Low temperature sintering and enhanced piezoelectric properties of BiFeO3-BaTiO3 3-BaTiO 3 ceramics by homogeneous calcination

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 degrees C-650 degrees 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 degrees C, other intermediate phase BaBi4Ti4O15 was formed concurrently with small amounts of unreacted BaCO3 and perovskite matrix phase. At 950 degrees 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 degrees 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 degrees C due to the nonuniform compositional distribution of the calcined powder. The homogeneous calcination at 950 degrees C for 2 h reduced greatly the optimum sintering temperature and significantly enhanced piezoelectric properties in the BFBT ceramics. High Curie temperature as well as high piezoelectric properties were obtained at the sintering temperature as low as 920 degrees C: kp = 0.361, d33 = 123 pC/N and TC = 653 degrees C in the 0.75BF-0.25BT ceramics and kp = 0.337, d33 = 183 pC/N and TC = 525 degrees 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.