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Refractory high entropy alloys have excellent high temperature mechanical properties， but the high temperature oxidation resistance has always been one of the limiting factors in their application. Four kinds of refractory high entropy alloys AlNbTaTiZr， AlMoNbTiZr， AlMoNbTaTiZr and AlMo0.5NbTa0.5TiZr were designed and prepared by laser additive manufacturing technology. The oxidation mass gain of AlNbTiZr-based refractory high entropy alloys was measured at 900 ℃ and 1000 ℃， and the oxidation layer structure of different samples was studied. The effects of Mo and Ta on the high temperature oxidation resistance of AlNbTiZr-based refractory high entropy alloys were compared and analyzed. The results show that the four kinds of as-deposited high entropy alloys prepared by laser additive manufacturing are BCC＋HCP dual-phase structures. The dendrites are mainly BCC phases with high melting points， and a small amount of HCP phase rich in Al and Zr is distributed among the dendrites. AlNbTaTiZr shows the best oxidation resistance after oxidation at 900 ℃ and 1000 ℃ for a long time， and Ta instead of Mo to some extent improves the oxidation resistance of refractory high entropy alloys.

Borates have emerged as a significant resource for exploring birefringent materials in the UV frequency region. The π‐conjugated planar anions, such as the [BO3], [B2O5], and [B3O6] units, exhibiting strong polarizability anisotropy, are traditionally good structural models. Both fluorination and hydroxylation have been proven effective strategies to modulate the optical properties of the planar anions. Controlling the ratio between F and OH is the key to realizing a balanced performance between birefringence and bandgap. Based on a fluorination mechanism proposed recently, a novel hydroxyfluorooxoborate (C3N2H5)B3O3F2(OH)2 with an optimal F/OH ratio of 1/1 is synthesized. During the synthesis, another strategy known as "cation activation" is also employed, which further increases birefringence by introducing active cation units. With its superior performance, this compound exhibits a short UV cutoff edge at 214 nm and a substantial birefringence of 0.205 at 546 nm, surpassing the commercial birefringent crystal α‐BBO (0.122@532 nm). The synergy between F/OH‐ratio optimization and cation activation offers a practical methodology for developing UV birefringent materials. [ABSTRACT FROM AUTHOR]

The substitution of fluorine atoms for oxygen atoms/hydroxyl groups has emerged as a promising strategy to enhance the physical and chemical properties of oxides/hydroxides in fluorine chemistry. However, distinguishing fluorine from oxygen/hydroxyl in the reaction products poses a significant challenge in existing characterization methods. In this study, we illustrate that terahertz (THz) spectroscopy provides a powerful tool for addressing this challenge. To this end, we investigated two fluorination reactions of boric acid, utilizing MHF2 (M=Na, C(NH2)3) as fluorine reagents. Through an interplay between THz spectroscopy and solid‐state density functional theory, we have conclusively demonstrated that fluorine atoms exclusively bind with the sp3‐boron but not with the sp2‐boron in the reaction products of Na[B(OH)3][B3O3F2(OH)2] (NaBOFH) and [C(NH2)3]2B3O3F4OH (GBF2). Based on this evidence, we have proposed a reaction pathway for the fluorinations under investigation, a process previously hindered due to structural ambiguity. This work represents a step forward in gaining a deeper understanding of the precise structures and reaction mechanisms involved in the fluorination of oxides/hydroxides, illuminated by the insights provided by THz spectroscopy. [ABSTRACT FROM AUTHOR]

In this study, the dynamic response and deformation mechanism of TiZrHfNb RHEA fabricated by laser directed energy deposition (L-DED) were researched under a dynamic compression test at a nominal strain rate of 3500 s−1. The L-DED TiZrHfNb alloy with columnar grains exhibits exceptional mechanical properties with a uniform dynamic flow stress of 1670 ± 10 MPa and a maximum plastic strain of 0.28 ± 0.03. The dislocation slipping and kinking behaviour dominate uniform plastic deformation. First, the dislocations are primarily confined within dislocation channels due to coplanar slip, and the evolution of them in dynamic compressive deformation process has undergone spacing refinement and crossing. Furthermore, the kinking behaviour induced by the lattice rotation with the T = <011> axis denotes the work hardening effect. Particularly, the second kinking behaviour effectively relieves local stress concentration and delays fracture before the formation of adiabatic shear band (ASB). [ABSTRACT FROM AUTHOR]

Although an increasing amount of attention is being paid to how human activities alter plant communities, little is known about the consequences of these changes on species' assemblages and biodiversity patterns. Using three forest types (a Pinus yunnanensis man-made forest; Eucalyptus smithii man-made forest; and natural secondary forest) in mid-Yunnan, China, we investigated the distribution patterns of species and traits and analyzed diversity patterns and relationships, including those between species diversity, functional diversity, and soil microbial diversity. We found that species co-occurrence patterns in the Pinus yunnanensis man-made forest and natural secondary forest were non-random. The specific leaf area in the Eucalyptus smithii man-made forest and leaf nitrogen concentration in the Pinus yunnanensis man-made forest were both over-dispersed according to the mean Euclidean neighbor distance in the trait space. The natural secondary forest had higher values of species diversity, functional diversity, community-weighted means, and soil microbial diversity than the man-made forest types did. An overall low covariation between species diversity and community-weighted means suggested that the coexistence of many species does not necessarily support functional differentiation among these species. Variance partitioning revealed that soil microbial diversity was mainly regulated by community-weighted means. In conclusion, our results suggest that the naturally recovering forest was better than man-made plantations based on biodiversity patterns. [ABSTRACT FROM AUTHOR]