Changes in the Cu K-edge XANES of Bi 2201 phase by N 2 annealing

Abstract

Tc of the Bi 2201 system is known to increase by annealing in the absence of oxygen. In order to understand the changes of the geometric or electronic structure in CuO 2 plane, the energy structure of Bi system is studied by Cu K-edge XANES. For the single crystal of Bi 2212, where the CuO 2 layer has pyramidal structure, 1s-4p π transition splits into two peaks. This splitting is neither observed for the single crystal of Bi 2201 phase nor for the Nd- or the La- systems. When the Bi 2201 phase is annealed in the absence of oxygen, the splitting in the 1s-4p π transition is also observed. This may be due to the fact that the apex oxygen in 2201 phase moves into the direction from CuO 2 plane to BiO plane, and as a result, the octahedral symmetry breaks, giving similar energy structure to pyramidal CuO 2 plane.