Composition-structure-property relationships in CeZr1·14Bi0.045A0.045Mo4·5O18 (A = Nb, Ta and Sb) microwave dielectric ceramics revealed by Raman, far-infrared and terahertz spectra

Abstract

Understanding composition-structure-property relationships is critical to developments and applications of novel microwave dielectric ceramics used in the field of wireless communications. Herein, a series of CeZr1·14Bi0.045A0.045Mo4·5O18 (abbreviated as CZA, A = Nb, Ta and Sb) ceramics were prepared through a solid-state reaction method. Density and scanning electron microscope results revealed dense and homogeneous microstructures. X-ray diffraction analysis indicated the formation of solid solutions. Accordingly, the effects of extrinsic factors were negligible and thus composition-structure-property relationships were systematically investigated by the combination of the chemical bond theory, Raman spectroscopy, far-infrared (FIR) spectroscopy and terahertz time-domain spectroscopy (THz-TDS) from an intrinsic perspective. Interestingly, the measured dielectric constants (εr) and quality factors (Q × f) are quite close to the extrapolated values from FIR and THz-TDS, and these values show a similar trend with varying components. In addition, Mo–O bonds play an important role in the coefficient of thermal expansion (α) and bond energy (E), and the composition dependent temperature coefficient of the resonance frequency (τf) can be well explained by variations of mean α and E of Mo–O bonds. Typically, excellent properties of Q × f = 116,485 GHz (at 9.58 GHz), εr = 9.91 and τf = −19.20 ppm °C−1 were achieved for the CZSb ceramic sintered at 700 °C. Notably, Q × f values of CZSb and CZTa ceramics are 6.13 and 4.16 times larger than that of the matrix, respectively. Ultra-high Q × f, low sintering temperatures (600 − 700 °C) and low εr make them potential candidates for low temperature co-fired ceramics (LTCC) applications.