Site occupancy and lattice parameters in sigma-phase Co–Cr alloys

Abstract

Neutron powder diffraction was used to study the distribution of Co and Cr atoms over different lattice sites as well as the lattice parameters of sigma-phase compounds Co100 − x Cr x with x = 57.0, 62.7 and 65.8. From the diffractograms recorded in the temperature range of 4.2–300 K it was found for the five crystallographically independent sites that A (2a) and D (8i) are predominantly occupied by Co atoms, while sites B (4f), C (8i) and E (8j) mainly accommodate Cr atoms. The lattice parameters a and c exhibit linear temperature dependencies, with different expansion coefficients in the temperature ranges of 4.2–100 and 100–300 K.