Yanling Zhuang,Quan Zong,Yuanzhe Wu,Chaofeng Liu,Qilong Zhang,Daiwen Tao,Jingji Zhang,Jiangying Wang,Guozhong Cao
The electrochemical properties of vanadium-based materials as cathode materials for aqueous zinc ion batteries are still restricted by low conductivity, sluggish reaction kinetics, and poor structural stability. Herein, the [VO 6 ] octahedron, as the basic unit of vanadium-oxide layer of ammonium vanadates (NH 4 V 4 O 10 , denoted as NVO), is incorporated by F atoms to regulate the coordinated environment of vanadium. Density functional theory (DFT) calculations and experimental results show that both physicochemical and electrochemical properties of NVO are improved by F-doping. The enhanced electronic conductivity accelerates the electron transfer and the expanded interlayer spacing expedites the diffusion kinetics of zinc ions. As a result, the F-doped NVO (F-NVO) electrode shows a high discharge capacity (465 mAh g −1 at 0.1 A g −1 ), good rate capability (260 mAh g −1 at 5 A g −1 ), and long-term cycling stability (88% capacity retention over 2000 cycles at 4 A g −1 ). The reaction kinetics and energy storage mechanism of F-NVO are further validated by in situ and ex situ characterizations.
Donglei Wei,Jingyi Fang,Jiuhui Bian,Xifeng Yang,Yushen Liu,Bo Ram Lee
Transition metal perovskite oxide is one of the most important functional materials for applications in light energy conversion due to the distinctive structures and characteristics. This work reports self-activated luminescence of Ba 3 WVO 8.5 , a hybrid hexagonal perovskite. Ba 3 WVO 8.5 acts as an indirect allowed transition, with a band gap energy of 3.2 eV. At 300 K, it exhibits a broad self-activated luminescence band peaking at 527 nm, with a decay lifetime of 0.09 μs. There are two distinct intrinsic centers, WO 6 and VO 6 , in the lattices that contribute to the self-activated luminescence. The photoluminescence (PL) and temperature-dependent spectra confirm the energy transfer process from WO 6 to VO 6 centers. The cation substitutions in Ba 3 WVO 8.5 can exert obvious effect on the luminescence efficiency. Especially, the substitution of Ba 2+ by Sr 2+ +Ca 2+ significantly enhances its self-activated luminescence. The maximum quantum efficiency (QE) in Ba 2.7 Sr 0.15 Ca 0.15 WVO 8.5 can reach up to 34 %. Moreover, Ba 3 WVO 8.5 exhibits scintillation characteristics under X-ray irradiation. Its emission efficiency is still significantly lower than that of the commercial Bi 4 Ge 3 O 12 scintillator, but Ba 3 WVO 8.5 shows advantages in QE under UV excitation and in fast decay lifetime. The experimental results may play a valuable role in the development of new luminescent materials and further understanding of the hybrid hexagonal perovskite oxides.
With the increasing significance of the laser industry, especially in the 3–5 μm range, mid-infrared (mid-IR) nonlinear optical (NLO) crystals have become crucial components to meet stringent requirements. Herein, a large birefringence is essential for a mid-IR NLO crystal, as it ensures the phase-matching condition for high-conversion efficiency in laser output operation. In this study, three vanadium selenites A(VO2)3(SeO3)2 (A = NH4+, K+, and H3O+) with hexagonal tungsten oxide-related structures were prepared, featuring two-dimensional layered structures composed of two second-order Jahn–Teller (SOJT) motifs: distorted VO6 octahedra and SeO3 pyramids. Owing to the highly anisotropic VO6 octahedra and SeO3 pyramids, the family of A(VO2)3(SeO3)2 (A = NH4+, K+, and H3O+) crystals shows significant birefringence, which represents the highest birefringence value among vanadium selenites, even surpassing some SOJT-cation-based oxides. In addition, the title crystals exhibit large second harmonic generation responses of powder of 0.28–0.58 × AgGaS2 (AGS) at 2.09 μm.
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