Despite the formation of twinned microstructures in grains of REBa 2 Cu 3 O y with y ∼ 7, their grains can be biaxial aligned under modulated rotating magnetic fields (MRFs). In the present study, ...direct observation of twinned microstructures by transmission electron microscopy (TEM) was examined for a magnetically biaxial aligned grain of DyBa 2 Cu 3 O y with y ∼ 7. Use of the biaxial aligned grain enabled us to obtain planar views by TEM easier from a technical viewpoint. Furthermore, an inhomogeneous abundance ratio of two different types of domains (domain ratio) was clarified from the planar view of the grain. The present study strongly suggested that triaxial magnetic anisotropy of RE123 was remained in the grain level due to the inhomogeneous domain ratio, and it led to the achievement of the biaxial alignment of RE123 grains under MRFs.
Abstract
Superconducting FeSe
0.8
Te
0.2
thin films on SrTiO
3
, LaAlO
3
and CaF
2
substrates were electrochemically etched in an ionic liquid, DEME-TFSI, electrolyte with a gate bias of 5 V. ...Superconductivity at 38 K was observed on all substrates after the etching of films with a thickness greater than 30 nm, despite the different
T
c
values of 8 K, 12 K and 19 K observed before etching on SrTiO
3
, LaAlO
3
and CaF
2
substrates, respectively.
T
c
returned to its original value with the removal of the gate bias. The observation of
T
c
enhancement for these thick films indicates that the
T
c
enhancement is unrelated to any interfacial effects between the film and the substrate. The sheet resistance and Hall coefficient of the surface conducting layer were estimated from the gate bias dependence of the transport properties. The sheet resistances of the surface conducting layers of the films on LaAlO
3
and CaF
2
showed identical temperature dependence, and the Hall coefficient was found to be almost independent of temperature and to take values of −0.05 to −0.2 m
2
/C, corresponding to 4–17 electrons per FeSe
0.8
Te
0.2
unit cell area in two dimensions. These common transport properties on various substrates suggest that the superconductivity at 38 K appears in the surface conducting layer as a result of an electrochemical reaction between the surface of the FeSe
0.8
Te
0.2
thin film and the ionic liquid electrolyte.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The potential of thermoelectric thin films lies in wide range of applications from micro-energy harvesting to the sensors. For this, it is essential to have high power factor and ultra-low thermal ...conductivity which have been reported in thin films produced by expensive vacuum techniques. However, for practical applications, it is essential to use inexpensive technique to grow thin film in large area. In this direction, we report the use of mist-chemical vapor deposition (CVD) technique to develop oxide thin films for thermoelectric application. We grow c-axis oriented nano-porous thin films of 2% Al-doped ZnO (AZO). These nano-porous films have enhance phonon scattering which results in the depression of thermal conductivity (κ) while maintaining similar order of magnitude of power factor as reported in dense films prepared by vacuum techniques. For example, κ300K decreases from 6.5 W/m.K for dense thin film (porosity = 7.9%) grown by pulsed laser deposition to 5.54 W/m.K for porous film (porosity = 24.2%) grown by mist-CVD while maintaining the power factor of similar order of magnitude for AZO film deposited on SrTiO3. The depression of thermal conductivity in porous films may lead to higher figure of merit which is promising for practical applications of thermoelectric oxide films.
•Mist-CVD technique allows introducing porosity in ZnO thin films for thermoelectric applications.•Porosity depresses thermal conductivity for higher ZT.•Oxide thermoelectric materials are promising for high temperature module application.•Low deposition temperature gives industrial opportunity and potential benefits for flexible energy generators.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The Vapor-Liquid-Solid (VLS) growth technique, which combines the Pulsed Laser Deposition (PLD) method with the Liquid Phase Epitaxy (LPE), is expected to achieve both high deposition rate and high ...crystallinities. To apply superconducting Coated Conductors (CCs) for applications such as superconducting magnets, it is indispensable to introduce Artificial Pinning Centers (APCs) such as BaHfO 3 (BHO). In this study, we aim to achieve high deposition rate, crystalline orientation, and APCs by using VLS growth technique. As a result, we confirmed that BHO was introduced without deterioration of crystallinities. Furthermore, critical current density J c in magnetic fields of the BHO-doped VLS-YBCO was improved at various temperatures compared with a sample fabricated by the PLD method. However, discontinuous BHO nanorods were observed in the BHO-doped VLS-YBCO from TEM and EDX mapping.
The vapor-liquid-solid (VLS) growth technique is a combination of pulsed laser deposition (PLD) method and liquid phase epitaxy (LPE) and is expected to fabricate structures with high crystallinity ...at a high deposition rate. To utilize superconducting coated conductors (CCs) for applications such as superconducting magnets, it is indispensable to decrease the fabrication cost of CCs. Therefore, we have devised a method to achieve a deposition rate of 26.0 nm/s by changing the partial pressure of O 2 during deposition. Furthermore, an enhanced crystallinity was maintained by using the VLS growth technique, with a thickness of up to 10 μm, and we achieved a critical current I c of 625 A/cm-w.
A new configuration of coated conductors (CCs), REBa2Cu3Oy (RE: rare earth elements such as Sm, Eu, Gd, and Y)/(Sr, La)TiO3 conductive buffer/Ni-electroplated {100}⟨001⟩ textured Cu and SUS316 ...lamination tape, has been proposed to reduce material costs. This conductive buffer layer is slightly modified from the previously reported Sr (Ti, Nb)O3 conductive buffer layers by changing the substitution element and site. However, a drastic change is found in the electric resistivity of the conductive buffer layers after oxygen annealing of YBa2Cu3Oy. The resistivity of Sr(Ti, Nb)O3 conductive buffer layers increases by more than three orders of magnitude, while the resistivity of (Sr, La)TiO3 is almost maintained and only minimally increases. Microscopic structural analysis of the CCs using the newly proposed conductive buffer layer is conducted using transmission electron microscopy (TEM). A very clean interface between the metal tape and the conductive buffer layer in the 600 nm thick (Sr, La)TiO3 buffer layers is confirmed by the TEM analysis, which has no reactive layers as well as no inter-diffusion of oxygen and metal elements. This result will soon lead to the development of low-cost and high-performance CCs.
Critical temperatures (Tc) comparable to those of bulk materials were achieved by post-annealing MgB2 thin films grown at a low temperature of 280 °C. The Tc was improved to 36.7 K under annealing ...conditions of 550 °C for 50 h or more. Under these annealing conditions, a critical current density several tens of times higher at than that of MgB2 wires processed by a powder-in-tube method was achieved at 20 K under 5 T. This is the highest value reported in MgB2 bulk wires and films. Film-based MgB2 is a promising candidate for next-generation MgB2 wires.
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