We fabricated NiO nanorings on SiC, a novel hierarchical architecture, by a facile two-step method. The dielectric properties depend on temperature and frequency in the range from 373 to 773 K and X band. The imaginary part and loss tangent increase more than four times and three times with increasing temperature, respectively. The architecture demonstrates multirelaxation and possesses high-efficient absorption. The reflection loss exceeds -40 dB and the bandwidth covers 85% of X band (approximately -20 dB). The synergistic effect between multirelaxation and conductance is beneficial to the microwave absorption. Our findings provide a novel and feasible strategy to tune microwave absorption.

Dielectric properties and weight are two key factors that can signifi cantly infl uence the practical applications of electromagnetic (EM)-wave absorbing materials, which have been widely applied in civil, commercial, military, and aerospace vehicles in service in extreme environments. [1][2][3][4] In addition, to use them in high temperatures, these materials should also have good thermal stability. Among many EM-wave absorbing materials, although silicon carbide (SiC) is has a good thermal stability, [5][6][7] its dielectric properties are poor due to single polarization and low conductivity, limiting its practical applications greatly. Therefore, the development of multiple polarizations and improvement of the conductivity of SiC is very important to enhance its dielectric properties and thereby increase its practical applications. [ 8 ] It has been reported that many methods can be employed to enhance dielectric properties of EM-wave absorbing materials. [ 7,9 ] For instance, decorating composite materials with nanocrystals is an effi cient route. On the basis of this route, we design a facile and novel strategy to improve the dielectric properties of SiC by assembling NiO nanorings on the surfaces of SiC powders, as shown in Scheme 1 a. The NiO nanorings induce interfacial polarization between the nanocrystals and the substrate, and excite hopping charges, which lead to enhanced dielectric properties and excellent microwave absorption of the SiC powders.NiO is a p -type semiconductor with a wide bandgap ranging from 3.6 to 4.0 eV, [ 10 ] and has drawn much attention in potential applications of p -type transparent fi lms, [ 11 ] gas sensing devices, [ 12,13 ] pollutant clean-up catalysts, [ 9 ] dye-sensitized solar cells, and solid oxide fuel cells (SOFCs), [ 14,15 ] due to its electronic, optical, and catalytic properties. Besides this, NiO is a kind of high-permittivity dielectric material, which has been intensively studied for use in important microelectronic devices such as capacitors and memory devices. [ 16,17 ] Furthermore, NiO may signifi cantly improve the dielectric properties of EM-wave absorbing materials owing to its high permittivity, oxidation resistance, and electronic properties.In this work, we successfully cover ring-like NiO nanoparticles on the surfaces of SiC powders (NiO@SiC) by chemical deposition and oxidation. The dielectric properties of the fabricated NiO@SiC are systemically investigated in the temperature range from 373 to 773 K at frequencies of 8.2-12.4 GHz (X-band). The results show that the imaginary permittivity and loss tangent of NiO@SiC have been increased more than three times at 673 K compared to those of pure SiC. The refl ection loss R L peak of NiO@SiC can reach -46.9 dB at 673 K and is 330% lower than that of pure SiC, showing that NiO@SiC have excellent microwave absorption in the investigated temperature region.Pure SiC powders are of irregular shape in the range from several hundreds nanometers to several micrometers. In order to improve the microwave absorptio...

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Dryopteris fragrans (L.) Schott is a fern growing on the surface of hot rocks and lava. It is exposed to sunlight directly and bears local hot environment. We sequenced the complete nucleotide sequence of its chloroplast (cp) genome. The cp genome was 151,978 bp in length, consisting of a large single-copy region (85,332 bp), a small single-copy region (31,947 bp) and a pair of inverted repeats (17,314 bp). The cp genome contained 112 genes and 345 RNA editing sites in protein-coding genes. Simple sequence repeats (SSRs) and long repeat structure pairs (30–55 bp) were identified. The number and percent of repeat structures are extremely high in ferns. Thermal denaturation experiments showed its cp genome to have numerous, dispersed and high GC percent repeat structures, which conferred the strongest thermal stability. This repeat-heavy genome may provide the molecular basis of how D. fragrans cp survives its hot environment.