151Eu-Mössbauer study of the high-Tc superconductor EuBa2Cu3O7−x

Abstract The temperature dependence of the isomer shift S and recoil-free fraction ƒ of the 21.6 keV Mossbauer resonance of 151 Eu is studied in the high- T c superconductor EuBa 2 Cu 3 O 7− x between 4.2 and 300 K. Eu is found to be present as stable Eu 3+ ion with an isomer shift and a Mossbauer Debye temperature typical for ionic oxygen surroundings. A possible change in S at T c is smaller than 0.02 mm/s. The Eu 3+ nuclei experience an electric-quadrupole interaction with a main axis of the electric-field gradient tensor V = −3.1(5) × 10 17 V cm 2 and an asymmetry parameter η ≠ 0.