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

The synthesis of Bi 0.5 Na 0.375 K 0.125 TiO 3 (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) 2 Ti 6 O 13 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 K 2 O 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 Bi 0.5 Na 0.4 K 0.1 TiO 3 .