Systematic copper deficiency in Y-Ba-Cu-O single crystals

Abstract
The structure of five YBa2Cu3-xO7-δ(0.09 ≤δ < 1) crystals is determined by X-Ray diffraction. Four crystals are orthorhombic (δ < 0.35) and twinned with a twin ratio deduced from refinement corresponding to 54-70% of the main sample. The last one is tetragonal (δ = 1). A new feature, not systematically reported, is a deficiency on the Cu(1) site, in the range of 4-8% , whereas the other cationic sites remain fully occupied. The oxygen ordering increases with concentration. The Ba site is found strongly anharmonic