2D tetragonal transition-metal phosphides: an ideal platform to screen metal shrouded crystals for multifunctional...

Two-dimensional (2D) metal shrouded crystals, a new kind of conceptional material, have attracted remarkable attention due to their unique properties. Here, we propose a novel class of 2D metal shrouded materials, tetragonal transition-metal phosphides (TM₂Ps), which show peculiar features of coexistence of in-plane TM-P covalent bonds and TM-TM interlayer metallic bonds. From a combination of high throughput searching and first-principles calculations, Fe₂P, Co₂P, Ni₂P, Ru₂P, and Pd₂P monolayer sheets stand out because they simultaneously have high thermal, dynamical, and mechanical stability. All these five TM₂P materials are metals, especially Pd₂P, which can be a promising catalyst for the hydrogen evolution reaction with a very low overpotential. Moreover, these 2D TM₂Ps show good ductility since they can withstand a tensile strain of up to 45%. Even in the large strain range, the strengthened interlayer TM-TM metallic bonds dominate the deformation behavior, and the corresponding metallicity of 2D TM₂Ps is well preserved. Due to the competition between the d-d direct exchange and d-p-d superexchange interactions, Fe₂P behaves as an antiferromagnetic material with a T_N of 23 K, while Co₂P is a ferromagnetic material with a T_C of 580 K. Our results not only enrich the database of 2D metal shrouded crystals, but also provide novel 2D materials as promising candidates for multifunctional applications in nanoelectronics, spintronics and electrocatalysis.