Search

The phase shift of the electron wave is a useful measure for the projected magnetic flux density of magnetic objects at the nanometer scale. More important for materials science, however, is the knowledge about the magnetization in a magnetic nano-structure. As demonstrated here, a dominating presence of stray fields prohibits a direct interpretation of the phase in terms of magnetization modulus and direction. We therefore present a model-based approach for retrieving the magnetization by considering the projected shape of the nano-structure and assuming a homogeneous magnetization therein. We apply this method to FePt nano-islands epitaxially grown on a SrTiO3 substrate, which indicates an inclination of their magnetization direction relative to the structural easy magnetic [001] axis. By means of this real-world example, we discuss prospects and limits of this approach.

Epitaxial Ba2YNbO6 (BYNO) films were deposited on textured NiW substrates via pulsed laser deposition. The films have dense and smooth surface structure, and more importantly, significantly improved out-of-plane texture, compared with the NiW substrate texture. Transmission electron microscopy study confirms the c-axis tilting of BYNO film and formation of misfit dislocations at NiW/BYNO interface, suggesting that the improved texture should be attributed to the tilted epitaxy via biased dislocation mechanism. YBa2Cu3O7_δ films deposited on BYNO single-buffered NiW substrates show further texture improvement, high superconducting transition temperature of ~91 K, and critical current density of 1.8 MA/cm2 at 77 K, self-field.

Nanostructured ferritic alloys (NFAs) have been considered as primary candidate materials for both fission and fusion reactors because of their excellent creep and irradiation resistances. It has been shown that high temperature fracture toughness could be significantly improved by appropriate thermo-mechanical treatments (TMTs). This article focuses on the static fracture behaviors of newly developed 9Cr NFAs with improved toughness. Optimal TMTs resulted in high fracture toughness at room temperature (>250 MPa √m) and in retaining higher than 100 MPa √m over a wide temperature range of 22–700 °C. Significant differences were found in fracture surfaces and fracture resistance ( J – R ) curves after different TMTs. Unique fracture surface features such as shallow nanoscale facets decorated with shear lips and flake-like grains were observed in high toughness specimens.

We report on the out-of-plane thermal conductivities of tetragonal L10 FePt (001) easy-axis and cubic A1 FePt thin films via time-domain thermoreflectance over a temperature range from 133 K to 500 K. The out-of-plane thermal conductivity of the chemically ordered L10 phase with alternating Fe and Pt layers is ~23% greater than the thermal conductivity of the disordered A1 phase at room temperature and below. However, as temperature is increased above room temperature, the thermal conductivities of the two phases begin to converge. Molecular dynamics simulations on model FePt structures support our experimental findings and help shed more light into the relative vibrational thermal transport properties of the L10 and A1 phases. Furthermore, unlike the varying temperature trends in the thermal conductivities of the two phases, the electronic scattering rates in the out-of-plane direction of the two phases are similar for the temperature range studied in this work.

Spontaneous self-assembly of a multication nanophase in another multication matrix phase is a promising bottom-up approach to fabricate novel, nanocomposite structures for a range of applications. In an effort to understand the mechanisms for such self-assembly, complimentary experimental and theoretical studies are reported to first understand and then control or guide the self-assembly of insulating BaZrO3 (BZO) nanodots within REBa2Cu3O7–δ (RE = rare earth elements including Y, REBCO) superconducting films. The strain field developed around BZO nanodots embedded in the REBCO matrix is a key driving force dictating the self-assembly of BZO nanodots along REBCO c-axis. The size selection and spatial ordering of BZO self-assembly are simulated using thermodynamic and kinetic models. The BZO self-assembly is controllable by tuning the interphase strain field. REBCO superconducting films with BZO defect arrays self-assembled to align in both vertical (REBCO c-axis) and horizontal (REBCO ab-planes) directions result in the maximized pinning and Jc performance for all field angles with smaller angular Jc anisotropy. The work has broad implications for the fabrication of controlled self-assembled nanostructures for a range of applications via strain-tuning.

Phase stability of cubic-pyrochlore-structured RE3TaO7 (RTO, where RE = rare earth elements) pinning additives in YBa2Cu3O7- (YBCO) superconductor and the pinning properties influenced by RTO addition into YBCO films were investigated. RTO completely reacts with YBCO and is converted to cubic-double-perovskite-structured Ba2RETaO6 (BRETO), a more thermodynamically stable tantalate phase within YBCO. In RTO-doped YBCO films, BRETO self-assembled nanocolumnns align along the c-axis of the film and play a major role in the improvement of flux pinning and Jc performance over wide magnetic field and angular ranges.

Oxide self-assembly is a promising bottom-up approach for fabricating new composite materials at the nanometer length scale. Tailoring the properties of such systems for a wide range of electronic applications depends on the fundamental understanding of the interfaces between the constituent phases. We show that the nanoscale strain modulation in self-assembled systems made of high-T(c) superconducting films containing nanocolumns of BaZrO(3) strongly affects the oxygen composition of the superconductor. Our findings explain the observed reduction of the superconducting critical temperature.

Epitaxial γ-Al 2 O 3 thin films were grown on diverse substrates using pulsed laser deposition. The high quality of epitaxial growth and cubic structure of γ-Al 2 O 3 films was confirmed by X-ray diffraction. SrTiO 3 and MgO single crystal substrates were used to optimize the growth conditions for epitaxial γ-Al 2 O 3 film. Under the optimized conditions, epitaxial γ-Al 2 O 3 thin films were grown on flexible, single-crystal-like, metallic templates. These included untextured Hastelloy substrates with a biaxially textured MgO layer deposited using ion-beam-assisted-deposition and biaxially textured Ni-W metallic tapes with epitaxially grown and a biaxially textured, MgO buffer layer. These biaxially textured, γ-Al 2 O 3 films on flexible, single-crystal-like substrates are promising for subsequent epitaxial growth of various complex oxide films used for electrical, magnetic and electronic device applications.

High quality, thick YBa2Cu3O7-delta (YBCO) films with splayed, self-assembled BaZrO3 insulating nanodot columns were epitaxially grown by pulsed laser deposition on short pieces of ion-beam-assisted deposition (IBAD) MgO substrate. Variations in superconducting and microstructural properties were observed for samples grown at different substrate temperatures between 790 and 810degC. At substrate temperatures between 790 and 800degC, samples were measured to have large self-field I c of 670-787 A/cm at 77 K and minimum I c of 353-392 A/cm for all angles at 65 K, 3 T.

Spinel -Al2O3 and NiAl2O4 thin films were grown on (001) SrTiO3 substrates by pulsed laser deposition. The high quality of epitaxial growth and cube-on-cube orientation of the films were confirmed by x-ray diffraction and transmission electron microscopy. The growth of NiAl2O4 thin films is related to the reaction between sequentially deposited -Al2O3 and NiO layers. These films were grown using a unique multi-target approach.

Crystallization studies were performed of epitaxial La{sub 2}Zr{sub 2}O{sub 7} (LZO) films on biaxially textured Ni-3at.%W substrates having thin Y{sub 2}O{sub 3} (10 nm) seed layers. LZO films were deposited under controlled humid atmosphere using reel-to-reel slot-die coating of chemical solution precursors. Controlled crystallization under various processing conditions has revealed a broad phase space for obtaining high-quality, epitaxial LZO films without microcracks, with no degradation of crystallographic texture and with high surface crystallinity. Crack-free and strong c-axis aligned LZO films with no random orientation were obtained even at relatively low annealing temperatures of 850-950 C in flowing one atmosphere gas mixtures of Ar-4% H2 with an effective oxygen partial pressure of P(O2){approx}10{sup -22} atm. Texture and reflection high-energy electron diffraction analyses reveal that low-temperature-annealed samples have strong cube-on-cube epitaxy and high surface crystallinity, comparable to those of LZO film annealed at high temperature of 1100 C. In addition, these samples have a smoother surface morphology than films annealed at higher temperatures. Ni diffusion rate into the LZO buffer film is also expected to be significantly reduced at the lower annealing temperatures.

NdBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (NdBCO) films were grown on rolling-assisted biaxially textured substrates (RABiTS) via pulsed laser deposition. c-Axis-oriented epitaxial NdBCO films with high performance were obtained under optimal deposition conditions. Transmission electron microscopy analysis shows that the NdBCO film grown on RABiTS has a clear interface with a CeO{sub 2} cap layer and a nearly perfect lattice structure. The NdBCO film exhibits higher {Tc} of 93.7 K and better in-field J c in magnetic fields and at all field orientations, compared to pure YBCO films.

We analyzed Nd1+x Ba2−x Cu3O7 (NdBCO) coated conductors grown at various substrate temperatures by using Raman spectroscopy. Epitaxial NdBCO films were deposited on ion beam assisted deposition yttrium stabilized zirconia (IBAD-YSZ) templates by pulsed laser deposition. Raman scattering spectroscopy shows that the NdBCO film grown at a relatively low substrate temperature of 750 ◦ C contains some a-axis oriented grains as well as c-axis oriented grains and an excess cation disorder between Nd 3+ ions and Ba 2+ sites, which result in degradation of superconducting properties with critical temperature (Tc )o f∼83 K and critical current density (Jc )o f less than 1 MA cm −2 at 77 K and self-field. The samples grown at higher temperatures ranging from 775 to 800 ◦ C are found to have strong c-axis orientation with little cation disorder, and subsequently excellent superconducting properties with Tc of 88–90 K and Jc of 1.2–1. 8M A cm −2 at 77 K and self-field. (Some figures in this article are in colour only in the electronic version)

We report significant enhancement in the flux-pinning of epitaxial NdBa2Cu3O7−δ (NdBCO) films on rolling-assisted biaxially textured substrates (RABiTS) via the incorporation of a two-dimensional array of columnar defects comprised of self-assembled BaZrO3 (BZO) nanodots. Pure NdBCO films and NdBCO films incorporating BZO nanodots, both with the same thickness of 0.6 µm, were epitaxially grown on RABiTS by pulsed laser deposition. A very dense and homogeneous distribution of BZO nanodot columns with typical intercolumn spacing of around 15–20 nm oriented along the c-axis of the film was observed in the NdBCO+BZO film. Compared to the pure NBCO film on RABiTS, the NdBCO+BZO film on RABiTS has an in-field critical current density (Jc) of a factor of more than 2 in 0.1–1.5 T and a smaller power-law exponent α~0.21 in the field regime where Jc~H−α.

Heteroepitaxial, single-crystal-like Cu2O films on inexpensive, flexible, metallic substrates can potentially be used as absorber layers for fabrication of low-cost, high-performance, non-toxic, earth-abundant solar cells. Here, we report epitaxial growth of Cu2O films on low cost, flexible, textured metallic substrates. Cu2O films were deposited on the metallic templates via pulsed laser deposition under various processing conditions to study the influence of processing parameters on the structural and electronic properties of the films. It is found that pure, epitaxial Cu2O phase without any trace of CuO phase is only formed in a limited deposition window of P(O2) - temperature. The (00l) single-oriented, highly textured, Cu2O films deposited under optimum P(O2) - temperature conditions exhibit excellent electronic properties with carrier mobility in the range of 40–60 cm2 V−1 s−1 and carrier concentration over 1016 cm−3. The power conversion efficiency of 1.65% is demonstrated from a proof-of-concept Cu2O solar cell based on epitaxial Cu2O film prepared on the textured metal substrate.

Epitaxial NdBa2Cu3O7−δ (NdBCO) films with and without the incorporation of self-assembled nanodots of BaZrO3 (BZO) were grown on rolling-assisted-biaxially-textured substrates (RABiTS) by pulsed laser deposition. Compared to epitaxial YBa2Cu3O7−δ (YBCO) films on RABiTS, NdBCO films are found to have superior performance in applied fields at all field orientations, suggesting the presence of an increased density of pinning centres. The incorporation of columns of self-assembled nanodots of BZO within the NdBCO films results in further enhancement of the in-field Jc at all field orientations. Jc varies as Jc~H−α at intermediate fields, with α values for NdBCO and BZO-doped NdBCO films being ~0.37 and ~0.43, respectively, which are significantly lower than α~0.52 for YBCO film.

We report the epitaxial growth and superconducting properties for NdBa2Cu3O7−δ (NdBCO) films grown on rolling-assisted, biaxially-textured substrates (RABiTS) by pulsed laser deposition. At the optimum deposition temperature of 760 °C, the critical current densities, Jc, at 77 K, self-field, of NdBCO films ranging in thickness from 0.13 to 0.25 µm were found to be in the range 2.2–3.4 MA cm−2, with a lower thickness corresponding to a higher Jc. Compared to epitaxial YBa2Cu3O7−δ (YBCO) films, these NdBCO samples are found to have superior field and angular dependences of Jc. In an applied field of 1 T, NdBCO of the same thickness has more than twice the Jc of YBCO films with a significantly enhanced Jc peak for a field applied parallel to the c-axis. These results suggest the presence of an increased density of c-axis correlated pinning centres within NdBCO films compared to YBCO films.

NdBa 2 Cu 3 O 7-δ (NdBCO) films were grown by pulsed-laser deposition (PLD) on SrTiO 3 (STO)(1 0 0), MgO(1 0 0), and STO-buffered MgO(1 0 0) substrates for a comparative study on the effect of substrate on the textures, microstructures, and superconducting properties of NdBCO films. All NdBCO films were deposited at the same substrate temperature of 800 °C under the same total pressure of 800 mTorr with 1%O 2 /Ar gas. The transport J c value of 3.5 MA/cm 2 at 77 K in self-field was obtained from the NdBCO/STO with T c value of 91.2 K, while the NdBCO/MgO with T c of 86.8 K exhibited the low J c value of 0.25 MA/cm 2 . On the other hand, J c value of 1.55 MA/cm 2 was obtained from NdBCO film on STO-buffered MgO(1 0 0) substrate with T c of 91.5 K. The higher J c value of the NdBCO/STO than NdBCO/STO/MgO resulted from much better in-plane and out-of-plane textures of NdBCO/STO, while the low J c value of the NdBCO/MgO can be attributed to both depressed T c value and the existence of 45°-rotated grains with [001] NdBCO ∥[110] MgO .

We report a successful fabrication of high- J c NdBa 2 Cu 3 O 7− δ (NdBCO) coated conductors on CeO 2 /IBAD-YSZ/SS templates (YSZ ∼ 2 μm thick, CeO 2 ∼ 20 nm thick). The NdBCO films were prepared by pulsed laser deposition (PLD) at the substrate temperatures ( T s ) ranging from 750 to 830 °C under the same total pressure of 800 mTorr with 1%O 2 /Ar gas. Transport J c values over 1 MA/cm 2 at 77 K in self-field were achieved for NdBCO coated conductors deposited at T s of 775–800 °C. The highest J c value of 1.8 MA/cm 2 was obtained from the NdBCO coated conductor deposited at 775 °C, implying that NdBCO is comparable to YBCO for coated conductors. These samples had T c values of 88–90 K, commonly exhibited good in- and out-of-plane textures with the FWHM values of (1 0 3) ϕ -scan and the (0 0 6) ω -scan of 7–8° and 3.5–4.5°, respectively, and the densities and sizes of outgrowth particles in the films were not apparently different from each other.

The BiVO4 additive was found effective for low-temperature firing of ZnNb2O6 polycrystalline ceramics below 950°C in air without a serious degradation in their microwave dielectric properties. Dense BiVO4-doped ZnNb2O6 samples of a relative sintered density over 95% could be prepared even at 925°C. An optimally processed specimen exhibited excellent microwave dielectric properties of Q·f= 55000 GHz, ɛr= 26, and τf=−57 ppm/°C. With increasing BiVO4 addition up to 20 mol% relative to ZnNb2O6, while the quality factor Q·f was gradually decreased, the relative dielectric constant, ɛr, was linearly increased and the temperature coefficient of resonant frequency, τf, was slightly increased. The variations in Q·f and ɛr are surely attributable to the residual BiVO4 in the ZnNb2O6 matrix. An unexpected slight increase in τf is probably due to the formation of the Bi(V,Nb)O4-type solid solution.

We have systematically investigated the effects of processing parameters, including various oxygen pressures (Po2) ranging from 200 to 1000 m Torr and substrate temperatures (Ts) ranging from 500 to 750°C, on the characteristics of Bi-substituted yttrium iron garnet (Bi:YIG) films grown on (111) gadolinium gallium gamet (GGG) substrates. Bi: YIG films were grown using a pulsed laser deposition method with an ArF excimer laser (λ=193 nm). Although the compositions of all the Bi:YIG films grown at the constant Ts of 600°C were close to the target composition irrespective of Po2, the Bi contents were slightly increased with increasing Po2, which was consistent with the variation in Faraday rotation angles (θF). In addition, the crystallinity of the Bi:YIG films was deteriorated with increasing Po2, and their grains became irregular. At Ts above 700°C, Bi-deficient yttrium iron garnet films were grown. Consequently, high quality epitaxial Bi:YIG films exhibiting Faraday rotation angles of −1.0≈−1.5 degree/μm were successfully grown at the substrate temperatures in the range of 500–650°C when the Po2 of 200 mTorr was used.

Long-length, high-temperature superconducting (HTS) wires capable of carrying high critical current, Ic, are required for a wide range of applications. Here, we report extremely high performance HTS wires based on 5 μm thick SmBa2Cu3O7 − δ (SmBCO) single layer films on textured metallic templates. SmBCO layer wires over 20 meters long were deposited by a cost-effective, scalable co-evaporation process using a batch-type drum in a dual chamber. All deposition parameters influencing the composition, phase, and texture of the films were optimized via a unique combinatorial method that is broadly applicable for co-evaporation of other promising complex materials containing several cations. Thick SmBCO layers deposited under optimized conditions exhibit excellent cube-on-cube epitaxy. Such excellent structural epitaxy over the entire thickness results in exceptionally high Ic performance, with average Ic over 1,000 A/cm-width for the entire 22 meter long wire and maximum Ic over 1,500 A/cm-width for a short 12 cm long tape. The Ic values reported in this work are the highest values ever reported from any lengths of cuprate-based HTS wire or conductor.

A correlation between flux-pinning characteristics and stacking faults (SFs) formed by Sm substitution on Y and Ba sites was found in Sm-doped YBa${}_{2}$Cu${}_{3}$O${}_{7\ensuremath{-}\ensuremath{\delta}}$ films. It was confirmed that 223-type-SFs, ${\mathrm{Y}}_{2}$Ba${}_{2}$Cu${}_{3}$O${}_{x}$, composed of extra Y and O planes aligned parallel to the $\mathit{ab}$-planes formed via Sm substitution on the Y site and increased in number with increasing Sm doping on the Ba site. The number density of 223 SFs is correlated strongly with the enhancement in $\mathit{ab}$-plane-correlated flux pinning, resulting in a sharpening of the $H$||$\mathit{ab}$ peak in the plot of critical current density versus magnetic field orientation.

We report rare earth barium tantalates, Ba2RETaO6 (BRETO, RE = rare earth elements) as a new class of additives for superior flux-pinning in YBa2Cu3O7- (YBCO) films. BRETO compounds have excellent chemical inertness to and large lattice mismatch with YBCO. This results in phase separation and strain minimization driven self-assembly of BRETO nanocolumns within YBCO films. YBCO+4 vol% Ba2GdTaO6 films show similar Tc to that of an un-doped film of ~ 88.3 K, a higher self-field Jc of 3.8 MA/cm2 at 77 K, and significantly improved in-field Jc higher by a factor of 1.5-6 over entire magnetic field and angular ranges.

We have investigated the superconductive transport properties of Y Ba2Cu3O7 films containing self-assembled columnar arrays of second phase SrZrO3 or BaSnO3 precipitates. A matching condition between columnar pinning sites (aligned at or near the c axis) and external magnetic flux, tilted with respect to them, is identified in the critical current JC(H) data. The results for the material containing SrZrO3-based pins are analyzed within a simple intuitive model. At matching, the critical current is enhanced above the model prediction. In complementary contact-free investigations of BaSnO3-doped material, matching effects are observed over a wide range of temperatures in the field dependence of JC(H). The deduced matching fields agree reasonably well with the densities of columnar pins directly observed by scanning electron microscopy.

We identify a phase transition in the vortex system of a high-temperature superconductor with nano-columnar stacks of precipitates as strong vortex pinning centers. Above a particular, temperature-dependent field $B_X(T)$ the vortex response is no longer determined by the nano-columns, and is instead determined by point-like pinning. This phase transition leads to the change in the measured critical current density as a function of angle between the applied magnetic field and the nano-columns. Below the unbinding, there is a strong maximum in $J_C$ when field is aligned parallel to the columns. Above the unbinding, there is a minimum for this orientation., Comment: Formatted for APL

The critical current density Jc and the magnetic relaxation (‘creep’) properties have been studied for a set of NdBa2Cu3O7−δ (NdBCO) films doped with BaZrO3 (BZO) nanoparticles to form columnar defects. The dependence of Jc on the magnitude and orientation of the applied magnetic field Happ (0–6.5 T) and temperature T (5 K–Tc) was investigated. The normalized flux-creep rate S =− dln(J)/dln(t) was determined as a function of T. The current dependence of the effective activation energy Ueff(J) was derived using the formalism developed by Maley. The results are well described by an inverse power law type barrier of the form Ueff(J) ∼ U0(J0/J)μ with fitted values for the pinning energy scale U0 and the glassy exponent μ. When comparing values for these parameters in the BZO-doped samples with those for their undoped control counterparts, the most striking difference is the larger scale of current density J0 in the doped samples (a factor of 2.4 higher), while the other pinning parameters do not differ strongly. In the BZO-doped materials, the pinning energy scale U0 increases with vortex density and J0 decreases, with both following simple power law dependences on the field.

To obtain an engineered surface for deposition of high-Tc superconductors, nanoscale modulations of the surface of the underlying LaMnO3 (LMO) cap layer is a potential source for generating microstructural defects in YBa2Cu3O7−δ (YBCO) films. These defects may improve the flux pinning and consequently increase the critical current density, Jc. To provide such nanoscale modulation via a practical and scalable process, palladium (Pd) or tantalum (Ta) nano-islands were deposited using dc-magnetron sputtering on the surface of the cap layer of commercial metal tape templates for second-generation wires. The size and density of these nano-islands can be controlled by changing sputtering conditions such as the power and deposition time. Compared to the reference sample grown on an untreated LMO cap layer, the YBCO films grown on the LMO cap layers with Pd or Ta nano-islands exhibited improved in-field Jc performance. Atomic force microscopy and transmission electron microscopy were used to assess the evolving size and density of the nano-islands.

Heteroepitaxial semiconductor films on low-cost, flexible metal foil templates are a potential route to inexpensive, high-efficiency solar cells. Here, we report epitaxial growth of Si films on low-cost, flexible, biaxially-textured Ni-W substrates. A robust buffer architecture comprised of multiple epitaxial oxide layers has been developed to grow high quality, heteroepitaxial Si films without any undesired reaction between the Si film and the metal substrate and with a single biaxial texture. XRD analysis including ω-scans, φ-scans, and pole figures confirms that the buffers and silicon are all epitaxial, with excellent cube-on-cube epitaxy. A photo-conversion efficiency of 1.1% is demonstrated from a proof-of-concept heteroepitaxial film Si solar cell.

Ba2RENbO6 (RE = rare earth elements including Y) compounds are considered new additives for superior flux-pinning in YBa2Cu3O7-δ (YBCO) films due to their excellent chemical inertness to and large lattice mismatches with YBCO. Simultaneous laser ablation of a YBCO target and a Nb metal foil attached to the surface of the target resulted in epitaxial growth of YBCO films having columnar defects comprised of self-aligned Ba2YNbO6 (BYNO) nanorods parallel to the c-axis of the film. Compared to pure YBCO, YBCO+BYNO films exhibited no Tc reduction as well as superior Jc performance with higher self- and in-field Jc by a factor of 1.5–7 and also exhibited a strong Jc peak for H∥c indicative of strong c-axis correlated flux-pinning.

Phase separated, epitaxial, nanostructured film comprised of BaTiO3 (BTO) and CoFe2O4 (CFO) composite has been developed as a potential multifunctional cap buffer layer for improved flux-pinning in YBa2Cu3O7−δ (YBCO) films. All films were deposited by pulsed laser deposition on SrTiO3 (STO) (100) single crystal substrates. The CFO fraction and growth temperature were identified as key factors for determining the areal number density and mean diameter of the CFO nanocolumns. Compared to the reference sample grown on a pure BTO cap layer, the YBCO films grown on BTO+CFO cap layers show a remarkable improvement in isotropic flux-pinning and, consequently, Jc over the entire field and angle ranges. Transmission electron microscopy analysis confirmed the presence of a very defective YBCO layer containing a high density of randomly distributed defects at the interface area, induced by nanostructural modulation on the surface of the BTO+CFO composite cap layer.

Nanostructural modulation in the cap layer used in coated conductors can be a potential source for nucleating microstructural defects into the superconducting layer for improving the flux-pinning. We report on the successful fabrication of phase separated, epitaxial, nanostructured films comprised of LaMnO3 (LMO) and MgO via pulsed laser deposition (PLD) on biaxially-textured MgO metallic templates with a LMO buffer layer. Scanning Auger compositional mapping and transmission electron microscopy cross sectional images confirm the nanoscale, spatial modulation corresponding to the nanostructured phase separation in the film. YBa2Cu3O7-δ films (0.8 µm thick) grown using PLD on such phase separated, nanostructured cap layers show reduced field dependence of the critical current density with an α value of ~0.38 (in Jc~H-α).

A unique, three-dimensional (3D), biaxially textured, MgO, nanofence comprised of single crystal MgO nanobelt segments or links was synthesized via epitaxial growth on (100) SrTiO(3) substrates. Individual single crystal MgO nanobelt segments comprising the nanofence have a square cross-section with dimensions in the range of 10-20 nm and with lengths in the range from 100 nm up to 1 microm. X-ray diffraction shows that the 3D MgO nanofence has an epitaxial relation with (100) SrTiO(3) substrates with a cube-on-cube, {100}100 orientation and with values of the full width at half-maximum of the (200) omega-scan and the (110) varphi-scan at 4.5 degrees and 5.5 degrees , respectively. Such a biaxially textured oxide nanofence with single crystal segments can be used as a 3D nanotemplated substrate for epitaxial growth of wide-ranging, 3D, electronic, magnetic and electromagnetic nanodevices.

High-temperature superconductors (HTS) are finding use as high - current wires for potential application in power devices. The dependence of their basal-plane critical current properties on orientation in a magnetic field can pose important design problems. Here we report material and operating parameter conditions where prototype HTS tape conductors exhibit critical current characteristics that are essentially field-orientation independent. The novel phenomenon is observed for specific magnetic field intensities that depend on the operating temperature, and in materials having strong flux pinning by extended nanoscale structures aligned roughly along the HTS crystalline c-axis. The effect can be described by a simple model for the field dependence of critical current density, generalized for anisotropic electronic response. This description may provide insight into means to fine-tune the material properties for nearly isotropic performance characteristics at a preferred field and temperature., 7 pages, 6 figures

Epitaxial NdBa2Cu3O7-x films with a hybrid nanoscale defect structure comprised of BaZrO3 nanodot arrays aligned along the c-axis in one half of the film thickness and aligned perpendicular to the c-axis in the other half thickness of the film were fabricated. Transmission electron microscopy images confirm the orientation of the nanoscale defect structures. The angular dependence of critical current density, Jc, at 77 K, 1 T, shows significantly reduced angular variation of Jc. This study nicely demonstrates how pinning characteristics can be tuned by tuning the nanoscale defect structures within the films., 13 pages, 3figures, submitted to Applied Physics Express

High temperature superconducting (HTS) wires capable of carrying large critical currents with low dissipation levels in high applied magnetic fields are needed for a wide range of applications. In particular, for electric power applications involving rotating machinery, such as large-scale motors and generators, a high critical current, Ic, and a high engineering critical current density, JE, in applied magnetic fields in the range of 3 5 Tesla (T) at 65 K are required. In addition, exceeding the minimum performance requirements needed for these applications results in a lower fabrication cost, which is regarded as crucial to realize or enable many large-scale bulk applications of HTS materials. Here we report the fabrication of short segments of a potential superconducting wire comprised of a 4 m thick YBa2Cu3O7− (YBCO) layer on a biaxially textured substrate with a 50% higher Ic and JE than the highest values reported previously. The YBCO film contained columns of self-assembled nanodots of BaZrO3 (BZO) roughly oriented along the c-axis of YBCO. Although the YBCO film was grown at a high deposition rate, three-dimensional self-assembly of the insulating BZO nanodots still occurred. For all magnetic field orientations, minimum Ic and JE at 65 K, 3 T for themore » wire were 353 A cm−1 and 65.4 kA cm−2, respectively.« less

We report magnetic properties of Y3Fe5O12 (YIG) films on thermally oxidized Si (100) and (Gd3Ga5O12) GGG (111) substrates. Amorphous YIG films with the cation ratio Y:Fe=3.04:4.96, deposited by rf-magnetron sputtering at room temperature in pure argon atmosphere, were crystallized by postannealing (600–900 °C) of amorphous films in air and in 500 ppm oxygen. While postannealed YIG films on GGG substrates were well textured, those on Si (100) were randomly oriented. High-quality YIG films could be better obtained in the reduced (500 ppm O2) oxygen atmosphere than air since more effective YIG growth during annealing process and lower FMR linewidth (ΔH) of films could be achieved.

The sintering behaviors and microwave dielectric properties of V2O5-added and -substituted ZnNb2O6 ceramics with columbite structure (abbreviated as ZNV and ZVN, respectively) have been investigated. It was found that the addition or substitution of V2O5 to ZnNb2O6 ceramics lowers the sintering temperature from 1150°C to ∼900°C, but the sintering mechanisms are different. The formation of a ternary liquid phase is attributed to enhanced sintering in ZNV samples. Interaction between ZnNb2O6 and V2O5 also led to the formation of a second phase, V3Nb17O50. In contrast, it has been observed that with up to 8 mol% substitution of V2O5 in ZnNb2O6, a complete solid solution is formed. The sintering temperature for the ZVN sample becomes lower due to the decreased temperature of liquidus according to the substitution of V for Nb ions. The microwave dielectric properties of ZNV samples are seriously degraded due to the presence of a V3Nb17O50 second phase. This was confirmed by measuring the dielectric properties of V3Nb17O50 second phase. However, V-substituted Zn(Nb0.94V0.06)2O6 samples sintered at 875°C for 2 h exhibit excellent microwave dielectric properties: Q×f of 65,000 GHz, ε r of 24, and τf of -72 ppm/°C.