Timothy A. Campbell

Flux pinning behavior of incomplete multilayered lattice structures in YBa2Cu3O7−d

Magnetization results of YBa2Cu3O7−d films processed with interlayers of CeO2 inclusions are presented. Unexpected flux pinning results that are different from previous observations with nanoparticulate layered inclusions were observed. Flux pinning was found to be in some cases either slightly improved at either low fields 8T although degraded, sometimes severely, at interim magnetic fields. Most unexpectedly, the pinning performance of the various samples rapidly converges as the temperature is reduced from 77 to 65K, causing all films to have similar Jc(H) behavior at 65K even though dramatically different at 77K.

Pulsed laser deposition of YBCO coated conductor using Y2O3 as the seed and cap layer

Although a variety of buffer layers have been routinely reported, a standard architecture commonly used for the Y Ba2Cu3O7−x (YBCO) coated conductor is Y BCO/CeO2/Y SZ/CeO2/substrate or Y BCO/CeO2/Y SZ/Y2O3/substrate where ceria is typically the cap layer. CeO2 is generally used as only a seed (or cap layer) since cracking within the film occurs in thicker CeO2 layers due to the stress of lattice mismatching. Y2O3 has been proposed as a seed and as a cap layer but usually not for both in a given architecture, especially with all layers deposited in situ. Yttrium oxide films grown on nickel by electron beam evaporation processes were found to be dense and crack free with good epitaxy. In this report, pulsed laser deposition (PLD) of Y2O3 is given where Y2O3 serves as both the seed and cap layer in the YBCO architecture. A comparison to PLD CeO2 is provided. Deposited layers of the YBCO coated conductor are also grown by laser ablation. Initial deposition resulted in specimens on textured Ni substrates with current densities of more than 1 MA cm−2 at 77 K, self-field.

Flux Pinning of Y-Ba-Cu-O Films Doped With

The superconducting properties of YBa₂Cu₃O_7-x (YBCO or 123) thin films doped with BaZrO₃ (BZO) nanoparticles by multilayer and single-target methods were studied and compared. Thin films of 123 + BZO were processed by pulsed laser deposition on LaAlO₃ and SrTiO₃ and single crystal substrates. Multilayer (BZO_0.6nm-1.4 _nm/123 ₁₅ _nm) structures were grown by alternating deposition from 123 and BZO targets, and BZO additions of 0-2 vol% were deposited using (123_1-xBZO_x) single-targets. The multilayer and single-target methods of BZO addition caused significant differences of superconducting transition temperatures (T_c) measured by AC susceptibility, and critical current densities (J_c) measured by both magnetic and transport methods as a function of temperature (T), applied magnetic field (H) and angle of H field incidence (thetas) . Single-target films had almost linear decrease T_c of and self-field J_c with BZO vol% addition, and compared to multilayer films had lower J_c (77 K, H < 4 T) however had improved high-field properties for J_c (77 K, H > 4T. Multilayer films had almost no decrease of T_c and self-field J_c for high BZO additions up to 10 vol% and very strong peak of J_c (H// ab in - plane) and constant and high J_c (H, 0 < thetas < 80 deg) . Single-target BZO-2 vol% films had slightly enhanced J_c(H//c-axis), consistent with results by other authors.

{\rm BaZrO}_{3}

The critical current density (J_c) of YBa₂Cu₃O_7-z films doped with varying flux pinning nanoparticle additions was systematically studied, for applied magnetic fields of H = 0-9 T and operation temperatures T = 20-77 K. Films were prepared with pulsed laser deposition by (M/YBCO)_N multilayer or (YBCO)_1-xM_x single-target methods, for different M phases including Y₂O₃, Y₂BaCuO₅ (Y211) green-phase, and BaZrO₃. Very significant differences of J_c(H//c,20-77 K) were measured for optimized M phase additions, that are difficult to model or predict at present. Multilayer films with Y211 and Y₂O₃ nanoparticle additions had the highest J_c (20-77 K) for H < 4 T, and YBCO+BZO-nanorod samples had the strongest J_c(H) for H > 4 T and 65-77 K, however not for T < 50 K. Seemingly unusual J_c(H,T) properties were measured for (BZO/YBCO)_N multilayer films when compared to YBCO and other doped films; J_c(H) was almost the same as YBCO at 77 K, however at 30 K J_c(H > 2 T) had the strongest properties increasing 70% compared to YBCO+nanoaddition films and increasing 400% compared to YBCO.

Nanoparticles by Multilayer and Single Target Methods

Thin films of (Y1?xEux)Ba2Cu3O7?? with x = 0?1 were grown by pulsed laser deposition on single crystal substrates, to determine the effect of Y and Eu substitution on the microstructural and superconducting properties. The film critical transition temperature (Tc), critical current density (Jc) and surface roughness were found to be strongly dependent on the substrate choice, with the best properties achieved on CeO2?YSZ substrates. Substrates with varying lattice mismatch from ?2% to +1% were studied, including LaAlO3, SrTiO3, CeO2-buffer-coated Zr0.905Y0.095O2 (YSZ), and (LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT). With increasing Eu substitution from x = 0 to 1, the Tc on CeO2?YSZ substrates increased steadily from 89 to 93?K. The value of Jc was measured by magnetic methods at 65 and 77?K, and by transport methods at 77?K for selected samples and different angles of orientation Happl(?) = 0??90?. As Eu substitution was increased from x = 0 to ???0.2, Jc at 77?K increased strongly more than two-fold for ?T and for H<0.5?T for all orientations 0????90?; but, it decreased more than two-fold for ?T. The Jc(H) properties at both low and high fields correlated well with microstructural features observed by scanning electron microscopy. The low-field was enhanced when the grain size was reduced to ~100?nm size, and the self-field and high-field Jc(H) appeared to be strongly affected by the film density and porosity. A controlled dense-island structure was noted for x = 0.75, on CeO2?YSZ substrate.

Temperature and Magnetic Field Dependence of Critical Current Density of YBCO With Varying Flux Pinning Additions

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.