Interface constitutes a significant volume fraction in nanocomposites , and it requires the ability to tune and tailor interfaces to tap the full potential of nanocomposites. However, the development and optimization of nanocomposites is currently restricted by the limited exploration and utilization of interfaces at different length scales. In this research, we have designed and introduced a relatively large-scale vertical interphase into carbon nanocomposites, in which the dielectric response and dispersion features in microwave frequency range are successfully adjusted. A remarkable relaxation process has been observed in vertical-interphase nanocomposites, showing sensitivity to both filler loading and the discrepancy in polarization ability across the interphase. Together with our analyses on dielectric spectra and the relaxation process, it is suggested that the intrinsic effect of vertical interphase lies in its ability to constrain and localize heterogeneous charges under external fields. Following this logic, systematic research is presented in this article affording to realize tunable frequency-dependent dielectric functionality by means of vertical interphase engineering. Overall, this study provides a novel method to utilize interfacial effects rationally. The research approach demonstrated here has great potential in developing microwave dielectric nanocomposites and devices with targeted or unique performance such as tunable broadband absorbers.
In this study, phosphorus enriched LiMgP 1+ x O 4 (0.00 ≤ x ≤ 0.04) ceramics were synthesized via the solid-state reaction route. The crystal and phase structure patterns were analyzed by the Rietveld refinement and Raman spectroscopy. The dielectric properties were obtained at both microwave and terahertz frequencies. Optimal microwave dielectric performance was obtained in LiMgP 1.01 O 4 , sintered at 875 °C for 4 h: ε r = 6.964, Q × f = 82,057 GHz, and τ f = −27.1 ppm/°C (at 15.361 GHz). Compared with the pure LiMgPO 4 ceramics sintered at 950 °C ( Q × f = 79,100 GHz and τ f = −55 ppm/°C), an appropriate amount of excessive P 5+ reduced the sintering temperature while improving the Q × f value and the thermal stability effectively. Within the terahertz frequency range of 0.2–1.2 THz, the ε r values were decreased to 5.40–6.65 while the tan δ values were ranged from 0.0039 to 0.1228. All experimental results suggested that the LiMgP 1+ x O 4 ceramics are promising for both microwave and terahertz frequency applications.
In this study, NaMg 1- x Mn x (PO 3 ) 3 (0.00 ≤ x ≤ 0.0625) ceramics with low dielectric constant were prepared via the solid-state reaction method. The effects of Mn 2+ substitution on the microstructure and dielectric properties (at microwave and terahertz frequencies) of the NaMg(PO 3 ) 3 ceramics were studied by means of the Rietveld refinement, morphology, and ionic polarizability analysis. It is obtained that the NaMg 0.0975 Mn 0.025 (PO 3 ) 3 ceramic sintered at 880 °C for 4 h exhibited optimal dielectric properties at microwave frequencies, where ε r = 4.585, Q × f = 48,313 GHz (@17.228 GHz), and τ f = −40.83 ppm/°C. The Q × f and τ f values were changed by 74.2 % and 27.8 %, as compared to the values of 27,728 GHz and −56.52 ppm/°C for the pure NaMg(PO 3 ) 3 ceramic, respectively. For terahertz frequencies (0.2–1.0 THz), the ε r values were decreased to 3.79–3.98, and the tan δ values were between 0.0203 and 0.1152. All the experimental results indicate that this system exhibits great potentials both at microwave and terahertz frequencies.
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