| In the wake of development in communication science and technology,the communication equipment has become high integration,high working frequency and low cost.The ceramic material plays an increasingly important role in the manufacture of filter and resonator.（1-x）LaAlO3-xSrTiO3 ceramic has the characteristics of high dielectric constant,low dielectric loss,and,the temperature coefficient of resonant frequency is approximately equal to zero.The relationships between the composition,structure and dielectric properties were investigated by using X-ray diffraction,Scanning Electron Microscopy and Agilent4284A LCR.Meanwhile,the ceramics were prepared by sintering aids,the low temperature sintering characteristics and dielectric properties of the ceramics were studied.In the first place,LAST ceramics were prepared by solid state processing and the sintering behavior,microstructure and dielectric properties of（1-x）LaAlO3–xSrTi03（0≤x≤1）ceramics were investigated.The results show that the main crystal phase shifts from rhombohedral phase to orthorhombic phase,then it changes to the cubic phase,the dielectric constant and temperature coefficient of resonance frequency increases with the increasing content of SrTiO3.The dielectric loss is directly related to the structural transformation.A compact structure and distinct grain boundary was observed as the x=0.46,0.56,sintered at1550℃for 4 h.The dielectric properties of samples areεr=35.7,tanδ=3.01×10-4,τf=-14.6×10-6/℃,andεr=44.7,tanδ=2.69×10-4,τf=1.17×10-6/℃,respectively.In the second place,in order to lower the cost of LAST ceramic,the LAST ceramics were doped with sintering aids,such as ZnO,CuO and ZnO-B2O3,to decrease sintering temperature.However,few research about the effect of sintering aids has been conducted at present,the types and amount of sintering aids should be determined in this work.The sintering temperature of 0.46LA0.54ST ceramics could be lowed and the sintering range could be enlarged with the additions of ZnO,CuO and ZnO-B2O3 obviously at the same time.The loss of oxygen and reduction of Ti4+ions were limited by low sintering temperature,the number of oxygen vacancy and electronic defects were also decreased,which made the dielectric loss decreased.With the addition of 5wt%ZnO or 1wt%CuO,the sintering temperature decreased from 1550℃to 1430℃,the samples showed distinct grain boundary and uniform in grain size,the optimum dielectric properties were:εr=42.1,tanδ=2×10-44 andεr=44.3,tanδ=1.4×10-3,respectively.By adding 3wt%ZnO-B2O3,the ceramic samples sintering at 1370℃,the grains grew up uniformly and showed:εr=38.2,tand=4×10-4.Furthermore,dielectric loss is low tand≈10-4,sintered from 1370℃to 1520℃.The charge compensation mechanisms,defect structure mechanism and the dielectric relaxation by substituting divalent Sr2+with trivalent Bi3+were also studied in this paper,.Sr1-x-x BixTiO3 ceramics were prepared by solid state reaction method.To investigate the dielectric properties,defect structure and defect dipoles of SrTiO3 ceramics doped with Bi The crystal structure were characterized by X-ray diffraction（XRD）,no second phase can be observed in doping range.As x=0.01,the unstable defect dipoles[BiS·r（10）Ti’Ti]were formed which include weakly bound electron,and the charge compensation mechanisms of SBT ceramics is electrical-compensation.With the increasing content of Bi3+,the charge compensation mechanisms changed into Sr vacancy,the stable defect dipoles[BiS·r（10）Ti’Ti]were formed under the coulomb force.The results suggested that all the dielectric relaxations are related to the thermally activated process by Arrhenius law.With the content of Bi increasing,the relaxation activation energy of the peaks increased and the degree of dielectric relaxation decreased. |
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