Relaxor Behavior And Dielectric Properties Of Barium Zirconate Titanate Based Ceramics

With the development of the new generation of portable information terminal products requiring components to ultra-miniature and ultra-high capacity,the demand for ultra-miniature ultra-high capacity capacitors of MLCC components is extremely urgent.The barium zirconate titanate（Ba（Zr,Ti）O₃）system has the advantages of high dielectric constant and relatively low dielectric loss,which has become one of the electronic pillar industries of components and materials.This thesis aims to obtain Barium zirconate titanate（BZT）based ceramic electronic materials which can meet the requirements of high dielectric constant and low dielectric loss of capacitor type EIA standard of MLCC.In this experiment,Ba[(Zr_0.2Ti_0.8)_1-xCe_x]O₃ main crystalline phase powder（x=0～0.08）was prepared by liquid phase encapsulation.The ceramic is sintered with Ba(Zr_0.2Ti_0.8)O₃main crystalline phase powder prepared by liquid phase reaction,followed by solid phase doping and introducing y mol%Ce O₂（y=0～8）.By exploring the preparation methods of the two,the latter solid-phase doping method was used to introduce 1 mol%Ce O₂ and z mol%Hf O₂（z=0,0.5,1,2,3,5）and other modifiers to sintered porcelain.The effects of Ce and Hf doping content and subsequent sintering process on the phase structure,microstructure and dielectric properties of Ba(Zr_0.2Ti_0.8)O₃-based ceramics were studied from the perspective of the combination of doping method and ion modification:Ba[(Zr_0.2Ti_0.8)_1-xCe_x]O₃ ceramics prepared by liquid phase encapsulation have cubic phase structure,and no second phase is precipitate.Proper doping of Ce³⁺/Ce⁴⁺has the effect of refining ceramic grains.When the doping amount of Ce³⁺/Ce⁴⁺is 1 mol%,the average grain size of 16.90μm is obtained.The maximum permittivity of pure BZT ceramics is 4688,and the temperature is stable from+18℃to-34℃at x=0.05,which is in line with the Y5U capacitance temperature stability standard.At different Ce³⁺/Ce⁴⁺contents,γvalues are high,the degree of dispersion phase transition is gradually enhanced,and the capacitance/loss-frequency stability of BZT ceramics is improved,but the dielectric properties are sacrificed.Ba(Zr_0.2Ti_0.8)O₃ powder was prepared by liquid phase coating method,and Ba(Zr_0.2Ti_0.8)O₃-y mol%Ce O₂ ceramics（y=0～8）were prepared by introducing dopant in solid phase method.The second phase of BZT ceramics was obviously separated,and all series of samples were cubic phase.With the increase of Ce O₂ doping content,the average grain size of the ceramic matrix increases first and then decreases.When the doping amount of Ce O₂ is2 mol%,the average grain size of the ceramic is 20.07μm.Compared with the liquid-phase synthesis method,the effect of the introduction of rare earth ions by solid-phase doping is greater.With the increase of Ce O₂ doping amount,the Curie temperature Tm of the ceramics gradually decreases to around-110℃and then becomes stable.The dielectric constant and maximum dielectric constant of the ceramics at room temperature decrease first and then increase.When y=6,the dielectric constant of the doped BZT-based ceramics decreases to the minimum value.Compared with undoped BZT ceramics,the dielectric loss of BZT based ceramics is particularly dependent on frequency change at low frequencies.Ba(Zr_0.2Ti_0.8)O₃ powder was prepared by liquid phase encapsulation method,and Ba(Zr_0.2Ti_0.8)O₃-1 mol%Ce O₂-z mol%Hf O₂ ceramics were prepared by solid phase doping method.BZT-based ceramics have cubic phase perovskite structure at room temperature.When z=5,the introduction of modifier precipitates Ti⁴⁺to produce Ba₂Ti₉O₂₀ phase.Proper doping of Hf O₂ can adjust the grain size of ceramics.The average grain size increases first and then decreases with the increase of doping amount.When z≥3,the grain size of BZT ceramics presents a polarization distribution phenomenon.The Curie temperature point T_m of BZT ceramics moves to low temperature with the increase of Hf O₂ doping amount,and the frequency dispersion degreeΔT_rs decreases gradually.Moreover,the increase of matrix dispersion degree leads to the gradual increase ofγvalue.