A method has been developed by the staff of the Solid State Physics Division for determining the orientation of crystallites in a multicrystalline, acicular particle by electron diffraction techniques.
In a particle with oriented crystallites, all of the crystallites have a common crystallographic direction along the axis of the particle; the crystallites may be rotated randomly about the common direction.
Utilizing the selected area diffraction unit of the RCA-EMU-2C electron microscope, a single particle can be isolated and its diffraction pattern obtained. At the same time, the spatial orientation of the particle with respect to the pattern is determined.
If the particle being studied is multi-crystalline with oriented crystallites, the diffraction pattern has the appearance of an X-ray rotation diffraction pattern of a single crystal; that is, a very definite pattern of well defined spots. If, however, the crystallites are not oriented, the pattern has the usual appearance with arcs or circles. Interpreting the oriented pattern by fairly standard methods, one can show which common crystallographic direction of the crystallites is along the axis of the particle.
Initial experiments were carried out on samples of r-FezOa with a particle size of approximately 1~ X 0.2~ and with crystallite sizes ranging from 50 A to 800 A as determined by X-ray line broadening.
In general, the data indicate that a large majority of the particles have oriented crystallites. This orientation direction varies from particle to particle, but within a given particle all the crystallites usually have a common orientation axis. The crystallographic direction found is generally of low order such as 210, 221, etc. Particles have been observed in which the orientation is not perfect, with the spots being slightly elongated, and a few particles observed have shown