Enthalpy and entropy of twin boundaries in superconducting YBa2Cu3O7−x

Twin boundary energy (γtw) and its temperature dependence are important factors to be evaluated for engineering twin morphology for strong flux pinning and high critical current density in superconducting YBa2Cu3O7−x. Here, it has been measured as a function of oxygenation temperature from 450 to 680 °C using both the twin spacing method and a twin tip method. By comparing the twin energies obtained by the two methods, the geometrical factor α used in twin spacing method is determined. This geometrical factor is directly related to the sharpness of the twin tips. From the temperature dependence of twin boundary energy per unit area, twin boundary entropy (Δs) and enthalpy (Δh) for twin boundaries are projected to be 0.24mJ∕Km2 and 246mJ∕m2, respectively.