Ba1+1/MSi2O5+1/M low‐permittivity microwave dielectric ceramics are prepared using the conventional solid‐state method. Pure phases are obtained in barium silicates with M = 1, 3, 4, 5, and ∞, except ...for M = 7, in which two phases, Ba5Si8O21 and BaSi2O5, are observed. As the complexity of the crystal structure described by the Shannon information per reduced unit cell increases, the τf value tends to change from a negative to a positive value, except for M = 5, which has the highest complexity. A single Ba5Si8O21 phase with εr anomaly peak at −180°C exhibits a rare positive τf value (+25 ppm/°C), which is a novel temperature compensator.
Novel NaAGeO4 (A = Sm, Y) ceramics with olivine structures were prepared and characterized. The phase composition, microstructural evolution, and densification behavior of the ceramics were ...investigated. The NaAGeO4 (A = Sm, Y) ceramics possessed a single orthorhombic crystal system with Pbn21 and Pnma space groups. The NaSmGeO4 ceramics had dense grains, clear boundaries, and low sintering temperatures, whereas a relatively wide range of sintering temperatures were feasible for the NaYGeO4 ceramics. The NaSmGeO4 ceramic material sintered at 1025 °C possessed excellent performance-related parameters, i.e., Q × f = 31,281 GHz, εr = 6.29, and τƒ = −48.3 ppm/°C, whereas those for the NaYGeO4 ceramic material were Q × f = 32,646 GHz, εr = 6.74, and τƒ = −39 ppm/°C at 1200 °C. Furthermore, doping the NaYGeO4 ceramic material with CaTiO3 to obtain 0.12CaTiO3-0.88NaYGeO4 yielded a τƒ value close to zero (−3 ppm/°C). The results demonstrate that NaAGeO4 (A = Sm, Y) ceramics have substantial potential for application in microwave devices.
In this work, MgF2–xwt%LiF (x = 0.5, 1.0, 2.5, 4.0, 5.0) ceramics have been prepared through the standard solid-state reaction method. X-ray diffraction patterns and scanning electron micrographs ...revealed the successful preparation of dense MgF2–LiF composite ceramics at an exceptionally low sintering temperature range of 525–600°C. The optimal microwave dielectric properties (εr = 5.09 ± 0.03, Qf = 100,733 ± 1646 GHz, τf = −67.4 ± 3.3 ppm/°C) were achieved in MgF2–0.5 wt%LiF ceramics after sintering at 550 °C for 3 h. The present ceramics exhibited an outstanding combination of low-εr, high Qf, and an ultra-low sintering temperature, surpassing the performance of most low-temperature-fired dielectric materials. Moreover, the theoretical Qf value, extrapolated from the fitting of infrared reflectivity spectra, was calculated to be 326,583 GHz, indicating significant potential for further Qf improvement. Additionally, the chemical compatibility with Al electrodes was confirmed, suggesting promising potential for ultra-low temperature co-fired ceramic (ULTCC) applications.
The dielectric spectra of a series of hybrid membranes prepared with sulfonated styrene-ethylene-butylene-styrene (sSEBS) as the polymeric matrix, and zirconia-modified phosphosilicate ...(40SiO2–40P2O5–20ZrO2), as inorganic filler through direct infiltration, was analysed. All the membranes displayed characteristic sSEBS spectra, consisting of three molecular relaxations: A non-cooperative (β) relaxation and two cooperatives (αEB, αPS) ones ascribed to the glass transition of the ethylene-butylene and the polystyrene blocks, respectively. As a result of the infiltration of the inorganic component (40SiO2–40P2O5–20ZrO2), the dielectric spectra were considerably modified. Accordingly, the formation of dynamic crosslinking (M-O-M′ bonds, with M = P, Si, Zr) difficulties the motion of the αEB process, thus shifting it towards higher temperatures. Moreover, a significant plasticisation effect was found at high temperatures, which facilitates the activation of the αPS process. Furthermore, the decreasing values of the fragility parameter, due to the infiltration of the inorganic filler, revealed that all hybrid membranes displayed an arrangement of molecular chains and a strong behaviour. Thus, higher resistance to sudden temperature changes is expected. The optimum infiltration time (τinf) is between 10 and 20 min since it provides acceptable values of electric permittivity, and the induced dynamic crosslinking brings the glass transitions of both blocks closer. Consequently, a complete characterisation of the molecular mobility by studying the spectrum of dielectric relaxations enables to fine-tune the membranes for an optimum design focused on its application in a proton exchange membrane fuel cell (PEMFC).
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•Short τinf increase filler at edges of the membrane and increase the permittivity.•High τinf equalize filler distribution and restricts molecular motions.•The inorganic network closes the gap between cooperative molecular processes.•SSEBS-Zr hybrid membranes display lower fragility values than sSEBS ones.
The temperature‐dependent energy storage and dielectric properties of Pb0.90La0.04Ba0.04(Zr0.7Sn0.3)0.88Ti0.12O3 were investigated in this work. With the phase transition from antiferroelectric to ...paraelectric induced by temperature rise, the releasable energy density decreases from 0.74 J/cm3 (20°C) to 0.29 J/cm3 (140°C), whereas the discharge efficiency increases from 75.0% to 93.4%. The pulsed discharge current indicates that the stored energy can be released in less than 1 μs. The temperature has little impact on the amplitude of the current but influences the discharge duration time greatly. In addition, with the comprehensive analysis of hysteresis loops, the DC‐bias character of dielectric constant and the discharge current, the transition from strong nonlinearity to linearity of the dielectric along with the phase switching was confirmed. It proves that the vanishment of high‐electric‐field nonlinear polarization contributions causes the declination of releasable energy with the temperature rise.
Dielectric polymer nanocomposites are rapidly emerging as novel materials for a number of advanced engineering applications. In this Review, we present a comprehensive review of the use of ...ferroelectric polymers, especially PVDF and PVDF-based copolymers/blends as potential components in dielectric nanocomposite materials for high energy density capacitor applications. Various parameters like dielectric constant, dielectric loss, breakdown strength, energy density, and flexibility of the polymer nanocomposites have been thoroughly investigated. Fillers with different shapes have been found to cause significant variation in the physical and electrical properties. Generally, one-dimensional and two-dimensional nanofillers with large aspect ratios provide enhanced flexibility versus zero-dimensional fillers. Surface modification of nanomaterials as well as polymers adds flavor to the dielectric properties of the resulting nanocomposites. Nowadays, three-phase nanocomposites with either combination of fillers or polymer matrix help in further improving the dielectric properties as compared to two-phase nanocomposites. Recent research has been focused on altering the dielectric properties of different materials while also maintaining their superior flexibility. Flexible polymer nanocomposites are the best candidates for application in various fields. However, certain challenges still present, which can be solved only by extensive research in this field.
BaAl2−2x(ZnSi)xSi2O8 (x=0.2–1.0) ceramics were prepared using the conventional solid-state reaction method. The sintering behaviour, phase composition and microwave dielectric properties of the ...prepared compositions were then investigated. All compositions showed a single phase except for x=0.8. By substituting (Zn0.5Si0.5)3+ for Al3+ ions, the optimal sintering temperatures of the compositions decreased from 1475°C (x=0) to 1000°C (x=0.8), which then slightly increased to 1100°C (x=1.0). Moreover, the phase stability of BaAl2Si2O8 was improved. A novel BaZnSi3O8 microwave dielectric ceramic was obtained at the sintering temperature of 1100°C. This ceramic possesses good microwave dielectric properties with εr=6.60, Q×f=52401GHz (at 15.4GHz) and τf=−24.5ppm/°C.
A novel (0.67-x)BiFeO3-0.33BaTiO3-x(K0.5Nd0.5)TiO3 (KNT100x, x = 0.0, 0.02, 0.04, 0.06, 0.08 mol%) ceramics were fabricated and their microstructure and electrical properties were studied. All ...samples displayed a pseudo-cubic symmetry, and adding of KNT had little effect on grain size. The dielectric analysis displayed the dispersion increases with the addition of KNT compositions, showing strong relaxor properties. Besides, high dielectric constant (ε’) of 23000 and dielectric peak temperature (Tm) of 390 °C remain at 1 kHz in the x = 0.02 sample while the dielectric loss (tanδ) dropped below 0.5 in the range of 30–400 °C, showing excellent electrical insulation performance. In addition, doping of KNT had obvious influence on the strain, and a large strain (Smax) of 0.26% was obtained at x = 0.02 due to the increase of electrical insulation. More importantly, the strain at 50 kV cm−1 enhanced significantly with temperature increasing, reaching a maximum strain of 0.75% with a small hysteresis coefficient of 30% at 110 °C. Particularly, KNT02 exhibited excellent fatigue resistance within 105 fatigue cycles. Presumably these results are attributed to the coexistence of ferroelectric and non-ergodic relaxor domains and the thermally activated domain wall motion.
Li3Mg2SbO6 ceramics without dehiscence were prepared using a two-stage process. The sintering behavior, structure, and microwave dielectric performances of Li3Mg2SbO6 ceramics had been investigated. ...XRD and Raman results showed that nearly pure phase Li3Mg2SbO6 were obtained in the sintering temperature range of 1225–1350 °C. The quality factor (Qxf) and relative permittivity (εr) values of samples were strongly influenced by the density, grain size, and cell volume. Typically, balanced microwave dielectric properties were obtained for Li3Mg2SbO6 ceramics sintered at 1300 °C:εr∼10.5, Qxf∼84,600 GHz (at 10.6 GHz), and temperature coefficient of resonance frequency τf ∼ -9.0 ppm/oC.
•Pure phase Li3Mg2SbO6 ceramics without dehiscence were prepared by a two-stage process.•The unit cell volume is affected by the sintering temperature was confirmed by XRD.•Li3Mg2SbO6 ceramics had good microwave dielectric properties.
