Perovskite materials are considered to be promising electrolyte membrane candidates for electrochemical applications owing to their excellent proton- or oxide-ion-conducting properties. RbBiNb₂O₇ is a double-layered Dion–Jacobson perovskite oxide, with Pmc2₁ symmetry. In this study, the electronic structure and proton-diffusion properties of bulk RbBiNb₂O₇ were systematically investigated using first-principles calculations. The unique layered crystal structure of RbBiNb₂O₇ plays a crucial role in proton storage and proton conductivity. Different proton-diffusion steps in RbBiNb₂O₇ were considered, and the activation energies of the relevant diffusion steps were evaluated using the climbing image-nudged elastic band (CI-NEB) technique. The proton diffusion in RbBiNb₂O₇ presents a two-dimensional layered characteristic in the a-b plane, owing to its layered crystalline nature. According to the transition state calculations, our results show that the bulk RbBiNb₂O₇ exhibits good proton-transport behavior in the a-b plane, which is better than many perovskite oxides, such as CaTiO₃, CaZrO₃, and SrZrO₃. The proton diffusion in the Rb–O and Nb–O layers is isolated by a higher energy barrier of 0.86 eV. The strong octahedral tilting in RbBiNb₂O₇ would promote proton transport. Our study reveals the microscopic mechanisms of proton conductivity in Dion–Jacobson structured RbBiNb₂O₇, and provides theoretical evidence for its potential application as an electrolyte in solid oxide fuel cells (SOFCs).

Non-diffracting beams play crucial roles in the field of free-space optical communication due to their robust resistance to distortion in atmospheric turbulence. As a non-diffracting beam characterized by multiple parameters, the Tricomi beam exhibits great versatility and adjustability, attracting considerable interest recently. In this paper, we study the propagation properties of Tricomi beam in atmospheric turbulence based on the theory of random phase screen. It is found that the performance of Tricomi beam in atmospheric turbulence shows strong dependence on its asymmetric constants, topological charge, and half-cone angle. Meanwhile, the Tricomi beam manifests superior resistance to distortion and spatial mode stability in contrast to the conventional non-diffracting Bessel beam. Our work provides a valuable theoretical foundation for the design and performance optimization of next-generation free-space optical communication systems, potentially enabling enhanced data transmission fidelity over long atmospheric paths.

In this study, we systematically investigated the piezoelectric and carrier transport properties of two-dimensional (2D) Bi-based chalcohalide monolayers (BiXY, X = Se, Te; Y = Br, I) using first-principles calculations. The phonon dispersion and elastic properties proved that BiXY monolayers are dynamically and mechanically stable. Our results reveal that the stereochemically active 6s² lone-pair electrons of Bi³⁺ play a crucial role in determining the structural and electronic characteristics of these systems. The simultaneous enhancement of Born effective charges and the strong sensitivity of atomic positions to external strain give rise to pronounced piezoelectric responses in BiXY monolayers. Specifically, the calculated piezoelectric coefficients (d₁₁) reached 13.16 and 17.76 pm/V for BiSeBr and BiSeI, respectively. The carrier transport properties were estimated using the deformation potential (DP) theory, which yielded upper-bound values under idealized conditions. For instance, in BiTeBr, the effective masses of electrons and holes were 0.15 and 0.40 m₀, respectively, leading to high carrier mobilities of 2736.1 and 2689.9 cm² V⁻¹ s⁻¹. These findings highlight the potential of Bi-based chalcohalide monolayers as promising candidates for next-generation multi-functional nanoelectronic and piezoelectric devices.