Study On Preparation And Properties Of Niobate Ferroelectric Glass-Ceramics With High Energy Storage Density

In this paper, the influences of adding Na₂O、TiO2 and BaF₂ in the BaO-SrO-Nb₂O₅-B₂O₃-SiO₂ system glass on the phase composition, microstructure, dielecrtric property, volume resistivity, breakdown strength and crystallization kinetics were investigated by using differential thermal analysis （DTA）, X-ray diffraction （XRD）, Scanning electron microscope （SEM） and electrical property tester. The main conclusion is as follows:The effects of Na₂O on the crystallization kinetics, phase composition, and dielectric property of SBN glass-ceramics were investigated. The glass transition temperature （Tg） and the first crystallization peak temperature （Tp1） decrease, while the second crystallization peak temperature decreases firstly and then increases with increasing Na₂O contents. The single Ba0.5Sr0.5Nb2O6 occurs in the sample without Na₂O. The Ba_0.25Sr_0.75Nb₂O₆ phase comes out when Na₂O=5%. As Na₂O=10%, the Ba_0.25Sr_0.75Nb₂O₆ is still main crystalline phase, however, the phases of NaSr_1.2Ba_0.8Nb₅O₁₅、Na₂Ba₂Si₂O₇ and Ba3Nb10O28 precipitate. For the sample with 15% Na₂O, the types of other crystalline phase are unchanged, the Na₂Nb₈O₂₁ phase comes out. With increasing Na₂O content, the dielectric constant of glass-ceramics changes like“N”letter, while the breakdown strength and volume resistivity decreases. The sample without Na₂O has the highest breakdown strength, 1500kv/cm, and its energy storage density is 3.0J/cm³. The glass-ceramic sample with 5% Na₂O heat treated at different temperatures exhibits a single phase, Ba_0.27Sr_0.75Nb₂O₆. Volume resistivity changes like“V”letter with increasing Na₂O content. The dielectric constant, breakdown strength and energy storage density increase with increasing crystallization temperature. The highest energy storage density is 4J/cm³.The effects of adding TiO2 on crystallization kinetics, phase composition and dielectric properties for SBN glass-ceramics were studied. The addition of TiO2 decreases the crystallization peak temperature （Tp）, while the crystallization activation energy （E） increases firstly and then decreases with the increase of TiO2 amount. The maximum crystallization activation energy （E） can reach 359.46 kJ/mol and the crystallization rate constant K （Tp） is 0.174 when TiO2 =5%. The single phase, Ba_0.25Sr_0.75Nb₂O₆ exits for sample without TiO2. As TiO2 =5%, the main crystalline phase is Ba_0.25Sr_0.75Nb₂O₆ and the diffraction intensity increase. When TiO2 is more than 3%, the main crystalline phase is still Ba_0.25Sr_0.75Nb₂O₆, and the second phase, Ba₃SrNb₂O₉ and NaBa₅TiNb₉O₃₀ are formed. The dielectric constant and volume resistivity increases firstly and then decrease with increasing content of TiO2. The breakdown strength, however, indeed decreases with the increase of TiO₂ content. The maximum breakdown strength is 1200 kV/cm and the storage energy density reaches 2.8 J/cm³ for the sample without TiO₂. The effect of heat treatment temperature on phase composition and electrical property was investigated based on the sample with 5% TiO₂. At 800℃, Ferroelectric phase, Ba_0.27Sr_0.75Nb₂O₆, precipitates, while the second phase Ba₃SrNb₂O₉ comes out at 850℃. When the crystallization temperature reaches 950℃, NaBa₅TiNb₉O₃₀ phase is formed while the type of the main phase remains unchanged. With the increase of crystallization temperature, the dielectric constant and dielectric loss firstly increase and then decrease, and the breakdown strength decreases, the storage energy density changes like“N”letter.The influence of BaF₂ on crystallization behaviour, phase composition and electrical property were researched. With the increase of BaF₂, the glass transition temperature （Tg） and first crystallization peak temperature （Tp1） change like“N”letter, however, the second crystallization peak temperature （Tp2）, crystallization activation energy （E） and crystallization kinetic parameter （K （Tp）） increase gradually. All of the glass ceramic samples were heated at 800℃/3h+900℃/3h. It is found that the sample without BaF₂ shows a single phase, Ba_0.25Sr_0.75Nb₂O₆. As BaF₂= 1%, the main crystalline phase remains unchanged and the intensity of diffraction peaks obviously increase. When BaF₂ > 3%, the diffraction intensity of Ba_0.25Sr_0.75Nb₂O₆ markedly decrease. For the sample containing 5% BaF₂, the main crystalline phase is still the Ba_0.25Sr_0.75Nb₂O₆, However, the secondary phases, Ba₃SrNb₂O₉ and BaBF5, appear. When the content of BaF₂ reaches 7%, the amount of non-ferrous phase of the BaBF5 will increase. The dielectric constant, volume resistivity and breakdown strength will change like the letter of“M”with the increase of BaF₂ content. The maximum breakdown strength （1400 kV/cm） and the energy storage density （5J/cm³） can be obtained for the glass-ceramic sample with 1% BaF₂.