| Li2ZnTi3O8 ceramics is one of the promising candidates for LTCC technology,due to its low raw material cost,low density,low sintering temperature and excellent microwave dielectric properties.Li2ZnTi3O8 ceramics were chosen as the research object in this dissertation,and effects of chemical composition on structure,microstructure and microwave dielectric properities have been investigated by X-ray diffraction?XRD?,scaning electron microscope?SEM?,Raman spectroscopy and network analyzer,etc.Finally,Li2ZnTi3O8 based LTCC ceramics with good microwave dielectric properities were prepared and the relationships among ionic ordering degree,lattice vibration and microwave dielectric properties were discussed.Firstly,the phase composition,ionic ordering degree and microwave dielectric properties of Li1.33x.33x Zn2-2x-2x Ti1+0.67x+0.67x O4 ceramics with different composition were studied.With the increase of x,the ionic ordering degree of Li1.33x.33x Zn2-2x-2x Ti1+0.67x+0.67x O4 ceramics first increased and then decreased,and the ion ordering degree was the highest when x=0.75.With the increase of x,the dielectric constant had a negative correlation with Raman shift of A1g?1?mode and a positive correlation with the molecular polarizability.The Q×f values had the opposite trend with the half width of A1g?1?mode.When x=0.75,Li2ZnTi3O8 ceramic sintered at 1075? had excellent comprehensive properties:?r=27.22,Q×f=76273GHz,?f=-7.8ppm/?.The effects of(Li1/3Al2/3)2+,?ZnAl?and(Zn1/3Nb2/3)4+substitution on the phase composition,ionic ordering degree and microwave dielectric properties of Li2ZnTi3O8 ceramics were studied,and the mechanisms of the ionic ordering degree and lattice vibration on the microwave dielectric properties of ceramics were also discussed.With the increase of the substitution amount of(Li1/3Al2/3)2+,Li2+xZn1-2xAlxTi3O8 ceramics changed from ordered phase to disordered phase;and the ionic ordering degree and Q×f values increased first and then decreased after reaching the maximum value at x=0.1,Li2.1Zn0.8Al0.1Ti3O8 ceramic sintered at 1100? had excellent comprehensive properties:?r=26.11,Q×f=96129GHz,?f=-3.2ppm/?.In the substitution of?ZnAl?,with the increase of substitution amount.The ionic ordering degree and dielectric constant of Li2-xZn1-xTi3-xAlxO8 ceramics decreased gradually;the Q×f values increased first and then decreased.When x=0.1,Li1.9Zn1.1Ti2.9Al0.1O8ceramic sintered at 1100? had optimum comprehensive properties:?r=25.72,Q×f=95161GHz,?f=-12.8ppm/?.When(Zn1/3Nb2/3)4+was substituted,with the increase of x,the order-disorder transition occurred;ionic ordering degree,dielectric constant and Q×f values decreased.When x=0.05,Li2Zn(Ti0.95(Zn1/3Nb2/3)0.05)3O8 ceramic sintered at 1075? had the highest ionic ordering degree and excellent comprehensive properties:?r=25.99,Q×f=92267GHz,?f=-9.8ppm/?.Finally,the effects of Li2Zn2Mo3O122 and?LiF/CaF2?addition on the sintering characteristics and microwave dielectric properties of Li2.1Zn0.8Al0.1Ti3O8 ceramics were studied.The addition of Li2Zn2Mo3O122 and?LiF/CaF2?could effectively reduce the sintering temperature of Li2.1Zn0.8Al0.1Ti3O8 ceramics to about 900?.The dielectric constant,Q×f values and?f values of the ceramics had changed correspondingly,which were mainly related to effect of the second phase and the sintering aid.When the content of Li2Zn2Mo3O122 was 0.2,the composite ceramic sintered at925? had excellent microwave dielectric properties:?r=22.08,Q×f=55658GHz,?f=-16.8ppm/?.When the content of?LiF/CaF2?was 2wt%,the ceramics had excellent comprehensive properties:?r=25.77,Q×f=34547GHz,?f=-8.89ppm/?. |
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