Journal of Advanced Dielectrics

With the increasing demand of high-power and pulsed power electronic devices, environmental-friendly potassium sodium niobate ((Na${}_{0.5}$K${}_{0.5}$)NbO₃, KNN) ceramic-based capacitors have attracted much attention in recent years owning to the boosted energy storage density ($W_{\mathrm{\text{rec}}}$). Nevertheless, the dielectric loss also increases as the external electric field increases, which will generate much dissipated energy and raise the temperature of ceramic capacitors. Thus, an effective strategy is proposed to enhance the energy storage efficiency ($\eta$) via tailoring relaxor behavior and bad gap energy in the ferroelectric 0.9(Na${}_{0.5}$K${}_{0.5}$)-NbO₃–0.1Bi(Zn${}_{2/3}$(Nb${}_x$Ta${}_{1-x}$)${}_{1/3}$)O₃ ceramics. On the one hand, the more diverse ions in the B-sites owing to introducing the Ta could further disturb the long-range ferroelectric polar order to form the short–range polar nanoregions (PNRs), resulting in the high $\eta$. On the other hand, the introduction of Ta ions could boost the intrinsic band energy gap and thus improve the $E_{\mathrm{\text{b}}}$. As a result, high $W_{\mathrm{\text{rec}}}$ of 3.29 J/cm³ and ultrahigh $\eta$ of 90.1% at the high external electric field of 310 kV/cm are achieved in $x$ = 0.5 sample. These results reveal that the KNN-based ceramics are promising lead-free candidate for high-power electronic devices.

Dielectric polymer film capacitors with a high-power density as well as efficient charge and discharge rates have great potential for application to fulfill the miniaturized and lightweight requirements of the electronic and stationary power systems. It was reported that the elastic recovery rate and energy storage density of poly (vinylidene fluoride-chlorotrifluoroethylene) [P(VDF-CTFE)] polymer film can be enhanced through thermostatic uniaxial stretching. But it is unknown about the relationship between the stretching rate and above properties. In this study, we investigated the effect of different stretching rates on the conformation, elastic recovery, dielectric constant, and energy storage density of stretched P(VDF-CTFE) polymer films. It was found that the stretching rate significantly affected the formation of polar $\beta$-crystal phase, causing different dielectric properties. The degrees of elastic recovery of P(VDF-CTFE) film vary with stretching rates. Among them, the elastic recovery rate of the P(VDF-CTFE) 94/6 film is 46.5% at a stretching rate of 15 mm/min, the dielectric constant is 12.25 at 100 Hz, and the energy density reaches 3.95 J/cm³ with the energy loss of 39% at 200 MV/m field.

In this work, (1 $-x$)(0.92NaNbO₃–0.08BaTiO₃)–$x$Ca${}_{0.7}$La${}_{0.2}$TiO₃ (NNBT – $x$CLT) ceramics were successfully designed and prepared by the solid-state reaction method. Investigations on the structure, dielectric, and energy storage properties were performed. The NNBT – 0.25CLT ceramic with orthorhombic phase at room temperature was found to exhibit extremely small grain size and compacted microstructure. A large $W_{\mathrm{\text{rec}}}$ of 3.1 J/cm³ and a high $\eta$ of 91.5% under the electric field of 360 kV/cm were achieved simultaneously in the sample. In addition, the energy storage performance of the sample exhibits thermal stability over the temperature range of 25–140${}^{\circ }$C and the frequency range of 5–500 Hz. The charge and discharge tests reveal that the ceramic shows a large current density $C_D$ of 965 A/cm² and power density $P_D$ of 154 MW/cm³. This work demonstrates that the NNBT–0.25CLT ceramic is a prospective energy storage material for potential application in the field of pulsed power devices.

Ferroelectric materials are considered to be the most competitive energy storage materials for applications in pulsed power electronics due to excellent charge–discharge properties. However, the low energy storage density is the primary problem limiting their practical application. In this study, (1$-x$)Na${}_{0.5}$Bi${}_{0.5}$TiO₃–$x$Sr${}_{0.7}$La${}_{0.2}$TiO₃[(1$-x$)NBT–$x$SLT] ferroelectric ceramics are found to exhibit excellent energy storage performances through a synergistic strategy. As the SLT concentration increases, the relaxation characteristic increases significantly and the breakdown strength increases dramatically from 150 kV/cm to 220 kV/cm. The recoverable energy storage density of the 0.55NBT–0.45SLT ceramic is 2.86 J/cm³ with an energy storage efficiency of 88% under an electric field of 220 kV/cm. Furthermore, the ceramic with $x$ = 0.45 mol exhibited excellent energy storage stability in the ranges of 20–180${}^{\circ }$C (temperature) and 1–125 Hz (frequency). These excellent properties demonstrate the potential of (1$-x$)NBT–$x$SLT ceramics when used as dielectric capacitors in pulsed power systems.

It is crucial to discover lead-free materials with ultrahigh recoverable energy density ($W$${}_{\mathrm{rec}}$) that can be employed in future pulse power capacitors. In this work, a high $W$${}_{\mathrm{rec}}$of 4.51 J/cm³ was successfully obtained in lead-free Nd-doped AgNb${}_{0.8}$Ta${}_{0.2}$O₃ antiferroelectric ceramics at an applied electric field of 290 kV/cm. It is discovered that Nd doping paired with Nb-site vacancies could stabilize the antiferroelectric phase by lowering the temperatures of the M1–M2 and M2–M3 phase transitions, which leads to higher energy storage efficiency. Furthermore, Nd and Ta co-doping will contribute to the electrical homogeneity and low electrical conductivity, resulting in large breakdown strengths. Aliovalent doping in Ag-site with Nb-site vacancies serves as a novel strategy for the construction of AgNbO₃-based ceramics with excellent energy storage performance.

In this work, novel (1 $-x$)(0.75Na${}_{0.5}$Bi${}_{0.5}$TiO₃)-0.25Sr(Zr${}_{0.2}$Sn${}_{0.2}$Hf${}_{0.2}$Ti${}_{0.2}$Nb${}_{0.2}$)O₃-$x$NaNbO₃ (NBT-SZSHTN-$x$NN, $x$ = 0.1, 0.15, 0.2, 0.25) ceramics were fabricated. The influence of co-doping of NN and high entropy perovskite oxide (SZSHTN) on the phase structure, microstructure and dielectric properties of NBT-based lead-free ceramics was investigated. Dense microstructure with a grain size of $\sim$5 $\mu$m is observed. When $x$ = 0.25, a wide dielectric temperature stable range of −35.4–224.3${}^{\circ }$C with a low temperature coefficient of capacitance of $<$ 10% is achieved, fulfilling the industry standard of Y9P specification. Furthermore, excellent energy storage performance with recoverable energy density of 2.4 J/cm³, discharge efficiency of 71%, power density of 25.495 MW/cm³ and discharge rate $<$ 200 ns are simultaneously obtained, which shows great potential for high temperature capacitor applications.

Lead-free relaxor ceramics (1 − $x$)K${}_{0.5}$Na${}_{0.5}$NbO₃ − $x$Bi(Mn${}_{0.5}$Ni${}_{0.5}$)O₃ ((1 − $x$ )KNN- $x$BMN) with considerable charge–discharge characteristics and energy storage properties were prepared by a solid state method. Remarkable, a BMN doping level of 0.04, 0.96KNN–0.04BMN ceramic obtained good energy storage performance with acceptable energy storage density $W$${}_{\mathrm{rec}}$ of 1.826 J/cm³ and energy storage efficiency $\eta$ of 77.4%, as well as good frequency stability (1–500 Hz) and fatigue resistance (1–5000 cycles). Meanwhile, a satisfactory charge–discharge performance with power density $P$${}_D$ $\sim$ 98.90 MW/cm³, discharge time $t$${}_{0.9}$ < 70 ns and temperature stability (30–180^∘C) was obtained in 0.96KNN–0.04BMN ceramic. The small grain size ($\sim$150 nm) and the high polarizability of Bi${}^{3+}$ are directly related to its good energy storage capacity. This work proposes a feasible approach for lead-free KNN-based ceramics to achieve high-energy storage and ultra-fast charge–discharge performance as well as candidate materials for the application of advanced high-temperature pulse capacitors.

Flexible dielectric materials with environmental-friendly, low-cost and high-energy density characteristics are in increasing demand as the world steps into the new Industrial 4.0 era. In this work, an elastomeric nanocomposite was developed by incorporating two components: cellulose nanofibrils (CNFs) and recycled alum sludge, as the reinforcement phase and to improve the dielectric properties, in a bio-elastomer matrix. CNF and alum sludge were produced by processing waste materials that would otherwise be disposed to landfills. A biodegradable elastomer polydimethylsiloxane was used as the matrix and the nanocomposites were processed by casting the materials in Petri dishes. Nanocellulose extraction and heat treatment of alum sludge were conducted and characterized using various techniques including scanning electron microscopy (SEM), thermogravimetric analysis/derivative thermogravimetric (TGA/DTG) and X-ray diffraction (XRD) analysis. When preparing the nanocomposite samples, various amount of alum sludge was added to examine their impact on the mechanical, thermal and electrical properties. Results have shown that it could be a sustainable practice of reusing such wastes in preparing flexible, lightweight and miniature dielectric materials that can be used for energy storage applications.

Dielectric capacitors with high capacitive energy storage are urgently needed to meet the growing demand for high-performance energy storage devices. Herein, a novel lead-free Sr₅BiTi₃Nb₇O${}_{30}$ (SBTN) tungsten bronze relaxor ferroelectric ceramic is prepared and explored for potential energy storage applications. A high recoverable energy density $W_{\mathrm{\text{rec}}}$ ($\sim$ 3.72 J/cm³) and ultrahigh efficiency $\eta$ ($\sim$ 94.2%) at 380 kV/cm are achieved simultaneously. Both $W_{\mathrm{\text{rec}}}$ and $\eta$ exhibit superior stabilities against temperature (30–140${}^{\circ }$C), cycles (10⁰ –10⁵) and frequency (1–500 Hz). In addition, a high current density of 796 A/cm² and a large power density of 71.7 MW/cm³ are achieved, together with good thermal endurance and fatigue resistance. These results demonstrate that the obtained SBTN ceramic can be deemed as the promising candidates for dielectric capacitor applications.