Axial electron-channelling analysis of perovskite: I. Theory and experiment for CaTiO₃

Abstract

Crystallographic site location of atoms, using the Borrmann effect in electron-induced characteristic X-ray emission, has usually been undertaken using systematic-row diffraction conditions. In this paper, the variation ofcharacteristic X-ray fluorescence from calcium and titanium in perovskite (CaTiO₃) is reported for three zone-axis orientations, and correlated with dynamical n-beam calculations. The axial electron-channelling effect is found to be large for these zone-axis orientations, and may be understood by referring to calculations that account for the variation in the fast-electron probability density ψψ* on calcium and titanium sites as a function of orientation. Zone-axis diffraction conditions enable a two-dimensional compression of ψψ* in the unit cell, instead of the usual one-dimensional variation under systematic-row diffraction conditions, and in general leads to an enhancement in sensitivity. Effects due to delocalization of the inner-shell ionization event are also considered.