Sang Yoon Park

The electromagnetically induced transparency-like characteristics of asymmetric nickel-ferrite metamaterials through near-field coupling are investigated in the terahertz regime. The nickel-ferrite metamaterial consists of a cut wire resonator on the front side and a disk resonator at the back of the quartz substrate. The analog of electromagnetically induced transparency is characterized by employing a finite difference frequency domain technique. By designing the nickel-ferrite metamaterial to overcome Snoek’s limitation of ferrite materials in the THz spectral region, electromagnetically induced transparency-like spectral features with a high quality factor and slow-light effect are achieved. These results may provide an important way to understand the coupling mechanism and ferrite material application in slow-light devices, THz sensors, and tunable switching in THz frequency bands.

Flexible and rechargeable Zn–air batteries (ZAB) are promising candidates for attaining the high energy density required for next‐generation energy storage devices given their half‐open cathode configuration. However, the poor interfacial contact between the immobilized solid‐state electrolyte and porous cathode, and drying‐out of water in the electrolyte at low relative humidity (RH) of 30% or less, cause low performance and short lifespan. Herein, a novel hygroscopic dough‐type electrolyte with water‐absorbing and malleable free‐standing configuration originating from deliquescent KOH and severe gelation of sodium alginate (SA) by facile kneading is proposed. Because appropriate contents are required to absorb water from the atmosphere and obtain the manageable form of the dough used here, the materials composing the dough electrolyte, i.e., SA, water, and KOH, are precisely controlled to ensure high malleability, scalability, ionic conductivity, and good water retention capabilities. The optimized dough inhibits evaporation at low RH and lowers the interfacial resistance with the cathode via tight adhesion. The dough‐type ZABs show noteworthy maximum power density of 160 mW cm −2 with low catalyst mass loading (0.4 mg cm −2 ), specific capacity of 632 mAh g Zn −1 , and stability for 60 h at RH 30% and 120 h even at low temperature of −20 °C, producing reasonable output.

Owing to its applicability in refractory ceramic synthesis, nanoelectronics, optoelectronic and sensing devices, and superconducting products, magnesium oxide (MgO) is recognized to be an important ceramic material. However, it has a relatively low dielectric constant compared to other metal oxide semiconductors, which restricts the range of its bandgap and limits its applicability. Therefore, in this study, we propose and verify a method to improve the dielectric constant of MgO. A sample of MgO powder doped with Be ions was prepared using the Pechini method. The crystal structure of the doped MgO powder was analyzed by x-ray diffraction. Through structural analysis, it was confirmed that a substitution amount of up to 5% of Be ions was possible without breaking the cubic structure. The bonding structure in the lattice of the sample was identified through x-ray photoelectron spectroscopy, and the change in the bonding structure according to the amount of substitution was identified. The dielectric properties of the samples were analyzed as a function of frequency at room temperature. The real and imaginary parts of the dielectric constant were studied at room temperature as a function of frequency and composition. It was confirmed that the dielectric constant increased as the Be ions were substituted. Our results show that improving the low dielectric properties of pure MgO can enable its application to wide bandgap and high voltage applications simultaneously.