The formation of secondary phases in Bi0.5Na0.375K0.125TiO3 ceramics

The synthesis of Bi0.5Na0.375K0.125TiO3 (BNT–BKT or NBT-KBT) by the mixed oxide route was investigated using thermogravimetry, X-ray diffraction, scanning electron microscopy and electron microprobe analysis. The results show the formation of a paraelectric secondary phase with the composition (K,Na)2Ti6O13 during sintering. Thermogravimetric measurements indicate that the main loss of volatile components mainly occurs during the calcinations step, exceeding the theoretical loss by more than 2%. These losses, most likely caused by evaporation of K2O induce a high number of Schottky-vacancies. These vacancies highly affect the electrical properties of the material. The formation of the secondary phase leads to a shifted composition of the ceramic to approximately Bi0.5Na0.4K0.1TiO3.