Ionic doping engineered Ce2(Zr1−xBx)3(MoO4)9 (BCd1/3Nb2/3, Cd1/3Ta2/3) ceramics: Structural, chemical bond, and microwave/terahertz dielectric performance

A series of Ce2(Zr1−xBx)3(MoO4)9 ceramics, where BCd1/3Nb2/3, Cd1/3Ta2/3 (abbreviated as CZ1−xNx, CZ1−xTx), were synthesized using the classical solid-state reaction method. This study focused on the intrinsic mechanisms affected by doping in terms of chemical bond parameters, polarizability, lattice parameters, and bond valence. X-ray diffraction (XRD) results showed that Cd/Nb and Cd/Ta were solidly dissolved into the matrix lattice, which crystallized in a pure trigonal structure (Space group of R-3c, No. 167). According to the Phillips-van Vechten-Levine (P–V-L) theory, the chemical bond features have been parameterized for exploring the relationships between crystal structure and property. Interestingly, the findings indicated that the dielectric parameters varied closely with the chemical bond features of Zr1–O4. Far-infrared reflectivity (FIR) spectrum and terahertz time-domain (THz-TD) were used to obtain information on lattice vibration. The results showed that the complex permittivity extrapolated from THz-TD was closer to the measured value (at microwave) than the former. The relaxation polarization mechanism may be a key intrinsic factor affecting dielectric loss. Additionally, the bond valence results showed a linear relationship between Zr1–O4 and τf. CZ1−xNx and CZ1−xTx exhibited Qf values that were 2.86 and 5.46 times greater than the matrix, respectively, with low permittivity (εr, roughly 10) suitable for high-frequency communication materials. Notably, CZ0.94T0.06 ceramic achieved excellent performance with Qf = 103,974 GHz, εr = 10.63, and τf = −17.68 ppm/°C at 725 °C.