Contraction of Pendellösung Fringes in Distorted Crystals

Abstract

It is theoretically shown that the spacing of X-ray Pendellösung fringes should contract in an arbitrarily strained crystal compared with that in the Perfect crystal, so far as the displacement of lattice points is given by a quadratic form of position. The result is an extension of the prediction previously obtained for the case of homogeneous bending.
In the light of this theory several experimental results, particularly Ando and Kato’s experiment which is to appear in Acta cryst. (1966), are discussed qualitatively. The term “the fringes of equal strain-gradient” is proposed for the Pendellösung fringes observed in X-ray traverse topographs of strained crystals having the form of parallel slab.