KNN system posses 3MPBs when X= 0.50,0.31 and 0.18. Near these MPB regions the compositions of KNN system are expected to exhibit better electrical properties .Till now the emphasis is around compositions close to 50/50 MPB. It is also difficult to sinter KNN ceramics because of its hygroscopic nature. This thesis presents results on growth and structural and electrical characterization of KNN ceramics near its 3MPB regions. In the current work emphasis has been given on low temperature synthesis of KNN ceramics near the three MPB regions using partial co-precipitation method and their characterizations. Using partial co precipitation method we have synthesized different compositions near the 3 MPB regions. Calcination temperature for single perovskite phase formation was optimized to ~7000C, which is much lower than the same system synthesized by solid state synthesis route (SSSR). The structural and electrical properties of different compositions near the 3 MPB regions were studied in detail .It was vi found that K0.5Na0.5NbO3 MPB composition showed better density (~ 4.4g/cc), piezoelectric coefficient (d33 ~ 71 pC/N) and ferroelectric properties (Ps~ 14.271 μC/cm2, Ec~ 9.8389KV/Pr~ 10.9336 cm2) . Therefore to further improve the electrical properties of this composition, we have synthesized this MPB composition by using combustion synthesis process using urea as fuel and carried out sintering in oxygen atmosphere.