Preparation And Properties Of Barium Zirconate Microwave Dielectric Ceramics

BaZrO₃ ceramics is a kind of intermediate electromicrowave dielectric ceramic material,which has a certain application prospect in the field of microwave dielectric ceramics,but the high sintering temperature（1600℃）limits the research of BaZrO₃ ceramics to a certain extent.Taking BaZrO₃ ceramics as the research object,the effects of different sintering additives on the sintering characteristics,phase composition and dielectric properties of BaZrO₃ ceramics were studied.In order to improve the microwave dielectric properties of BaZrO₃ ceramics by using ion substitution method,a broadband dielectric resonant antenna is designed and simulated by using HFSS software to explore the possibility of its practical application.In order to reduce the sintering temperature of BaZrO₃ ceramics,Zn O and B₂O₃ are used to reduce the sintering temperature of BaZrO₃ ceramics.It is found that the addition of Zn O can increase the density value of BaZrO₃ ceramics,but it has little promotion effect on the grain growth.In addition,Zr⁴⁺will be replaced by Zn²⁺,resulting in defect deterioration of dielectric properties.Finally,the optimal dielectric properties are obtained when the addition amount is 0.5wt%at 1350℃:ε_r=41.67,Q×f=12,267GHz.Due to the liquid phase sintering mechanism,the addition of B₂O₃ promoted the grain growth of BaZrO₃ and reduced the sintering temperature of BaZrO₃ ceramics from 1600℃to 1300℃.BaZr（BO₃）₂ phase will be produced when the addition of B₂O₃ is too much,resulting in the decrease of dielectric properties.Finally,the best dielectric properties are obtained when the addition of 3wt%sintered at 1300℃:ε_r=33.02,Q×f=32,761GHz,τ_f=+152 ppm/℃.In order to explore the application possibility of BaZrO₃ ceramics in LTCC field,binary compound Cu O-B₂O₃ and glass CBSL（Ca O-B₂O₃-Si O₂-La₂O₃）were used to reduce the firing of BaZrO₃ ceramics.When the addition of Cu O-B₂O₃ reduces the sintering temperature of BaZrO₃ ceramics to 1100℃,the addition of Cu O can reduce the generation of BaZr（BO₃）₂phase,and at the same time,Cu²⁺will replace Zr⁴⁺into the crystal structure,leading to the deterioration of the performance.The dielectric properties ofε_r=36.3,Q×f=4,410GHz were obtained at 1200℃with 2wt%.The addition of CBSL glass can promote the grain growth of BaZrO₃ ceramics at low sintering temperature and reduce the sintering temperature to 960℃.However,after the addition of CBSL glass,crystal precipitation will lead to Ca₂Ba Si O₃ phase and a large number of small grains in the ceramics.The final dielectric properties ofε_r=14.32,Q×f=6,078GHz are obtained when the addition of 30wt%is sintered at 960℃.In order to improve the microwave dielectric properties of BaZrO₃ ceramics,BaZrO₃ceramics with good performance and addition of 3wt%B₂O₃ were selected as the research object,and Ba²⁺was replaced by Ca²⁺and Sr²⁺,respectively.The substitution of Ca²⁺and Sr²⁺did not result in the formation of a second phase.A small amount of Ca²⁺substitution can promote the grain growth of BaZrO₃ ceramics,but excessive substitution will increase the grain boundary strength and lead to abnormal grain growth and porosity,which will reduce the quality factor.Ba_0.98Ca_0.02ZrO₃ ceramics sintered at 1200℃obtained the best dielectric properties:ε_r=36.274,Q×f=20,854GHz,τ_f=144 ppm/℃.The replacement of Sr²⁺increases the quality factor of BaZrO₃ and decreases the temperature coefficient of resonant frequency.However,the phenomenon of uneven grain will occur when Sr²⁺is excessive.Ba_0.94Sr_0.06ZrO₃ceramics sintered at 1275℃obtained the best dielectric properties:ε_r=34.85,Q×f=39,070GHz,τ_f=+140ppm/℃.Ti⁴⁺and(Al_1/2 Nb_1/2)⁴⁺are used to replace Zr⁴⁺.The substitution of Ti⁴⁺promoted the sintering of BaZrO₃ ceramics,but had a great impact on the dielectric properties.After the substitution of Ti⁴⁺,the dielectric constant of BaZrO₃ ceramics was greatly improved,while the quality factor was significantly reduced.BaZr_0.98Ti_0.02O₃ceramics sintered at 1300℃obtained the best dielectric propertiesε_r=35.179,Q×f=17,036GHz,τ_f=+158 ppm/℃.However,Al³⁺and Nb⁵⁺do not all enter into the crystal structure,but some of them react with B₂O₃ and attach to the surface of BaZrO₃ crystal in the form of small grains,which inhibits the growth of BaZrO₃ crystal.BaZr_0.98(Al_1/2Nb_1/2)_0.02O₃ceramics sintered at 1350℃achieve the best dielectric properties:ε_r=31.569,Q×f=15,486GHz.Designing a dielectric resonant antenna in the form of a combination of circular and cylindrical shapes can broaden the antenna bandwidth and increase the gain,resulting in a relative bandwidth of 11%and a maximum gain of 5d B.This has certain reference significance for the practical application of BaZrO₃ ceramics.