Preparation and Properties of Two Ti-based Microwave Dielectric Ceramics
|School||University of Electronic Science and Technology|
|Course||Microelectronics and Solid State Electronics|
|Keywords||Microwave dielectric ceramics temperature coefficient of resonance frequency liquid sintering BaTi4O9 ZrTi2O6|
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 （εr）, low dielectric loss （tan δor high Q×fvalue,Q=1/tanδ） and small temperature coefficient of resonance frequency （τf）. 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）BaTi4O9-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, theτfvalue 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:εr=34.2, Q×f=60600GHz andτf=-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:εr=36.4,Q×f=62600GHz andτf=+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:εr=30.9, Q×f=20200GHz andτf=+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:εr=45.3, Q×f=43300GHz andτf=-0.5ppm/℃.Ⅴ. The phase composition, microstructure and microwave dielectric properties ofZr(Zn1/3Nb2/3)xTi2-xO6（0.2≤x≤0.8） solid solution ceramics were investigated. All of thecompound ions (Zn1/3Nb2/3)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, theεrandτfvalue 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 (Zn1/3Nb2/3)4+for Ti4+ions.