Eu atomic motion in EuSr2Cu3O7-delta and EuBa2Cu3O7-delta: a comparative Mossbauer study

We present a comparative Mössbauer study of the 151Eu motions in the nonsuperconducting and superconducting cuprates EuSr2Cu3O7-delta (ESCO) and EuBa2Cu3O7-delta (EBCO), respectively, with the aim of investigating atomic-motion anharmonicities in these materials. In this study, a comparison with the results of a similar analysis of powdered samples of EBCO having oriented grains is also performed. We show that the Eu ion in ESCO, as well as in the common EBCO cuprates, does not move in a parabolic potential, but in a potential with a flat bottom. Moreover, for ESCO the flat part is about 1.5 times larger than for EBCO.