| In this paper, glass-ceramic materials of SrO–BaO–Nb2O5–B2O3(SBNB) system havebeen prepared by conventional melt casting and heat-treated crystallization method. Theeffects of heat treatment temperature, Sr/Ba ratio, adding Gd2O3and CeO2on the phaseevolution, microstructure, dielectric properties and energy storage characteristics for theSBNB glass ceramics were investigated by DSC, XRD, SEM, impedance analysis andelectrical properties measurement. The main conclusion is obtained as follows:1. The effects of heat treatment temperature and Sr/Ba ratio on the phase composition,microstructure and electric properties were studied. The results show that with the increaseof crystallization temperature from700℃to800℃, only one phase Ba0.5Sr0.5Nb2O6comesout from the glass matrix，while the secondary phase SrNb2O6appears as the heatingtemperature exceeds850℃. The dielectric constant firstly increases and then decreasesgradually with the increase of crystallization temperature. When Sr/Ba0.82, the maincrystal phase Ba0.5Sr0.5Nb2O6is formed in glass ceramic samples. However，SrNb2O6occurs as Sr/Ba0.82. At fixed heat treatment temperature, the dielectric constant of thesamples decreases with the increase of the Sr/Ba ratio. But its breakdown strength isimproved with the increase of Sr/Ba ratio. The glass ceramic heated at800℃for3h hasthe best overall performance:=117, Eb=1050kV/cm, J=5.71J/cm3, Jc=1.01J/cm3(Jcisthe actual energy densities calculated from P–E hysteresis loops at applied maximumelectric field of600kV/cm).2. The influences of Gd2O3addition on the phase composition, microstructure andelectric properties for SBNB glass-ceramics were investigated. The addition of appropriatecontent of Gd2O3can improve the microstructure and obviously contribute to theoptimization of the dielectric and ferroelectric properties of the glass–ceramics. Thethermal stability of the glasses is also increased by adding Gd2O3. All the glass ceramicsheated at630℃/2h+800℃/3h have the same crystallographic phase of Sr0.5Ba0.5Nb2O6with tungsten–bronze structure. The glass-ceramic with0.5mol%Gd2O3exhibits a highbreakdown strength of1075kV/cm, a dielectric constant of136and an energy density of6.94J/cm3.3. The effects of CeO2on the phase composition, microstructure, dielectric propertiesand energy storage behavior for SBNB glass-ceramics were studied. The small amount ofCeO2addition in the basic glass hinds the formation of the low-permittivity crystallinephases of SrNb2O6and promotes the main crystal phase precipitation of Ba0.5Sr0.5Nb2O6, as well as optimizes the microstructure of the glass-ceramics. The dielectric constant andbreakdown strength firstly increase and then decrease with increasing CeO2concentration.With the increase of the content of CeO2, the charged energy density (Jc), dischargedenergy density (Jd) and unreleased energy density (Ju) first increase and then decrease withthe increase of CeO2addition. The glass-ceramics added with0.5mol%CeO2exhibitexcellent performance:=144，Eb=1092kV/cm，J=7.44J/cm3, Jd=3.39J/cm3，η=71.3%.4. AC impedance spectroscopy was used to study the mechanism of dielectricbreakdown in glass-ceramics with different composition. The research results revel that theinternal resistivity of glass-ceramics decreases with increasing temperature. The glassphase has high resistivity and the grain phase has low resistivity. By comparing thebreakdown strength and activation energy of the samples with different composition, it isfound that the internal interface polarization and space charge mobility is a major reasonfor the breakdown of the glass-ceramics. |
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