Evidence of the breakdown of Frieders law in the Kikuchi patterns of tellurium crystals has been observed with a standard transmission electron microscope (TEM). These observations give a direct method of identifying enantiomorphously related phases in the TEM. An interpretation of the observed deviations from Frieders law is proposed on the basis of the model of Thomas & Humphreys [Phys. Status Solidi A (1970). 3, 599-6151 for Kikuchi patterns. The possible differences between the phases of the Fourier coefficients of the crystal potential and of the absorption potential have to be taken into account. Some light is thrown on the physical significance of the phenomenological parameters.

Kikuchi patterns of crystals of low-symmetry exhibit features which cannot be observed in common crystals. Two kinds of effects have been studied on Te crystals ; these crystals have a 3 atoms basis and belong to the enantiomotphous space-groups D3(fig- 1).1. “UNUSUAL” BANDSSystematic diffractions may be classified according to the profile of their Kikuchi band at 100 kV.In the “usual” case, to which the quasi-totality of the diffractions belong, the band at 100 kV has its principal maxima near the first Bragg position (at ± ) and has no central maximum (at the O-position). We call this type of diffractions A-type.For the “unusual” cases, we define two extreme situations which have been observed in Te (fig. 3 and 4) :(i) A'-type [Te-]. The band presents at 100 kV a profile similar to those which are observed at higher voltage for diffractions of the “usual” type : a strong central maximum and principal maxima at n (n >1).