The effects of microwave sintering on the sintering behaviour, microstructure and piezoelectric properties of ZnO-doped (Bi 0.5 Na 0.5)TiO 3 (ZnO:NBT) ceramics were investigated. The microstructure and piezoelectric properties of a lead-free NBT ceramic were also studied given different amounts of ZnO doping. X-ray diffraction shows that Zn 2+ diffuses into the lattice of (Bi 0.5 Na 0.5)TiO 3 to form a solid solution with a pure perovskite structure. Microwave heating with sintering temperatures below 1000°C significantly improves the densification of ZnO:NBT ceramics. The piezoelectric coefficient d 33 for the 0.5 wt % ZnO:NBT ceramics, sintered at 950°C, was found to be 108 pC/N, with a electromechanical coupling factor kp = 0.17.
The substitution of up to 5% Ca2+ for Ba2+ in BaTiO3 results in a shift in the oxygen pressure dependence of the equilibrium electrical conductivity that is in the same direction as that caused by addition of acceptor impurities such as Al3+ or Ca2+ substituted for Ti4+. In contrast to the latter effect, however, the shape of the conductivity plot is not changed, the conductivity value at the conductivity minimum is not affected, and the amount of the shift increases with decreasing temperature of measurement. It is shown that the shift is primarily due to an increase in the enthalpy of reduction and a decrease in the enthalpy of oxidation as increasing amounts of Ba2+ are replaced by Ca2+.
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