Nonequilibrium Solid Phase Formation Studied by Lattice Dynamics Calculation and Ion Beam Mixing in an Immiscible Co−Ag System

Abstract

For the equilibrium immiscible Co-Ag system, a proven realistic ab initio derived n-body potential is applied to study the nonequilibrium solid phase formation at three chemical stoichiometries of Co/Ag = 1:3, 1:1, and 3:1. To predict the structural stability, the elastic constants and the phonon spectra are calculated at the chosen stoichiometries with a total of eight hypothetical crystalline structures. The calculated results suggest that four compounds, that is, D0(3) CoAg3, B1 CoAg, B2 CoAg, and D0(3) Co3Ag, are unstable, as they all feature negative elastic constants as well as imaginary phonons, and that another four compounds of both fcc-type L1(2) and hcp-type D0(19) structures at chemical stoichiometries of Co/Ag = 1:3 and 3:1, respectively, may elastically be favored and therefore obtainable under some specific conditions. It is also found that all the calculated elastic constants and phonon spectra are coincident within the framework of the elastic theory. Moreover, the calculated elastic constants are in good agreement with those acquired directly from ab initio calculations, lending support to the validity of the ab initio derived n-body Co-Ag potential as well as its resultant elastic constants and the phonon spectra. Interestingly, some of the predicted nonequilibrium solid phases, that is, two hcp-type compounds at chemical stoichiometries of Co/Ag = 1:3 and 3:1, respectively, are indeed obtained in ion beam mixing experiments and their lattice constants determined by diffraction analysis are in good agreement with those from calculations.

Metastable Structures of Co and Co−Ag Detected in Electrodeposited Coatings

“…In the present study, using the electrodeposition technique it was possible to form an unusual CoAg 3 hcp phase (hP2) in the Co−Ag system (immiscible under equilibrium conditions) and in a wide range of compositions. This structure is similar to those found in silver base alloys, such as GaAg 3 , CeAg 3 , and NiAg 3 phases. ,, Furthermore, ab initio calculations confirmed that the presence of the corresponding metastable state in the Co−Ag system and the stability of the CoAg 3 hcp phase may have originated from its electronic structure. , CoAg 3 has been previously detected in multilayers obtained using electron beam evaporation and after irradiation of the sample with a specific fluence of ions …”

“…20,22,23 Furthermore, ab initio calculations confirmed that the presence of the corresponding metastable state in the Co-Ag system and the stability of the CoAg 3 hcp phase may have originated from its electronic structure. 24,25 CoAg 3 has been previously detected in multilayers obtained using electron beam evaporation and after irradiation of the sample with a specific fluence of ions. 26 The influence of temperature over the Co-Ag deposits was also studied.…”

Spherical granular structures of Ag/Co nanoparticles: Synthesis, characterization and magnetic properties

“…Much attention has been paid on the nanocrystalline alloys of noble-ferromagnetic immiscible metal systems such as Ag-Co, Ag-Fe and Ag-Ni, owing to their interesting physical properties and applications in magnetic recording, optical devices and sensors [1][2][3][4]. The formation of nanocrystalline alloys of immiscible metals can be achieved through non-conventional techniques such as sputtering, thermal evaporation, ion-beam mixing, laser ionization and electrodeposition [5][6][7][8].…”