Journal of Advanced Dielectrics

In order to improve the limited compatibility of existing polymer/ceramic dielectric composites and further enhance the energy storage density, MOF/polymer composite dielectrics have been explored, which exhibit good compatibility to the polymer matrix from abundant organic groups of the inorganic–organic hybrid metal-organic framework (MOF) fillers. However, they still lack a clear composition–structure–property rule, and the precise design of MOF fillers and polymer matrix becomes a prominent problem in these composites due to the diversity of the metal ions and the organic groups. Thus, in this paper, we present a series of formic acid MOFs/polylactic acid dielectric composites in which ferroelectric formic acid MOFs, namely PDLLA/[NH${}_3$(CH${}_2$)${}_4$NH${}_3$][M${}^{II}$(HCOO)${}_3$]${}_2$ and PDLLA/[CH${}_3$NH${}_3$][M${}^{II}$(HCOO)${}_3$]${}_2$, in which the formic acid MOFs are with different structures and different metal ions as fillers, including [NH₃(CH${}_2{)}_4$NH₃][M^II(HCOO)₃]₂ (namely MOF– Co (M $=$ Co), MOF– Mg(M $=$ Mg), MOF– Mn (M $=$ Mn), with 1, 4-butanediamine ion as guest) and [CH₃NH₃][M${}^{II}$(HCOO)₃]₂ (namely MOF– Co${}_2$ (M = Co), MOF– Ni${}_2$ (Ni), with methylamine ion as guest). The composition and morphology of composite films were characterized by XRD, IR, SEM, DSC and UV, respectively, while the dielectric characterizations of the composites including the dielectric permittivity, the dielectric loss, the breakdown field strength and the energy density were also performed. The composition–structure–property relationships were also investigated including the influence of MOF content and MOF category. With the introduction of MOFs, the dielectric constant of the polylactic acid substrate was improved slightly while the breakdown field strength can be improved in some systems. Interestingly, the Co(II)-containing formic acid MOF has advantages over other formic acid MOFs with similar structure for the enhancement of the dielectric constant and breakdown field strength. Also, in some composite films with methylamine ion guest MOF fillers and low-MOF content ( MOF– Co${}_2$ (1 vol.%) and MOF– Ni${}_2$ (1 vol.%)), the breakdown electric field enhanced significantly and further led to improved energy storage density which was about 43% higher than that of the polylactic acid matrix. The possible reason is that in these composites, the orientation of C–H bonds of MOFs seems more beneficial to the formation of hydrogen bonds between the carboxyl group of formic acid and the polylactic acid matrix. These relationships obtained from formic acid MOFs/polylactic acid composites are valuable to the design of high-performance polymer/MOF energy storage composites and may be a new perspective to the practical use of ferroelectric MOFs.

Bi${}_{0.5}$Na${}_{0.5}$TiO₃ (BNT)-based lead-free ceramics with superior ferroelectric properties are considered to be extremely advantageous in energy storage capacitors for future green technologies. Here, we demonstrate an approach to achieve both ultrahigh energy density $W_{\mathrm{\text{rec}}}$ and efficiency $\eta$ by regulating the multiscale electropolar structures and microstructure. A satisfactory energy storage performance of a high $W_{\mathrm{\text{rec}}}$ of $4.02\mathrm{\text{J}}\cdot {\mathrm{\text{cm}}}^{-3}$, and a decent $\eta$ of 80% under $415\mathrm{\text{kV}}\cdot {\mathrm{\text{cm}}}^{-1}$ are attained in the 0.5(BNT-CS)-0.5SB${}_{0.2}$T ceramic (abbreviated as BNT-0.2SBT). Moreover, BNT-0.2SBT exhibits superior power density ($P_D=107\mathrm{\text{MW}}\cdot {\mathrm{\text{cm}}}^{-3}$), ultrafast discharge time ($t_{0.9}=116$ns) at $150\mathrm{\text{kV}}\cdot {\mathrm{\text{cm}}}^{-1}$, and good temperature stability. The findings in this work not only demonstrate that a valid candidate, but also provide a new idea of how to achieve both high-energy storage density and efficiency in lead-free ferroelectric materials.

Pb(Mg${}_{0.5}$W${}_{0.5}$)O₃–Pb(Ni${}_{1∕3}$Nb${}_{2∕3}$)O₃–Pb(Zr${}_{0.5}$Ti${}_{0.5}$)O₃ (PNN–PMW–PZT) piezoceramics were sintered at a low temperature of 900^∘C by the mixed metal oxide powder solid-state reaction route. CaCO₃ and Li₂CO₃ as sintering aids and Yb₂O₃ as a dopant were added into the PNN–PMW–PZT ceramic system for low-temperature sintering and enhancement of electrical properties, respectively. The effects of different Yb₂O₃ doping amounts on the microstructure, dielectric, piezoelectric and ferroelectric properties of the samples were systematically investigated. The piezoceramics doped with 0.1mol% Yb₂O₃ have optimal electrical properties ($d_{33}=563$pC/N, $k_p=0.66$, ${\epsilon }_r=2728$ (1kHz), $tan\delta =0.0176$ (1kHz), and $T_C=301^{\circ }$C). While the piezoceramics doped with 0.3mol% Yb₂O₃ have optimal energy conversion properties: the piezoelectric voltage coefficient $g_{33}=26.7\times 10^{-3}$Vm/N and the effective piezoelectric energy conversion coefficient $d_{33}\times g_{33}=14366\times 10^{-15}$m²/N.

Polystyrene (PS) microspheres have the advantages of good stability, corrosion resistance and low density, which have a broad application prospect. In this paper, PS composite microspheres with 20% silver plating content were prepared by chemical plating method and incorporated into polydimethylsiloxane (PDMS) flexible matrix to prepare Ag@PS/PDMS flexible wave-absorbing materials. The electromagnetic parameters were adjusted to optimize the dielectric and wave-absorbing properties by varying the additional amount of Ag@PS composite microspheres in Ag@PS/PDMS composites. The X-ray diffraction (XRD) results proved the successful preparation of Ag@PS composite microspheres. The SEM and EDS images indicated that the Ag particles were attached to the external surface of PS. The presence of Ag particles in the Ag@PS composite microspheres enhances their electrical conductivity and enables the formation of a conductive network. This, in turn, improves the composites’ dielectric constant. The optimal wave-absorbing capability of the composites was achieved when the Ag@PS composite microspheres were added at a weight percentage of 50%. When the sample attains a thickness of 1.8mm, a reflection loss of at least −39.8dB is attained at 10.4GHz, along with a bandwidth of 1.6GHz (9.1–10.7GHz) for the effective absorption bandwidth (EAB). The pressure-sensitive properties of the pliable composites were investigated as well. The optimal pressure-sensitive performance of Ag@PS/PDMS composites was achieved with a 60wt.% addition of Ag@PS composite microspheres. The resistance undergoes significant changes when subjected to pressure with a sensitivity of 9.7. The results indicate that the flexible composites’ wave-absorption and pressure-sensitivity properties can be modulated by adjusting the amount of Ag@PS composite microspheres added.

In this work, a traditional solid-state method was adopted to prepare dense Ba${}_{0.85}$Ca${}_{0.15}$[(Zr${}_{0.1}$Ti${}_{0.9}$)${}_{1-x}$–(Nb${}_{0.5}$La${}_{0.5}$)_x]O₃(BCZT–xNL) lead-free relaxation ferroelectrics with excellent energy storage performance (ESP). Remarkably, a large breakdown field strength of BDS ($\sim 410$kV/cm) resulting from decreased grain size by double ions doping at the B-site was achieved in BCZT–xNL ceramics. Especially, the BCZT–0.12NL ceramic displays a good recoverable energy density ($W_{\mathrm{\text{rec}}}$) of 3.1J/cm³, a high efficiency of 86.7% ($\eta$) and a superior fatigue resistance, as well as a superior charge–discharge performance ($C_D\sim 1623.14$A/cm², $P_D\sim 162.31$MW/cm³, $W_D\sim 1.30$J/cm³, $t_{0.9}\sim 49.6$ns) and good thermal stability. Besides, upon NL doping, the FE to RFE phase transition results in a dielectric behavior traversing the relaxation phase ($\gamma \sim 1.84$) accompanied by frequency dispersion, which is beneficial to improve ESP. The superior ESP in this work indicates that BCZT–0.12NL ceramics are a promising candidate used in energy storage capacitors.

BiFeO₃ (BFO), Mn-doped-BFO (BFMO), Ti-doped-BFO (BFTO), and (Mn,Ti)-codoped-BFO (BFMTO) thin films are fabricated on the Pt/TiO₂/SiO₂/Si substrates via a sol–gel method combined with spin-coating and the subsequent layer-by-layer annealing technique. Compared with BFO film, the BFMTO film exhibits the lowest leakage current density ($\sim 10^{-4}$A/cm²@290kV/cm). Notably, the polarization–electric field (P–E) loop of BFMTO film exhibits a positive displacement along the x-axis due to the existence of internal bias electric field, which is in agreement with the results of the PFM phase and amplitude curves. Especially, a very prominent inverse piezoelectric constant of $d_{33}\sim 160$pm/V was obtained, which overcomes other related thin films. The internal bias electric field of BFMTO film can be caused by the different work functions of the thin film and the bottom electrode, accumulation of oxygen vacancies and the formation of defect dipoles. Besides, the internal bias electric field of BFMTO film has a good stability at the same electric field after experiencing the test cycle from low electric field to high electric field (400–1900kV/cm). These results indicate that self-polarized BFMTO film can be integrated to devices without additional polarization process, and have a wide range of application in microelectromechanical systems.

Recently, high-performance lead zirconate titanate (Pb(${\text{Zr}}_{1-x}$Ti_x)O₃, PZT) ferroelectric ceramics have attracted intensive attention due to their wider operating temperature range, better temperature stability, as well as larger piezoelectric properties and higher energy conversion efficiency. In this study, the perovskite-type ferroelectric ceramics with a chemical formula of ${\text{Pb}}_{0.99-x}$${\text{Gd}}_{0.01}$Sr_x${\text{Zr}}_{0.53}$${\text{Ti}}_{0.47}$O₃ ($x=0$ and 0.02, abbr. PGZT and PGSZT, respectively) were prepared by the traditional solid-state reaction route. The influences of Sr-doping on the phase structure, dielectric properties, ferroelectric properties and piezoelectric properties of the PGZT ceramics were comprehensively investigated. The field-dependent P–E hysteresis loops of PGSZT were measured in the frequency range of 0.05–10Hz and temperature range of 20–100^∘C. The results show that Sr-doping not only enhances the dielectric permittivity and piezoelectric coefficient of PGZT, but also decreases its dielectric loss tangent, with the $d_{33}$ value of 473pC/N, ${\epsilon }_r$ value of 1586 and $tan\delta$ value of 0.016 found in PGSZT. Also, PGSZT shows a high Curie temperature ($T_C$) of $350^{\circ }$C. The underlying mechanisms of the property enhancement were identified as that the introduced ${\text{Sr}}^{2+}$ replaces the volatile ${\text{Pb}}^{2+}$ located at the A-site of the perovskite structure, thereby reducing the concentration of lead vacancies and promoting the grain growth of the ceramics, consequently enhancing the dielectric and piezoelectric properties of PGZT. On the other hand, the frequency change in the low-frequency range ($<1$Hz) played a significant impact on the remanent polarization ($P_r$) and internal biased electric field ($E_i$) of PGSZT, but the frequency dependence of coercive field ($E_c$) tends to diminish in the high-frequency range ($\ge 1$Hz).

As a functional composite material, nickel-coated aluminum powder has been widely used in conductive fillers, electromagnetic shielding materials and other fields due to its advantages of low density, high conductivity and low cost. In this paper, nickel-plated aluminum powder was prepared by a sodium hypophosphite system. The effects of different nickel coating amounts (the percentage of nickel-plating quality to nickel-plated aluminum powder quality) on the morphology, phase, compaction resistivity and electromagnetic parameters of nickel-plated aluminum powder coating were studied. The X-Ray Diffraction (XRD) results proved the successful preparation of nickel-coated aluminum powders with different nickel coating amounts. The Scanning Electron Microscope (SEM) images clearly show the coating effect under different nickel coating amounts. By plating nickel on the surface of aluminum powder, the surface characteristics of aluminum powder are changed, so as to adjust its conductivity, resistance, stability and other properties, thus affecting its electromagnetic performance and wave absorption performance. The results show that the comprehensive absorbing performance is excellent when the nickel coating amount is 40%. The reflection loss of the sample with a thickness of 2.0mm is less than $-10$dB in the frequency range of 10.17–12.38GHz. When the frequency is 10.72GHz, the minimum reflection loss reaches $-33.17$dB.

Calcium bismuth niobate (CBN) ceramic, as a core element of high-temperature piezoelectric sensors, has attracted widespread attention due to its high Curie temperature within the class of Aurivillius compounds. However, CBN usually faces two shortcomings: poor piezoelectric constant and low resistivity. In this work, CBN-based ceramics with donor–acceptor ions (W/Co) co-substituted at B-site were prepared by solid-state reaction method, and structure–property relationship of ceramics was studied in detail. Co-substitution of W/Co ions effectively improved the electrical property and hardness of CBN ceramics. CaBi₂Nb${}_{1.91}$(W${}_{2/3}$Co${}_{1/3}{)}_{0.09}$O₉ exhibits enhanced electrical and mechanical properties including high resistivity of $\sim 10^7\mathrm{\Omega }\cdot$cm at 500°C, piezoelectric constant of $\sim 15.3$ pC/N and hardness value of $\sim 3.57$GPa. These values are two orders of magnitude, over two times, and 1.36 times higher than those of pure CBN ceramic, respectively. This work provides a reference for exploring other bismuth-layered structural ceramics.

Statins are widely used in the treatment of hyperlipidemia disease, which are refractory in the municipal sewage treatment plant. The photocatalytic degradation of statins by the Z-scheme heterostructured photocatalyst is confirmed, but the degradation mechanism of statins needs to be further revealed. In this study, the effects of photocatalyst dosage, solution pH and humic acid (HA) on the photocatalysis of fluvastatin by ZnIn₂S₄/Bi₂WO₆ Z-scheme heterostructured photocatalyst (ZIS/BWO photocatalyst) were investigated and the degradation mechanism was proposed. Results showed that adsorption of fluvastatin was improved with the increase of photocatalyst dosage, but photoinduced desorption and light scattering resulted in the decrease of the removal of fluvastatin with high dosage. 0.2g/L of the ZIS/BWO photocatalyst was optimal dosage. 65.21% of fluvastatin was removed at pH=9, because high concentration of OH⁻ was conducive to produce ⋅OH. The change of pH, competition of photons and active sites, and trapping of reactive oxygen species (ROS) by carboxyl group of HA combined to inhibit the photocatalysis of fluvastatin in the presence of HA. The C–C, C$=$C and C–N bonds of fluvastatin were attacked by a variety of ROS to generate degradable intermediates that were easily mineralized to H₂O and CO₂.