Microstructure and superconducting properties of the DyBaCuO ceramic doped with Na2CO3, NaCl, and KClO3

Abstract

This paper reports on a study of the effect of doping with Na2CO3, NaCl, and KClO3 salts on the microstructure and superconducting characteristics of ceramics with nominal compositions Dy1 − xMxBa2Cu3 − yO7 − δ and DyBa2Cu3 − yO7 − δ: Mx for M = Na, K; x = 0.2, 0.3, and y = 0, 0.2. The microstructure was characterized by transmission electron microscopy with local energy-dispersive x-ray in situ analysis (probe size ∼1 nm). An analysis shows that none of the doping elements (Na, K, or Cl) enters into 123 grains in sizable amounts and that, as a result, the critical temperature of the superconducting transition remains practically constant in the range 90.0–93.5 K. Potassium and chlorine segregate at grain boundaries. It is shown that grain-boundary segregation of chlorine leads to a substantial increase in the superconducting critical current (by a factor 3–5 at 70 K) as compared to the undoped sample. The possible mechanisms accounting for the effect of Cl on intergrain critical current are discussed.