CHARACTERIZATION AND STRUCTURAL-ANALYSIS OF TWINNED LA2-XSRXCUO4+/-DELTA CRYSTALS BY NEUTRON-DIFFRACTION

The microstructure of La2-xSrxCuO4 +/- delta crystals has been studied by neutron diffraction. Profile analysis of the intensity of Bragg reflections shows that the large crystals consist of domains of four different orientations, which are related to the symmetry reduction of the phase transition I4/mmm-Abma. The domain structure has a strong influence on the extinction, therefore it may be studied macroscopically. The microstructure is formed at the phase transition and does not change in the orthorhombic phase. After a first cooling cycle the formation of the domains appears to be reversible without a temperature hysteresis. The same domain structure appears in consecutive cooling cycles. This indicates a pinning of the domain structure by lattice defects. A data set of Bragg reflection intensities obtained on a twinned La1.93Sr0.07CuO4 crystal at room temperature could be refined with special consideration of the microtwinning. The achieved precision of structural parameters is almost comparable to structural analyses on monodomain single crystals.