(Na 0.4 Bi 0.5K 0.1 )Ti 1-x M X O 3-? (M 3+ =Co 3+ /Al 3+ /Fe 3+ ) Study On The Structure And Electrical Properties Of Lead-free Piezoelectric Ceramics

Bi_0.5Na_0.5TiO₃ -based ceramics are lead-free piezoelectric materials. The doping of M³⁺ (M³⁺ = Al³⁺?Fe³⁺?Co³⁺) into Bi_0.5Na_0.5TiO₃ can form solid solutions and cause oxygen vacancies in the samples. Effect of point defects including oxygen vacancies on electric properties is very important. In this work, ?1-x?[0.80Bi_0.5Na_0.5TiO₃-0.20Bi_0.5K_0.5TiO₃]-xBiM03 ?M = Co, AL Fe? ?x = 0, 0.02, 0.05? lead-free ceramics were studied. The samples were prepared via a solid state reaction method. Effects of the ions doping on phase structure, microstructrue, dielectric, ferroelectric, piezoelectric properties were investigated, which are shown as following:1. For ?1-x?[0.80Bi_0.5Na_0.5TiO₃-0.20Bi_0.5K_0.5TiO₃]-xBiCo03 ?BNKT-xCo, x = 0, 0.02, 0.05? lead-free ceramics, X-ray diffraction ?XRD? results show that all BNKT-xCo ceramics exhibit pure perovskite structure and lattice parameters decrease with increasing the content of Co³⁺. Raman spectroscopy results suggest a lattice distortion due to the doping of Co³⁺. Scanning electron microscope ?SEM? results demonstrate that the doping of Co³⁺ promotes the growth of grains. The doping of Co³⁺ enhances the maximum permittivity ?sm?, enhances Curie temperature ?rm?, decreases piezoelectric constant ?d33?. The depolarization temperature ?7d? values were obtained by means of dielectric constant-temperature curves, thermally stimulated depolarization current ?TSDC? curves and the variation of J33 with thermal annealing temperature. The 7d values are different obtaind from the different methods. It increases with the increase in the amount of Co³⁺. P-E Loops show that the ferroelectric properties of the ceramics are weakened due to the doping of Co³⁺, the remnant polarization ?PT? decreases from 30 ?x = 0? to 26 uC/cm2 ?x = 0.05?, the coercive field ?Ec? increases from 39 to 50 kV/cm. Combined with the results of the Ultraviolet-visible diffuse reflectance spectra, impedance analysis and Rayleigh analysis, the changes in structure and electrical properties of the BNKT-xCo ceramics were discussed according to the doping of Co³⁺ and oxygen vacancies.2. For ?1-x?[0.80Bi_0.5Na_0.5TiO₃-0.20Bi_0.5K_0.5TiO₃]-xBiAl03 ?BNKT-xAl, x = 0, 0.02, 0.05? lead-free ceramics, X-ray diffraction ?XRD? results show that all BNKT-xAl ceramics exhibit pure perovskite structure and the doping of Al + induces lattice distrotion. The doping of Al³⁺ has no obvious effect on grain size of the ceramics. Ultraviolet-visible diffuse reflectance spectra show that the optical band gap ?Eg? is decreased with increasing the content of Al+. Permittivity vs temperature spectroscopy reveals that there are two dielectric abnormal peaks. The dielectric, ferroelectric and piezoelectric properties of the samples are weakened due to the doping of Al³⁺3. For ?1-x?[0.80Bi_0.5Na_0.5TiO₃-0.20Bi_0.5K_0.5TiO₃]-xBiFe03 ?BNKT-xFe, x=0, 0.02,0.05? lead-free ceramics, X-ray diffraction ?XRD? results show that all BNKT-xFe ceramics exhibit pure perovskite structure and lattice parameters decrease with increasing the content of Fe³⁺. The doping of Fe³⁺ has no obvious effect on grain size of the ceramics. The optical band gap ?Eg? decreases with increasing the content of Fe³⁺. The doping of Fe³⁺ decreases ?m, enhances Tm, decreases Td. The d33 values increases due to the doping of Fe³⁺?x= 0.02, d33= 104 pC/N?.4. Effects of the doping of the three differnt ions on structure and electrical properteis of the BNKT-based ceramics were studied comparatively. All ceramics with the doping of Co³⁺, Al³⁺ and Fe³⁺ have pure perovskite structure and show lattice distrotion. The doping of Co³⁺ promotes the growth of grains, while the doping of Fe³⁺ and Al³⁺ has no obvious effect on grain size of the ceramics. All ceramics shows decreased Eg values with the doping of the ions. All ceramics show the character of diffuse phase transition. ?m increases with the increase in the Co+ amount, while decreases with the increase in the Al³⁺ and Fe³⁺ amount. Tm increases with the doping amount for all ceramics except BNKT-005Al. Ta increases with the increase in the Co³⁺ amount, while decreases with the increase in the Al³⁺ and Fe³⁺ amount. The ferroelctric and piezoelectric properties are related to the doping of the ions.The difference in electrical properties was discussed according to the effects of oxygen vacancies and grain size.