Ce2(Zr0.94Sn0.06)3(MoO4)9 (CZSM) ceramics were synthesized via a traditional solid-state method. The effects of Sn-substitution on phase composition, microstructure, and microwave dielectric properties as a function of sintering temperature were discussed. The XRD results indicated that all the samples exhibited a single phase. The chemical bonds of CZSM ceramics were calculated based on P-V-L theory, which could be used to evaluate the relationship between structure and microwave dielectric properties. The tendency of dielectric constant was depended on the theoretical dielectric polarizability and bond ionicity. Moreover, the improvement of Q·f value was ascribed to the increase of packing fraction. The reduced τf value could be explained by decrease of the bond energy, enhanced the co-efficient of thermal expansion and increase of bond valence (VZr(Sn)). The complex permittivity values were obtained from infrared reflectivity spectra. The dielectric permittivity and loss were 10.92 and 3.08 × 10−4, respectively, which agreed well with the measured value. Typically, the optimal microwave dielectric properties of εr = 10.35, Q·f = 59,660 GHz (at 9.70 GHz), and τf = −7.52 ppm/°C were achieved in CZSM ceramics sintered at 800°C for 6 h.
BNT (BaO–Nd 2 O 3 –TiO 2 ) system was modified via doping using sol–gel method, and BNST-Mn/PTFE microwave dielectric composite was prepared by mechanical blending. Scanning electron microscopy (SEM), thermal dilatometer, and split post-dielectric resonator (SPDR) were used to characterize the microstructure, dielectric properties, and thermal properties of the composite materials. The results indicate that as the amount of ceramic filler supplied grows, the agglomeration of fillers becomes more pronounced. At a filler content of 10 wt%, the dispersion of the filler in the matrix resin is relatively uniform. The dielectric constant and dielectric loss of the composites increased, and the bonding ability between the two phases diminished with the increase in filler content. When the mass fraction of the ceramic was increased to 70 wt%, the dielectric constant of the composite was 10.92 and the Q·f value was measured at 3584 GHz. At the same time, the coefficient of thermal expansion (CTE) of the composites reached 23 ppm/°C, which was a good compatibility with the copper foil. Lichtenecker equation, Maxwell–Wagner equation, Jayasundere–Smith equation, and effective medium theory equation (EMT) were used to predict the dielectric constant of the composites. In comparison, the dielectric constant values calculated using the EMT equation were in good agreement with the experimental values, especially at low filling volumes. Also, the simulation results of the thermal expansion coefficient of composite materials using the Lichtenecker equation and its improved form are in good agreement with the experimental values.
La 2 (Zr 1− x Ti x ) 3 (MoO 4 ) 9 (0 ≤ x ≤ 0.1) ceramics were prepared by the traditional solid-state reaction method. XRD analysis showed that La 2 (Zr 1− x Ti x ) 3 (MoO 4 ) 9 (0 ≤ x ≤ 0.1) ceramics belonged to a trigonal system. Based on the chemical bond theory, the consequences of bond energy, bond ionicity, lattice energy, and thermal expansion coefficient of ceramics on microwave dielectric properties were discussed. As Ti 4+ addition was increased, the reduction in dielectric constant was ascribed to the fact that the polarizability of Ti 4+ is smaller than Zr 4+ , and the downward trend was related to the bond ionicity. Besides, the tendency of Q·f value depended on the packing fraction and the lattice energy. The improvement in τ f value, the increase in bond energy, and the decrease in the coefficient of thermal expansion were all correlated. The far-infrared spectra implied that the absorptions of structural phonon oscillation were the main reason for the maximum polarization contribution. La 2 (Zr 0.92 Ti 0.08 ) 3 (MoO 4 ) 9 ceramics sintered at 750°C for 4 hours exhibited the best dielectric properties ( ε r = 10.33, Q·f = 80 658 GHz, and τ f = 3.48 ppm/°C).
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