Strain effects on point defects and chain-oxygen order-disorder transition in 123 cuprate compounds.

Abstract

The energetics of Schottky defects in 123 cuprate superconductor series RBa2Cu3O7 (where R

=lanthandies) and YA2Cu3O7 (A=alkali earths), were found to have unusual relations if one considers only the

volumetric strain. Our calculations reveal the effect of nonuniform changes of interatomic distances within the

R-123 structures, introduced by doping homovalent elements, on the Schottky defect formation energy. The

energy of formation of Frenkel pair defects, which is an elementary disordering event, in 123 compounds can

be substantially altered under both stress and chemical doping. Scaling the oxygen-oxygen short-range repulsive

parameter using the calculated formation energy of Frenkel pair defects, the transition temperature between

orthorhombic and tetragonal phases is computed by quasichemical approximations (QCA’s). The theoretical

results illustrate the same trend as the experimental measurements in that the larger the ionic radius of

R, the lower the orthorhombic/tetragonal phase transition temperature. This study provides strong evidence of

the strain effects on order-disorder transition due to oxygens in the CuO chain sites.