X-ray Studies on the Structures of Solid Solutions NaCl-CaCl2 I. Main Results and General Considerations

Stationary X-ray diffraction patterns from transparent single crystals of solid solutions of NaCl dissolved with a few per cent of CaCl 2 show a number of diffuse spots. Their displacements with the change of the direction of incident X-rays reveal the existence of several kinds of rods in reciprocal space. Among them, the rods running along <111> and <310> rows are most remarkable. The appearance of these rods are considered as the result of the formation of thin plate-like precipitates in the matrix because of the homogeneous solid solutions being unstable at room temperatures. The precipitates may be the places where Ca ++ ions replacing Na + ions, and vacancies of Na + sites, are locally concentrated. It was shown, by a general consideration, that the plate-like precipitate responsible for <111> or <310> rods is likely composed of an assembly of anti-phase, domains of super structures.