Effects of Debye-Waller factors and compositional uncertainties on the 200 structure factor refinement eta in-TiAl

Abstract

The effects of uncertainties in Debye-Waller factors and chemical composition on 200 structure factor refinement in eta-TiAl have been investigated. Energy-filtered convergent-beam electron diffraction has been used to record 200 rocking curves from two different thicknesses of a thin foil taken from a Ti-51.3 1Al alloy (all compositions in atomic per cent). The structure factor has been refined by matching rocking curves determined by experiment to those theoretically calculated using the Bloch wave formalism of the dynamical theory of electron diffraction. The influence of uncertainties in the Debye-Waller factors and sample composition have been assessed: for samples deviating from stoichiometry, the need to use accurate site-specific Debye-Waller factors has been demonstrated. Also, to extract accurate structure factors, it is necessary to make use of homogeneous samples, the compositions of which must be known to better than 0.2%, a rather restrictive limitation.