Vibrational and electronic anomalies near Tc in tetragonal superconducting YBa2(Cu0.9557Fe0.05)3O7.1

Abstract Mossbauer effect studies have been made as a function of temperature for the orthorhombic ( χ =0.01, 0.02) and tetragonal ( χ =0.05) superconducting compounds YBa 2 (Cu 1−χ 57 Fe χ ) 3 O 7 + y . For Fe in or slightly displaced from the Cu1 (000) site, temperature dependent measurements yield Debye temperatures for the Mossbauer shift θ δ in the range of 601 to 698 K and for the resonant fraction θ f in the range from 333 to 568 K, depending on the local oxygen configuration. Very little change is observed in the region of the superconducting transition T c for the orthorhombic phase samples, but both phonon and electronic changes occur near T c in the tetragonal phase. The vibrational behavior of Fe in the Cu1 site shows a dramatic hardening near and below T c in tetragonal YBa 2 (Cu 0.95 Fe 0.05 ) 3 O 7.1 . The quadrupolar splitting E Q indicates a change in field gradient in this same temperature region. The Mossbauer shift also behaves anomalously near T c .