We report on the reduction of band gap in Bi0.5(Na0.82-xLixK0.18)0.5(Ti0.95Sn0.05)O3 from 2.99 eV to 2.84 eV due to the substitutions of Li+ ions to Na+ sites. In addition, the lithium substitution samples exhibit an increasing of the maximal polarizations from 21.8 to 25.7 μC/cm2. The polarization enhancement of ferroelectric and reduction of the band gaps are strongly related to the Li substitution concentration as evaluated via the electronegative between A-site and oxygen and tolerance factor. The results are promising for photovoltaic and photocatalytic applications.
The lead-free piezoelectric ceramics display good piezoelectric properties which are comparable with Pb(Zr,Ti)O3(PZT) and these materials overcome the hazard to the environment and human health. The Bi0.5(Na,K)0.5TiO3(BNKT) is rapidly developed because of good piezoelectric, ferroelectric, and dielectric properties compared to PZT. The origin of giant strain of BNKT piezoelectric materials was found at morphotropic phase boundary due to crystal change from tetragonal to orthorhombic and/or precipitation of cubic phases, in addition to domain switching mechanism. The dopants or secondary phases withABO3structure as solid solution are expected to change the crystal structure and create the vacancies which results in enhancement of the piezoelectric properties. In this work, we reviewed the current development of BNKT by dopants and secondary phase as solid solution. Our discussion will focus on role of dopants and secondary phase to piezoelectric properties of BNKT. This result will open the direction to control the properties of lead-free piezoelectric materials.
Lead-free (1-x)Bi0.5Na0.4K0.2TiO3-xBiFeO3 (abbreviated as BNKT-xBFO) ferroelectric films with x in the range from 0.00 to 0.10, were synthesized by the chemical solution deposition technique on Pt/Ti/SiO2/Si substrates. The microstructures and magnetic behaviors of BNKT-xBFO films were analyzed in detail as a function of BFO concentration. X-ray diffraction patterns indicated that BNKT-xBFO films were grown with a single-phase perovskite structure. The pure films showed an antiferromagnetic behavior. The magnetic properties of the films were gradually transferred from antiferromagnetic to ferromagnetic properties when BFO concentration was raised. The saturated magnetization (M
S) reached the highest value of 10.3 emu cm−3 at the BFO-doped concentration x = 0.10. Our work will contribute to illuminate the impact of BFO (ABO3 perovskite structure) on the magnetic properties of BNKT materials at room temperature.
Lead-free Bi0.5(Na0.8K0.2)0.5TiO3 (abbreviated as BNKT) films have been synthesized via a sol-gel technique on Pt/Ti/SiO2/Si substrates, and the dependence of the physical properties in BNKT films were investigated as a function of the crystallization temperature. The BNKT films were annealed at different temperatures (600, 650, 700, and 750°C) for 60 min in the air. The results of this study showed that the optimal crystallization temperature is 700°C. At this, the BNKT films exhibited a single perovskite phase structure and high-dense surface. Besides, the remanent (Pr) and maximum (Pm) polarization reached their highest values of 9.2 µC/cm2 and 30.6 µC/cm2, respectively. All the films showed a weak ferromagnetic behavior with the maximum saturated magnetization (Ms) of 2.1 emu/cm3. These values are equivalent to the highest Pr and Pm values in previous reports on lead-free films.
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