STUDY OF THE ORDERING OF SC AND TA ATOMS IN PB2SCTAO6 BY X-RAY-DIFFRACTION AND HIGH-RESOLUTION ELECTRON-MICROSCOPY

Single crystals of Pb2ScTaO6 were grown by slow cooling of the melt. X-ray single crystal methods led to a cubic structure with a primitive unit cell with a = 4.07 Å. X-ray powder diffraction on crushed crystals reveals weak lines indicating some degree of ordering. High resolution electron microscopy (HREM) has been done along the [110] direction: ordered and disordered domains actually exist, with a domain size between a few angstroms and roughly 1000 Å. In the present case ordered domains were just at the limit of detection by X-ray methods. It has been shown that high resolution electron microscopy is a powerful method for the study of ordering, especially in the case of small domains. © 1990.