Primitive unit cell volumes obtained from unindexed convergent-beam electron diffraction patterns

Provided that multiple reflection is present, a common occurrence with electron diffraction on microcrystallites, a single unindexed convergent-beam electron diffraction (CBED) pattern taken with the beam axis parallel to any direct lattice row allows the volume of the primitive cell to be calculated. The film measurements required are the diameters of the successive high-order Laue zones (HOLZ), the lengths of any two coprime vectors in the zero-order Laue zone (ZOLZ), and the angle between them. The primitive cell volume is an objective criterion allowing in a simplification in the identification of a phase under study by rapidly eliminating other possible phases. The computer program CELVOL for the calculation of the primitive cell volume from film measurements, or from literature cells, is available from the authors.