T2 phase site occupancies in the Cr--Si--B system: a combined synchroton-XRD/first-principles study

Boron and Silicon site occupancies of the T2 phase in the Cr-Si-B system were investigated experimentally and by first-principles electronic-structure calculations within the scope of the Density Functional Theory (DFT). A sample with nominal composition Cr$_{0.625}$B$_{0.175}$Si$_{0.2}$ was arc-melted under argon, encapsulated in a quartz-tube and heat-treated at 1400{\deg}C for 96 hours. It was then analyzed using Scanning Electron Microscopy (SEM) and X-Ray Diffractometry (XRD) with synchrotron radiation. An excellent agreement was obtained between experiments and theoretical calculations, revealing that Si occupies preferably the $4a$ sublattice of the structure due to the presence of weak B bonds, making the site preferences a key factor for its stabilization. The results of this work provide important information to support a better description of this phase in alloys with Si and B, since T2 phases are known to occur in many important Transition Metal-Si-B ternary systems, such as Nb/Mo/W/Ta/V-Si-B.