Microstructure and superconducting properties of sintered DyBa₂Cu_3-xO_y/1 wt% Pt ceramics

Abstract

The correlation between microstructure and superconducting properties of copper-deficient sintered DyBa2Cu3-xOy (0 x0.4) ceramics doped by 1 wt% Pt has been studied. For non-stoichiometric compositions with x0.2 magnetoresistance measurements showed a large widening of the resistance-temperature transition in low magnetic fields in the region corresponding to the transition of intergranular material. Such an enhancement of the effect of granularity in these samples is in good agreement with the estimation of their normal state resistivity at working temperatures and the observed refinement of grains. Doping by Pt was found to assist the formation of submicron size secondary phases homogeneously located in 123 grains. In addition, in the compositions with x0.2, Pt was also incorporated into intergranular BaCuO2 secondary phases. The addition of Pt had no influence on the size and distribution of Y2BaCuO5. Traces of Pt in the 123 grains were revealed in all compositions doped with Pt. Platinum doping only slightly increased the critical current Ic in stoichiometric composition, but it resulted in a substantial increase in Ic and pronounced `fish-tail' effect in magnetic field at T77 K in non-stoichiometric composition with x = 0.2. Better behaviour of Ic in magnetic fields in these samples may be associated with the substantial increase in the proportion of clean boundaries and the decrease of twin spacing. The measurements of Ic(T) at temperatures close to Tc indicated the SIS character of the grain boundary weak links in all compositions with x0.2 whether they were doped by Pt or not.

Effect of ZrO2doping on structure and superconducting properties of sintered DyBaCuO ceramics

“…As in [5], such statistical results can explain the sharp drop of J c under a very low magnetic field ( 10 G) in the undoped stoichiometric composition. This is associated with the small amount of clean boundaries.…”

“…The grain size decreased strongly with the amount of doping (table 1). Precipitations of the secondary phases which may interfere with the grain growth during sintering are the most probable reason for the formation of a fine-grain microstructure, as earlier noted for Cu-deficient YBCO ceramics in [4,5].…”

“…Doping by different elements can substantially change the microstructure of GBs. Thus, in the Cu-deficient samples with a small deviation from stoichiometry, doping by Ag or Pt led to a substantial increase in portion of clean GBs in a sample [4,5]. Addition of different elements can also cause the formation of fine precipitations on or near clean GBs, which contribute highly to the value of J c , as, for example, was observed in [4] for samples doped by Ag.…”

“…We made a systematic statistical study of GBs similar to that performed earlier for YBaCuO ceramics doped with Ag [3,4] and DyBaCuO doped with Pt [5]. So 40 to 50 consecutive boundaries in each sample were characterized by bright field tilting imaging in TEM.…”

“…It is well known that in sintered bulk high-T c superconductors, the superconducting properties are mainly determined by their grain boundary (GB) behaviour [1,2]. The value of the critical current density J c depends primarily on the portion of clean boundaries in a sample, the crystallographic misorientation (relationship) between the adjacent grains and their chemical composition [3][4][5].…”