No abstract

The complex impedance spectra Z * (ω) were studied for as-grown and annealed in air Na0.5Bi0.5TiO3 single crystals. Experimental data showed that annealing significantly increased impedance and led to appearance of low frequency Z * relaxation. The detected relaxation processes were associated with charge transfer within the regions with initial and reduced after annealing concentration of oxygen vacancies.

BiFeO3 is a multiferroic material with the perovskite structure which is promising for use in sensors and transducers. Single phase production of BiFeO3 remains a challenge, however. In this study, the optimal calcination temperature to obtain close to single phase powder was determined to be 750 °C. The sintering temperature of 775 °C was also found to obtain high density ceramics ( ≈ 95 % of theoretical density). It is shown that off-stoichiometry of bismuth oxide in precursors effects the content of secondary phase. Impedance spectroscopy indicates that the content of secondary phases has a large effect on the electrical conductivity BiFeO3 .

No abstract

Bismuth ferrite is a potentially interesting lead-free piezoelectric material for use in high-temperature applications due to its high Curie temperature. However, the high coercive field and high leakage currents of pure BiFeO3 (BFO) prevent reaching its theoretical performance level. The classic approach to tailoring piezoceramic properties to their desired use conditions is the use of doping. In this work, we produce bulk BFO piezoceramic by the conventional sintering method with single element doping with cobalt (0.125–3 at. %) or titanium (1–5 at. %) and dual doping (Co and Ti added simultaneously). Cobalt doping reduces the required field for poling and also increases the leakage currents. Titanium doping reduces the leakage currents but destroys the piezoelectric properties as the coercive field strength cannot be reached. However, when both elements are used simultaneously at their appropriate levels (0.25 at. % each), a piezoelectric ceramic material is obtained, requiring a low field for full poling (9 kV/mm) and showing excellent room temperature performance such as a d33 = 40 pC/N, a dielectric constant in the region of 100 and dielectric losses less than 1%.