The fine structure of YCuO2+x delafossite determined by synchrotron powderdiffraction and electron microscopy

YCuO2 delafossite crystallizes into two stacking variants; hexagonal 2H or rhombohedral 3R, depending on the preparation conditions. The structure of the fully oxygenated material YCuO2.50 has been determined as orthorhombic (a(O) = 6.1961 Angstrom; b(O) = 11.2158 Angstrom; c(O) = 7.1505 Angstrom; s pace group Pnma). The structure is based on the hexagonal 2H structure (a(O ) = a(H)root3; b(O) = c(H); c(O) = 2a(H)). Upon incomplete oxidation, a dif ferent YCuOZ phase with ideal composition YCuO2.33 and lattice parameters a (H root)3, a(H)root3, c(H) is also formed. Diffraction patterns are often v ery complex because of the presence of planar defects and intergrowth of bo th phases. Under electron beam irradiation, oxygen is released from the str ucture and one phase gradually transforms into the other. (C) 2001 Academic Press.