First-principles calculations of the structural stability and magnetic property of the metastable phases in the equilibrium immiscible Co–Au system

Abstract

To reveal the energetic sequence of the alloy phases in the Co-Au system, the lattice constants, cohesive energies, and bulk modulus of the fcc Au, hcp Co, the B1, B2, and L1(0) structured CoAu phases, and the D0(3), L1(2), and D0(19) structured Co(3)Au and CoAu(3) phases, respectively, are acquired by first-principles calculations within the generalized-gradient approximation (GGA) as well as within the local density approximation (LDA). In addition, the magnetic moment of the Co atom in the studied phases are also calculated. To further examine the structural stability, the elastic constants of the studied phases are calculated and the results suggest that the fcc-type structures could be elastically stable at Co/Au = 1:3, 1:1, and 3:1, whereas the hcp-type structures could be stable at Co/Au = 1:3 and 3:1. Moreover, the spatial valence charge density (SVCD) and spin density of the studied phases are also calculated to clarify the physical origin of the structural stability. It turns out that, in the relatively stable phases, the high SVCDs mostly distribute between the similar atoms, thus forming the attractive covalent bonding to stabilize the respective structures, and that the spin density may also play an important role in influencing the stability of the ferromagnetic metastable phases.

Au1Co1 Alloy Supported on Graphene Oxide with Enhanced Performance for Ambient Electrolysis of Nitrogen to Ammonia

“…04-0784), However, the (200) peak was wider than that of monometallic Au and had a slight shift to smaller values of 2θ as the content of Co increased (Figure S4), which further confirmed that the element Co was introduced into the Au structure, and it was possible to form alloyed intermetallic compounds when the particle was on the nanoscale and the atomic ratio of Au/Co was 1:1. 35,36 The XPS full survey of Au 1 Co 1 @GO shown in Figure 2b exhibited the presence of relevant elements. Concretely, Figure 2c shows that the Au XPS spectrum could be deconvoluted to two satellites.…”

Optimized Synthesis and Magnetic Properties of Intermetallic Au3Fe1−x, Au3Co1−x, and Au3Ni1−x Nanoparticles

“…Borohydride reduction of metal salts contained within dendrimer templates generated Au−Ni alloy nanoparticles, and chemically synthesized Au−Ni alloy nanoparticles were used as precursors to Au-NiO/SiO 2 catalysts for CO oxidation . Computational studies have identified L 1 2 -type intermetallic Au 3 Co as having interesting magnetic properties, , and Au−Co alloys have been successfully prepared using ion beam manipulation and coevaporation methods. , Recently, paramagnetic Au/Co bimetallic nanoparticles have been synthesized by reducing gold(III) chloride in the presence of premade Co nanoparticles . Despite these reports, it remains a significant challenge to generate bulk-scale quantities of nonequilibrium intermetallics in the Au−Fe, Au−Co, and Au−Ni systems.…”

Nanoscale Effects on Phase Separation

“…Marbella et al produced intermixed AuCo nanoalloys of diameters in the range 2–3 nm by coreduction in aqueous medium. Even the chemical synthesis of Au 3 Co intermetallics ( L 1 2 ordered phase) has been achieved. , These ordered phase were predicted to be metastable in bulk AuCo crystals. , On the other hand, several groups have been able to synthesize Co@Au phase-separated nanoparticles, both by wet chemistry methods , and by gas-phase growth. − Finally, also the inverted core–shell Au@Co structures have been obtained, ,, which were however shown to be metastable upon annealing . At least in some cases, the nanoparticle structures were strongly influenced by Co oxidation …”

“…7,8 These ordered phase were predicted to be metastable in bulk AuCo crystals. 9,10 On the other hand, several groups have been able to synthesize Co@Au phase- separated nanoparticles, both by wet chemistry methods 11,12 and by gas-phase growth. 13−15 Finally, also the inverted core− shell Au@Co structures have been obtained, 13,16,17 which were however shown to be metastable upon annealing.…”