ON THE TEMPERATURE DEPENDENCE OF THE Cu-O STRUCTURE IN EuBa2Cu3O7−δ

Abstract

We have have investigated the temperature dependence (83−300 K) of the Cu-O bonds in EuBa2Cu3O7−δ through the extended absorption finestructure (EXAFS) beyond the Cu 1s (K) absorption threshold. The data were recorded from bulk polycrystalline material in the fluorescence mode simultaneously together with the electrical resistance. The temperature change of the relative mean square displacement, δσ2(T), of the Cu-O pairs exhibits a kink at T ≤ 110 K and a singularity at 250 K. The kink at T ≤ 110 K is due to the decomposition of the nonstoichiometric sample into oxygen rich and oxygen lean products. The singularity at 250 K is attributed to a displacive phase transition. We have extracted the temperature dependence of the Cu(1)-O(1) bondlength from the beats (jumps and minima in the total phase shift and amplitude, respectively) in the filtered absorption fine structure. The Cu(1)-O(1) bond stretches by about + 0.01 A as the temperature decreases from 300 K to 90 K.