Preparation And Properties Of Two Ti-based Microwave Dielectric Ceramics

Microwave dielectric ceramics have been one of the fast-developing newfunctional electronic materials in the past30years, which are widely applied atmicrowave frequencies of300MHz³000GHz. Microwave dielectric ceramics have thehigh dielectric constant （ε_r）, low dielectric loss （tan δor high Q×fvalue,Q=1/tanδ） and small temperature coefficient of resonance frequency （τ_f）. Theyusually work as the dielectric resonators in the microwave components such asoscillators, filters and antennas. Moreover they also can be used as the dielectricsubstrates in the microwave circuits. In recent years, the demand of microwavedielectric ceramics continues exuberantly, so it has been a strategic, leading edge andforesight work to develop new microwave dielectric ceramics with own intellectualproperty rights. For the practical application, all of the ceramic samples in this paperwere prepared by the traditional solid-state reaction. The influences of the materialscomposition on the phase composition, microstruture and microwave dielectricpropertires of BaTi₄O₉-BaZn₂Ti₄O₁₁and ZrTi₂O₆-ZnNb₂O₆based ceramics wereinvestigated in detail.Ⅰ. The complex phase ceramics （1-x）BaTi₄O_9-xBaZn₂Ti₄O₁₁were prepared byone synthetic process. The two phases BaTi₄O₉and BaZn₂Ti₄O₁₁could perfectlysymbiose and coexist. When the value of x was increased from0.05to0.50,BaZn₂Ti₄O₁₁phase gradually became more and more, thus the dielectric constant of thesamples decreased form37.3to32.8, and the Q×fvalue first increased from45300GHz to the peak value60600GHz （x=0.30）, and then declined to58700GHz（x=0.40）. Meanwhile, theτ_fvalue almost went down linearly from+12ppm/℃to-3ppm/℃. At last, the complex phase ceramics0.7BaTi₄O₉-0.3BaZn₂Ti₄O₁₁weresintered well at1240℃for3h, and they showed the optimal microwave dielectricproperties:ε_r=34.2, Q×f=60600GHz andτ_f=-2.0ppm/℃.Ⅱ. By doping CuO to form the liquid-phase sintering mechanism, the sinteringtemperature of the complex phase ceramics BaTi₄O₉-BaZn₂Ti₄O₁₁was lowerd to1150℃. In addition, Cu²⁺ions could substitute for Zn²⁺ions in BaZn₂Ti₄O₁₁, which could lead to the increase of BaZn₂Ti₄O₁₁phase and the decrease of its latticeparameters. Both of these two results were beneficial to the enhancement of the Q×fvalue. The substitution of Cu²⁺ions could also restrain the loss of oxygen ions in theseTi-based ceramics when they were sintered in air. Therefore, the stability andrepeatability of the Q×fvalue were improved.1.0wt%CuO doped0.85BaTi₄O₉-0.15BaZn₂Ti₄O₁₁ceramics sintered at1150℃for3h showed densemicrostructure and more excellent microwave dielectric properties:ε_r=36.4,Q×f=62600GHz andτ_f=+0.2ppm/℃，which were superior to many reportedproperties of BaO-TiO2based ceramics, so it was suggested that our new microwavedielectric ceramics owned the potential to be practically applied.Ⅲ. For the application in LTCC technology, the sintering aids BaCu（B₂O₅） wereadded into BaTi₄O₉-BaZn₂Ti₄O₁₁ceramics and the sintering temperature wassuccessfully lowered to900℃. The doping of BaCu（B₂O₅） could cause thedecomposition of BaTi₄O₉to Ba4Ti13O30and the new generation of BaTi（BO3）2. Thedensification at900℃was due to the liquid-phase sintering mechanism formed by themelt of BaCu（B₂O₅）.0.85BaTi₄O₉-0.15BaZn₂Ti₄O₁₁ceramics with11wt%BaCu（B₂O₅）addition could be sintered well at900℃for2h and they had good microwave dielectricproperties:ε_r=30.9, Q×f=20200GHz andτ_f=+11.7ppm/℃, which had theadvantage when they were compared to the properties of other BaO-ZnO-TiO₂basedlow-temperature sintered ceramics, especially in terms of the Q×fvalue.Ⅳ. When the pure ZrTi₂O₆-ZnNb₂O₆ceramics were sintered in air, they wouldlose oxygen ions, which could cause very low Q×fvalue. By doping Mn4+ions tosubstitute for Ti⁴⁺ions, some TiO2phase from the raw materials was left as the secondphase. And the adding of Mn⁴⁺ions could promote the grain growth. Because of theacceptor effect of Mn4+ions,0.7wt%MnCO₃doped ZrTi₂O₆-ZnNb₂O₆ceramicsshowed the maximum Q×f=44800GHz, which was15times higher than that of thepure samples sintered in air. At last,0.69ZrTi₂O₆-0.31ZnNb₂O₆ceramics with0.7wt%MnCO₃addition sintered at1270℃for7h in air had good microwave dielectricproperties:ε_r=45.3, Q×f=43300GHz andτ_f=-0.5ppm/℃.Ⅴ. The phase composition, microstructure and microwave dielectric properties ofZr(Zn_1/3Nb_2/3)_xTi_2-xO₆（0.2≤x≤0.8） solid solution ceramics were investigated. All of thecompound ions (Zn_1/3Nb_2/3)⁴⁺could enter Zr-Ti crystal lattice, and when x=0.5⁰.8, pure ZrTi₂O₆solid solution phase was formed. In this single-phase area, as theincreasing of the value of x, theε_randτ_fvalue of the ceramics samples went downfrom43.0to39.2and from-10.2ppm/℃to-25.5ppm/℃, respectively. At the same time,the Q×fvalue increased from40900GHz to43200GHz, which was attributed to theenhancement of the covalent bonds in ZrTi₂O₆crystal structure caused by thesubstitution of the compound ions (Zn_1/3Nb_2/3)⁴⁺for Ti⁴⁺ions.