Correlations between the crystal structure and microwave dielectric properties in Ce2[Zr1-xMx]3(MoO4)9 (M = Mn1/3Nb2/3, Mn1/3Ta2/3) solid-solution ceramics

Abstract

Ce2[Zr1-xMx]3(MoO4)9 (M = Mn1/3Nb2/3, Mn1/3Ta2/3;x = 0.02, 0.04, 0.06, 0.08 and 0.10) (abbreviated as CZ1-xNx and CZ1-xTx) ceramics were prepared through the solid-state reaction method. Effects of (Mn1/3Nb2/3)4+ and (Mn1/3Ta2/3)4+ ions on the sintering characteristics, crystal structures, microwave dielectric properties and infrared vibrational modes were studied in detail. X-ray diffraction (XRD) results reveal the formation of solid solutions for all components. Based on the chemical bond theory and Rietveld refinement, intrinsic structure parameters including the polarizability (P), the packing fraction (P.F.) and the octahedral distortion (Δocta.), and bond parameters including the lattice energy (U), bond energy (E) and thermal expansion coefficient (α) were calculated. Interestingly, the Ce–O bond plays a major role in the bond ionicity (fi), while Mo–O bond dominates the contributions in the lattice energy (U), bond energy (E) and thermal expansion coefficient (α). In addition, these parameters are used to explain the variations of the microwave dielectric properties of ceramics either changing the doping contents or replacing different ions at x = 0.06. Furthermore, far infrared (FIR) spectra uncover that the phonon modes provide the major polarization contribution of 68.59% in the CZ0.9T0.1 ceramic, implying that the main contribution to εr stems from the ionic polarization instead of the electronic polarization. Typically, the optimum microwave dielectric properties are achieved for the CZ0.9N0.1 and CZ0.9T0.1 ceramics with εr = 10.76, Q × f = 85,893 GHz (at 9.52 GHz), τf = −14.83 ppm °C−1 and εr = 10.72, Q × f = 87,355 GHz (at 9.81 GHz) and τf = −8.68 ppm °C−1, respectively. Notably, the CZ0.9T0.1 ceramic has a markedly increased Q × f while maintaining a good τf = −8.68 ppm °C−1 and a low sintering temperature of 700 °C.