YBa2Cu3O x superconducting thin films prepared by low temperature vacuum codeposition

Y-Ba-Cu-O films were prepared by low temperature codeposition of three components. The Y and Cu contents were evaporated from metallic sources, while Ba was vacuum-evaporated from Ba, BaO and BaF₂ sources in separate codeposition experiments. The lowest temperature at which superconducting YBa₂Cu₃O _x thin films (about 0.5μm thick) preparedin situ was near 500°C. This process enables preparation of superconducting films on various substrates (SrTiO₃, MgO, Al₂O₃, Si) without a buffer layer. Zero-resistance critical temperature was as high as 88 K and the critical current density was 10⁴ A/cm² at 4.2 K. The morphology of the films was granular with disordered grain orientation, the average grain size being typically 0.5μm.     

Cu2O thin films deposited by reactive direct current magnetron sputtering

The Cu₂O thin films were prepared on quartz substrate by reactive direct current magnetron sputtering. The influences of oxygen partial pressure and gas flow rate on the structures and properties of deposited films were investigated. Varying oxygen partial pressure leads to the synthesis of Cu₂O, Cu₄O₃ and CuO with different microstructures. At a constant oxygen partial pressure of 6.6 × 10^− 2 Pa, the single Cu₂O films can be obtained when the gas flow rate is below 80 sccm. The as-deposited Cu₂O thin films have a very high absorption in the visible region resulting in the visible-light induced photocatalytic activity.     

Influence of BaZrO<Subscript>3</Subscript> Amount on Microstructure and Properties in YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−<Emphasis Type="Italic">x</Emphasis></Subscript> Films Prepared by TFA-MOD Process

Epitaxial YBa₂Cu₃O_7−x /BaZrO₃ films were prepared by complex metal–organic solutions including Y, Ba and Cu anhydrous trifluoroacetate precursors and Zr acetylacetonate precursors. The influence of the amount of BaZrO₃ (BZO) on the structure and properties of YBa₂Cu₃O_7−x (YBCO) films was systematically investigated. The YBCO films having 7 mol % BZO have a maximum critical current density (J _c) value (77 K, 0 T) of 6.0 MA/cm². The enhanced J _c derives from a high density of BZO nanoparticles existing in the YBCO matrix. With increasing BZO amount, J _c of the YBCO films begins to decrease due to larger particles.     

Effect of B2O3 and CuO additives on the sintering temperature and microwave dielectric properties of Ba(Mg1/3Nb2/3)O3 ceramics

B₂O₃ added Ba(Mg_1/3Nb_2/3)O₃ (BBMN) ceramics cannot be sintered below 930 °C. However, when CuO was added to them, they were sintered even at 850 °C. The amount of the Ba₂B₂O₅ second phase, which was formed in the BBMN ceramics decreased with the addition of CuO. Therefore, the CuO additive is considered to react with the B₂O₃ inhibiting the reaction between B₂O₃ and BaO. A dense microstructure without pores developed with the addition of a small amount of CuO. The bulk density, dielectric constant (ɛ_r) and Q-value increased with the addition of CuO, but decreased when a large amount of CuO was added. Excellent microwave dielectric properties were obtained for the Ba(Mg_1/3Nb_2/3)O₃ + 2.0 mol% B₂O₃ + 10.0 mol% CuO ceramic sintered at 875 °C for 2 h, with values Q_xf = 21 500 GHz, ɛ_r = 31 and temperature coefficient of resonance frequency (τ_f) = 21.3 ppm/°C.     

Chemical characterization of melt-textured YBCO produced by hybrid powder metallurgy

Monolithic YBCO samples were made by traditional top-seeded melt-texturing processes from cold-milled mixtures of Y123 (YBa₂Cu₃O_7−δ) and elemental Y. The bulk composition does not lie on the Y211 (Y₂BaCuO₅)–Y123 join so, formation of Y123 from liquid and Y211 is not an essentially isothermal process on cooling. The reaction liquid + Y211 = Y123 is a ternary reaction and occurs over several tens of degrees. The Y123 thus produced has a range in compositions – particularly in Cu:(Y + Ba) – which may reflect crystallization over the thermal interval. The liquid migrates to an invariant point at which CuO also crystallizes with complete loss of liquid. The presence of trains of CuO grains in the YBCO indicates the locations of the last liquids to be preserved in the sample. These trains are dominantly in an annulus 1–3 mm from the edge of the 20-mm diameter sample. Mapping the compositional variation in Y123 may allow mapping the path of crystallization of these monolithic YBCO samples.     

The New Superconductors of YBaCuO Materials

The new YBaCuO superconductors are synthesized by using the standard solid-state reaction method as compositions of Y5-6-11, Y7-9-16,Y358, Y5-8-13, Y7-11-18, Y156, Y3-8-11, and Y13-20-23, where the numbers indicate Y, Ba, and Cu atoms respectively; all show the Meissner effect at 77 K. The resistivity measurements used by the four-probe method have shown the highest T _c onset is 94 K. The XRD spectra are shown and they have a similar crystalline structure as Y123 and Y358 materials with some impurities peaks.     

Enhancing efficiency of crystalline silicon solar cells by the mixture of downshifting CaAlSiN3:Eu2+ and Y2O3:Eu3+ phosphors

Y₂O₃:Eu³⁺ (YO) phosphors which have high quantum yield in the range 200–280 nm are mixed with downshifting CaAlSiN₃:Eu²⁺ (CASN) phosphors to improve CASN’s low quantum yield in the wavelength range below 280 nm. The luminescence downshifting ethyl vinyl acetate films with the mixture of YO and CASN phosphors are fabricated and then used to package crystalline silicon solar cells. Experimental results show that the introduction of YO phosphors not only improves the external quantum efficiency of the solar cells in the range below 280 nm but also leads to the better absorption of the light in the range 280–500 nm due to the scattering by YO phosphors. The conversion efficiency of the solar cells with the mixed phosphors can be enhanced from 19.60 to 19.98% after packaging.

     

Oxygen partial pressure dependence of the properties of MgZnO thin films during annealing

Undoped n-type MgZnO films were deposited on c-plane sapphire substrates by molecular-beam epitaxy and subsequently annealed in O₂ at different pressures. After annealing at 3.03 × 10⁵ Pa, oxygen content in the annealed films show increases and the films transform into p-type conduction. However, the decreases of oxygen content and the increases of electron concentration were obtained while the films annealed at 1.01 × 10⁵ Pa or 2.05 × 10⁻³ Pa. The changes in intensity of the emission peak located at 2.270 eV are similar to the changes of the oxygen content in the films annealed at different pressures. According to the defect levels and the relationship between photoluminescence spectra and annealing condition, it was suggested that this emission peak was related to interstitial oxygen (O_i). The obtained p-type conduction is attributed to that the O_i acceptor can compensate oxygen vacancy and interstitial zinc donor.     

Property variations of direct-current reactive magnetron sputtered copper oxide thin films deposited at different oxygen partial pressures

Cuprous oxide (Cu₂O) and cupric oxide (CuO) thin films were deposited on glass substrates at different oxygen partial pressures by direct-current reactive magnetron sputtering of pure copper target in a mixture of argon and oxygen gases. Oxygen partial pressure was found to be a crucial parameter in controlling the phases and, thus, the physical properties of the deposited copper oxide thin films. Single-phase Cu₂O thin films with cubic structure were obtained at low oxygen partial pressure between 0.147 Pa and 0.200 Pa while higher oxygen partial pressure promoted the formation of CuO thin films with base-centered monoclinic structure. Polycrystalline Cu₂O thin films deposited with oxygen partial pressure at 0.147 Pa possessed the lowest p-type resistivity of 1.76 Ω cm as well as an optical band gap of 2.01 eV. On the other hand, polycrystalline CuO thin films deposited with oxygen partial pressure at 0.320 Pa were also single phase but showed a n-type resistivity of 0.19 Ω cm along with an optical band gap of 1.58 eV.     

Cu?C(O) Interfaces Deliver Remarkable Selectivity and Stability for CO2 Reduction to C2+ Products at Industrial Current Density of 500 mA cm−2

The electrocatalytic CO₂ reduction reaction (CO₂RR) is an attractive technology for CO₂ valorization and high-density electrical energy storage. Achieving a high selectivity to C₂₊ products, especially ethylene, during CO₂RR at high current densities (>500 mA cm⁻²) is a prized goal of current research, though remains technically very challenging. Herein, it is demonstrated that the surface and interfacial structures of Cu catalysts, and the solid–gas–liquid interfaces on gas-diffusion electrode (GDE) in CO₂ reduction flow cells can be modulated to allow efficient CO₂RR to C₂₊ products. This approach uses the in situ electrochemical reduction of a CuO nanosheet/graphene oxide dots (CuO C(O)) hybrid. Owing to abundant Cu O C interfaces in the CuO C(O) hybrid, the CuO nanosheets are topologically and selectively transformed into metallic Cu nanosheets exposing Cu(100) facets, Cu(110) facets, Cu[n(100) × (110)] step sites, and Cu⁺/Cu⁰ interfaces during the electroreduction step,  the faradaic efficiencie (FE) to C₂₊ hydrocarbons was reached as high as 77.4% (FE_ethylene ≈ 60%) at 500 mA cm⁻² . In situ infrared spectroscopy and DFT simulations demonstrate that abundant Cu⁺ species and Cu⁰/Cu⁺ interfaces in the reduced CuO C(O) catalyst improve the adsorption and surface coverage of *CO on the Cu catalyst, thus facilitating C C coupling reactions.     

Effect of additives on the structure characteristics,thermal stability,reducibility and catalytic activity of CeO<Subscript>2</Subscript>–ZrO<Subscript>2</Subscript> solid solution for methane combustion

M _y O _x -modified CeO₂–ZrO₂ (M = Al, Ba, Cu, La, Nd, Pr, Si) solid solutions with the atomic ratio of Zr/Ce = 1 were prepared by the reverse microemulsion method, and the effect of different additives on the structure characteristics, thermal stability, reducibility, and catalytic activity of CeO₂–ZrO₂ solid solution for methane combustion were investigated. According to their different effects, M _y O _x can be classified into three groups. The first group includes SiO₂ and Al₂O₃ which do not vary the crystalline phase of CeO₂–ZrO₂ solid solution but distort the crystal lattice obviously. They are the most effective additives for improving the surface area, thermal stability, and reducibility of CeO₂–ZrO₂, and they can also promote the catalytic activity of Pd/CeO₂–ZrO₂ for methane combustion. The second group includes La₂O₃, Pr₂O₃, and Nd₂O₃, which can also keep the same crystalline phase, distort the crystal lattice, and improve the surface area and thermal stability of the solid solution, but their effects are much weaker and they decrease the reducibility of the solid solution. The third group includes BaO and CuO, whose effects on the property of CeO₂–ZrO₂ are much different. BaO and CuO, especially CuO, can decrease the thermal stability, and reduction extent of CeO₂–ZrO₂. CuO-modified CeO₂–ZrO₂ calcined at 550 °C shows the comparable high activity for the methane combustion, but after being calcined at 900 °C, CuO-modified CeO₂–ZrO₂ would separate into three phases as CeO₂, ZrO₂, and CuO, resulting in the much lower activity for the methane catalytic combustion.     

Reproducibility of transition temperature and critical current density of thin films of YBa2Cu3O7 on (100) LaAlO3

Submicrometer epitaxial films of YBa₂Cu₃O₇(YBCO) on (100) LaAlO₃ were made by coevaporation and furnace annealing. Samples from more than a dozen runs are used in this study. The zero resistance transition temperature (T _c) is high (89 or 90 K) if the film composition is phase pure (Ba/Y=2, Cu/Y=3) or if it is enriched in Ba and Cu. For these compositions the critical current density (J _c) at 77 K has an average value of 2×10⁵ A cm^–2, with a tendency for decreasingJ _c with increasing film thickness (0.2 to 0.8m). Variations inJ _c are not correlated with deviations from ideal stoichiometry. Steeper slopes of the resistance-temperature curves above 100 K and lower values of the room-temperature resistivity are associated with high values ofJ _c. If the film composition is enriched in Y relative to Ba and Cu,T _c decreases by several degrees.     

Growth and characterisation of CaCu2Ox thin films by pulsed injection MOCVD

Oxides with the structure MCu₂O₂ (M = Ca, Ba, Mg and Sr) are promising materials for the development of new p-type transparent conducting oxide thin films. This paper reports preliminary results on the growth and characterisation of CaCu₂O_x thin films by pulsed injection MOCVD. By using as precursors calcium and copper tetramethylheptanedionate dissolved in meta-xylene, mixed calcium-copper films have been grown in the temperature range from 450 °C to 550 °C. At these temperatures, deposited films exhibited a high mirror reflection effect, good adherence and were reasonably uniform with the cationic composition of the films being easily controlled by adjusting the copper-calcium ratio in the precursor solution. In CaCu₂O₂, copper is in the Cu¹⁺ oxidation state and depending on the oxygen partial pressure used, the films either contained CaCu₂O₃ or a mixture of CaO, CuO and Cu₂O. Optimisation of annealing conditions increased the presence of Cu¹⁺ in the film. Films had a maximum transmittance of 50% in the visible range and were highly resistive. Appropriate annealing conditions reduced the resistivity of the films.     

ZnO nanostructured film deposition using the separated pulsed laser deposition (SPLD) assisted by electric and magnetic drift motion

We have developed the separated pulsed laser deposition (SPLD) technique to prepare high quality ZnO based films exhibiting uniform and droplet-free properties. This SPLD consists of an ablation chamber and a deposition chamber which can be independently evacuated under different ambient gases.The gas species and the pressures in both chambers can be arbitrarily chosen for the specific deposition such as nanostructured films and nanoparticles. The ablation chamber is a stainless steel globe and the deposition chamber is a quartz tube connected to a metallic conic wall with an orifice. We used a KrF excimer laser with λ = 248 nm and 25 ns pulse duration. The different gas conditions in two chambers allow us to realize optimal control of the plasma plume, the gas phase reaction and the film growth by applying the bias voltage between the conic wall and the substrate under the magnetic field. We can expect that at appropriate pressures the electric and magnetic field motion (E × B azimuthal drift velocity) gives significant influences on film growth.We have deposited ZnO thin films at various pressures of ablation chamber (Pab) and deposition chamber (Pd). The deposition conditions used here were laser fluence of 3 J/cm², laser shot number of 30,000, Pab of 0.67-2.67 Pa (O₂ or Ar), Pd of 0.399-2.67 Pa (O₂), and substrate temperature of 400 °C. Particle-free and uniform ZnO films were obtained at Pab of 0.67 Pa (Ar) and Pd of 1.33 Pa (O₂). The ZnO film showed high preferential orientation of (002) plane, optical band gap of 2.7 eV, grain size of 42 nm and surface roughness of 1.2 nm.     

Observation of Room Temperature Ferromagnetism in Conducting and Insulating Cu doped ZnO Thin Films

With pulsed laser deposition, the Cu_0.04Zn_0.96O thin films are grown at 600 °C under three different oxygen pressures, namely PO₂ = 0.00, 0.02, and 1.00 Pa. X-ray diffraction shows single-phase material for the samples grown under PO₂ = 0.00 and 1.00 Pa and CuO secondary phase for the PO₂ = 0.02 Pa grown sample. The observation of satellite structures in the Cu 2p core level X-ray photoelectron spectroscopy (XPS) spectra suggest the presence of Cu²⁺ and CuO secondary phases in the samples grown at PO₂ = 0.02 and 1.00 Pa. The sample grown under vacuum (PO₂ = 0.00 Pa) shows mixed Cu oxidation state of 1 + or 2 + . The sample grown without oxygen is n-type and those grown with oxygen are highly insulating. The insulating sample grown at PO₂ = 0.02 Pa shows highest magnetization due to possible collective behavior of Cu²⁺ – O _v – Cu²⁺ network in the form of bound magnetic polaron (BMP) and ferromagnetic superexchange interaction coming from uncompensated surface spins of the Cu ions in the CuO secondary phase. Both delocalized electrons (～3.32 × 10¹⁸) due to oxygen deficient defects and reduced amount of effective Cu²⁺ ions discredit the BMP model for this vacuum grown sample, and magnetism is suggested due to O _v and presence of possible CuO secondary phase.     

Growth of lithium tantalate thin films by radio-frequency magnetron sputtering with lithium enriched target

LiTaO₃ thin films were deposited by radio-frequency magnetron sputtering with a Li enriched target composed of Li₂O₂/Ta₂O₅ (55:45 at.%). Morphology, crystallinity, dielectric and pyrolectric properties of thin films of LiTaO₃ are studied according to the temperature of deposition and the nature of the back electrode (Ru/RuO₂ and RuO₂). In order to develop thermal microsensors containing pyrolectric thin layers deposited on membranes of SiN_x ensuring the thermal isolation of the device, the final aim is to improve the pyroelectric coefficient for infrared pyroelectric detectors applications. The best pyroelectric coefficient of LiTaO₃ thin films (400 nm), obtained for a growth temperature of 620 °C and a pressure of 0.67 Pa, is equal to 40 µC/m² K.     

Structure,magnetic, and electrical studies on vanadium phosphate glasses containing different oxides

Glass system with molar composition (60% P₂O₅–30%V₂O₅–10%X) where X is Li₂O, Na₂O, K₂O, and BaO was prepared. The density and molar volume indicate that the density decreases while the molar volume increases with increasing ionic radius of doped oxides. IR studies reveal the coexistence of V⁴⁺ and V⁵⁺ ions (act as glass modifier and glass former, respectively). The observed paramagnetic behavior of samples indicates that V⁴⁺ > V⁵⁺ (the ratio V⁴⁺/V⁴⁺ + V⁵⁺ > 0.52 as obtained from chemical titration analysis). Mott’s model of conduction was applied to discuss DC electrical conduction mechanism. The prepared glass exhibits semiconducting behavior. However, Ba ion is the only ion which did not contribute to the ionic conduction. The conductivity increases with decreasing ionic radius of doped oxides due to high mobility due to their small size. The effect of hopping distance on the electrical conduction and magnetic properties were discussed. An attempt was done to determine the expected temperature of Ba ionic conduction and its ionic activation energy.     

Structural and discharging properties of MgO thin films prepared by pulsed laser deposition

In this work, pulsed laser-deposited thin films of MgO were studied for application in plasma display panels. The firing voltage (FV) of discharge cells with MgO films was measured and the film structure was investigated as a function of film deposition conditions. MgO thin films were deposited at oxygen pressure and substrate temperature between 0.02-5 Pa and 260-600 °C, respectively. The structure of thin films was investigated by using X-ray diffraction, X-ray reflection and atomic force microscopy methods. It was found that the FV is strongly correlated with the film deposition conditions and structural properties. In general, the FV values were smaller for the films with higher crystallinity and density. The crystallinity and the density of the films increased when the deposition temperature was raised and the O₂ pressure was reduced. The lowest FV values (~ 120 V) were obtained at the growth temperature of 550 °C and at O₂ pressures below 1 Pa.     

Reproducibility of transition temperature and critical current density of thin films of YBa2Cu3O7 on (100) LaAlO3

Submicrometer epitaxial films of YBa₂Cu₃O₇(YBCO) on (100) LaAlO₃ were made by coevaporation and furnace annealing. Samples from more than a dozen runs are used in this study. The zero resistance transition temperature (T _c) is high (89 or 90 K) if the film composition is phase pure (Ba/Y=2, Cu/Y=3) or if it is enriched in Ba and Cu. For these compositions the critical current density (J _c) at 77 K has an average value of 2×10⁵ A cm^?2, with a tendency for decreasingJ _c with increasing film thickness (0.2 to 0.8μm). Variations inJ _c are not correlated with deviations from ideal stoichiometry. Steeper slopes of the resistance-temperature curves above 100 K and lower values of the room-temperature resistivity are associated with high values ofJ _c. If the film composition is enriched in Y relative to Ba and Cu,T _c decreases by several degrees.     

Oxygen partial pressure dependence of the structural properties of CdO thin films deposited by a modified reactive vacuum evaporation process

Thin films of cadmium oxide were thermally deposited on glass substrates at partial pressures of oxygen, pO₂ in the range 1.33×10⁻² to 0.133 Pa at a substrate temperature of 160 °C. Energy dispersive analysis of X-ray fluorescence (EDAX) revealed that the CdO films deposited at pO₂ value of 4.00×10⁻² Pa were nearly stoichiometric. X-ray diffractometry (XRD) confirmed the polycrystalline nature of the film structure. All the films showed an fcc structure of the NaCl-type, as the dominant phase. The films exhibited preferred orientation along the (1 1 1) diffraction plane. The texture coefficients calculated for the various planes at different oxygen partial pressures (pO₂) indicated that the maximum preferred orientation of the films occurred along the (1 1 1) plane at an oxygen partial pressure of 4.00×10⁻² Pa. This was interpreted in terms of oxygen chemisorption and desorption processes. The lattice parameters determined from the diffraction peaks were in the range 4.655–4.686 Å. The average lattice parameter a₀ found by extrapolation using the Nelson–Riley function was 4.696 Å. Both the lattice parameter and the crystallite size were found to increase with increased partial pressure of oxygen. On the other hand, the strain and dislocation density were found to decrease as the partial pressure of oxygen was raised. A maximum (80%) in the optical transmittance at λ=600 nm and minimum in the electrical resistivity (9.1×10⁻⁴ Ω cm) of the films occurred at an optimum partial pressure of oxygen of 4.00×10⁻² Pa. The results are discussed.