The Fabrication And Investigation Of BNT-PMN Based Ceramics For High-temperature-stable Capacitors

Capacitors,as typical electronic devices,are applied in different power electronics and systems.With rapid developments of information technology industry,the high demands for electronic devices on high temperature operation are unprecedented.The working temperature usually reaches 200? in fields like aviation,aerospace,electric automobiles and deep oil drilling,exceeding the upper temperature limit of X7R-X9R capacitors substantially.It's quite a challenge for power electronics to enhance the high temperature endurance of ceramic capacitors at present.Bi1/2Na1/2TiO3(BNT)ceramics is a typical high curie peak material(?320?),which is considered as potential material used in high temperature stable capacitors.On basis of this,plenty of works focusing on the dielectric temperature stability of BNT-based ceramics were conducted.Even though some material systems with high temperature stability were obtained,their permittivities are below 3000.Low permittivity is detrimental to the high capacitance and the volumetric efficiency of capacitors.It is crucial to find a ceramic system with both high temperature stability and high permittivity simultaneously.In view of the current research results of high temperature ceramic capacitors,this paper has carried out a series of research work from the aspects of composition variation and modification by PbMg1/3Nb2/3O3(PMN).The microstructure,phase structure,dielectric and ferroelectric properties of BNT-PMN ceramics were characterized and systematically analyzed.The BNT-PMN ceramics with good temperature stability and high permittivity were obtained,and the origin of the temperature stability was explored by the study on structure and properties under different temperatures.The KNN modification effects on microstructure,dielectric and ferroelectric properties of BNT-PMN ceramics were characterized and studied.The paper provides design and option for materials used in high temperature ceramic capacitors,which promotes the development of capacitors with wide working temperature and high volumetric efficiency in future.The PMN-modified BNT ceramics were fabricated by a conventional solid-state method.XRD pattern certified perovskite phase with no secondary phase in all compositions.As PMN concentration increased,the phase of(1-x)BNT-xPMN ceramics transformed from ferroelectric to relaxor gradually at room temperature,with prominent enhancement of dielectric temperature stability.For the composition x=0.2,the temperature coefficient of capacitance(TCC)was less than 15%in a wide temperature range from 56? to 350? with high relative permittivity(3372)at 150?,and low dielectric loss(<0.02)from 90 to 290?,which indicated promising future for(1-x)BNT-xPMN system as high temperature stable capacitor materials.The structure and properties at different temperatures of 0.8BNT-0.2PMN were studied.The XRD patterns and Raman spectra at different temperatures showed the phase transition from pseudocubic to cubic between 200?250?.The ceramic kept relaxor behavior between 20?180?,but turned into paraelectric phase at higher temperature.The existence of polar nanoregions in BNT-PMN ceramics was evidenced,and the anomalies in dielectric permittivity versus temperature might be attributed to the thermal evolution and mutual transformation of two kinds of PNRs with R3c and P4bm symmetry like other BNT-based materials.The 0.9BNT-0.1PMN ceramic system was modified by different KNN content.The microstructure,dielectric and ferroelectric properties of KNN-modified BNT-PMN ceramics were systematically analyzed.XRD pattern certified perovskite phase with no secondary phase in all compositions,and the grain size was reduced sharply with KNN modification.All ceramics were relaxor at room temperature,with prominent broadening and shifting of dielectric peaks as KNN concentration increased.The composition with 0.2 KNN concentration showed the best temperature stability.