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1. Naturally occurring van der Waals heterostructure lengenbachite with strong in-plane structural and optical anisotropy

   https://doi.org/10.1038/s41699-021-00271-8  

   Dasgupta, Arindam; Yang, Xiaodong; Gao, Jie (November 2021, npj 2D Materials and Applications)

   Abstract Lengenbachite is a naturally occurring layered mineral formed with alternating stacks of two constituent PbS-like and M₂S₃-like two-dimensional (2D) material layers due to the phase segregation process during the formation. Here, we demonstrate to achieve van der Waals (vdW) heterostructures of lengenbachite down to a few layer-pair thickness by mechanical exfoliation of bulk lengenbachite mineral. The incommensurability between the constituent isotropic 2D material layers makes the formed vdW heterostructure exhibit strong in-plane structural anisotropy, which leads to highly anisotropic optical responses in lengenbachite thin flakes, including anisotropic Raman scattering, linear dichroism, and anisotropic third-harmonic generation. Moreover, we exploit the nonlinear optical anisotropy for polarization-dependent intensity modulation of the converted third-harmonic optical vortices. Our study establishes lengenbachite as a new natural vdW heterostructure-based 2D material with unique optical properties for realizing anisotropic optical devices for photonic integrated circuits and optical information processing. 

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2. Fluorides of Silver Under Large Compression**

   https://doi.org/10.1002/chem.202100028  

   Kurzydłowski, Dominik; Derzsi, Mariana; Zurek, Eva; Grochala, Wojciech (February 2021, Chemistry – A European Journal)

   Abstract The silver‐fluorine phase diagram has been scrutinized as a function of external pressure using theoretical methods. Our results indicate that two novel stoichiometries containing Ag⁺and Ag²⁺cations (Ag₃F₄and Ag₂F₃) are thermodynamically stable at ambient and low pressure. Both are computed to be magnetic semiconductors under ambient pressure conditions. For Ag₂F₅, containing both Ag²⁺and Ag³⁺, we find that strong 1D antiferromagnetic coupling is retained throughout the pressure‐induced phase transition sequence up to 65 GPa. Our calculations show that throughout the entire pressure range of their stability the mixed‐valence fluorides preserve a finite band gap at the Fermi level. We also confirm the possibility of synthesizing AgF₄as a paramagnetic compound at high pressure. Our results indicate that this compound is metallic in its thermodynamic stability region. Finally, we present general considerations on the thermodynamic stability of mixed‐valence compounds of silver at high pressure. 

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3. High-entropy engineering of the crystal and electronic structures in a Dirac material

   https://doi.org/10.1038/s41467-024-47781-9  

   Laha, Antu; Yoshida, Suguru; Marques dos Santos Vieira, Francisco; Yi, Hemian; Lee, Seng Huat; Ayyagari, Sai Venkata Gayathri; Guan, Yingdong; Min, Lujin; Gonzalez Jimenez, Jose; Miao, Leixin; et al (April 2024, Nature Communications)

   Abstract Dirac and Weyl semimetals are a central topic of contemporary condensed matter physics, and the discovery of new compounds with Dirac/Weyl electronic states is crucial to the advancement of topological materials and quantum technologies. Here we show a widely applicable strategy that uses high configuration entropy to engineer relativistic electronic states. We take theAMnSb₂(A= Ba, Sr, Ca, Eu, and Yb) Dirac material family as an example and demonstrate that mixing of Ba, Sr, Ca, Eu and Yb at theAsite generates the compound (Ba_0.38Sr_0.14Ca_0.16Eu_0.16Yb_0.16)MnSb₂(denoted asA⁵MnSb₂), giving access to a polar structure with a space group that is not present in any of the parent compounds.A⁵MnSb₂is an entropy-stabilized phase that preserves its linear band dispersion despite considerable lattice disorder. Although bothA⁵MnSb₂andAMnSb₂have quasi-two-dimensional crystal structures, the two-dimensional Dirac states in the pristineAMnSb₂evolve into a highly anisotropic quasi-three-dimensional Dirac state triggered by local structure distortions in the high-entropy phase, which is revealed by Shubnikov–de Haas oscillations measurements. 

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4. Natural 2D layered mineral cannizzarite with anisotropic optical responses

   https://doi.org/10.1038/s41598-022-14046-8  

   Dasgupta, Arindam; Yang, Xiaodong; Gao, Jie (June 2022, Scientific Reports)

   Abstract Cannizzarite is a naturally occurring mineral formed by van der Waals (vdW) stacking of alternating layers of PbS-like and Bi₂S₃-like two-dimensional (2D) materials. Although the PbS-type and Bi₂S₃-type 2D material layers are structurally isotropic individually, the forced commensuration between these two types of layers while forming the heterostructure of cannizzarite induces strong structural anisotropy. Here we demonstrate the mechanical exfoliation of natural cannizzarite mineral to obtain thin vdW heterostructures of PbS-type and Bi₂S₃-type atomic layers. The structural anisotropy induced anisotropic optical properties of thin cannizzarite flakes are explored through angle-resolved polarized Raman scattering, linear dichroism, and polarization-dependent anisotropic third-harmonic generation. Our study establishes cannizzarite as a new natural vdW heterostructure-based 2D material with highly anisotropic optical properties for realizing polarization-sensitive linear and nonlinear photonic devices for future on-chip optical computing and optical information processing. 

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5. A Self‐Healing, Flowable, Yet Solid Electrolyte Suppresses Li‐Metal Morphological Instabilities

   https://doi.org/10.1002/adma.202406315  

   He, Yubin; Wang, Chunyang; Lin, Ruoqian; Hu, Enyuan; Trask, Stephen E; Li, Ju; Xin, Huolin L (December 2024, Advanced Materials)

   Abstract Lithium metal (Li⁰) solid‐state batteries encounter implementation challenges due to dendrite formation, side reactions, and movement of the electrode–electrolyte interface in cycling. Notably, voids and cracks formed during battery fabrication/operation are hot spots for failure. Here, a self‐healing, flowable yet solid electrolyte composed of mobile ceramic crystals embedded in a reconfigurable polymer network is reported. This electrolyte can auto‐repair voids and cracks through a two‐step self‐healing process that occurs at a fast rate of 5.6 µm h⁻¹. A dynamical phase diagram is generated, showing the material can switch between liquid and solid forms in response to external strain rates. The flowability of the electrolyte allows it to accommodate the electrode volume change during Li⁰stripping. Simultaneously, the electrolyte maintains a solid form with high tensile strength (0.28 MPa), facilitating the regulation of mossy Li⁰deposition. The chemistries and kinetics are studied by operando synchrotron X‐ray and in situ transmission electron microscopy (TEM). Solid‐state NMR reveals a dual‐phase ion conduction pathway and rapid Li⁺diffusion through the stable polymer‐ceramic interphase. This designed electrolyte exhibits extended cycling life in Li⁰–Li⁰cells, reaching 12 000 h at 0.2 mA cm⁻²and 5000 h at 0.5 mA cm⁻². Furthermore, owing to its high critical current density of 9 mA cm⁻², the Li⁰–LiNi_0.8Mn_0.1Co_0.1O₂(NMC811) full cell demonstrates stable cycling at 5 mA cm⁻²for 1100 cycles, retaining 88% of its capacity, even under near‐zero stack pressure conditions. 

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