Oxygen-vacancy-formation enthalpy in YBa2(Cu0.985Fe0.015)3O7−δ oxide superconductor

Abstract

${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mossbauer spectra of ${\mathrm{YBa}}_2$(${\mathrm{Cu}}_{0.985}$ ${\mathrm{Fe}}_{0.015}$ ${)}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ samples display multiple sites (n=A, B, C, and D) with the site intensity ratios $I_n$/I exhibiting profound thermal annealing effects in the temperature range 150 °C<$T_a$<550 °C associated with oxygen desorption. Specifically, the ratio $I_A$/I is a function of $T_a$, and displays an activation enthalpy of site formation Δ$H_A$=104(3) meV. We ascribe it to the filling of O(1) oxygen vacancy sites in chains. The miniscule Δ$H_A$ is probably the consequence of the under-coordinated nature of the orthorhombic structure which globally promotes a superelastic (soft) lattice.