Study On Low Temperature Sintering And Dielectric Properities Of BaO-TiO₂ Ceramics

With the rapid development of communication technology,electronic equipment,such as active phased array radar,electronic pods,and electronic countermeasure systems,have higher performance requirements for miniaturization,high frequency and integration of passive electronic components.Low-loss microwave dielectric ceramic BaTi4O9 is an optional material in the BaO-Ti O₂ system which can meet this performance requirement.But its sintering temperature is too high,which make it difficult to achieve high-density integrated packaging and miniaturization through low-temperature co-fired ceramic（LTCC）technology.In order to solve this problem,this paper delves into BaTi4O9 ceramics by optimizing its preparation process and composition to obtain the best microwave dielectric properties.The low melting point glass-ceramics was added in the BaTi4O9 ceramic to study its low-temperature sintering properities,in order to prepare BaTi4O9-based LTCC materials with excellent comprehensive performance.BaCO₃ and TiO₂ were used as raw materials.The effect of solid-phase sintering program（pre-sintering time and sintering temperature）on the structure and properties of BaTi4O9 ceramics was studied.The results showed that as the pre-sintering time was extended to 4 h,the formation of BaTi4O9 single phase was hard.Therefore,the optimal pre-sintering time was determined to be 2 h.As the sintering temperature increased from1150℃to 1250℃,the sintering density of BaTi₄O₉ ceramic gradually increased.The ceramic grains growed abnormally when the temperature was too high,which adversely affected its dielectric properties.Therefore,the best sintering process is pre-burning for2 h and sintering at 1250℃,and the BaTi₄O₉ ceramics prepared had the best dielectric properties:εr=33.4,Q·f=15532.2 GHz,τf=+12.74 ppm/°C.The lanthanide oxides Ln2O₃（Ln=La,Nd and Sm）with different cation ionic radii were selected for doping modification of BaTi4O9 ceramics.The results showed that the BaLn2Ti4O12 phase generated in the samples was the key factor to change the dielectric properties of the system.When the content of Ln2O₃ was 11 mol%,the dielectric constant values of the Ln2O₃-BaTi4O9 had no significant difference,ranging from 42 to 46 which was higher than BaTi4O9 ceramics.The La2O₃-BaTi4O9 ceramics had the lowest quality factor 8760 GHz,while the Nd2O₃-BaTi4O9 and Sm2O₃-BaTi4O9 ceramics had similar quality factors,which were 12909 GHz and 12555 GHz.The temperature coefficient of resonant frequencyτf of La2O₃-BaTi4O9,Nd2O₃-BaTi4O9 and Sm2O₃-BaTi4O9 ceramics were+65.81 ppm/℃,+24.62 ppm/℃and+3.62 ppm/℃respectively.It can be concluded that Sm2O₃-BaTi4O9 ceramics had the optimal microwave dielectric properties.BaO-Al₂O₃-SiO₂（BAS）and La2O₃-B2O₃-CaO（LBC）glass-ceramics with low softening point were designed and prepared as sintering aids of Sm2O₃-BaTi4O9 ceramics.The effects of glass ceramics content and sintering temperature on low temperature sintering behavior and microwave dielectric properties of the composites were systematically studied.The results showed that the sintering shrinkage rate of the glass-ceramics/ceramics composites increased first and then decreased with the increase of glass ceramic content and sintering temperature.So the microwave dielectric properties of the composites showed similar curve.Finally,two kinds of composites used for LTCC technology were selected:50 wt%BAS/50 wt%Sm2O₃-BaTi4O9 composites and 50wt%LBC/50 wt%Sm2O₃-BaTi4O9 composites.The dielectric properties of the 50 wt%BAS/50 wt%Sm₂O₃-BaTi₄O₉ sintered at 925℃were the best:ε_r=13.59,Q·f=4793GHz,τ_f=-15.58 ppm/℃and the dielectric properties of the 50 wt%LBC/50 wt%Sm₂O₃-BaTi₄O₉ sintered at 875℃were the best:ε_r=24.97,Q·f=7167 GHz andτ_f=-74.4 ppm/℃...