Revealing low-temperature atomic ordering in bulk Co-Pt with the high-throughput ab-initio method

摘要

The low-temperature phase diagram of bulk Co-Pt is studied with a high-throughput ab-initio method. Global, hcp-, and fcc-restricted convex hulls are constructed to evaluate stable and metastable phases. It is found that fcc-L1_0 is energetically degenerate with hcp-B19. Both structures are unstable with respect to phase decomposition into hcp-D0_(19)↔fcc-β_2 at low temperature. Furthermore, L1_0 is an adaptive structure on the fcc-restricted convex hull which relates to the low energies of antiphase boundaries. Fcc-L1_2 is energetically degenerate with fcc-D0_(23) for both Co_3Pt and CoPt_3. L1_2-Co_3Pt and L1_0-CoPt belong to the fcc-restricted convex hull. They might stabilize above the Co hcp/fcc transition and remain kinetically frozen below. L1_2-CoPt_3 is energetically well above the convex hull. Its experimental observation may result from yet unexplained finite-temperature effects.