Research On The Preparation And Microwave Dielectric Properties Of The Li₂ZnTi₃O₈Ceramics

In this thesis, the development and present research situation of the microwave dielectricceramics had been critically overviewed, based on above work, Li₂ZnTi₃O₈（LZT） microwavedielectric ceramics were chosen as research objective, and the relationship among sintering processes,phase constituent, microstructure and microwave dielectric properties of LZT c eramics had beensystematically investigated by thermal analysis （DSC）, X-ray diffraction （XRD）, scanning electronmicroscopy （SEM）, energy dispersive X-ray analysis （EDS）.The LZT ceramics were prepared by the conventional solid-state reaction sintering technique, theeffects of main sintered technical parameters on sintering characteristics, phase constituent,microstructure and microwave dielectric properties of the LZT ceramics had been investigated. Only asingle LZT phase formed in the prepared ceramics calcined at900℃for4h and subsequent sintered at1075℃for4h with a heating rate of3℃/min, the prepared ceramics were characterized as uniformmicrostructure and relative density of98.5%, and microwave dielectric properties of the ceramicswere achieved: a r value of26.6, a Q·fvalue of75563GHz and a value of-12.4ppm/℃.Sintering characteristics, phase constituent, microstructure and microwave dielectric propertiesof the Li₂Mg_xZn_1-xTi₃O₈（0≤x≤1） ceramics had been studied. When x=0.4, only main crystal-phaseformed in the prepared ceramics sintered at1075℃for4h. With increasing of X, relative density andQ·fvalue of the LZT ceramics increased firstly and then decreased, and relative density reachedmaximum value of96.5%and Q·fvalue of59886GHz at x=0.4; the permittivity increasedslightly, value would gradually tend to be positive. The Li2Mg0.4Zn0.6Ti3O8ceramics sintered at1075℃for4h were characterized as uniform microstructure, and microwave dielectric properties wereachieved as follow: a r value of26.71, a Q·fvalue of59886GHz and a of-7.1ppm/℃.The influences of TiO₂addition（≤3.0wt.%）on sintering characteristics, phase constituent,microstructure and microwave dielectric properties of the LZT ceramics had been studied. When TiO₂addition less than2.0wt.%, only a single LZT phase formed in the prepared ceramics sintered at1100℃for4h; but when TiO₂addition was up to3.0wt.%, there would be a small amount of secondphase rutile. With increasing of TiO₂addition, relative density of the LZT ceramics firstly increasedand then decreased; when TiO₂addition was1.5wt.%, relative density of the LZT ceramics was up to96.9%by sintered at1100℃for4h. With increasing of TiO₂addition, the LZT ceramics grain wastend to grow, the permittivity presented a tendency to increase, the resonant frequency temperature coefficient tended to be positive. TiO₂addition had a great influence on the quality factor of the LZTceramics, when TiO₂addition was1.5wt.%, Q value of the LZT ceramics was up to61153GHzsintered at1100℃for4h, and a r value of26.53, a value of-5.8ppm/℃.The influence of B₂O₃addition （≤2.5wt.%） on sintering at low temperature of LZT ceramics hadbeen studied. When B₂O₃addition less than2.0wt%, only a single LZT formed in the preparedceramics sintered at925℃for4h; but when B₂O₃addition was up to2.5wt.%, a small amount ofsecond phase B₂O₃would appear. Relative density of the LZT ceramics with increasing of B₂O₃addition firstly increased and then decreased; when B₂O₃addition was1.5wt.%, relative density of theLZT ceramics sintered at925℃for4h was up to maximum value94.5%. Adding B₂O₃couldsignificantly refine the grains of the LZT ceramics, but value had little change. With increasing ofB₂O₃addition, the permittivity and Q value of the LZT ceramics firstly increase and thendecreased, When B₂O₃addition was1.5wt.%, microwave dielectric properties of the LZT ceramicswere achieved as a r value of24.96, a Q value of49600GHz and a value of-11.3ppm/℃.The influence of Bi₂O₃addition （≤2.5wt.%）on sintering at low temperature of LZT ceramicshad been studied. When Bi₂O₃addition less than1.5wt.%, only a single LZT formed in the preparedceramics sintered at950℃for4h; but when Bi₂O₃addition more than1.5wt.%, there would be a smallamount of second phase Bi2Ti2O7. With increasing of Bi₂O₃addition, relative density of the LZTceramics firstly increased sharply and then slightly. Adding Bi₂O₃could refine grains effectively, andpromote the grain size more uniform and its coalescence. With increasing of Bi₂O₃addition, thepermittivity of the LZT ceramics increased gradually, the resonance frequency temperature coefficienttended to be negative. When Bi₂O₃addition was1.0wt.%, relative density of the LZT ceramics was96.9%sintered at950℃for4h, and the prepared ceramics were characterized as uniformmicrostructure, and microwave dielectric properties were achieved: a r value of26.73, a Q valueof36386GHz and a value of-15.4ppm/℃.The influence of ZBS glass addition （≤1.0wt.%）on sintering at low temperature of LZTceramics had been studied. When ZBS glass addition less than1.0wt.%, only a single Li₂ZnTi₃O₈phase formed in the prepared ceramics sintered at925℃for4h, no impurity phase appeared. WhenZBS glass addition less than0.5wt.%, with increasing of sintering temperature, relative density of theLZT ceramics increased continuously; when ZBS glass addition more than0.5wt%, with increasing ofsintering temperature, relative density of the LZT ceramics increased firstly and then decreased. WhenZBS glass addition was0.75wt.%, relative density of the LZT ceramics sintered at925℃for4h was95.9%. Adding ZBS glass could greatly refine grain size of the LZT ceramics to1³μm. The changing tendency of permittivity and Q·fvalue was similar to the variation of relative density inthe prepared ceramics, value of the LZT ceramics changed slightly. When ZBS glass addition was0.75wt.%, microwave dielectric properties of the LZT ceramics sintered at925℃for4h were achieved:a ε_r value of25.61, a Q·fvalue of51615GHz and a τ₁value of-11.78ppm/℃.