Site Occupancy-Valence Measurements Using Channelling and Related Effects in Microanalysis

The current status of a novel crystallographic technique to determine specific site occupations of elemental additions in crystalline materials, using the channelling or Borrman effect in electron diffraction, is discussed. This technique is based on the effect of incident beam orientations on the intensities of either the characteristic X-ray emissions or the characteristic electron energy loss edges. In general, this technique is in good agreement with other well-established methods such as X-ray and neutron diffraction but has superior spatial resolution (approx. 10–40 nm). It involves no adjustable parameters, external standards or special specimen preparations; can distinguish neighbours in the periodic table; is very accurate and is applicable to trace elemental concentrations (0.2–0.3 wt.% or 10 atoms m –3 ). In the electron energy loss spectroscopy formulation, the technique can also provide specific site valence information. Finally, its applicability to the study of site occupancies in magnetic materials (spinels, Sm 2 (Co,TM) 17 alloys, (Y,RE) 3 Fe 5 O 12 epitaxial films, etc.) has been well demonstrated.