Improved Properties of Doped BaTiO3 Piezoelectric Ceramics

(CazBa1 - z)(Ti1 - x - wCoxNbw)O3 - delta lead-free piezoelectric ceramics are prepared using solid-state reactions. The use of a Li2O sintering aid enables one to obtain dense ceramics at a temperature of 1100 degrees C instead of the 1350 degrees C used for BaTiO3 (BT) in conventional sintering. X-ray diffraction (XRD) data indicate structural modifications, suggesting insertion of the doping elements into the tetragonal structure. The insertion of Li/Ca/Co/Nb improves piezoelectric properties: for micrograin-size ceramics, a piezoelectric charge constant and an electromechanical coupling factor of d(33) = 255 pC N-1 and k(p) = 43.5% are reached, respectively. Furthermore, a thermal annealing of the cobalt-doped sample at 1080 degrees C under O-2 atmosphere leads to d(33) = 280 pC N-1 and k(p) = 44.6%. BaTiO3:Co ceramics present distorted ferroelectric cycles due to the occurrence of an internal bias field. The high mechanical quality factors (Q(m) > 1000) obtained for the doped BT ceramics afford stability against electrical stress of up to 500 V-RMS mm(-1), which makes these materials competitive with PZT4 for some applications.