Oxygen reordering near room temperature inYBa2Cu3O6+x: A thermodynamic model

Abstract

We propose a thermodynamic model to explain an unusual phase transformation occurring near room temperature in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+\mathrm{x}}$ that greatly affects properties of the superconductor. Based on our model, the material's thermodynamic response functions, specific heat, thermal-expansion coefficient, and elastic compliances are deduced at the critical temperature of the phase transformation. We discuss the change of critical temperature with stress, and analyze the anomaly of specific heat in critical temperature of the phase transformation.