High- <i>Q</i> enstatite microwave/terahertz dielectric ceramics modulated by phase transition and lattice distortion
Yutian Lu, Weijia Guo, Chongyang Zhang, Hui Zhang, Zhenxing Yue
Abstract
The rapid development of fifth-/sixth-generation telecommunication technologies has increased the demand for silicate ceramic materials with low permittivity and low dielectric loss. However, few silicate ceramics with ultrahigh <i>Q</i>×<i>f</i> values (≥ 200,000 GHz) have been developed to date. In this study, a slight substitution of Ge<sup>4+</sup> ions in MgSi<sub>1−<i>x</i></sub>Ge<sub><i>x</i></sub>O<sub>3</sub> (MSG<i>x</i>, <i>x</i> = 0 to 0.6) ceramics caused a phase transition from clinoenstatite (<i>x</i> = 0) to orthoenstatite (<i>x</i> = 0.2), and the <i>Q</i>×<i>f </i>value increased from 70,600 GHz to 148,800 GHz. Following the phase transition, the cations change from a “compressed” state to a “rattle” state, and the lattice distortion continues to rise with <i>x</i>, resulting in the optimal microwave dielectric properties (<i>ε</i><sub>r</sub> = 7.21, <i>Q</i>×<i>f </i>= 259,300 GHz) of the MgSi<sub>0.5</sub>Ge<sub>0.5</sub>O<sub>3</sub> ceramics. Significant discrepancies in the dielectric properties are found in the microwave and terahertz bands. There is an anomalous increase in <i>ε</i><sub>r</sub> and a decrease in the <i>Q</i>×<i>f </i>value in the terahertz band, which is due to the change in polar phonon modes revealed by the terahertz time-domain spectra. Consequently, MgSi<sub>0.7</sub>Ge<sub>0.3</sub>O<sub>3</sub> ceramics display superior dielectric properties, with <i>ε</i><sub>r</sub> = 7.02, <i>Q</i>×<i>f </i> = 191,300 GHz in the terahertz band. These novel materials have the potential to serve as promising dielectric materials for future microwave or terahertz mobile communication systems.