Local Structural Properties Around Cu Atoms in Checkerboard Phased Ca2−xNaxCuO2Cl2

We examined the local structural properties of checkerboard phased Ca2−x Na x CuO2Cl2 (T c =0, 15, 21, 27 K) using extended X-ray absorption fine structure (EXAFS) measurements at the Cu K edge. EXAFS revealed anomalous disorders existing in the bond lengths of Cu–Cu and Cu-Ca/Na pairs for all crystals below 50 K. A static disorder was observed even at room temperature. The disorders of the Cu–Cu in the a- and b-axes were independent of the T c value whereas these of the Cu–Ca/Na pairs located about 30∘ off from the Cu–O, ab-plane decreased, as T c increased.