Shuyao Lin

Machine-learning interatomic potential (MLIP)-based molecular dynamics enables efficient exploration of mass-transport mechanisms in complex materials together with quantitative determination of diffusion coefficients at finite temperatures. Using an identical training dataset, we develop and assess three MLIP formalisms [moment tensor potentials (MTP), atomic cluster expansion (ACE), and message passing ACE (MACE)] and evaluate their transferability for diffusion simulations in hexagonal transition metal diborides. After benchmarking against 0 K ab initio migration energies and comparison of computational efficiency, the MTP model is employed to investigate boron-vacancy diffusion in α-TiB2, α-TaB2, and ω-WB2, representing group IV–VI transition metal diborides. Two distinct monovacancy diffusion pathways are identified within the puckered boron layer of ω-WB2 and analyzed as a function of temperature. The combined effects of strain and temperature on diffusivity are further examined, revealing a weak sensitivity to external stress under conditions relevant to high-temperature machining applications. Overall, nanosecond-scale finite-temperature simulations demonstrate the reliability and practical applicability of MLIPs for studying diffusion phenomena in complex ceramic materials.

This study uses machine-learning interatomic potentials (MLIP) and molecular dynamics to simulate nanoindentation on defective TiB ₂ . Results reveal that Ti-rich planar defects may preserve hardness of TiB ₂ , unlike boron vacancies.

Fundamentally understanding lattice dynamics and thermal transport behavior in liquid‐like, partially occupied compounds remains a long‐standing challenge in condensed matter physics. Here, the microscopic mechanisms are investigated underlying the ultralow thermal conductivity in ordered/liquid‐like Cu ₃ BiS ₃ by combining experimental methods with first‐principles calculations. The ordered structure and liquid‐like are first experimentally synthesized and characterized, partially Cu‐atom occupied Cu ₃ BiS ₃ structure with increasing temperature. Selfconsistent phonon calculations are then combined, including bubble‐diagram corrections, with the Wigner transport equation, considering both phonon propagation and diffuson contributions, to evaluate the anharmonic lattice dynamics and thermal conductivity in phase‐change Cu ₃ BiS ₃ . The theoretical model predicts an ultralow thermal conductivity of 0.34 W m ⁻¹ K ⁻¹ at 400 K, dominated by diffuson contributions, which accurately reproduces and explains the experimental data. Importantly, the machine‐learning‐based molecular dynamics (MD) simulations not only reproduced the partially Cu‐atom occupied Cu ₃ BiS ₃ structure with the space group Pnma but also successfully replicated the thermal conductivity obtained from experiments and Wigner transport calculations. This observation highlights the negligible impact of ionic mobility arising from partially occupied Cu sites on the thermal conductivity in diffuson‐dominated thermal transport compounds. This work sheds light on the minimal impact of ionic mobility on ultralow thermal conductivity in phase‐change materials. It demonstrates that the Wigner transport equation accurately describes thermal transport behavior in partially occupied phases with diffuson‐dominant thermal transport.

The layered character of transition metal diborides (TMB2:s)---with three structure polymorphs representing different stackings of the metallic sublattice---evokes the possibility of activating phase-transformation plasticity via mechanical shear strain. This is critical to overcome the most severe limitation of TMB2:s: their brittleness. To understand finite-temperature mechanical response of the α, ω, and γ polymorphs at the atomic scale, we train machine-learning interatomic potentials (MLIPs) for TMB2:s, TM=(Ti, Ta, W, Re). Validation against ab initio data set supports the MLIPs' capability to predict structural and elastic properties, as well as shear-induced slipping and phase transformations. Nanoscale molecular dynamics simulations (>104 atoms; ≈53 nm3) allow minimizing size effects, thus evaluating theoretical shear strengths attainable in single-crystal TMB2:s and their temperature evolution from 300 up to 1200 K. Quantitative structural analysis via angular and bond-order parameter descriptors shows that xz and yz shearing activates transformations between the (energetically) metastable and the preferred phase of TiB2, TaB2, and WB2. These transformations can be promoted by additional tensile or compressive strain along the [0001] axis. The preferred phase of ReB2 shows negative thermal expansion and an unprecedented shear-induced plasticity mechanism: metallic/boron layer interpenetration and uniform lattice rotation.

The comprehensive investigation of transport properties and thermoelectric performance of APV compounds within Ca₃XN family, which maintain promising thermoelectric properties in both high- and medium-T ranges, along with abnormal T-dependent κ_L.