Ferroelasticity in Y-Ba-Cu-O

Abstract

Abstract A spring-defect model has been developed by us earlier for describing the connection between elastic distortion and oxygen ordering and the concomitant structural phase transition (from tetragonal to orthorhombic at Ts∼900 K) in the high Tc (∼ 90 K) superconductor YBa2Cu3O7–δ (Y-Ba-Cu-O). This model is used to discuss ferroelasticity, exhibited in the orthorhombic phase of Y-Ba-Cu-O. Ferroelasticity is shown to be a consequence of the interaction between elastic (Zener) dipoles, formed around each oxygen defect. The effective Ising interaction between the defects mediated by host springs, derived earlier, can be recast in the equivalent form of a strain-strain interaction. This form is eminently suitable for discussing the paraelastic to ferroelastic transition, temperature dependence of the ferroelastic order parameter and the static compliance. Results for these quantities, obtained in mean field theory, are presented. The notable feature of this work is not only a derivation of the defect-defect interaction, but also an explicit calculation of the strain dipole tensor associated with each defect, from a microscopic model.