DIFFRACTION STREAKS FROM THE CHIMNEY LADDER STRUCTURE IN AN (SR1.5CA1.5)CU5+DELTA-OY CRYSTAL

A crystal of (Sr1.5Ca1.5)Cu5+delta-Oy has been studied by means of electron diffraction analysis and high-resolution transmission electron microscopy. A chimney ladder structure has been identified in the crystal, which is composed of two sets of incommensurate orthorhombic sublattices L1 and L2 with a = a1 = a2 = 1.28, b = b1 = b2 = 1.13, c1 = 0.390 and c2 = 0.275 nm. Diffraction streaks have been observed in electron diffraction patterns, i.e. there is a set of reflection planes parallel to a*b* related to L2. A structure model with initial phase disorder has been proposed to explain such diffraction streaks. A mathematical inference as well as an optical diffraction method have confirmed this model. Observed high-resolution images together with calculated ones gave a direct verification for the initial phase disorder.