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

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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. A sample with nominal composition Cr0.625B0.175Si0.2 was arc-melted under argon, encapsulated in a quartz-tube and heat-treated at 1400∘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, as boron atoms in 8h nearest-neighbors form very stable dumbbell bonds. Site preferences are thus a key factor for the stabilization of the structure. 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.