Joseph W. Kell

Minute doping with deleterious rare earths in YBa2Cu3O7−δ films for flux pinning enhancements

To enhance the critical current density of YBa2Cu3O7−δ films, flux pinning centers are intentionally added to inhibit flux flow in applied magnetic fields. Here we provide an initial demonstration that the incorporation of very minor additions (⩽1% of Y as opposed to the 10%–40% in standard substitutions) of typically deleterious rare earths into high quality YBa2Cu3O7−δ thin films provides significant improvement of the film’s in-field current density. This is accomplished without reoptimization of the deposition parameters. Instead of site substitution for Y as might be expected, the deleterious rare earths potentially result in the formation of nanoparticulates.

Tb and Ce doped Y123 films processed by pulsed laser deposition

To evaluate possible flux pinning enhancement in YBa/sub 2/Cu/sub 3/O/sub 7-z/ (Y123) films due to partial rare-earth ion substitutions, Ce and Tb doping are studied. Bulk ceramic targets of varying compositions (Y/sub 1-x/RE/sub x/Ba/sub 2/Cu/sub 3/O/sub 7-z/) were made with several doping levels (x=0.001 to 0.1, RE=Ce or Tb) by using regular solid-state reaction and sintering procedures. These targets were used to deposit Ce and Tb doped YBCO films onto SrTiO/sub 3/ single crystal substrates by pulsed laser ablation. Doped YBCO films were characterized for T/sub c/, magnetic field dependence of J/sub c/ (at 77 K), microstructure, and other properties. The results are compared to undoped YBCO films processed in similar manner.

Addition of alternate phase nanoparticle dispersions to enhance flux pinning of Y-Ba-Cu-O thin films

Nanoparticle dispersions of various phases were added to YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO or 123) thin films by multilayer pulsed laser deposition, to determine their effect on flux pinning. The different pinning materials examined include Y/sub 2/BaCuO/sub 5/ (Y211 or green-phase), La/sub 2/BaCuO/sub 5/ (La211 or brown-phase), Y/sub 2/O/sub 3/, CeO/sub 2/, and MgO, with lattice constant mismatches varying from 0.5% to 12% with respect to YBCO. Y211 and Y/sub 2/O/sub 3/ provided significant pinning increases at temperatures of 65 K and 77 K, however other phases provided enhancements only at 65 K (for CeO/sub 2/ and La211) for limited range of applied field strengths. An interesting correlation between T/sub c/ transition widths and pinning strengths was observed. The additions produced markedly different nanoparticle and film microstructures, as well as superconducting properties.

Nanoparticulate Flux Pinning Centers for YBa

YBa2Cu3O7-delta high temperature superconductors can maintain fairly high critical current densities (Jc) with increasing magnetic field. This in-field performance can be further improved upon by incorporating nanoparticulate magnetic flux pinning centers into the superconductors. This short paper briefly discusses and compares recent efforts by the U.S. Air Force Research Laboratory to incorporate insulating nanoparticles into the YBCO superconducting thin films by pulsed laser deposition.

_{2}

Pr doped YBa 2 Cu 3 O 7-d targets with composition Y 1-x Pr x Ba 2 Cu 3 O 7-d where × = 0.0001, 0.001, 0.01, and 0.1 were prepared from oxide powders and were used to deposit thin films by pulsed laser deposition using conditions previously optimized for pure YBa2Cu3O7-d. The Pr dopant was found to be dispersed throughout the film by secondary ion mass spectrometry and found to have an increased density of nanoparticles on the surface. The pinning force of the doped samples was found to decrease with increasing concentration of Pr; however, at 0.01% concentration the doped film displayed a significant enhancement over pure YBa 2 Cu 3 O 7-d for nearly the full range of 0 – 9 T.

Cu

Superconducting power devices made of high temperature superconductors (HTS) can enable megawatt‐class power systems which are lighter in weight and smaller in size than their conventional counterparts. The YBCO coated conductor is expected to be the premiere HTS conductor in making these systems. With advances in YBCO deposition techniques and the establishment of reel‐to‐reel processing, new research should address enhancement of the YBCO coated conductor’s performance. These improvements in the YBCO conductor must include maintaining high critical current densities in fields of a few tesla and minimizing ac losses. This paper first discusses a current sharing scheme in the multifilamentary YBCO conductor to circumvent filamentary breakage. Also, a method for providing magnetic flux pinning to increase the current capacity of the YBCO conductor is outlined using minute additions of rare earth dopants.