Relaxor Behavior And Dielectric Properties Of Gadolinium Ion Modified Barium Zirconate Titanate Based Ceramics

Barium zirconate titanate（BZT）ceramics are widely used in multilayer ceramic capacitors（MLCCs）industry because of their high relative dielectric constant,low loss and low cost.In recent years,the ceramic medium for MLCCs has gradually developed from micron level to nano level,which requires ceramic materials to have the characteristics of small grain and superior dielectric properties at the same time.The purpose of this thesis is to obtain barium zirconate titanate（BZT）based ceramic capacitor materials with high relative dielectric constant,low dielectric loss and low capacitance temperature change rate.In this experiment,x wt%（x=0,2,4,6）Gd₂O₃ doped Ba(Zr_0.1Ti_0.9)O₃ ceramics were prepared by solid-phase method,y wt%（y=0,1,2,3,4,5,6）Gd₂O₃ doped Ba(Zr_0.1Ti_0.9)O₃ceramics and(Ba_1-zGd_z)(Zr_0.1Ti_0.9)O_3+z/2（z=0.01,0.02,0.03,0.04,0.05,0.06,0.07）ceramics were synthesized by sol-gel method respectively.The effects of gadolinium ion content and sintering process on the relaxation behavior and dielectric properties of Ba(Zr_0.1Ti_0.9)O₃ ceramics were systematically studied from the perspectives of ion modification and ceramic particle size control.The main research results are as follows:Ba(Zr_0.1Ti_0.9)O₃ powder prepared by solid-state method is tetragonal perovskite structure with particle size of 800 nm.With the increase of Gd₂O₃ doping,Gd³⁺is gradually replaced by B-site to a and B-site at the same time,and BZT based ceramics change from tetragonal phase to cubic phase.An appropriate amount of Gd₂O₃ doping can refine the ceramic grains,when x=4,the grain size is about 1.95μm and EDS results show that there are local component fluctuations.Doping Gd₂O₃ makes ceramicsε_rRT first increases and then decreases,tanδ_RT and T_m decrease gradually,and the degree of frequency dispersion and dispersion phase transition increases gradually.When x≥4,the ceramics are relaxor ferroelectrics.The best sintering process of ceramics is 1380℃for 2 hours,whichε_rRT is 5547.6,tanδ_RT is 0.009.The Ba(Zr_0.1Ti_0.9)O₃ powders prepared by sol-gel method showed obvious agglomeration phenomenon,and the particle size of aggregates was 80～150nm.The change of the p H value and calcination temperature of the sol had a great influence on the powder.XRD results show that gadolinium ions can replace both A and B sites,and BZT based ceramics change from tetragonal phase to cubic phase.An appropriate amount of Gd₂O₃doping can refine the ceramic grains and when y=3,the grain size is about 1.63μm.The grain boundary buffer effect brought by small grains enhances the degree of dispersion phase transition of ceramics.When y≥5,the ceramics are close to ferroelectrics with complete dispersion phase transition.When y=3,the dielectric properties of ceramics at room temperature are the best whichε_rRT is 4373,tanδ_RT is 0.0268 and y≥2,the ceramics are relaxor ferroelectrics.Increasing the sintering temperature and prolonging the holding time are helpful to further reduce the T_m of ceramics.The best sintering process is holding at 1350℃for 3h,whichε_rRT is 3523.3,tanδ_RT is 0.0182.XRD results show that(Ba_1-zGd_z)(Zr_0.1Ti_0.9)O_3+z/2 powder and ceramic are cubic perovskite structure.When z≥0.06,Gd³⁺replaces B position,resulting in cell volume expansion.When z=0.01～0.06,the average grain size of(Ba_1-zGd_z)(Zr_0.1Ti_0.9)O_3+z/2 ceramics increases from 1.24μm increased to 3.8μm.The grains are uniform.When z=0.01～0.07,(Ba_1-zGd_z)(Zr_0.1Ti_0.9)O_3+z/2 ceramics are relaxor ferroelectrics.The enhancement of relaxation behavior is related to the increase of lattice distortion and oxygen ion vacancy concentration.Compared with solid-state method,the BZT based ceramic prepared by sol-gel method has better temperature stability and better room temperature dielectric properties,which is related to the size of ceramic grains.Where(Ba_0.97Gd_0.03)(Zr_0.1Ti_0.9)O_3.015 ceramics have high relative permittivity at room temperature(ε_rRT=4462),low dielectric loss at room temperature(tanδ_RT=0.0133),+0.3%～-21%in the range of-30℃～+85℃,which has great market application potential.