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

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 Co(100 - 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.