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Boron nitride nanotubes were prepared by ball milling and annealing method using boron oxide and ammonia as raw materials and iron or magnesium powder as catalyst. The effect of iron or magnesium content on morphology and yield of boron nitride nanotubes was studied. The results show that uniform fine boron nitride nanotubes can be obtained by annealing process when the precursor of boron oxide does not contain catalyst, but the yield is very low. Appropriate iron can play a good catalytic role, a large number of boron nitride nanotubes with uniform size can be obtained. With the increase of iron content, the productivity of the product decreases and the morphology of the annealed products changes from boron nitride nanotubes with uniform size to boron nitride nanotubes with uneven diameter and length. When the molar ratio of boron oxide and iron content reaches 1∶1, the productivity of the product increases and the morphology of them changes from smooth boron nitride nanotubes to coral-like boron nitride micro-nanostructures with a large number of boron nitride nanosheets growing vertically on the surface of boron nitride nanotubes, and the diameter of the product increases obviously. The change of magnesium content only affects the size, uniformity and productivity of the product, no effect on morphology was observed. Changes in morphology and yield of boron nitride nanotubes can be explained by gas-liquid-solid growth mechanism.

A bidirectional quasi-endfire patch antenna with a low elevation angle has promising applications for wireless communication systems that are vehicle-based, airborne, and shipborne. In this paper, the shortened patch resonators and open patch resonator are integrated to form a bidirectional quasi-endfire patch antenna with low elevation angle. The open patch resonator operates with a TM20 mode to realize bidirectional radiation. The two shortened patch resonators operate with a TM01 mode coupled with a TM20 mode to control the phase difference between them at a suitable angle, so that the shortened patch resonators act as directors to tilt the dual beams toward the endfire direction and achieve low elevation angle. Compared with reported patch antennas with dual beams, the proposed antenna has the lowest elevation angle and a compact structure. For demonstration purposes, an antenna prototype operating at 3.5 GHz is fabricated and measured, exhibiting a low elevation angle of ±28°, a −10 dB impedance matching bandwidth from 3.44 GHz to 3.61 GHz, and a size of 1.36 λ0 × 0.57 λ0 with a profile of 0.036 λ0. A prototype with two pair of shortened patch directors further reduces the elevation angle to ±19° with the size of 2.3 λ0 × 0.57 λ0. [ABSTRACT FROM AUTHOR]

NiO, an anodic electrochromic material, has applications in energy‐saving windows, intelligent displays, and military camouflage. However, its electrochromic mechanism and reasons for its performance degradation in alkaline aqueous electrolytes are complex and poorly understood, making it challenging to improve NiO thin films. We studied the phases and electrochemical characteristics of NiO films in different states (initial, colored, bleached and after 8000 cycles) and identified three main reasons for performance degradation. First, Ni(OH)2 is generated during electrochromic cycling and deposited on the NiO film surface, gradually yielding a NiO@Ni(OH)2 core–shell structure, isolating the internal NiO film from the electrolyte, and preventing ion transfer. Second, the core–shell structure causes the mode of electrical conduction to change from first‐ to second‐order conduction, reducing the efficiency of ion transfer to the surface Ni(OH)2 layer. Third, Ni(OH)2 and NiOOH, which have similar crystal structures but different b‐axis lattice parameters, are formed during electrochromic cycling, and large volume changes in the unit cell reduce the structural stability of the thin film. Finally, we clarified the mechanism of electrochromic performance degradation of NiO films in alkaline aqueous electrolytes and provide a route to activation of NiO films, which will promote the development of electrochromic technology. [ABSTRACT FROM AUTHOR]

Inorganic metal oxide electrochromic materials have good application prospects for energy‐saving windows in buildings and smart display applications. Therefore, the development of electrochromic films with good cycling stabilities, fast color‐change response times, and high coloring efficiencies has attracted considerable attention. In this study, nanoflake Li‐doped NiO electrochromic films were prepared using a hydrothermal method, and the films exhibited superior electrochromic performances in the LiOH electrolyte. Li+ ions doping increased the ion transmission rates of the NiO films, and effectively promoted the transportation of ions from the electrolyte into NiO films. Meanwhile, the nanoflake microstructure caused the NiO films to have larger specific surface areas, providing more active sites for electrochemical reactions. It was determined that the NiO‐Li20% film exhibited an ultra‐fast response in the LiOH electrolyte (coloring and bleaching times reached 3 and 1.5 s, respectively). Additionally, the coloration efficiency was 62.1 cm2 C−1, and good cycling stability was maintained beyond 1500 cycles. Finally, the simulation calculation results showed that Li doping weakened the adsorption strengths of the NiO films to OH−, which reduced the generation and decomposition of NiOOH and helped to improve the cycling stabilities of the films. Therefore, the research presented in this article provides a strategy for designing electrochromic materials in the future. [ABSTRACT FROM AUTHOR]