Oxygen stoichiometry and mobility effects on domain wall motion in ferroelastic YBa2Cu3O7-δ

The purpose of this paper is to examine the interrelationship between oxygen stoichiometry and mobility with ferroelastic properties in YBa 2 Cu 3 O 7-δ . Changes in oxygen stoichiometry, δ, affect the orthorhombic-tetragonal phase transformation behavior and consequently can be expected to directly affect the ferroelastic domain structure and switching properties. A free energy formulation is used to derive an expression for the energy γ T of a {110} twin wall in YBa 2 Cu 3 O 7-δ in terms of the spontaneous strain, coercive stress, and twin wall separation. An upper limit of 40 mJ/m 2 was estimated. Ferroelastic viscosity, η, of YBa 2 Cu 3 O 7-δ was assumed to be an activated process which depends on both the diffusivity and concentration of oxygen according to the relation η = η 0 (0.6-δ)exp(-E/kT) for δ < 0.6. Two types of domain reorientation mechanisms are proposed, a cooperative shear process of oxygen along a twin wall and a stress-assisted short-range oxygen hopping process in the bulk of the domain, both of which are expected to be strongly dependent upon the oxygen content and mobility.