Defect Chemistry And Dielectric Behavior Of SrTiO₃-Based Ceramics With High Permittivity

The rapid development of microelectronics information makes demands on the miniaturization and integration of electronic components.Therefore,dielectric ceramic materials with high dielectric constant and low dielectric loss have become a major project in the new field.This thesis has selected SrTiO3 ceramics as the research material and studied the effect of composition and structure on the dielectric properties of dielectric ceramic materials by study on with Ce element doping and non-stoichiometry.The relationship between the defect structure and the dielectric properties of the ceramic material was initially established.The Sr1-1.5xCexTiO3 dielectric ceramics were fabricated by the solid state reaction methods.The influence with Ce element doping on the dielectric properties and crystal structure of SrTiO3 ceramics was studied.And the physical models were established to discuss the intrinsic mechanism of SrTiO3 ceramics with high permittivity by Ce doping.It was found that the slight Ce element doping can effectively promote the growth of ceramic grains.The cell parameters of the ceramics were decreased owing to the substitution of CeGIions for Sr2+ ions.At x = 0.01,the dielectric constant of the samples reached the maximum(~3900),which is about 13 times higher than that of pure SrTiO3 ceramic;the dielectric loss was～0.99%.The changes of the dielectric constant of ST0.01 ceramics was less than 15%between 10 kHz and 1 MHz,which illustrate it displayed a wide frequency independence.The activation energies corresponding to the dielectric loss relaxation peaks of Ce doping SrTiO3 ceramic were attributed to the fully ionized oxygen vacancies and the(V"Sr-VO)dipole.The changes in the dielectric properties of Sr0.985Ce0.01TiO3 and Sr0.99Ce0.0o1TiO3 samples were investigated.The physical models were established to discuss the changes in structural and dielectric properties.The permittivity and dielectric loss of the Sr0.99Ce0.0iTiO3 ceramics were shown 3,000 and 4.55%at room temperature and 1 kHz.And the dielectric loss is about 4.6 times higher than that of Sr0.985Ce0.01TiO3 ceramics.Complex impedance analysis,XPS analysis and other techniques were studied the mechanism of the difference in the dielectric properties of the two materials.The high permittivity and relatively low dielectric loss of Sr0.985Ce0.01TiO3 ceramics were attributed to the(V"Sr-VO)and[Ti4+·e-VO-Ti4+.e]bonds in the materials.However,titanium element might be in the form of Ti4+ ions for Sr0.99Ce0.01TiO3 ceramics.These conducting electrons,generated by secondary ionization of oxygen vacancies,were mainly in the form of free electrons in an electric field or bonded by CeSr to form CeSr·e,which lead to in a higher dielectric loss in Sr0.99Ce0.01TiO3 ceramics.Non-stoichiometric Sr0.99Ce0.01Ti1-xO3(SCT)ceramics were prepared by the solid state reaction methods.The changes in dielectric properties and structural of Ti-deficient and Ti-rich ceramics sintered in air or oxygen were analyzed.The physical models were established to discuss the changes in dielectric properties and structural.The high permittivity and relatively low dielectric loss of Ti-deficient samples were attributed to the fully ionized oxygen vacancies and giant defect-dipoles[Ti4+·e-Vo-Ti4+·e]in the materials.However,Ti-rich samples lead to a higher dielectric loss because of the destruction of giant defect dipoles,in that case highly localized electrons transformed into hopping electrons.