Extinction in deformed copper single crystals. A combined study by γ-ray diffractometry and neutron structure refinement

Abstract

Neutron diffraction and γ-ray rocking-curve measurements were performed on plastically deformed single crystals of Cu in order to compare the mosaic distribution parameters obtained from least-squares structural refinement with those seen by the γ-diffractometer. Neutron data were collected at two wavelengths (λ = 0.538 and 0.741 A) for one crystal with very homogeneous mosaic distribution, and for another crystal with less good but more typical mosaic structure data were collected for λ = 0.538 A. Maximum sin θ/λ was 1.52 A-1 and maximum extinction correction was less than 30%. For the latter crystal no comparison could be made between the two sets of observed distribution parameters because of the uneven mosaic distribution. The former crystal was found from the γ-ray measurements to be bent, but when this was taken into consideration in the Coppens-Hamilton [Acta Cryst. (1970), A26, 71-83] formalism for anisotropic extinction correction good agreement was found between mosaic parameters obtained by γ-ray and neutron measurements for directions not affected by the crystal curvature, whereas the structure refinement did not, as expected, reflect the complete crystal curvature when this effect was dominant.