Translated Abstract
Dielectric materials possessing high-energy storage density and high-power density are urgently needed for the potential application in advanced pulsed capacitors. There are growing needs for pulsed capacitor, power electronics, electric car and power supply network. BaTiO3-based ferroelectric ceramics were studied in this paper. The dielectric materials with good temperature and frequence stability, high breakdown strength and high energy storage density are expected. BaTiO3-ZnNb2O6, BaTiO3-Bi(Mg2/3Nb1/3)O3, BaTiO3-BiFeO3 and Ba0.4Sr0.6TiO3 ceramics system were chosen to be studied. The Curie temperature of BaTiO3 ceramics were decreased by introducing ZnNb2O6, the relaxor ferroelectric BaTiO3-Bi(Mg2/3Nb1/3)O3 ceramics were fabricated, Na2O5 was added to BaTiO3-BiFeO3 ceramics to improve dc resistivity, and high conductive BaO-B2O3-SiO2- Na2O-K2O glass additives were added to Ba0.4Sr0.6TiO3 ceramics to improve the energy density of BaTiO3-based ferroelectric ceramics. The influence of additive on processing, microstructure, dielectric properties, and energy storage properties was investigated systematically. Dense and uniform BaTiO3-based ferroelectric ceramics with good dielectric properties were prepared. The research work was carried out as following:
In order to decrease the Curie temperature of BaTiO3 ceramics, BaTiO3 – x ZnNb2O6 (x = 1.50, 3.03, 4.60, 6.20, 7.83, 11.18 wt%) (BTZN1–6) ceramics ceramics were prepared using solid state reaction. The results show that the ZnNb2O6 addition lowers sintering temperature, decreases grain size, while introduces second phase (Ba2Ti5O12) for x≥7.83 wt%. The Curie temperature of BaTiO3 ceramics decrease with increasing ZnNb2O6 content. The dielectric breakdown strength is enhanced with the increasing doping level of ZnNb2O6 and reaches a maximum value at x = 7.83 wt%, exhibiting a maximum energy storage capability.
In order to investigate the energy storage property of BaTiO3–BiMeO3 relaxor ferroelectric ceramics, perovskite solid solution ceramics of (1–x) BaTiO3–x Bi(Mg2/3Nb1/3)O3 (BTBMN) (x = 0.05-0.2) were synthesized by solid-state reaction technique. The results show that the Bi(Mg2/3Nb1/3)O3 (BMN) addition could lower the sintering temperature of BaTiO3-based ceramics. X-ray diffraction studies, TEM and Raman results reveal a stable single perovskite structure for all samples. Raman results do not show any obvious structural phase transition with increasing BMN content. Dielectric measurements exhibit a diffused ferroelectric phase transition characteristic of BTBMN ceramics, where broadened phase transition peaks change to a temperature-stable permittivity plateau (from ?50 °C to 300 °C) with increasing the BMN content (x = 0.2). The temperature dependence of dielectric constant under a dc bias and PFM results show that the polar nanoregions of BTBMN ceramics decrease with increasing BMN content. Slim polarization-electric field hysteresis loops were observed in x ≥ 0.1 samples. The dielectric breakdown strength and electrical resistivity of BTBMN ceramics reach their maxima of 287.7 kV/cm and 1.53×1013 Ω?cm at x = 0.15, and an energy density of about 1.13 J/cm3 is achieved for x = 0.1 sample.
In order to improve dc resistivity of BiFeO3–BaTiO3 (BF-BT) ceramics, the effects of Nb2O5 addition on microstructures, dielectric breakdown strength, and energy storage properties of BiFeO3-BaTiO3 (BF-BT) ceramics were investigated. (1-x) (0.65BiFeO3–0.35BaTiO3) – x Nb2O5 (x = 0, 1, 3, 5 mol%) ceramics were synthesized by solid-state reaction technique. X-ray diffraction patterns suggested a perovskite pseudocubic structure when the addition content was less than 3 mol%. The electrical resistivity of 1 mol% Nb2O5-doped BF-BT ceramic was increased by approximately six orders of magnitude compared to the corresponding undoped composition. The dielectric breakdown strength was enhanced with increasing Nb2O5 content and reached a maximum value at the composition with 3 mol% Nb2O5, with a maximum discharge energy density of 0.71 J/cm3 at 90 kV/cm.
In our previous work, we developed a reverse boundary layer capacitor (RBLC) configuration model. Initial results suggested that the grain boundary has a higher electrical conductivity than the grain in glass/ceramic composites. It is worthy to underline that employing glass additive as grain boundaries (with higher electrical conductivity than that of
ceramic grains), a steady electric field across grains can be larger than that of the grain boundaries as desired due to the difference of the electrical conductivity between them. High conductive BaO–B2O3–SiO2–Na2O–K2O glass additives were added to Ba0.4Sr0.6TiO3 (BST) ceramics to investigate its influences on the microstructure, dielectric properties, breakdown strength (BDS), and energy storage density. The sintering temperatures were lowered about 150 °C with a high relative density (~98%). X-ray diffraction patterns of all BST glass ceramics suggest perovskite structures without any detectable secondary phase. Room temperature dielectric constant of BST glass ceramics decreases with increasing Na2CO3 content. BDS and energy storage density of BST glass ceramics increase with increasing Na2CO3 content, and reach their maxima of 280 kV/cm and 0.72 J/cm3 at the highest Na+ and K+ content. These results suggest that the BST glass ceramics could find their potential applications in energy storage capacitor devices.
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