A comparative study of single-line and Rietveld strain-size evaluation procedures using MgO ceramics

Strain-size evaluations from diffraction line broadening for MgO ceramic materials have been compared using single-line integral-breadth and Rietveld procedures with the Voigt function. Diffraction data were measured by Bragg-Brentano X-ray diffractometry (XRD), without incident beam monochromatization, and neutron diffractometry (ND) to encompass near-surface and bulk effects, respectively. The specimens consisted of sets of MgO ceramics and MgO-Y₂O₃ ceramic composites sintered over a range of temperatures. An MgO ceramic sintered at 1723 K for 2 h exhibited slightly less XRD broadening than the standard LaB₆ NIST 660 SRM, and was therefore selected to make instrument profile corrections for both XRD and ND data. It was found for both data types that: (a) sintering initially relieves residual strain present in the MgO powder used to sinter the ceramics and also promotes grain growth; (b) residual strain of the MgO ceramic minimizes as the sintering temperature increases, and then increases with further rise in the sintering temperature, presumably as a result of intragranular interactions associated with grain growth; and (c) introduction of the second phase (Y₂O₃) increases strain and inhibits crystal growth. The single-line and Rietveld methods gave similar strain values from both the XRD and ND data within the limits of experimental error, but there were substantial differences between the single-line and Rietveld size estimates determined with the XRD and ND data.