The (1− x )BaTiO 3 – x Bi(Zn 2/3 Nb 1/3 )O 3 ( x = 0.01–0.30) ceramics were synthesized by solid-state reactions. The solubility limit was determined to be x = 0.20. A systematic structural transition from a tetragonal phase ( x ≤ 0.034), to a mixture of tetragonal and rhombohedral phases (0.038 ≤ x ≤ 0.20), and finally to a pseudocubic phase ( x ≥ 0.22) at room temperature was identified. Dielectric measurement revealed a ferroelectric ( x ≤ 0.04) to relaxor ( x ≥ 0.06) transition with permittivity peak broadening and flattening, which was further verified by Raman spectroscopy and differential scanning calorimetry (DSC). Activation energies obtained from the Vogel–Fulcher model displayed an increasing trend from ~0.03 eV for x ~ 0.05, to unusually high values (>0.20 eV) for the compositions with x ≥ 0.15. With the increase in Bi(Zn 2/3 Nb 1/3 )O 3 content, the polarization hysteresis demonstrated a tendency from high nonlinearity to sublinearity coupled with the reduction in remnant polarization and coervice field. The deconvolution of the irreversible/reversible polarization contribution was enabled by first-order reversal curve distributions, which indicates that the decreasing polarization nonlinearity with the increase in Bi(Zn 2/3 Nb 1/3 )O 3 concentration could be related with the change from the ferroelectric domain and domain wall contributions to the weakly coupled relaxor behaviors.
Lead-free (1 − x)BaTiO3–xBi(Zn2/3Nb1/3)O3 (x = 0.05–0.20) materials were fabricated via solid-state reactions. A pure perovskite pseudocubic structure is obtained for all compositions. Dielectric measurements reveal an intensified diffusion and relaxor-like characteristics from 5 mol% to 20 mol% Bi(Zn2/3Nb1/3)O3. Weakly coupled relaxor behavior is concluded from the exceptionally high activation energies of ∼0.20–0.22 eV from the Vogel–Fulcher model for x ≥ 0.10, which possibly results in the extremely low dielectric nonlinearity and extra slim polarization–electric field loops. An optimal discharged energy density of 0.79 J cm−3 with a high energy efficiency of 93.5% is achieved at 131 kV cm−1 for x = 0.15, which proves that the BaTiO3–Bi(Zn2/3Nb1/3)O3 material is a promising candidate for high energy storage applications.
Yan Tianxiang,Chen Kaiyuan,Li Chengqi,Liu Min,Wang Jie,Fang Liang,Liu Laijun
(1− x )K 0.5 Na 0.5 NbO 3 − x Bi(Zn 2/3 Nb 1/3 )O 3 ((1− x )KNN− x BZN, x = 0.010, 0.015, 0.020, 0.025, and 0.030) lead-free ceramics were fabricated via a traditional solid-state method. The crystal structure, microstructure, dielectric, and conductivity behavior of this system were studied. Combined with X-ray diffraction (XRD) patterns, Rietveld refinement, and dielectric spectroscopy, an orthorhombic phase was determined for x = 0.010, an orthorhombic-tetragonal mixed phase was identified for x = 0.015, and a rhombohedral symmetry appears in 0.020 ⩽ x ⩽ 0.030. Both 0.98KNN−0.02BZN and 0.975KNN−0.025BZN ceramics exhibit stable permittivity and low dielectric loss tangent (tan δ ) in wide temperature ranges owing to the combination of rhombohedral-tetragonal step-like feature and the diffuse phase transition from tetragonal to cubic. The activation energies of dielectric relaxation and conductivity behavior at high temperatures initially decrease slightly, then drop sharply, and finally decline slowly, which could be attributed to microstructure morphologies and the concentration of oxygen vacancies.
The application of lead-free dielectric ceramics for energy storage has received extensive attention because of their remarkable potential as pulse capacitors in power electronic devices. The current study developed a strategy for improving the energy storage performance of (K 0.5 Na 0.5 )NbO 3 (KNN)-based ceramics by incorporating Bi(Zn 2/3 Nb 1/3 )O 3 to reduce grain size, increase dielectric breakdown strength, and enhance ferroelectric relaxation degree. The resulting 0.87KNN–0.13BZN ceramics exhibited a high energy density (7.4 J/cm 3 ) and moderate energy efficiency (74%) at an ultrahigh electric field (750 kV/cm) as well as excellent optical properties. Therefore, the 0.87KNN–0.13BZN ceramic is a promising candidate for pulse capacitors, providing a feasible approach for the development of new lead-free energy storage materials.
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