Layered Dielectric Complex Structures

In the recent years, layered dielectric complex structures have attracted more and more scientific attentions for their unique and useful dielectric, ferroelectric, piezoelectric and pyroelectric characteristics. This thesis focused on the microwave dielectric characteristics and ferroelectric characteristics of the layered dielectric complex structures, which were two important issues in this area.The dielectric characteristics of the co-sintered MgTiO₃-CaTiO₃ and MgTiO₃-SrTiO₃ layered composite ceramics were investigated at high frequency (1MHz) and microwave frequency. The effective dielectric constant and temperature coefficient of dielectric constant at 1MHz fit the series model well. They were determined by the volume fraction of the end-member and independent of the stacking scheme, while the effective dielectric constant at microwave frequency with TEon resonant mode derived from the series model much, and the stacking scheme had significant effect on it as well as the volume fraction of the end-member.The individually sintered MgTiO₃ and CaTiO₃ ceramics were stacked together directly to yield the "layered dielectric resonator". The stacking scheme and resonant mode were found to have significant effect on the microwave dielectric characteristics of the layered dielectric resonator, as well as the volume fraction of CaTiO₃. Finite element analysis could predict the microwave dielectric characteristics accurately and showed that the effects were due to the varying electric field distribution. It was also responsible for the different dielectric behaviors of the layered composite ceramics at high frequency and at microwave frequency with TE₀₁₁ mode.To attain near-zero temperature coefficient of resonant frequency, the Ca(Mg_1/3Nb_2/3O₃-Ba(Zn_1/3Nb_2/3)O₃ layered dielectric resonators with TE_01δmode were investigated. By adjusting the volume fraction of Ba(Zn_1/3Nb_2/3)O₃, good combination of high dielectric constant, high Qf value and nero-zero temperature coefficient of resonant frequency could be attained for each stacking scheme. The volume fraction of Ba(Zn_1/3Nb_2/3)O₃ where the temperature coefficient of resonant frequency annulled wasdetermined by the stacking scheme, while it only had a little effect on the corresponding effective dielectric constant and Qf value.Considering the practical applications, the adhesive-bonded Ca(Mgi/3Nb2/3)O3-Ba(Zni/3Nb2/3)O3 layered dielectric resonators with TEois mode were investigated. The adhesive only had a little effect on the resonant frequency, effective dielectric constant and temperature coefficient of resonant frequency, and the Qf degradation was acceptable. The adhesive-bonded layered dielectric resonator was a simple and effective method for preparing microwave dielectric resonator with layered complex structure and it proved suitable for practical applications. Good combination and optimization of the microwave dielectric properties could be obtained by assembling materials with opposite temperature coefficients of resonant frequency freely. Meanwhile, the designing process for such resonators was simplified with the aid of finite element analysis.Further investigation on layered dielectric resonator was carried out by finite element analysis. The dimension of the layered dielectric resonator was also found to have effects on the microwave dielectric characteristics as well as the stacking scheme and resonant mode. It could be concluded that the microwave dielectric characteristics of the layered dielectric resonator were extrinsic properties, which were different from those of the monomorph dielectric resonator. With increasing the layer number, the effective dielectric constant and Qf value of the layered dielectric resonator with TEois mode approached parallel model for each series of stacking schemes ((A/B)n, (B/A)n, (A/B)n/A or (B/A)n/B), and the temperature coefficient of resonant frequency approached an extreme near parallel model. This approaching behavior acted for all TEonp modes.The ferroelectric characteristics of the Pb(Zr,Ti)O3-based and Pb(Nb,Zr,Sn,Ti)O3-based ferroelectric/antiferroelectric layered composite ceramics were also investigated. When the maximum external electric field was 40kV/cm, the Pb(Zr,Ti)O3-based layered composite ceramics had hysteresis loops between ferroelectric and antiferroelectric loops, and the maximum and remanent polarizations decreased significantly with increasing the volume fraction of the antiferroelectric layer.The behaviors were consistent with the reported ferroelectric-antiferroelectric heterostructures. However, the Pb(Nb,Zr,Sn,Ti)O3-based layered composite ceramics always showed ferroelectric-like loops when the maximum external electric field was 40kV/cm. The maximum and remanent polarizations only decreased slightly with increasing the volume fraction of the antiferroelectric layer and high polarizations could always be maintained. The distinguished ferroelectric characteristics of the Pb(Nb,Zr,Sn,Ti)O3-based layered composite ceramics were due to the very low ferroelectric-antiferroelectric transition electric field of the antiferroelectric phase. The result is important for the applications of ferroelectric-antiferroelectric heterostructures in ferroelectric nonvolatile random accessed memories.