Stabilization of the Ti₃Co₅B₂-type structure for Ti_3-xSi_xRu₅B₂ through Si-Ti substitution

Abstract We report a route for designing and synthesizing Ti₃Co₅B₂-type compounds in the Ti-Ru-B system by using chemical substitution of Si for Ti to decrease the d-electron-based antibonding interactions that it is argued would otherwise drive an instability in this structure for unsubstituted Ti₃Ru₅B₂. Ti_3-xSi_xRu₅B₂ with x=0.75, 1.00 and 1.25 nominal compositions crystalizes in the Ti₃Co₅B₂ structure type using arc melting methods, whereas at lower doping levels (x=0.0, 0.25 and 0.50) the more complex Zn₁₁Rh₁₈B₈-type structure is stable. Electronic structure calculations show that in hypothetical, unsubstituted Ti₃Ru₅B₂ with the Ti₃Co₅B₂-type structure, the antibonding interactions are strong around the Fermi level between the Ti and Ru in the structure that form tetragonal prisms. We propose that weakening these strong interactions through the partial substitution of isovalent Si for Ti leads to the observed stability of the Ti₃Co₅B₂-type structure for Ti_3-xSi_xRu₅B₂ for x≈1.