Transmission electron microscopy study of one-dimensional incommensurate structural modulation in superconducting oxides Bi_2+<i>x</i>Sr_2−<i>x</i>CuO_6+δ(0.10≤<i>x</i>≤0.40)

Abstract

The one-dimensional incommensurate structural modulation in Bi2+xSr2−xCuO6+δ (0.10≤x≤0.40) has been studied by electron diffraction and high-resolution electron microscopy. The modulation wave vectors and four-dimensional symmetry were determined from electron diffraction patterns. The quality of high-resolution electron microscope images was improved by noise filtering and symmetry averaging so that the displacive and compositional modulation could be seen in images much more clearly than usual. The atomic substitution in Bi and Sr sites was analyzed based on the image contrast variation and the arrangement of Bi-concentrated regions was studied. The dependence of modulation wave vectors, twinning modulation and Bi-concentrated regions on the amount of Bi doping, x, is demonstrated. By considering the relationship between Tc and x reported by Luo et al (2007 J. Cryst. Growth 305 222) the relationship between the transition temperature and incommensurate modulated structure is discussed.