Dielectric Temperature Stability Over A Broad Temperature Range In BaTiO₃-Ba(Fe_0.5Nb_0.5)O₃-based Ceramics

With the rapid development of microelectronic science and technology,there is a growing application for multilayer ceramic capacitors fields in aerospace,oil exploration,defense technology,automobile under extreme conditions.In space,temperature outside spacecraft is from minus 100°C to 100°C above.In response to the environment protection and the strategy of sustainable development,it is necessary to prepare a dielectric material with pollution-free,high dielectric constant,high temperature stability,low dielectric loss to meet the needs.Therefore,BaTiO₃ ceramics with excellent heat-resistance and high dielectric constant that are extensively used in the electronics industry are chosen as research subjects to explore the relationship between composition,structure and property.BaTiO₃ was the matrix with Ba(Fe_0.5Nb_0.5)O₃,(Bi_0.5Na_0.5)TiO₃,Bi(Mg_2/3Nb_1/3)O₃ and Bi(Mg_0.5Zr_0.5)O₃ were added separately to modify its dielectric properties,to improve the temperature stability through shifting,depressing and boradening the dielectric peak,promoting the application of dielectric capacitor in the harsh environments.Most BaTiO₃-based ceramics has been reported as a promising candidate material for high temperature capacitor applications.In this paper,the lead-free perovskite（1-x）BaTiO₃-xBa(Fe_0.5Nb_0.5)O₃（BT-xBFN）ceramics were firstly obtained by a solid-state reaction technique for moving the Curie point below the room temperature.Moving mechanism and relaxation behavior were studied.The normal ferroelectric behavior,diffused ferroelectric and relaxor ferroelectric were observed with increasing BFN.Based on the previous study,(Bi_0.5Na_0.5)TiO₃ was added in 0.9BT-0.1BFN formed（1-x）[0.9BaTiO₃-0.1Ba(Fe_0.5Nb_0.5)O₃]-x(Bi_0.5Na_0.5)TiO₃（BT-BFN-xBNT）solid solutions,and the ceramics satisfied X8R specification.The phase transition,and dielectric properties have been studied,and the reason for the optimization of dielectric temperature stability was analyzed.EDX and TEM confirmed that there was a core-shell structure in the ceramics due to the inhomogeneous elements.Hence the double peaks in-curve attributed to the two difference polarization characteristics inside the ceramic at-58°C and144°C,and they shifted towards a higher temperature with increasing BNT.When 0.06 x 0.10,dielectric constant value at room temperature is in the range of 1864²189,dielectric loss is in the range of 0.031⁰.137.BT-BFN-xBNT ceramics satisfied the temperature stability of X8R specification,and showed excellent dielectric temperature stability at low temperature.In order to broaden the range of temperature stability,（1-x）[0.846BaTiO₃-0.094Ba(Fe_0.5Nb_0.5)O₃-0.06(Bi_0.5Na_0.5)TiO₃]-xBi(Mg_2/3Nb_1/3)O₃（BT-BFN-BNT-x BMN）relaxor ferroelectric were synthesized via a standard solid state reaction.The non-ferroelectric phase was supposed to reduce the ferroelectricity of the ceramics,and the overall dielectric constant decreased.The ceramics satisfied X9R specification.The phase composition and microstructure had been studied,dielectric properties and ferroelectricity in the broad temperature and frequency were researched,and the reason for the optimization of dielectric temperature stability was also analyzed.EDX and TEM confirmed that core-shell structure disappeared,accompanied by the emergence of polar nanoregions（PNRs）.The non-ferroelectric phase BMN were homogeneous in the ceramic x=0.2,disrupting the long-range dipolar interaction and forming the local distortion of the polar region.Dielectric constant stabled in the range of-55⁴50°C.When measured at 1 kHz,BT-BFN-BNT-0.20BMN ceramic satisfied TCC_25°C±15%from-55 to 222°C,dielectric constant value at room temperature is 617,dielectric loss is 0.0268.When measured at 10 kHz,the 0.15 x 0.20 ceramics satisfied TCC_25°C±15%from-55 to 450°C,dielectric constant value at room temperature is in the range of 604⁶48,dielectric loss is in the range of0.0172⁰.0203.The BT-BFN-BNT-xBMN system would have a promising future in application as ultra-broad working temperature and high frequency dielectrics.And then for further research of the reason for the optimization of dielectric temperature stability by adding Bi-based oxide and BFN,Bi(Mg_0.5Zr_0.5)O₃ was firstly added in 0.94BaTiO₃-0.06(Bi_0.5Na_0.5)TiO₃.The ferroelectricity of the ceramics were reduced,the peaks in-curve were shifted towards a higher temperature and depressed.BT-BNT-xBMZ ceramics did not stability any XnR（n=7,8,9）specification.Dielectric constant value at room temperature is in the range of 604⁶48,dielectric loss is in the range of 0.0172⁰.0203.And then,BFN was added in 0.752BaTiO₃-0.048(Bi_0.5Na_0.5)TiO₃-0.2Bi(Mg_0.5Zr_0.5)O₃.Elements such as Fe³⁺and Nb⁵⁺mainly concentrate in grain boundaries in the form of non-ferroelectric phase.The ferroelectricity and relaxation of the ceramics were reduced,-curve was depressed.BT-BNT-BMZ-0.1BFN ceramic satisfied the temperature stability of X9R specification,dielectric constant value at room temperature is 853,and dielectric loss is 0.0202.BT-BNT-BMZ-0.125BFN ceramic satisfied the temperature stability of X8R specification,dielectric constant value at room temperature is 712,and dielectric loss is 0.0307.Finally the structure and performance of BT-0.1BFN,BT-BFN-0.06BNT and BT-BFN-BNT-0.2BMN ceramics were compared.It is found that the phase of ceramics changed from cubic to pseudocubic.Becauce of its inhomogeneous elements,there was a core-shell structure in BT-BFN-0.06BNT ceramic.The core-shell domain structure formed in the grains,the unobvious PNRs existed in in the grain boundaries.The ferroelectric phases and relaxation coexisted in the BT-BFN-0.06BNT ceramic.Ferroelectric and relax properties presented in BT-BFN-0.06BNT ceramic.However in BT-BFN-BNT-0.20BMN ceramic,core-shell structure disappeared,accompanied by the emergence of PNRs.The long-range dipolar interaction was disrupted and the local distortion of the polar region formed.The ferroelectricity was weakened,dielectric constant and dielectric loss were decreased,and broad dielectric temperature stability was optimized.