Experimental procedures for the determination of invariant phases of centrosymmetric crystals

The [222] n-beam pattern of germanium has been recorded using Cu Kα₁ radiation and newly developed instrumentation. The asymmetric unit of the pattern contains 17 interaction maxima. At least one invariant triplet phase may be derived from each maximum. Two of the latter are considered unsuitable for phase determination owing to overlap with adjacent peaks. The phases of the remaining 15 were determined. Relevant experimental data are presented and from these the validity of the authors' phase assignments can be readily checked. Techniques for indexing n-beam patterns and for improving the visibility of triplet phase interactions are discussed. It is shown that procedures for improving the visibility of n-beam interactions do not necessarily lead to increased visibility of phase indications.