Study On The Structure And Properties Of Re₂Ce₆O₁₅ Microwave Dielectric Ceramics

CeO₂ is a unique rare earth oxide material that is favored by researchers in different fields due to its excellent properties.Ce O₂ belongs to a typical cubic fluorite structure,and the space group is Fm-3m;Because of its simple structure and high stability,it is often used as a basic structure for solid solution expansion in the field of microwave dielectric ceramics,so as to obtain new high-performance materials.In this thesis,Re₂Ce₆O₁₅（Re=Y,Sm,Nd,La）microwave dielectric ceramics were prepared by adding different rare earth ions by solid-phase reaction method for sintering.The main work and research contents are as follows:（1）The high-performance Y₂Ce₆O₁₅ microwave dielectric ceramics were prepared for the first time by the solid phase method,and the phase analysis was carried out by XRD,and it was found that it was consistent with the Ce O₂ structure and belonged to the Fm-3m space group,and the lattice constant was obtained by Rietveld refinement,and after establishing the crystal structure model,the band and state density of the Ce O₂and Y₂Ce₆O₁₅ ceramic structures were calculated using first-principles calculation methods.It is found that the band gap value of ceramic energy band gap after adding Y element is not much different from the band gap value of Ce O₂,and Y element does not participate in the composition of valence band top and conduction band bottom.The density,grain size and micromorphology of ceramics were characterized,and it was found that the density of ceramics determined their dielectric constant,and the quality factor was mainly determined by grain size.The best microwave dielectric properties of ceramics are:ε_r=22.32,Q×?=149958GHz,τ_?=-21.38ppm/℃.（2）Based on Y₂Ce₆O₁₅ ceramics,Re₂Ce₆O₁₅（Re=Sm,Nd,La）microwave dielectric ceramics were designed and successfully prepared,and XRD was used for phase analysis,and it was found that it was consistent with the structure of Ce O₂ and belonged to the Fm-3m space group.The density,grain size and micromorphology of the three ceramics were characterized,and it was found that the dielectric constant was mainly affected by density,and the quality factor was mainly affected by grain size.At the same time,it is found that with the change of rare earth elements,the dielectric properties of the three ceramics have certain internal change laws.The dielectric properties of Re₂Ce₆O₁₅（Re=Sm,Nd,La）ceramics are:ε_r=23.12,Q×?=89901GHz,τ_f=-16.8ppm/℃;ε_r=23.54,Q×f=61596GHz,τ_f=-20.64ppm/℃;ε_r=19.00,Q×f=13555GHz,τ_f=-26.8ppm/℃.（3）The longitudinal analysis of Re₂Ce₆O₁₅（Re=Y,Sm,Nd,La）microwave dielectric ceramics by Rietveld refinement was carried out,and the difference between the crystal structures of Re₂Ce₆O₁₅ series ceramics was studied,and it was found that the unit cell volume decreased with the decrease of（Re=Y,Sm,Nd,La）ion radius,and was consistent with the offset law of the measured XRD diffraction peak.Using the dielectric constant correction formula,the internal pores are theoretically excluded,and the theoretical molecular polarizability calculated by the Clausius-Mosotti equation is found to be dependent on the molecular polarizability.The valence parameter of Re₂Ce₆O₁₅ series ceramics was calculated by valence bond theory,and after comparison withτf value,it was found that theτf value depended on the valence bond parameter...