Oxygen order and electronic structure at Cu(1) sites in Y1−xPrxBa2(Cu0.9957Fe0.01)3Oy and Y(Ba1−xSrx)2(Cu0.9957Fe0.01)3Oy

Abstract Mossbauer effect measurements have been made at 57 Fe nuclei in Pr x Y 1− x Ba 2 (Cu 0.99 57 Fe 0.01 ) 3 O y and in Y( Ba 1− x Sr x ) 2 (Cu 0.99 57 Fe 0.01 ) 3 O y as a function of x . For all Pr concentrations (0⩽ x ⩽0.7) studied, the Mossbauer spectra are nearly identical in character and comparison of Mossbauer shift and of quadrupole splitting E Q with composition indicates that oxygen order and electronic structure at the Cul site are virtually unaffected by changing the relative Y to Pr composition. Hence, the rapid depression of T c with increasing x is inferred to be due to electronic changes caused by changes in the Pr bonding to the Cu2-O plane. In contrast to the behaviour of compounds with Pr substituted for Y, Mossbauer spectra for Y( Ba 1− x Sr x ) 2 (Cu 0.99 57 Fe 0.01 ) 3 O y show systematic pattern changes similar to those observed upon Fe substitutions for Cul in YBa 2 ( Cu 1− x Fe x ) 3 O 7+δ . That is, oxygen order and stoichiometry are strongly affected by Sr substitution for Ba.