Theoretical investigation of thermal disorder in CuCo alloys

Abstract

In this work, we investigate thermal disorder in intermetallic CuCo alloys by extending the anharmonic correlated Einstein model in extended X-ray absorption fine structure (EXAFS) theory. The expressions of bond-stretching force constants, Einstein frequency and temperature, the atomic mean-square relative displacement characterizing the EXAFS Debye–Waller factor have been derived in terms of Morse potential parameters. We perform numerical calculations for CuCo alloys up to temperature 800 K to study the temperature effects on these thermodynamic quantities. Our research shows that Co–Co bonds are stiffer than Cu–Cu bonds. This leads to the atomic mean-square relative displacement curve of CuCo alloys is lower than the one of Cu metal, but higher than the one of bulk Co. The increasing of Co concentration in CuCo alloys will make the increasing of thermal disorder in the alloy system. Moreover, the dynamic disorder caused by thermal lattice vibrations gives significant contribution to the EXAFS Debye–Waller factor at high temperature.