Modulation On Interface And Giant Dielectric Propertirs Of Bismuth Layered Ferroelectric Ceramics

Bismuth layered ferroelectric ceramic have the characteristics of high Curie temperature,low dielectric loss,good fatigue resistance and no environmental pollution,so it has a broad development prospect in the field of ferroelectric memory and high temperature capacitors.At present,the research indicates that doped bismuth layered ferroelectric ceramics have large dielectric constants at low frequencies,and accompanied by the appearance of anomalously large grains in microstructure,but the mechanism of the giant dielectric response in bismuth layered ferroelectric ceramics and the regulation method of large grains on the giant dielectric constant remain unclear.In this paper,K_0.5B_4.5Ti₄O₁₅（KBT）ceramics were used as matrix,introduces high and low ions to co-doped KBT ceramics,and introduces high and low melting point ion combination to further explore the source of abnormally large grain growth,and explore the influence of abnormally large grain growth on dielectric properties.Then,the influencing factors of sintering process on the dielectric properties of ceramics were studied by changing the sintering temperature,heating rate and holding time,and the mechanism of the giant dielectric response of bismuth layered ferroelectric ceramics was analyzed.Firstly,four kinds of high and low valence ions Zn²⁺,Al³⁺,V⁵⁺and W⁶⁺were selected for pairwise combination doping to replace KBT-based ceramics.K_0.5Bi_4.5Ti_3.8(Zn_1/2W_1/2)_0.2O₁₅,K0.5Bi4.5Ti3.8（Zn1/3V2/3）0.2O15,K0.5Bi4.5Ti3.8（Al1/2V1/2）0.2O15 and K0.5Bi4.5Ti3.8（Al2/3W1/3）0.2O15ceramic samples（abbreviated as:KBT-0.2Zn W,KBT-0.2Al W,KBT-0.2Zn V,KBT-0.2Al V）were synthesized by conventional solid-state reaction method,and the effects of B-site co-doped ions on the microstructure and electrical properties of KBT ceramics were investigated.In this study,it is found that the B-site co-doped ion modified KBT ceramics produce abnormal grain growth,which significantly improves the dielectric constant of the ceramics.KBT-0.2Al W and KBT-0.2Al V large grain size of the ceramic is about 20～60μm.KBT-0.2Al V ceramic dielectric constant is 1.0×10⁶（～10 k Hz）.Secondly,in order to further study the factors affecting the macrodielectric properties of KBT-Al V ceramics,the conventional solid-state reaction method was used to prepare KBT-Al V ceramics.The effect of Al³⁺/V⁵⁺content on the microstructure and dielectric properties of KBT ceramics was investigated.The results showed that with the increase of Al³⁺/V⁵⁺content,the number of abnormally large grains increased and the grain size decreased.The KBT-0.2Al V ceramics had the best frequency stability,the low frequency dielectric response is mainly derived from the polarization response of the defect dipole.On this basis,the influence of sintering process on the dielectric properties of KBT-Al V ceramics was explored,and the rapid sintering at different sintering temperatures was increased at the heating rate.It was found that abnormally large grains were formed by the aggregation and growth of small grains.The low frequency giant dielectric properties were the best at 1160℃,and the dielectric constant could reach 10⁶（～1 k Hz）or above,dielectric loss is lowest.KBT-Al V ceramics with different components were sintered by rapid temperature rise and then held for 10 min,the grain size up to 50μm,the frequency dependence of dielectric constant has a strong,including KBT-0.3Al V ceramic dielectric constant is more than 2.0×10⁶（～1 k Hz）,and the dielectric loss peaks move to high frequency.Rapid heating sintering can increase the grain size of ceramics and further improve the dielectric properties.The low frequency giant dielectric response is mainly contributed by the interface response between large and small grains.Finally,in order to investigate the effect of Al³⁺/W⁶⁺on the giant dielectric properties of KBT ceramics,KBT-Al W ceramics were prepared by conventional solid-state reaction method.The crystal structure of KBT-Al W ceramics is single solid solution structure.In KBT-0.2Al W ceramics have anomalously large grains appearing in the ceramics with grain size about 20～30μm,the large dielectric constants 10⁴（～1k Hz）at low frequency and the dielectric loss is smaller.To further investigate the effects of sintering temperature and holding time on the dielectric properties of KBT-Al W ceramics and optimize the sintering process,it is found that KBT-0.2Al W ceramics have a large low frequency giant dielectric response at 1120℃,the dielectric constant reaches 10⁵（～1 k Hz）,and the dielectric loss peak appears at more than 10 k Hz.On the basis of extending the holding time,when the holding time is 10 h,large grains with abnormal growth appear in the microstructure of KBT-0.2Al W ceramics,and their dielectric constant reaches 10⁶（～1 k Hz）.By optimizing the sintering process of ceramics,the best dielectric properties were obtained when the ceramics were kept at 1120℃for 10 h.Impedance analysis showed that the low frequency giant dielectric response was affected by many factors,which was mainly related to the interface polarization response and the polarization response of defective dipoles.