Prediction of the ductility of B2 type yttrium-based intermetallic compounds

Using the first-principles pseudo-potential plane-wave CASTEP code, the electronic structures and the elastic constants of C₁₁, C₁₂, C₄₄ as well as the bulk modulus B₀ of yttrium-based intermetallic compounds, i.e., YX (X= Ag, Cu, In, Rh, were calculated. As comparing with the experimental and other theoretical results of YAg and YCu, a good agreement between this work and literatures has been found. Based on several empirical criterions, i.e., Pugh rule (the ratio of shear modulus to bulk modulus G/B₀), Cauchy pressure parameter C₁₂-C₄₄ and Poisson's ratio ν, the ductility or brittleness of these intermetallic compounds are characterized and analyzed. The experimental result of which YAg has a better ductility than YCu has been verified, and the order of ductility as follow YRh >YAg>YCu>YIn is also further predicted. The analysis of electronic structures of YX (X=Ag, Cu, In, Rh) indicates the good ductility of these intermetallic compounds originates from their strong metallic bonding. And it is found the discrepancy of ductility in these intermetallic compounds results from the different extent of hybridization between Y(d) and X(p) electrons. Because of In of YIn having the most p electrons relative to other X elements in YX intermetallic compounds, the strongest hybridization between Y(d)-X(p) electrons causes a high directionality of covalent bonding in YIn, and then its ductility is the lowest. For YRh intermetallic compound, its better ductility can attribute to a enhanced metallic bonding between Y(d) and Rh(d) electrons.