Strain Effects on Point Defects and Chain-Oxygen Order-Disorder Transition in 123-Structure Cuprate Superconductors

TL;DR

This study investigates how strain, doping, and ionic size influence defect formation and phase transition temperatures in 123 cuprate superconductors, revealing that larger ionic radii lower the orthorhombic-tetragonal transition temperature.

Contribution

It introduces a detailed analysis of strain effects on point defect energetics and order-disorder transitions in 123 cuprates, combining defect calculations with quasi-chemical approximations.

Findings

Defect formation energies are significantly affected by non-uniform interatomic distances.

Larger ionic radii of rare-earth elements correlate with lower phase transition temperatures.

Strain and doping can substantially alter the disordering energy of oxygen defects.

Abstract

The energetics of Schottky defects in 123 cuprate superconductor series, $\rm REBa_2Cu_3O_7$ (where RE = lanthandies) and $\rm YAE_2Cu_3O_7$ (AE = alkali-earths), were found to have unusual relations if one considers only the volumetric strain. Our calculations reveal the effect of non-uniform changes of interatomic distances within the RE-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 quasi-chemical approximations (QCA). The theoretical results illustrate the same trend as the experimental measurements in that the larger the ionic radius of RE, 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.