T. Petrisor

Properties of in-situ laser-pulsed deposited YBCO thin films on MgO with SrTiO3 buffer layer

Abstract Epitaxial YBa 2 Cu 3 O 7− y films were grown by pulsed-laser ablation on SrTiO 3 buffered (100) MgO substrate without any pre- or postannealing of the substrate or STO buffer layer. The role of the SrTiO 3 layer is to provide a better lattice mach to the YBCO film and to prevent the interaction between YBCO and MgO. The as-obtained YBCO films exhibit excellent structural and superconducting properties with T c (R = 0) = 90 K , R(300) R(100) = 2.8, Δ T = 0.8 K , J c ≈ 10 6 A/cm 2 (at 77 K and zero magnetic field) and a full width half maximum of the (005) YBCO peak of about 0.18°. These characteristics are very close to those of the YBCO film deposited on SrTiO 3 single crystal.

Brazing of SiC and SiCf/SiC composites performed with 84Si-16Ti eutectic alloy: microstructure and strength

The microstructure and strength of brazed joints for monolithic SiC and SiCf/SiC composites are presented and discussed; the brazing technique is based on the use of the 84Si-16Ti (at%) eutectic alloy. The rather low melting point of the used alloy allows to avoid a degradation of the fibre/matrix-interfaces in the composite materials. All the joints did not show any discontinuities and defects at the interface and revealed a fine eutectic structure. Moreover, in the case of composites, the joint layer appeared well adherent both to the matrix and the fibre interphase, and the brazing alloy infiltration looked sufficiently controlled. High resolving electron microscopic investigations of the microstructure and of the nanochemistry (HREM, EELS, esp. ELNES) revealed atomically sharp interfaces without interdiffusion or phase formation at the interlayer leading to the conclusion that direct chemical bonds are responsible for the adhesion. The joints of SiCf/SiC composites showed 71 ± 10 MPa shear strength at RT and nearly the same values at 600°C.

Laser-ablation deposition of CeO2 thin films on biaxially textured nickel substrates

Abstract Ceria buffer layers were deposited by pulsed laser ablation on (100)[001] cube-textured Ni substrate for the fabrication of high-current Y–Ba–Cu–O tapes for power applications. The films were grown both on Pd-buffered Ni and on pure Ni substrates. The CeO 2 film deposited directly on Ni was not fully epitaxially grown as it had a polycrystalline component. On the contrary, the θ –2 θ X-ray diffraction pattern of Ni–Pd–CeO 2 architecture contained only the (h00) peaks of Pd, Ni and CeO 2 , indicating good epitaxy of Pd and CeO 2 on Ni, and the pole figure showed (100)[001] texture for Pd film and Ni substrate, and (100)[011] for CeO 2 film. The surface of the as-obtained CeO 2 films was smooth and continuous, hence appropriate for further YBCO film deposition.

Biaxial texturing of Ni alloy substrates for YBCO coated conductors

Abstract Biaxial cube texturing and surface quality of the metallic substrate are key parameters for high J c coated conductors. Experiments have demonstrated that the sharp cube texture can be developed up to 11 at.% V, 12 at.% Cr and 5 at.% W alloys; the respective cube textured area fractions result to be 96%, 97% and 99%. For all the studied alloys, FWHM values of ω - and φ -scans are in the range of 5–6° and 6–8°, respectively. Microstructural analyses reveal smooth surfaces with grooves localized at the grain boundaries of twinned cube textured and misoriented grains.

Development of biaxially aligned buffer layers on Ni and Ni-based alloy substrates for YBCO tapes fabrication

This paper presents the development of the CeO/sub 2/ buffer layers on both the non magnetic Ni-V and the Pd-buffered Ni substrates by pulsed laser ablation (PLD). The CeO/sub 2/ films show strong in-plane and out-of-plane orientations. The SEM studies showed that the CeO/sub 2/ films are both smooth and continuous. The magnetic and structural properties of the new Ni-V substrate are also presented. The results demonstrate that Ni-V is an alternative substrate for the fabrication of textured YBCO conductors.

Static and dynamic magnetic properties of epitaxial Co2FeAl Heusler alloy thin films

Structural and magnetic properties of epitaxial Co2FeAl Heusler alloy thin films were investigated. Films were deposited on single crystal MgO (001XS) substrates at room temperature, followed by an annealing process at 600u2005°C. MgO and Cr buffer layers were introduced in order to enhance crystalline quality, and improve magnetic properties. Structural analyses indicate that samples have grown in the B2 ordered epitaxial structure. VSM measures show that the MgO buffered sample displays a magnetization saturation of 1010u2009±u200930 emu/cm3, and Cr buffered sample displays a magnetization saturation of 1032u2009±u200940 emu/cm3. Damping factor was studied by strip-line ferromagnetic resonance measures. We observed a maximum value for the MgO buffered sample of about 8.5u2009×u200910−3, and a minimum value of 3.8u2009×u200910−3 for the Cr buffered one.Structural and magnetic properties of epitaxial Co2FeAl Heusler alloy thin films were investigated. Films were deposited on single crystal MgO (001XS) substrates at room temperature, followed by an annealing process at 600u2005°C. MgO and Cr buffer layers were introduced in order to enhance crystalline quality, and improve magnetic properties. Structural analyses indicate that samples have grown in the B2 ordered epitaxial structure. VSM measures show that the MgO buffered sample displays a magnetization saturation of 1010u2009±u200930 emu/cm3, and Cr buffered sample displays a magnetization saturation of 1032u2009±u200940 emu/cm3. Damping factor was studied by strip-line ferromagnetic resonance measures. We observed a maximum value for the MgO buffered sample of about 8.5u2009×u200910−3, and a minimum value of 3.8u2009×u200910−3 for the Cr buffered one.

Pulsed laser deposition of high critical current density YBa2Cu3O7−x/CeO2/Ni–W architecture for coated conductors applications

Epitaxial YBa2Cu3O7−x (YBCO) films with critical current densities exceeding 1 MA cm−2 (at 77 K in self magnetic field) were epitaxially grown on biaxially textured Ni 5 at% W (Ni–W) substrate using only a CeO2 buffer layer. Both YBCO and CeO2 films were deposited in situ by pulsed laser ablation. The oxidation behaviour of the Ni–W substrate enables the epitaxial growth of a CeO2 oxide buffer layer without using the forming gas (Ar 4%H2). SEM investigations of YBCO and CeO2 films reveal a dense microstructure without cracks or porosity. X-ray pole figures show a cube-on-cube epitaxy with a [100]YBCO//[110]CeO2//[100]Ni–W epitaxial relationship. The YBCO superconducting film has a good out-of-plane and in-plane texture with a full-width-half-maximum of 5.8° and 6.6°, respectively. No severe degradation of JC with film thickness, up to 1 μm thick films, was observed. The use of a single buffer layer on Ni–W substrates represents an important simplification in the scaling-up for long tape fabrication.

Transport Property Improvement by Means of BZO Inclusions in PLD Grown YBCO Thin Films

A detailed study on YBa₂Cu₃O_7-delta (YBCO) films with BaZrO₃ (BZO) inclusions (YBCO-BZO) deposited on SrTiO₃ substrate with different BZO contents is presented. X ray diffraction, SEM imaging and superconductive critical temperature (<i>T</i> _c) measurements were performed to evaluate film growth quality. Independently from the BZO content, all YBCO-BZO films showed <i>T</i> _c values close to that of pure YBCO indicating that the <i>T</i> _c reduction which is usually observed on YBCO-BZO films can be successfully recovered by changing the deposition conditions. All YBCO-BZO films showed an improved critical current density (<i>J</i> _c) dependence on magnetic field if compared to the typical <i>J</i> _c(<i>H</i>) of YBCO, resulting in higher irreversibility fields up to 9 T at 77 K. SEM observation on etched samples suggests a direct link between the defect density measured in YBCO-BZO samples and that calculated from the observed in field performances. The analysis of <i>J</i> _c(<i>B</i>) as a function of applied magnetic field direction revealed that the pinning due to isotropic pinning centers typical for YBCO is coupled with a <i>c</i>-axis correlated pinning in YBCO-BZO which can be ascribed to BZO induced columnar defects. <i>J</i> _c (<i>B</i>) recorded at several temperatures down to 10 K revealed matching effect features.

Epitaxial growth of YBa2Cu3O7-δ on Ni89V11 non-magnetic biaxially textured substrate using NiO as buffer layer

The superconducting YBa2Cu3O7-δ/CeO2/NiO multilayer structure was grown in situ by pulsed-laser deposition on biaxially textured Ni89V11 non-magnetic alloy. The role of vanadium is to decrease the Curie temperature of Ni and to favour the formation of oriented NiO. The (00l)NiO buffer layer has been formed by the controlled oxidation of the Ni-V substrate under 10 mTorr oxygen pressure and at 700 °C. The critical current density of 0.6 MA cm-2, at 77 K and zero magnetic field, was obtained for 0.7 µm thick YBa2Cu3O7-δ films.

High-quality surface YBCO thin films prepared by off-axis pulsed laser deposition technique

Abstract Epitaxial YBCO superconducting thin films have been grown in-situ by XeCl excimer laser ablation using an off-axis deposition geometry. This PLD geometry allows to obtain films with an excellent surface morphology without droplets or other particulates. The as-obtained YBCO films exhibit good structural and superconducting properties with T c( R = 0) =89.5 K, R (300) / R (100) =2.8, ΔT = 1.3 K, J c = 2 × 10 6 A/cm 2 (at 77 K and zero magnetic field) and full width half maximum of the rocking curve of the (005) YBCO peak of about 0.16°. These structural and electrical properties are very close to those of the YBCO films deposited by the conventional PLD on-axis geometry.