High entropy BaFe12-x(Ti/Mn/Ga/In)xO19 (x = 1–7) oxides: Correlation of the composition,entropy state,magnetic characteristics,and terahertz properties

The BaFe_12-x (Ti/Mn/Ga/In)_xO₁₉ (x = 1–7) high-entropy oxides (HEOs) were obtained by solid-phase synthesis. The correlation of the chemical composition (the level of the Fe replacement), structural parameters, magnetic characteristics, and terahertz (THz) properties was investigated. All studied samples were single-phase (SG: P6₃/mmc). Lattice parameters showed a monotonic increasing trend with an increase of (x). The key role in increasing the lattice parameters of HEOs may belong to the influence of In³⁺ ions, which are much larger in size than Fe³⁺ ions. As one of the possible reason for explanation of the lattice parameters behavior we hypothesized that partial charge transformation of the Mn³⁺ state to the Mn²⁺ state takes place in order to maintain electrical neutrality. Other cations (Ti/Ga/In) have stable oxidation state. The anisotropic nature of the increase in lattice parameters was demonstrated. No strong correlation between chemical composition and microstructural parameters of the investigated HEOs was observed. The magnetic characteristics of the BaFe_12-x (Ti/Mn/Ga/In)_xO₁₉ (x = 1–7) HEOs were investigated at broad intervals of magnetic fields and temperatures. The behavior of the magnetic characteristics was shown to be the result of the magnetic structure frustration. In addition, terahertz electrodynamic properties were studied by measuring spectra of complex dielectric permittivity at frequencies 0.2–1.2 THz in the temperature interval 20–300 K. The spectra indicate the presence of a higher-frequency infrared phonon resonance, whose damping decreases with cooling, as well as an excitation below 0.2 THz that freezes out at low temperatures, the origin of which is associated with the polycrystalline nature of the materials.     

THz dielectric properties of AlPO4-BPO4-SiO2 ternaries

0.05AlPO₄-0.05BPO₄-0.90SiO₂ glass-ceramic and glass-free 0.45AlPO₄-0.45BPO₄-0.10SiO₂ ceramic have been prepared by a solid-state reaction process and their terahertz (THz) dielectric responses were characterized by time-domain spectroscopy (TDS) techniques in the frequency range from 0.2 to 1.6 THz. Both samples demonstrate little dielectric dispersions in the (sub) THz frequency range, having dielectric permittivities (ε_r) of ∼3.35(7) and ∼4.06(8), respectively. The dielectric responses are dominated by the phonons and electronic polarizations in the (sub) THz frequency range. The contributions to the relative permittivities from electronic polarization ε_{r ∞} are 1.85(4) and 1.99(4), which are ∼55% and ∼49% of the total ε_r at THz frequencies, respectively_. The dielectric losses of both samples continuously increase with increasing frequency in the THz band, while the loss factor of glass-ceramic is one order of magnitude higher than that of glass-free ceramic. The glass-free sample exhibits extremely high Q×f values of 100,000–190,000 GHz in the THz band, being much higher than that of the glass-ceramic (∼7000–25,000 GHz).     

基于零偏置肖特基二极管的270 GHz高性能波导检波器

根据InP二极管的物理结构, 采用三维高频电磁仿真软件对其精确建模仿真, 获得二极管的物理模型和匹配电路的精确参数, 而后将此模型利用谐波平衡进行仿真设计.最后, 在此基础上采用InP肖特基二极管, 设计制作并测试了国内首款270GHz的零偏置检波器.检波器的最大电压响应度为1600V/W, 在260~280GHz范围内, 电压响应的典型值为1400V/W, 其对应的等效噪声功率典型值为18pW/Hz.实验结果与仿真结果比较吻合, 其结果表明, 设计方法较为精确, 具有设计简单、优化方便等优点.