Study On Preparation And Modification Of （1-x）Ba_4.2Nd_9.2Ti₁₈O_54-xNdAlO₃ Ceramics

With the development of modern information and communication technology,the arrival of the 5G era requires the development of integrated and miniaturized communication equipment,and the development of integrated circuits in the direction of high frequency and broadband.Terminal products such as mobile phones and televisions are becoming thinner and lighter,so a compact MLCC（multilayer ceramic capacitor）is required to save equipment space.At the same time,in order to meet the requirements of large capacity and high speed of 5G communication,microwave high-Q MLCC will develop towards higher frequency of use.Therefore,multilayer ceramic capacitor（MLCC）has been widely used.It is formed by the internal electrode of the metal material and the ceramic material stacked together in multiple layers,and then co-fired into a whole.For some miniaturized electronic products,miniaturized MLCC products are even more needed.Therefore,we mainly focus on two basic directions:（1）Explore ceramic materials with a dielectric constant（ε_r）between 60-70;this dielectric ceramic material has high capacity accuracy.（2）Reduce the sintering temperature of the ceramics by additives to make it co-fired with the palladium-silver paste and adjust the dielectric constant temperature coefficient（τε）to near zero.The focus of this thesis is on BaO-Nd₂O₃-TiO₂ materials.In the entire BaO-Nd₂O₃-TiO₂ material,we focused on the Ba_4.2Nd_9.2Ti₁₈O₅₄（BNT）dielectric material.Taking the BNT material with tungsten bronze structure（εr=88 and sintering temperature at 1350℃）as the research object,the composite low-dielectric NdAlO₃（NA）（ε_r=22）material was used to adjust the dielectric constant of the system,and simultaneously Incorporation of MnO₂improves the dielectric properties of the material and adjusts the dielectric temperature coefficient and broadens the sintering temperature of the system to a certain extent.Finally,Li₂CO₃-B₂O₃-SiO₂（LBS）and BaO-ZnO-B₂O₃（BZB）are added to reduce the sintering temperature of the system.The research results of this paper are as follows:（1）BNT ceramic material belongs to tungsten-bronze-like structure.It has excellent dielectric properties and has the advantages of high frequency and high capacity,but its dielectric constant is high and its temperature stability is poor.In order to reduce the dielectric constant to meet the application,the dielectric temperature coefficient is adjusted to near zero.We choose a two-phase composite of NA material withε_r=22 and BNT.The composite quantity of NA changes from 0-0.9,and when the composite quantity is 0.6,its sintering temperature is 1370℃,and itsε_r can be reduced from 88 to 65.Q×f=10345 GHz,τ_f≈4.5ppm/°C.（2）On the basis of（1）,we choose 0.4BNT-0.6NA ceramic material and mix it with MnO₂.Since MnO₂ is a low-melting substance,it can form a liquid phase in the system,so it can be reduced sintering temperature of the system to a certain extent.At the same time,the incorporation of Mn⁴⁺can inhibit the reduction of titanium,so it can improve the dielectric properties of ceramic materials to a certain extent.In the study of this paper,we designed the doping amount of MnO₂ to dynamically change between 0.1wt%and 0.7wt%,and obtained the best after holding the sintering temperature at 1300℃for 4 hours when the doping amount was 0.4wt%.Dielectric properties:ε_r=67,Q×f=13346 GHz,τ_f=2.2ppm/℃.（3）In order to obtain a ceramic material that can be co-fired with palladium 30,we need to reduce the sintering temperature of the system to about 1100°C.Therefore,it is necessary to incorporate low melting point materials to reduce the sintering temperature of 0.4BNT-0.6NA ceramic materials.For low melting point materials,we choose LBS and BZB glass.First we set the doping amount of LBS to 0.4wt%,and then change the doping amount of BZB to continuously change from 0.1wt%to 0.5wt%.When the doping amount of LBS is 0.4 wt%and the doping amount of BZB is 0.3 wt%,the system has obtained the best performance:ε_r=63,Q×f=6627 GHz,tanδ<10^-3,τ_ε=6.8 ppm/℃,the electric resistance is greater than 10KV/mm.