| The development of microwave dielectric resonators for communication system required the dielectric materials with high dielectric constant, high quality factor and near-zero temperature coefficient of resonant frequency. In this thesis, lead-based perovskites, which were relaxor ferroelectrics or antiferroelectrics with high dielectric constant and relatively low dielectric loss, were modified for the application of high-frequency capacitors and microwave dielectric resonators. The structures were analyzed together with dielectric properties.Incorporating SrTiO3 into relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 modified the stability of perovskite structure due to the increased tolerance factor and average electronegativity difference with increasing SrTiO3 content. The dielectric constant decreased nonlinearly with increasing SrTiO3 content, obeying the series model of dielectric mixtures. The dielectric loss was reduced to the order of 10-4at 1MHz) where the dielectric constant was in the range of 289-2022.According to X-ray diffraction, the single phase structure was obtained in CaTiO3 modified Pb(Fe1/2Nb1/2)O3. The structure deviated from the ideal cubic perovskite structure due to the smaller tolerance factor of CaTiO3. For the appearance of the peaks near 800cm"1 which were assigned to A1g mode in doubled perovskite, the Raman spectra were consistent with the Fm3m space symmetry which implied the existence of similar 1:1 ordered domains. In the present system, low loss dielectrics (-10-4 at 1MHz) with high dielectric constant (165-250) and reduced temperature coefficient (T-800 to -1200ppm/) were obtained. Good microwave dielectric properties were obtained for x=0.9: e=164, Qf=6,180GHz, tf=+583ppm/. Moreover, the markedly non-linear P-E behavior was observed at x=0.1.The low-loss dielectrics with high dielectric constant and reduced temperature coefficient were obtained by incorporating Ca(Fei/2Nb1/2)O3 into PbZrO3, where the rhombohedral phase for x equals 0.2 and orthorhombic phase for x equal 0.8 and 1 were observed. Higher symmetry was observed at x=0.4~0.6. The ordering was observed in all compositions for the existence of near 800cm"1 lines. Raman spectra also disclosed that Fe/Nb ordered region dispersed in the disordered Zr-rich matrix at x=0.2. The zero temperature coefficient was expected for some composition between x=0.6 and x=0.8 where the dielectric constant was between 55 and 84. Good microwave dielectric properties were obtained at the composition of x=0.4: 8=140, Qf=l,776GHz, -cr+120ppm/.Modification of PbZrO3/Ca(Fei/2Nb1/2)O3 dielectric ceramics was performed by Ca substitution for Pb or Zr substitution for (Fe, Nb). The good microwave dielectricproperties were obtained in Pbo.6Cao.4Zro.9(Fei/2Nbi/2)o.iO3: 8r=100, Qxf =3,600GHz, Tf=+6ppm/. According to the Rietveld refinement, the space group Pbnm was suggested to the crystal structure of Pbo.6Cao.4Zr0.9(Fei/2Nbi/2)o.iO3. The further modification of Pbo.6Cao.4Zro.9(Fei/2Nbi/2)o.iO3 by Ce, Sn and Ti substitution for Zr was also performed. The dielectric constant correlated roughly with the value of o/rjon3. The observed polarizability was fit well with the calculated polarizability, and the results showed that the Vox effect on the polarizability of oxygen must be considered.In (l-x)Pb(Mgi/3>tt>2/3)O3-xLa(Mgi/2Tii/2)O3 system, the pyrochlore-free ceramics were obtained with increasing La(Mgi/2Tii/2)O3 content due to the increased electronegativity difference. 1:1 B-site cation order with the !/2(lll) superlattiece reflection was observed in the perovskite phase for all compositions. Antiphase tilting of oxygen octahedra was observed according to the superlattice reflections and A-site cation displacing appeared at x=0.9. Raman spectra confirmed the B-site order in perovskite phase. Two different types of order region accounted for the two-mode behavior on Aig mode. Low loss (10"4) dielectrics with high dielectric constant (36-900) were obtained by incorporating La(Mgi/2Tii/2)O3 into Pb(Mgi/3Nb2/3)O3. Antiphase tilting of oxygen octahedra...
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