THE MODELLING OF THE REAL STRUCTURE OF SINGLE CRYSTALS WITH CHEMICAL INHOMOGENEITY. T. I. Ivanova and O. V. Frank-Kamenetskaya, Department of Crystallography, St. Petersburg State University, 199034 St. Petersburg, Russia

We have studied the possibilities of the analysis of basal peak profiles based on the theory of X-ray diffraction by disordered lamellar structures (V. Drits, C. Tchoubar, 1990) in revealing and describing with statistical parameters some structural peculiarities of single crystals consisting of layered modules with different composition, which are invisible for commonly used X-ray structural analysis.

The approach has been succesfully applied to the study of various perovskite-like HTSC single crystals with layered structure. Their structural inhomogeneity along [001] has been described in terms of two-component irregular interstratified structures with different nature of admixture layers, their proportion and character of distribution within the crystal. It has been shown that the statistical parameters of these structures, varying from one crystal to another, determined the scale of inhomogeneity and were connected with the formation conditions of crystals and their SC-properties.

The use of the approach for the study of real structure of single crystal of edenite, a representative of natural calcium amfiboles from Khibins, helped revealing the irregular alternation of layers with different composition along two directions [010] and [001]. Thus, the crystal contains two sets of lamellae with essentially different thickness.

The data obtained proved the advantages of the approach in studying a real structure of single crystals with chemical inhomogeneity. The restrictions of the modelling originate from the use of method of trials and errors. In this connection it is expedient to combine it with other techniques such as high-resolution electron microscopy, detailed electron probe microanalysis and electron diffraction.