Main- and superstructure by X-ray scattering for annealed single crystal of YBa2Cu3O6.5
A single crystal of YBa2Cu3O6.5 was annealed at 430, 510, 570 and 590 K in the furnace of a four-circle X-ray diffractometer, cooled down slowly to room temperature and investigated structurally. From the dataset of about 200 reflections with 40 superstructure reflections, the main- and superstructure models have been derived. Displacements of Cu atoms, changes of oxygen populations in the basal plane and the small displacements of Y, Ba and apex-oxygens were observed. The changes of atom positions have been correlated with the superconducting transition temperature Tc. With increasing annealing temperature, the phase separation, a characteristic diffuse scattering in the 00l-direction, changes of oxygen population in the basal plane and after annealing at 430 K, the disappearance of twinned reflections in the a*–b* plane have been seen.