Anomalous Thermal Expansion in Solid-Phase Synthesis of Piezoceramic Material Based on Solid Solutions of Potassium and Sodium Niobates

Abstract

Anomalous thermal expansion of the pressed mixture of initial reactants is observed in solid-phase synthesis of piezoceramic materials based on complex oxides with perovskite structure. Under certain conditions the magnitude of this expansion can be an indicator of the degree of completion of the solid-phase reactions. The thermal expansion of the pressed mixture of powders of potassium and sodium carbonates and niobium oxide in the synthesis of the complex oxide potassium niobate and sodium niobate KNN is analyzed. It is shown that the temperature and completeness of the synthesis reaction can be determined on the basis of this analysis. The obtained material was used to prepare samples of piezoceramic with density to 92% of the theoretical value and piezoelectric modulus d₃₃ to 1.0 × 10^–10 C/N.