Compositional evolution of structural phase transitions in sodium niobates

LixNa1−xNbO3 ceramics with 5⩽x⩽12% have been studied in the temperature range RT–773 K through elastic, thermal expansion and dielectric measurements as a function of the temperature. Thermal expansion behaviour shows single, (for x⩽8%) or double, (for x⩾10%), reversible anomalies in the complete thermal cycle. The elastic behaviour shows single, for x=5%, or double and reversible anomalies, for x⩾8%. In both cases the thermal behaviours scarcely depend on the thermal rate. The dielectric permitivity shows reversible single anomalies in the phase transition temperature for x⩽8% and double non-reversible anomalies for x⩾8% that are very dependent on the thermal rate and thermal history of the sample. The crossover composition for the appearance of a double anomaly can be established close to x=8%. The main (FE–PE) phase transitions and their temperatures have been established using three measuring techniques.