First-principle Study Of The Solution And Diffusion Behavior Of The Interstitial Atom In Substitutional Solid Solutions

Point defects, such as interstitial atoms, are inevitable in materials. Thethermodynamic behavior of the interstitials, especially the solution and diffusion, hasgreatly changed the physical and mechanical properties of the materials. Now, manyfunctional materials such as Snoek-type high damping materials have been developedbased on these point defects.The addition of the alloying elements may result in complex interactions betweeninterstitial and substitutional atoms, and the interactions influence the alloy propertiesto a marked degree. The intrinsic interaction consists of elastic interaction caused bythe misfit of the different atomic sizes and chemical interaction caused by the changeof the electronic structure results. However, how the alloying elements influence thebehavior of the interstitials is not clear yet. In this paper we carried out a firstprinciple study in substitutional solid solution Nb-Cr-O system to explore theinfluence of substitutional elements on the behaviors of interstitial atoms.According to the results, the changes of the solution enthalpy and diffusion barriercan be decomposed into two contributions: the volume contribution due to the elasticinteraction and chemical contribution due to the chemical interaction. Both of the twocontributions varied with the concentration of substitutional Cr. When theconcentration of Cr was low, the change of the interstice volume hindered thedissolving and diffusion of the oxygen atoms, while the dissolving and diffusionwere promoted by the chemical interaction, which was predominate over theinhibition, therefore, the oxygen atoms were much easier to dissolve and diffuse whenthe alloying Cr were added into the matrix Nb. When the concentration ofsubstitutional Cr was high, both the elastic and chemical interaction hindered thedissolving and diffusion of the interstitial Cr, eventually the solution enthalpy of theoxygen and its diffusion barrier increased a lot.The elastic and chemical interactions have been separated successfully using thismethod and the influence on the solution enthalpy and diffusion barrier can bemeasured. This method can be used in many other systems with interstitials, which isvery useful in alloy design.