High energy storage and ultrafast discharge in NaNbO3-based lead-free dielectric capacitors via a relaxor strategy

Dielectric capacitors with decent energy storage and fast charge-discharge performances are essential in advanced pulsed power systems. In this study, novel ceramics (1-x)NaNbO₃-xBi(Ni_2/3Nb_1/3)O₃(xBNN, x = 0.05, 0.1, 0.15 and 0.20) with high energy storage capability, large power density and ultrafast discharge speed were designed and prepared. The impedance analysis proves that the introducing an appropriate amount of Bi(Ni_0·5Nb_0.5)O₃ boosts the insulation ability, thus obtaining a high breakdown strength (E_b) of 440 kV/cm in xBNN ceramics. A high energy storage density (W_total) of 4.09 J/cm³, recoverable energy storage density (W_rec) of 3.31 J/cm³, and efficiency (η) of 80.9% were attained in the 0.15BNN ceramics. Furthermore, frequency and temperature stability (fluctuations of W_rec ≤ 0.4% over 5–100 Hz and W_rec ≤ 12.3% over 20–120 °C) were also observed. The 0.15BNN ceramics exhibited a large power density (19 MW/cm³) and ultrafast discharge time (~37 ns) over the range of ambient temperature to 120 °C. These enhanced performances may be attributed to the improved breakdown strength and relaxor behavior through the incorporation of BNN. In conclusion, these findings indicate that 0.15BNN ceramics may serve as promising materials for pulsed power systems.     

High recoverable energy storage density and large energy efficiency simultaneously achieved in BaTiO3–Bi(Zn1/2Zr1/2)O3 relaxor ferroelectrics

Relaxor ferroelectrics have attracted much attention as electric energy storage materials for intermittent energy storage because of their high saturated polarization, near-zero remnant polarizations, and considerable dielectric breakdown strength (BDS). Despite the numerous efforts, the dielectric energy storage performance of relaxor ferroelectric ceramics is incomplete or unsatisfactory. The enhancement of recoverable energy storage density W_rec usually accompanies with the sacrifice of discharge-to-charge energy efficiency η; therefore, it is an important issue to achieve high recoverable W_rec and large efficiency η simultaneously. In this work, the (1-x)BaTiO₃-xBi(Zn_1/2Zr_1/2)O₃ (abbreviated as BT-100xBZZ, 0 ≤ x ≤ 0.20) ferroelectric ceramics were prepared using the conventional solid-state reaction method. The phase structure, microstructural morphology, dielectric and ferroelectric properties, relaxation behaviors, and energy storage properties of BT-BZZ ceramics were investigated in detail. X-ray powder diffraction, dielectric spectra, and ferroelectric properties confirm the transformation of tetragonal phase for normal ferroelectrics (BT) to pseudo-cubic phase for relaxor ferroelectrics (BT-8BZZ). A high recoverable energy storage density W_rec of 2.47 J/cm³ and a large energy efficiency η of 94.4% are simultaneously achieved in the composition of BT-12BZZ, which presents typical weakly coupled relaxor ferroelectric characteristics, with an activation energy E_a of 0.21 eV and a freezing temperature T_f of 139.7 K. Such excellent energy storage performance suggests that relaxor ferroelectric BT-12BZZ ceramics are promising dielectric energy storage materials for high-power pulsed capacitors.     

Large piezoelectricity and potentially activated polarization reorientation around relaxor MPB in complex perovskite

Improving piezoelectric performance is always favorable to further enhance the sensitivity and accuracy of piezoelectric devices. Here, a complex piezoelectric system of Pb(Ni_1/3Nb_2/3)O₃-Pb(Yb_1/2Nb_1/2)O₃-Pb(Hf_0.1Ti_0.9)O₃ is designed and investigated in detail. Optimized piezoelectric response of ～ 880 pC/N is achieved at the composition of 0.51PNN-0.09PYN-0.40PHT. The characterization of TEM and In-situ high-energy synchrotron diffraction indicate that nanodomain growth and microdomain switching occurs in succession at around coercive electric field. Most interestingly, the coexisted tetragonal and rhombohedral-like phase transforms into multiple monoclinic-like phases with polarization vectors aligned as close to the electric field direction as possible under the strong electric field. The enhanced polarization instability in this complex morphotropic phase boundary sample should be ascribed to the strong local heterogeneity. The novel polarization rotation behavior found in this work would be important guidance for designing high-performance piezoceramics.     

Improved energy storage density and energy efficiency of Samarium modified PMNT electroceramic

We report the improved energy storage density and efficiency after 2.5% of Samarium substitution in ferroelectric Pb[(Mg_1/3Nb_2/3)_0.80Ti_0.20]O₃ (PMNT) electroceramic. The microstructure and surface morphology were analyzed and correlated with various functional properties. The energy storage density, leakage current density, ferroelectric and dielectric properties were investigated thoroughly, indicating that Samarium's substitution significantly modified the microstructure, the dielectric strength, breakdown electric field, and turned ferroelectric PMNT to relaxor ferroelectrics. Due to the relaxor nature, the gap between remanent polarization and maximum polarization increases with the substitution of Samarium in PMNT matrix, which further increases the recoverable energy storage density and energy efficiency. A nearly 100% increase in recoverable energy density and efficiency was obtained at an electric field strength of 35 kV/cm at room temperature (～296 K). The electroceramic shows maximum energy density near the ferroelectric phase transition temperature (325 K–345 K) region and provides a moderate energy storage density for possible applications in power microelectronics.     

Structure,dielectric properties of novel Ba(Zr,Ti)O3 based ceramics for energy storage application

(1-x) Ba(Zr_0.2Ti_0.8)O₃-x Na_0.5Bi_0.5TiO₃ (x = 0, 10, 20 30, 40, 50 mol%) (BZTN) ceramics are prepared by the traditional solid phase method. All BZTN ceramics exhibit a pseudo-cubic BZT based perovskite structure. Both the average grain size and the relaxor ferroelectricity of BZTN ceramics gradually increase with increasing NBT content. The W_rec of 3.22 J/cm³ and η of 91.2% is obtained for the BZTN40 ceramic at 241 kV/cm. BZTN40 ceramic also exhibits good temperature stability from room temperature to 150 °C and frequency stability from 1 Hz to 100 Hz. A P_D of 0.621 J/cm³ and a t_0.9 of 82 ns is obtained for the BZTN40 ceramic at 120 kV/cm. BZTN ceramics show application potential in energy storage and pulse power capacitors.     

Effect of hot pressing on processing and properties of BBN ceramics

BBN (BaBi₂Nb₂O₉) is very interesting and promising lead free material with relaxor properties in capacitors, sensors and actuators.     

Structural properties of 0.65Pb(Mg1/3Nb2/3)O3–0.35PbTiO3 relaxor ferroelectric thin films on SrRuO3 conducting oxides

Coating of 0.65Pb(Mg_1/3Nb_2/3)O₃–0.35PbTiO₃ (PMN–PT) relaxor ferroelectrics by a sol–gel method is followed by growth of epitaxial SrRuO₃ (SRO) metallic oxide electrodes on SrTiO₃ (STO) single-crystal substrate by pulsed laser deposition. High-quality PMN–PT films on SRO with preferred growth orientation were successfully fabricated by controlling the operation parameters. Structural properties of relaxor ferroelectric PMN–PT thin films on SRO/STO substrates have been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM). In-plane and out-of-plane alignments of the heterostructure are confirmed and the structural twinning of the materials are also revealed.     

Relaxor behavior and superior ferroelectricity of Y2O3-doped (Ba0.98Ca0.02) (Ti0.94Sn0.04Zr0.02)O3 lead-free ceramics

To upgrade the electric properties of lead-free piezoceramics, (1–x)(Ba_0.98Ca_0.02Ti_0.94Sn_0.04Zr_0.02)O₃-xY₂O₃ (abbreviated as (1–x)BCTSZ-xY, x = 0 mol%, 0.02 mol%, 0.04 mol%, 0.06 mol%, 0.08 mol% and 0.1 mol%) ceramics were successfully synthesized by traditional solid-state sintering method. The phase structure and microstructure of ceramics were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and piezoresponse force microscopyeramics (PFM). The electric properties of ceramics were researched through piezoelectric, dielectric and ferroelectric test instruments. The results show that all samples have pure perovskite structure and favorable electric properties. The optimal electric properties which especially include superior ferroelectric properties are gained when Y₂O₃ content is 0.06 mol% (d₃₃ = 419 pC/N, k_p = 52%, T_c = 89.5 °C, ε_r = 26900, tanδ = 2.86%, P_r = 14.41 μC/cm², E_c = 1.8 kV/cm). Moreover, the temperature-dependent dielectricity of samples shows apparent relaxor behavior under different frequencies. The Curie–Weiss law further proves that all samples are typical relaxor ferroelectrics, and the relaxor degree of samples decreases with increase of Y₂O₃ content. In conclusion, Y₂O₃ plays a significant role in enhancing electric properties of BCTSZ ceramics.     

钨青铜陶瓷Sr0.6Ba0.4Nb2O6的合成、结构与介电性能

通过固相反应法合成了Sr0．6Ba0．4Nb2O6陶瓷，并对其进行了结构、介电性能的表征。结果表明Sr0．6Ba0．4Nb2O6陶瓷为四方钨青铜结构单相，其在60℃附近存在一个明显的弥散介电峰，峰值温度随频率向高温偏移，为典型的弛豫铁电相变。室温时，10kHz频率下，其介电常数约为1404，介电损耗为0．03。     

Study of the structure and electrical properties of PMN-PNN-PT ceramics near the morphotropic phase boundary

A series of Pb(Mg_1/3Nb_2/3)O₃-Pb(Ni_1/3Nb_2/3)-O₃-PbTiO₃ (PMN-PNN-PT) ceramics with compositions of (1–x)(0.67PMN-0.33PT)-x(0.64PNN-0.36PT) (x = 0.1–0.9) were synthesized using the columbite precursor method. The phase structures, as well as the dielectric and piezoelectric properties of the ceramics were investigated in detail. X-ray diffraction results demonstrate that all the samples possess a pure perovskite structure. It is found that the morphotropic phase boundary (MPB) region of the PMN-PNN-PT ternary system is located near the line connecting the MPBs of the PMN-PT and PNN-PT binary systems. A high value of the maximum dielectric constant (ɛ_m = 45540, at 1 kHz), together with a high value of the piezoelectric coefficient (d₃₃ = 780 pC/N), were obtained for the composition x = 0.2. The results show that a partial substitution of PNN-PT for PMN-PT can lead to improved electrical properties in this ternary system.