Piezoelectric properties of Fe₂O₃-doped (1 - X)BiScO₃-xPbTiO₃ ceramics

Effects of Fe substituents on bismuth scandium lead titanate ceramics (1 - x)BiScO₃-xPbTiO₃ (BSPT) at x = 0.64 were investigated in order to improve the piezoelectric properties. The density of Fe-doped BSPT ceramics tends to slightly decrease when Fe contents increase; except at 1.50 mol% Fe at which the highest density value about 7.43 g/cm³ is achieved. The Rietveld refinements of crystal structure of all samples show that they are of pure tetragonal phase. The Curie temperature (T_c) increases with doping Fe content and the highest T_c of 451 °C is reached for 2 mol% Fe-doped BSPT sample. All these ceramics yield higher Curie temperatures (T_c) than that of PbZr_0.52Ti _0.48O₃ (386 °C), the standard piezoceramics. Meanwhile, the dielectric constant and piezoelectric properties of the Fe-doped BSPT samples were significantly improved compared with those of the undoped sample. Electron spin resonance spectra clearly show that the iron is in the valence state 3+, which indicates that Fe³⁺ ions replace either Ti⁴⁺ or Sc³⁺ at B-sites. This gives rise to oxygen vacancies to maintain the charge balance and results in three Fe³⁺ ESR signals. The first and the third asymmetric signals at around 100 and 300 mT clearly arise from octahedral sites. The second ESR broad peak at around 190 mT implies that the neighboring O^2- vacancies are randomly distributed. It is evident that the 1 mol% Fe-doped sample yields the best over all piezoelectric properties. Furthermore, these new enhanced-piezoelectric materials can effectively reduce at least 36 mol% of the lead content in the ceramics employed in the high power applications so that they are more environmentally friendlier.