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

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-beta(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(3)Pt and CoPt(3). L1(2)-Co(3)Pt 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. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3671992]