Low temperature sintering and enhanced piezoelectric properties of BiFeO3–BaTiO3 ceramics by homogeneous calcination

Abstract

The effect of calcination process on a phase evolution, a microstructure development and the piezoelectric properties were investigated in 0.75BiFeO3-0.25BaTiO3 (0.75BF-0.25BT) ceramics. At the relatively low calcination temperatures of 600 °C–650 °C, a Bi25FeO40 impurity phase was formed in addition to some unreacted raw materials and a perovskite phase. As the calcination temperature increased to the range of 700–900 °C, other intermediate phase BaBi4Ti4O15 was formed concurrently with small amounts of unreacted BaCO3 and perovskite matrix phase. At 950 °C a pure single perovskite phase of 0.75BF-0.25BT solid solution was observed. The sintered samples produced by using the raw powder calcined at a relatively low temperature of 600–900 °C showed a large fraction of pseudo-cubic relaxor phase (0.54–0.71 mass fraction) with the rest of a rhombohedral ferroelectric phase. They showed poor piezoelectric properties at sintering temperature below 1000 °C due to the nonuniform compositional distribution of the calcined powder. The homogeneous calcination at 950 °C for 2 h reduced greatly the optimum sintering temperature and significantly enhanced piezoelectric properties in the BF-BT ceramics. High Curie temperature as well as high piezoelectric properties were obtained at the sintering temperature as low as 920 °C: kp = 0.361, d33 = 123 pC/N and TC = 653 °C in the 0.75BF-0.25BT ceramics and kp = 0.337, d33 = 183 pC/N and TC = 525 °C in the 0.7BF-0.3BT ceramics. This low temperature sintering of the BF-BT ceramics by a homogeneous calcination could be applied to the fabrication of the lead-free multi-layer piezoelectric devices with inexpensive internal electrodes.