Study Of Microstructure And Dielectric Properties Of KBT Based Ferroelectric Ceramics

Ceramic capacitors are one of the most widely used electronic components in the field of the electronic industry.With the development of industry,large capacity ceramic capacitors which can work stably in high-temperature environments are urgently needed in the fields of aerospace,energy and nuclear power.Bismuth layer ferroelectric materials are considered as one of the most promising materials in the field of high-temperature electronic components due to their high Curie temperature,high spontaneous polarization and low dielectric loss.K_0.5Bi_4.5Ti₄O₁₅（KBT）is one of the members of the bismuth layered ferroelectric material system.The modified KBT ceramics show an obvious low-frequency giant dielectric response.However,due to the unclear origin of the giant dielectric response of KBT ceramics and the regulation mechanism of microstructure on the giant dielectric properties,the giant dielectric constant is accompanied by a high dielectric loss.Its application in high-temperature capacitors is limited.This paper aims at KBT performance to the organization of the giant dielectric ceramic dependencies,the mixed oxide was studied different properties（melting point,radius,etc.）influence on ceramic microstructure with composite ion modified and explore ceramic preparation process control structure and organization of the ceramic,analyses the relationship between the ceramic microstructure and dielectric properties.Firstly,(Mg_1/3V_2/3)⁴⁺,(Mg_1/2W_1/2)⁴⁺,(Zn_1/2W_1/2)⁴⁺,and(Zn_1/3V_2/3)⁴⁺composite ions are selected to replace the Ti⁴⁺ions at the B site of KBT ceramics,and the effects of composite ion substitution on the crystal structure,histomorphology,and electrical properties of KBT ceramics were investigated.The composite ion substitution causes distortion of the ceramic cells and the appearance of abnormally large-sized grains in the microstructure,leading to a significant increase in the dielectric constant.Among them,the dielectric constant of KBT-ZnV ceramics reaches 5×10~4 at 10 k Hz.In order to regulate the organization and properties of KBT ceramics by components,the influence law of(Zn_1/3V_2/3)⁴⁺doping content on the organization of large grains and electrical properties of KBT ceramics was investigated.The results show that the number of abnormally grown in the microstructure increased and the size kept decreasing with the increase of(Zn_1/3V_2/3)⁴⁺content.When x=0.06,the frequency stability of the dielectric constant is better and the dielectric loss is lower.The structure and dielectric properties of KBT-6ZnV ceramics were further regulated by changing the sintering time,the dielectric loss of KBT-6ZnV decreased and the dielectric properties were optimized as the holding time increased from 4 to 10 h.The K_0.5Bi_4.5Ti_4-x(Mg_1/2W_1/2)_xO₁₅（KBT-MgW）ceramics are prepared.And the effect of(Mg_1/2W_1/2)⁴⁺content on the microstructure and electrical properties of KBT ceramics was investigated.With the increase of(Mg_1/2W_1/2)⁴⁺content,the orientation of ceramic grains along the（001）direction and the dielectric constant gradually increases.In order to further enhance the orientation of KBT-MgW ceramics,the preforming pressure of KBT-MgW20 ceramics before calcination was adjusted.When the preforming pressure increases,the orientation of ceramic grains was more obvious,the dielectric constant and loss first increased and then decreased,and the dielectric constant of KBT-MgW20 ceramics is maximum under the axial pressure of 20 MPa.The sintering time of KBT-MgW20 ceramics was adjusted using a preforming pressure of 20 MPa,and the grain lamellar growth and oriented arrangement in the ceramic tissue were observed when the holding time increased.Finally,an optimized preparation process was used for KBT-MgW20 ceramics:20 MPa preforming pressure and 8 h sintering holding time,and the sintered ceramics were sliced in two directions,and the orientation factors and electrical properties of the sliced ceramic samples are systematically studied and discussed.