Superconductor Substrate Research Articles

Characterization of Buffer Layers on Ni-based Substrates for YBCO Superconductors

Metal oxide buffer layers provide a continuous, smooth textured and chemically inert surface for growth of the YBCO (YBa2Cu307-x) film and prevent metal diffusion from the substrate into the superconductor. Ce02, Gd203 and EU203 buffer layers were grown on metallic Ni substrates using a sol-gel method by using metal 2,4-pentanedionate and acetate precursors. The films were annealed at 1150°C under 4%H2-Ar gas mixture. Textured, crack free and continuous buffer layers were obtained through the sol-gel technique. Prior to the coating process, solution characterization was performed by turbidimeter, pH meter, contact angle goniometer and rheometer. Heat treatment profiles were determined by using DTA-TG and FTIR. The coated layers were characterized by means of XRD, SEM-EDS, AFM and a scratch tester. As a result, textured growth of Ce02, EU203 and Gd203 thin films on textured Ni tapes by the sol-gel dip coating process were successfully performed.

Processing and Characterization of Ni Base Coated Superconductor Substrate Tapes With Layered Architecture

Ni/Ni-5 at.%Mo and Ni/Ni-5 at.%Mo/Ni multilayer tapes were prepared from elemental powders by a powder metallurgy route for coated superconductor substrate applications. The development of cube texture ({001}(100)) following heavy cold rolling ( ~95%) and annealing has been studied in the Ni side(s) of these multilayer tapes and compared to a nonalloyed Ni tape. Although the deformation textures in the Ni side(s) of these multilayer tapes appear quite similar to that of the nonalloyed Ni tape cold rolled to a similar deformation level, the volume fraction of the cube grains in the Ni side(s) of the multilayer tapes following annealing shows marked improvement as compared to the nonalloyed Ni tape after different annealing treatments. X-ray area mapping from typical cross-sectional areas of the multilayer compacts in the sintered condition reveals significant diffusion of the alloying element Mo from the alloy side(s) to the Ni side. These facts amply corroborate the earlier observation on the beneficial role of Mo on the development of cube texture in Ni. The yield strength of the annealed multilayer tapes shows marked improvement over nonalloyed Ni tapes.

The pre-oxidation process of electropolishing for the textured {113} <121> Ag substrate for Tl-1223 superconductor substrate

The surface roughness of a substrate is typically influenced by grain boundaries, grooves and voids. In an effort to improve the surface roughness, a textured {113} Ag substrate was electropolished using a new method that causes the formation of an oxidation layer at the constant current density before electropolishing at a constant voltage of 1.75 V vs. SCE. The constant current density and potential were determined using the anodic polarization method. The pH effect for the optimized electropolishing condition was also investigated by adding phosphoric acid. The edges of the grain boundaries, grooves and voids became smoother when a constant current density was supplied with the pre-oxidation. A RMS (root mean square) value of 5.90-nm regarding the surface roughness of the Ag substrate was obtained without a final surface treatment before electropolishing, while a RMS surface roughness value of 34.12-nm was obtained for an Ag substrate that was given a final surface treatment for mechanical polishing.

Time-domain terahertz spectroscopy of (100) MgO and (100) LaAlO3 substrates

THz(teraherz)properties of high-Tc superconductor substrates(100)MgO and (100)LaAlO3 are measured using time-domain spectroscopy at frequency range between 0.2 and 2 THz.The complex refractive index and dielectric function of the MgO substrate is independent of frequencies;those of LaAlO3 increase slightly with increasing frequency.We determine=3.46+i0.001 and=12.27+i0.06 for the MgO substrate and =4.78+i0.02 and =22.5+i0.2 for the LaAlO3 substrate at 1THz.The dielectric loss tanδ of both LaAlO3 and MgO substrate is less than 0.01The tanδ of LaAlO3 in nearly five times larger than MgO,but both of them are less than 0.01.

Preparation and properties of Ba 2− xSr xSmTaO 6 ( x=0–2): a group of new perovskite materials

A new group of complex oxide materials were synthesized by the conventional solid state method. These compounds have the general formula Ba 2− x Sr x SmTaO 6 ( x=0, 0.5, 1.0, 1.5 or 2) and complex perovskite structures. The compounds belonging to this Ba 2− x Sr x SmTaO 6 group exhibited a regular transition from the ideal cubic structure to a pseudocubic structure as the strontium content is increased. Pure Ba 2SmTaO 6 gave an ideal cubic perovskite crystal structure of A 2(BB′)O 6 type, while pure Sr 2SmTaO 6 was found to have a pseudocubic structure. The unit cell dimensions of these compounds varied from 8.4687 to 8.3232 Å as the amount of Sr ( x) in Ba 2− x Sr x SmTaO 6 increased from 0 to 2. The theoretical density of these samples also decreased from 7.6756 to 6.9401 gm/cm 3 as the value of x is changed from 0 to 2. All these powders could be sintered to more than 90% theoretical density at 1650 °C in 4 h. These compounds were found to be thermally stable and did not show any phase change. They had dielectric constants in the range 14–18 and the loss factor values were about 2×10 −3 at a frequency of 10 7 Hz. These Ba 2− x Sr x SmTaO 6 ceramics gave moderate values of dielectric constant and loss factor, in the range suitable for use as substrates for superconductors.

Dielectric properties of nanoparticulate Ba2EuZrO5.5 perovskite at microwave frequencies

Dielectric properties of a complex perovskite material, Ba2EuZrO5.5, which was proposed as a suitable substrate for high TC superconducting films [R. Jose et al., J. Mater. Res., 15, 2125 (2000)], were measured in the frequency range from 0.47 to 26 GHz and in the temperature range from 77 to 350 K. In the present research, sintered bulk Ba2EuZrO5.5 material composed of nanocrystallites was used. The dielectric constant: ε′=32,25±0.3% was measured at 300 K, and the material was found to be rather lossy with tan δ close to 10−2. The temperature measurements show unusual behavior of the dielectric properties. In the range from 100 to 250 K, a considerable increase of the dielectric constant and losses were observed. This effect might be due to the tilting of B(B′)O6 octahedra commonly found in complex perovskite materials. Due to such behavior, the applications of Ba2EuZrO5.5 as a substrate for YBCO and BISCCO superconductors at high and microwave frequencies should be rather ruled out.

Nanoparticles of Ba 2MSnO 6− x (M=Ce, La and Nd; x=0 or 0.5): a new group of complex perovskite oxides

Three new mixed oxide ceramic compounds viz., Ba 2CeSnO 6, Ba 2LaSnO 5.5 and Ba 2NdSnO 5.5, were prepared as nanoparticles using a polymeric combustion method. These compounds were characterized using X-ray powder diffraction, infrared spectroscopy, particle size analysis, surface area measurements, differential thermal analysis, thermogravimetric analysis, dielectric constant determination at room temperature as well as scanning electron microscopy. The X-ray diffraction patterns of these samples are indexed and they are found to have an ordered cubic perovskite structure. The unit cell dimensions of the three samples are a=8.5484 Å for Ba 2CeSnO 6, a=8.5305 Å for Ba 2LaSnO 5.5 and a=8.5054 Å for Ba 2NdSnO 5.5. The SEM studies of the as-prepared powders of Ba 2CeSnO 6, Ba 2LaSnO 5.5 and Ba 2NdSnO 5.5 have shown that they have an average size less than 50 nm. Their dielectric constant values are 25.67, 20.36 and 18.69, respectively, at a frequency of 10 7 Hz. The samples are sintered at much lower temperatures of (1425–1475 °C) compared to similar samples prepared by conventional methods. They have reasonably low dielectric constant and are thermally stable. Hence, they have the potential for use as a substrate for superconductors. In this paper, we present the results and details of preparation and characterization of three new compounds Ba 2CeSnO 6, Ba 2LaSnO 5.5 and Ba 2NdSnO 5.5.

DEVELOPMENT AND CHARACTERISATION OF Ba2RENbO6 (RE = Yb, Er AND Ho) AND POTENTIAL USE AS SUBSTRATE FOR SUPERCONDUCTING YBCO FILMS

A group of complex perovskite oxides Ba2RENbO6 (RE = Yb, Er and Ho) have been synthesised and developed for their use as substrate for YBa2Cu3O7-δ superconductors. These materials have a complex cubic perovskite ( A2BB′O6 ) structure with lattice constants, a=8.3–8.5 Å. Ba2RENbO6 did not show any phase transition in the temperature range 30–1100°C. The dielectric constant and loss factor of Ba2RENbO6 are in the range suitable for their use as substrate for microwave applications. YBa2Cu3O7-δ superconductors did not show any detectable chemical reaction with Ba2RENbO6 even under extreme processing conditions. Dip-coated YBa2Cu3O7-δ thick films on polycrystalline Ba2RENbO6 substrate gave a T c (0) of 92 K and a current density of ~ 1.2 × 104 A cm-2.

Study of thermal oxidation of NiO buffers on Ni-based tapes for superconductor substrates

NiO on Ni-based textured substrates is a potential buffer layer system for growth of superconductor films for conductor applications. In this work, the high temperature oxidation of NiO has been studied under different oxygen partial pressures. Pure Ni, Ni–10%Cr and Cr-coated Ni have been studied. Pure Ni when oxidised at 1250°C for 3 h in P O 2 ∼1 atm has shown excellent pure cube texture. Ni–10%Cr oxidised under the same condition has shown the same texture, however the tape becomes very brittle. The conditions for reproducible growth of highly cube textured NiO are determined.

A study on textured silver tapes used as substrates for YBCO high temperature superconductors

A single-component, {110}〈211〉, biaxially textured silver tape was obtained by cold-rolling and annealing. The cold-rolling textures and recrystallization textures of silver were studied systematically. It is shown that a sharp biaxial {110} texture can be obtained by using higher total rolling reduction, lower reduction per pass and higher annealing temperature. In-plane aligned YBCO film was deposited directly by pulsed laser deposition (PLD) on a textured silver foil having {110}〈211〉 orientation. The critical current density J c value of 5×10 5 A/cm 2 was obtained at 77 K, 0 T.

Barium Rare‐Earth Hafnates: Synthesis, Characterization, and Potential Use as Substrates for YBa2Cu3O7‐delta Superconductor

A new group of complex perovskites Ba2REHfO5.5 (where RE = La, Pr, Nd, and Eu) has been synthesized and sintered as single‐phase materials with high sintered density and stability using a solid‐state reaction method for the first time. The structure of Ba2REHfO5.5 has been studied by X‐ray diffactometry (XRD) and all of the perovskites are isostructural and have a cubic structure. The dielectric constant and loss factor values of these materials are in a range suitable for their use as substrates for YBa2Cu3O7‐delta superconductors. XRD and resistivity measurements show that there is no detectable reaction between YBa2Cu3O7‐delta and Ba2REHfO5.5, even when the two substances are mixed thoroughly and sintered at 950°C for 15 h. The addition of Ba2REHfO5.5 up to 20 vol% in YBa2Cu3O7‐delta‐Ba2REHfO5.5 composite shows no detrimental effect on the superconducting transition temperature of YBa2Cu3O7‐delta. Thick films of YBa2Cu3O7‐delta fabricated on polycrystalline Ba2REHfO5.5 substrate have a superconducting zero resistivity transition of 92 K, indicating the suitability of these new materials as substrates for YBa2Cu3O7‐delta films.

Cube-textured nickel substrates for high-temperature superconductors

The biaxial textures created in metals by rolling and annealing make them useful substrates for the growth of long lengths of biaxially textured material. The growth of overlayers such as high-temperature superconductors requires flat substrates with a single, sharp texture. A sharp cube texture is produced in high-purity Ni by rolling and annealing. We report the effect of rolling reduction and annealing conditions on the sharpness of the cube texture, the incidence of other orientations, the grain size and the surface topography. A combination of high reduction and high-temperature annealing in a reducing atmosphere leads to >99% cube texture, with a mosaic of about the rolling direction, about the transverse direction, and about the normal direction.

Processing and characterization of cobalt-stabilized YBa 2Cu 3O y as a substrate for bulk superconductors

The physical properties of ceramic YBa 2Cu (3− x) Co x O y were investigated to evaluate its usefulness as a substrate material for bulk YBa 2Cu 3O y superconductors. YBa 2Cu (3− x) Co x O y is thermally and chemically compatible with YBa 2Cu 3O y and displays adequate electrical properties for a substrate material. An intensive investigation of materials with the nomial composition of YBa 2Cu 2.2Co 0.8O y revealed semiconductor-like behavior, with a room-temperature resistivity of 70 mωcm and a 77 K resistivity of 4 × 10 6 mωcm. Measured mechanical properties YBa 2Cu (3− x) Co x O y indicated that its flexural strength is low (60 MPa) and highly dependent on sintering conditions. YBa 2Cu (3− x Co x O y was found to be a good substrate material for bulk YBa 2Cu 3O y superconductors. Coils with a continuous superconducting path, made from superconductor/substrate composites, were characterized, and Co diffusion into the superconducting layer was investigated. Optimal processing conditions are discussed.

A ferroelectric-superconducting photodetector

A ferroelectric-superconducting photodetector has been developed and characterized. An atomically ordered PbZrTiO3 (PZT) ferroelectric gate was grown over a c-oriented YBa2Cu3O7−x (YBCO) high Tc superconductor substrate by excimer laser deposition. Irradiation of the PZT gate with photons near the ferroelectric gap energy resulted in a measurable change of the drain-source photocurrent with the device at a temperature near Tc of the YBCO. The critical temperature of the YBCO base was shifted up to 4 K when the PZT gate was irradiated with photon flux of wavelength from 300 to 500 nm. A responsivity of 360 A/W was measured and an upper bound on response time to optical irradiation of 100 ns was determined.

Biaxially oriented metallic tape substrates for high-temperature superconductors

We report a practical synthesis route for the production of long length, biaxially-oriented high-temperature superconducting (HTS) deposits on metallic tapes. The technique involves epitaxial vapor deposition of appropriate oxide buffer layers on rolled, thermo-mechanically processed fcc-structure base-metal tape substrates. Short segments of ≈1 μm thick YBa2Cu3O7-δ deposits produced by pulsed laser ablation on CeO2 and yttria-stabilized ZrO2 (YSZ) buffered nickel exhibit epitaxial biaxial alignment and have critical current densities over 106 A/cm2 at 77 K in zero applied magnetic field.

Use of a Self-Assembled Monolayer for the Preparation of Crystalline Organic Superconductor/High-Tc Superconductor Structures

Thin films of (BEDT−TTF)2I3 have been deposited by vapor-phase deposition onto high-temperature superconductor substrates. Results from X-ray powder diffraction, atomic force microscopy and scannin...

DyBa 2SnO 5.5 a new ceramic substrate for superconducting YBCO ( Tc( o) = 92 K) and Bi(2223) ( Tc( o) = 110 K) thick films

A new ceramic material, DyBa 2SnO 5.5, has been synthesised and sintered as single-phase material for its use as a substrate for both YBCO and BiSCCO superconductors, for the first time. DyBa 2SnO 5.5 has a complex cubic perovskite (A 2BB'O 6) structure with the lattice constant a = 8.520 Å. The dielectric constant and loss factor of DyBa 2SnO 5.5 are in a range suitable for its use as substrate for microwave applications. YBCO and Bi(2223) superconductors did not show any detectable chemical reactivity (within the precision of the X-ray diffraction technique) with DyBa 2SnO 5.5 even under severe heat treatment. The thick film of YBCO screen printed on polycrystalline DyBa 2SnO 5.5 substrate gave a T c(o) of 92 K and a critical current density ( J c) of 3 × 10 4 A/cm 2 at 77 K. A screen-printed Bi(2223) thick film on a DyBa 2SnO 5.5 substrate gave a T c( o) = 110 K and current density 5 × 10 3 A/cm 2 at 77 K.

YBa2SnO5·5, a novel ceramic substrate for YBCO and BiSCCO superconductors

YBa2SnO5·5 has been synthesized and sintered as single phase material for its use as substrate for both YBCO and BiSCCO superconductors. YBa2SnO5·5 has a complex cubic perovskite (A2BB’O6) structure with the lattice constanta = 8·430 Å. The dielectric constant and loss factor of YBa2SnO5·5 are in a range suitable for its use as substrate for microwave applications. YBa2SnO5·5 is found to be chemically compatible with both YBCO and BiSCCO superconductors. The thick film of YBCO screen printed on polycrystalline YBa2SnO5·5 substrate gave aT c(0) of 92 K and a critical current density (J c) of 4 × 104 A/cm2 at 77 K. A screen printed BiSCCO thick film on YBa2SnO5·5 substrate gaveT c(0) = 110 K and current density 3 × 103 A/cm2 at 77 K.

Modified mixed oxide perovskites 0.7Sr(Al1/2B1/2) O3�0.3LaAlO3 and 0.7Sr(Al1/2B1/2) O3�0.3NdGaO3 (B=Ta5+ or Nb5+) for high-T c superconductor substrate applications

Single-crystal fibres of modified strontium aluminium tantalum oxide (1-x)Sr(Al1/2Ta1/2) O3·xLaAlO3(SAT-LA) and (1-x)Sr(Al1/2Ta1/2)O3·xNdGaO3 (SAT·NG), and modified strontium aluminum niobium oxide (1-x)Sr(Al1/2Nb1/2)O3·xNdGaO3(SAT·NG) and (1-x)Sr (Al1/2Nb1/2)O3·xLaAlO3 (SAN·LA) were grown using a laser-heated pedestal growth technique. 0.7SAT·0.3LA grows congruently and retains a twin free simple cubic perovskite structure (as the SAT) when cooled down to room temperature. 0.7SAT·0.3LA crystals have a moderate dielectric constant (κ = 21.7) and low dielectric loss (tan δ = 7.5 × 10−5) at 10 kHz and 90 K. The reduction problem of Ta5+ is eliminated (which is common in the case of SAT growth). 0.7SAT·0.3NG and 0.7SAN·0.3NG have lower melting temperatures and crystal growth is easier. NdGaO3 addition to the SAT and SAN enhances the potential of SAT and SAN as large-area substrates for high-Tc superconductor growth. However, the dielectric constants increased from κ∼-12 to κ∼-16(0.7SAT·0.3NG) and from κ∼18 to κ∼23 (0.7SAN·0.3NG) as a result of NdGaO3 incorporation.

Ca-Sr-Ga-Nb mixed oxide system for high temperature superconductor substrate applications

Twin-free crystals with relatively low melting temperatures are desirable as substrates for high temperature superconductor (HTSC) oxide substrate materials. In the selection of new oxide substrate compositions, special requirements (e.g. suitable dielectric properties for microwave application and perovskite structure with good lattice matching with YBa 2Cu 3O 7-δ) were considered. In this study the calcium-strontium gallate-niobate (CSGN) system has been investigated in both ceramic and single crystal samples, focusing on their crystal growth. The CSGN compositions were formed by mixing orthorhombic calcium gallate-niobate (CGN) and cubic strontium gallate-niobate (SGN) complex perovskites. CGN-excess mixtures do not create a single phase, as opposed to SGN-excess compositions, where single phase solid solutions are formed. The SGN-excess compositions can produce twin-free CSGN single crystals, which have excellent room temperature dielectric loss (tan δ ≤ 3 x 10 -4) and reasonably low dielectric constant ( K = 41) values at 100 kHz. The growth temperature for a 50 mol% SGN starting composition (CSGN1) was about 1600°C, but for a 65 mol% SGN concentration (CSGN2) it increased to 1750°C. A lattice parameter a = 3.939 Å was obtained for the CSGN1 crystal increasing with SGN concentration. A significant drawback was observed for the Ca-Sr-Ga-Nb oxide system: the effective distribution coefficient of Ca 2+ is very small ( k eff(Ca 2+) ≈ 0.4). This can cause crystal growth difficulties due to constitutional supercooling phenomena.