DIFFUSE-X-RAY SCATTERING STUDY OF AN OXYGEN-DISORDERED TETRAGONAL YBA2(CU0.955AL0.045)3O7 CRYSTAL

X-ray scattering from a tetragonal single crystal of YBa2(Cu0.955Al0.045)3O7 shows diffuse streaking in [110] directions about the Bragg peaks. Through a quantitative calculation using a coupled concentration wave, static displacement wave approach, we show that this is essentially attributable to the shear displacement field produced by a disordered oxygen array on the Cu(1)-O "chain" plane. We also observe pronounced short-range chain order (local orthorhombic fluctuations) whose correlation range is considerably greater than the superconducting coherence length. This suggests that on a scale relevant for superconductivity the (local) orthorhombicity remains important in this tetragonal structure.