X-ray diffraction study of HTSC single crystals

Superconducting single crystals have been investigated by precise X-ray diffraction technique. In La-phases different ordering of Sr atom distribution over La sites has been established. In the Y-123 phases with oxygen amount varying from 6 to 7 per formula unit the character of ordering in the arrangement of oxygen atoms was found to be different. The anomalies in the behaviour of some structural parameters were fixed in the vicinity of the transition to the superconducting state for single crystals of Tl-2212 and Y-124 phases. It is shown that thermal vibrations of atoms in the vicinity of second order transition provides the information on changes in electronic structure during the transition