Raising critical currents in YBaCuO-type high-temperature superconductors by Mo substitution

Abstract

In this work, we investigated the critical currents and pinning mechanisms in single crystals of the high-temperature superconductor Y123 with Mo substituted into CuO chains. The single crystals were annealed in oxygen at low (130–140 atm) and high (255 atm) pressure, which significantly influenced the observed properties. Magnetic hysteresis loops were measured at various temperatures in fields up to 14 T, for both H||c and H⊥c. On the basis of these measurements, the densities of critical currents were calculated using the Bean critical state model. Then, using the Kramer approach and the Dew-Hughes model, scaling of the pinning force was performed and the type of pinning centers and pinning mechanisms dominant in different field and temperature ranges were determined. Due to Mo substitution, the critical current density in single crystals annealed in oxygen under high pressure increased several times at lower temperatures, e.g., 3–4 times for T = 4–35 K and μ0H = 1–8 T, and by an order of magnitude at higher temperatures, e.g., for T = 65–75 K and μ0H = 2–3 T. For these single crystals, Δκ volume-like pinning centers (Mo2O11 octahedra dimers) and normal point-like pinning centers (interstitial oxygen) were identified as dominant at lower and higher fields, respectively.