X-ray diffraction contrast of inversion twin boundaries in BeO crystals

Abstract

Inversion twin boundaries in BeO crystals (wurtzite structure) can be studied by X-ray topography. They can be regarded as a special kind of stacking fault. The section topograph images of a twin boundary, lying parallel to the c axis, agree well with the theory for a single stacking fault. From the contrast variation of the images for various reflections, it is concluded that the oxygen sublattice on one side of the twin boundary is displaced from that on the other side by 1(1/16)[00111 so that the oxygen layer parallel to the basal plane on one side is located at the center of the oxygen and beryllium layers on the other side. The image contrast in section topographs is very sensitive to the phase shift due to a fault. The phase shift of a few degrees can be detected easily. This sensitivity leads to an accurate structure determination of the inversion twin boundary.

Polarity reversal and symmetry in semiconducting compounds with the sphalerite and wurtzite structures

“…Detailed diffraction contrast studies of inversion twin interfaces were carried out in this material using X-ray topography [14].…”

Observation of Pendellösung fringes in a melt-grown lithium niobate single crystal

“…Compared to melt-grown Ge and Si crystals, complex oxide ferroelectrics, such as LiNbOa are far less nearly perfect because of their complex compositions and structures, ferroelectric domain structures and anisotropy of crystal properties (Sugii, Iwasaki, Miyazawa & Niizeki, 1973). Observation of Pendell6sung fringes is one of the useful tools for evaluating crystal quality, and it has been successfully used for several oxide crystals, such as Verneuilgrown MgO (Lang & Miles, 1965) and flux-grown A1203 (Belt, 1966) and BeO (Austerman, Newkirk & Smith, 1965;Chikawa & Austerman, 1968) crystals. This communication reports the observation of Pen-dell6sung fringes as well as various types of lattice imperfection in a LiNbO3 single crystal grown from the melt by the Czochralski method.…”

Stacking faults in BeO crystals

“…Also some fringes are seen in AEFO and AGHO. Although the fringes are distorted by some lattice strains in the crystal, there seem to be the typical fringes of a stacking fault in AGHO which should be of a form similar to a hyperbola with the lines OH and OG as asymptotes (Chikawa & Austerman, 1968). The very high intensity along the line EG is due to the interbranch scattering of the X-rays deviated from the Bragg condition at the stacking fault.…”

“…The crystal studied was grown from LizMoO4-MoO3 (Austerman, 1964) ing several percent LiPO3 as an added impurity at a temperature of approximately ll00°C. For identification of stacking faults, the following distinctive features of stacking-fault images were examined: (1) The defects are two-dimensional defects on the basal plane; (2) Stacking-fault images show the typical fringe pattern in so-called section topographs (Kato, Usami & Katagawa, 1967;Authier & Sauvage, 1966;Authier, 1968;Chikawa & Austerman, 1968); (3) Stackingfault images must disappear for the reflections that satisfy h. f= n (n = 0 or integer) where h is the reciprocal-lattice vector and f is the fault vector (Whelan & Hirsch, 1957). For hexagonal closest-packed structures, the hkl reflections satisfy h. f= n when h-k = 3m (m = 0 or integer).…”