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It has been accepted that the uniform distribution of magnetic metal particles is beneficial to microwave absorption, while why the homogeneous magnetic particles on the dielectric substrate improve the electromagnetic loss is still unclear. Herein, metal Ni nanoparticles, two-dimensional (2D) basalt/scattered Ni, and basalt/uniform Ni microflakes are obtained through a pretreatment and electroless deposition process. In comparison to Ni nanoparticles and basalt/scattered Ni, the basalt/Ni microflakes with largely uniform and compact Ni nanolayers on basalt, breaking the percolation limit, are favorable for enhanced electromagnetic attenuation. The Ni nanolayers are convenient for construction of a microscale conductive net and migration of an electron. The 2D heterostructures constructed by basalt substrates and decorated Ni layers boost multiple scattering absorption and promote interfacial polarization. Meanwhile, exposed Ni does not inhibit magnetic resonance, enabling strong magnetic coupling. Consequently, the basalt/Ni microflakes with uniform Ni nanolayers demonstrate better microwave absorption with a minimum reflection loss of -30 dB and an effective absorption bandwidth of 3 GHz at 1 mm. This work shows that the uniform and compact magnetic metal nanolayers are effective in improving the dielectric loss and magnetic loss simultaneously to achieve the high-performance microwave absorption.

The heterostructure has attracted widespread attention in improving microwave absorption due to the unique composition and structure. Herein, a novel two-dimensional (2D) plate@shell basalt@NiO heterostructure is synthesized through a sequential process of water bath method followed by a sintered operation. The sintering temperature helps regulate the microwave absorption performance by controlling the heterogeneous interface and vacancy defects of basalt@NiO to optimize the dielectric loss. The RL of the prepared basalt@NiO with the sintering temperature of 300 °C reaches up to −15.93 dB at 16.13 GHz, which is attributed to the polarization loss enhanced by vacancy defects (O, Ni vacancies) introduced by low-temperature sintering and large heterogeneous contacts constructed by basalt and NiO. Meanwhile, the high concentration of vacancy defects also leads to a large electrical conductivity that positively contributes to dielectric loss. Furthermore, the basalt@NiO composite possesses relatively low density, high thermal stability and anticorrosion. This finding provides a way for designing the light microwave absorption materials with excellent environmental stability.

The earliest microwave absorbing materials (MAMs) are fabricated in the early 20th century for military purpose to inhibit radar detection. Currently, the application of MAMs has been existing in every part of human's life to prevent radiation and interference. The microwave absorbant and microwave absorbing coatings classified by composition including alloys, metal oxides, conductive polymers, carbon materials, ceramic materials both in traditional and innovative forms are introduced in this work. Considering the harsh and complex application environment, MAMs with high temperature resistance and infrared-compatible stealth performance are involved. Metamaterials, showing excellent electromagnetic properties which are far beyond that of the materials can achieve, including perfect absorber, digitally coded control metamaterials, bionic structural materials, and adjustable smart metamaterials, are also introduced specifically in this work. In addition, to investigate electromagnetic response of absorbant, the first-principles calculations works are overviewed. The electromagnetic properties, loss mechanisms, structure, fabrication method, regulation approaches, designing principles, current applications, and future prospects of MAMs are involved in this work. This work gives a comprehensively overview over the MAMs for their theoretical and experimental advances in recent years including the military radar (frequency range of 2–18 GHz) stealth materials, relevant infrared compatible (infrared-visible, infrared-radar, infrared-laser) stealth materials, and other stealth materials with multifrequency adaptability.

CL (cathodoluminescence) and FTIR (Fourier Transform Infrared) techniques have been used to study internal structure, variations of N abundance and aggregation states of diamonds collected from kimberlite pipe No.50, Fuxian, Liaoning province, China. Three kinds of internal structures can be recognized: (1) single stage of growth structure, (2) multi-stage of complex growth structure, and (3) rare agate-like structure. Most of diamonds exhibit complex growth histories recording processes in the lithosphere over the residence time of diamond. Three diamonds were cut and polished parallel to (110). Diamonds with bright blue CL have higher N contents whereas dark green or green-blue CL duplicated oscillatory zone has moderate N content. The aggregation states and nitrogen data across the plate indicate that the diamond Lc35 (0.26 ct., 3.2×3.6 mm) experienced at least four growth stages. Two resorptions and one abrupt were occurred between four stages. N content varies from 679 to 244 atom ppm in this diamond. The variation of N contents is irregularly from core to rim, and it is individuals within single growth stage. N concentrations decrease form earlier to later growth in third and fourth stages respectively. The sharp increase of N contents have been found at the boundaries between second and third stages and decrease at third and forth stages indicating the different environments occurred during crystallized period of diamond. In the earlier period (may be before 1.3 to 1.4Ga) the environment was relative unstable with rapid growth rate of diamond, whereas in the later period (after 1.3 to 1.4Ga) the environment was stable with slower growth rate of diamonds and enhanced fluid activity. The results of calculated t MR supported the longevity of diamonds over than a thousand million years at mantle lithosphere.

The CL images show that the internal structures of the diamonds in Wafangdian, Liaoning Province is classified as three types: simple growth girdle zone, multi-stage growth complex girdle zone, and rare agate-like structure. These internal features reflect the complexity of growth processes of the diamonds. The FTIR analyses in micro area on diamond plates reveal the heterogeneity of the impurities of nitrogen and hydrogen. The variety of nitrogen contents and nitrogen aggregation states have been revealed not only in different diamonds from one kimberlite pipe but also in different zones of one diamond. The extent of conversion A defects to the aggregated B form is a function of the nitrogen aggregation temperature (T NA), mantle residence time (t MR), and nitrogen concentration of diamond. The interval of 0.6–0.7Ga from core to rim of diamond growth is obtained by using the FTIR curves and some geological data. The long period of diamond growth is identical with the feature in CL image.