Polycrystalline MgO Substrates Research Articles

Effect of substrate material to the properties of screen-printed lead free (Bi0.5Na0.5)TiO3-based thick films

Lead-free piezoelectric 0.83(Bi0.5Na0.5)TiO3-0.17BaTiO3 (BNT-17BT) thick films were grown on MgO ceramic substrates via screen printing. Thick films with compressive stress formed a c-domain preferentially with a volume fraction of 0.88. High-temperature X-ray diffraction and piezoresponse force microscopy and the temperature dependence of the piezoelectric coefficient d33 data indicated that the thick films had a preferred c-domain during the transformation from the tetragonal phase to the cubic phase with temperature increasing. Based on polycrystalline MgO substrates with high thermal expansion coefficients, the thick films displayed a higher phase transition temperature and larger remanent polarization (Pr) values over 220 °C than those of thick films on Al2O3 substrates. The ferroelectric properties of BNT-17BT/MgO were better than those of soft PZT/YSZ and hard PZT/YSZ over 220 °C. The results showed the possibility of applying BNT-17BT thick films in a wide temperature range.

Processing and properties of Bi2Sr2CaCu2Ox thick films on polycrystalline magnesium oxide substrates

Abstract In this paper we report on the processing parameters and resulting critical current densities of Bi 2 Sr 2 CaCu 2 O x (Bi-2212) thick films on polycrystalline MgO substrates. Bi-2212 tapes were cast by the doctor blade technique and laminated onto flat MgO-ceramic substrates. The tapes were produced via the partial melt-process in a single cycle. Silver(I)oxide (Ag 2 O) was added to the powder and the maximum process temperature was varied in order to optimize the transport current density at 77 K in self-field. It was found that both parameters, maximum process temperature during partial melting and amount of Ag 2 O added have a strong influence on the critical current density at 77 K. The highest J c of 1900 A/cm 2 was achieved in the 130 μm thick films with an addition of 4 wt% Ag 2 O processed at a maximum temperature of 900 °C. In addition, large components were processed with 1 cm wide conductors meandering over 150 cm on 20 cm diameter MgO plates.

Electron localization induced by grain boundary disorder in the normal state of high- Tc superconductors

We have studied the effects of superconducting grain boundary disorder on the normal state transport properties of cuprate films. Dip-coated granular YBa 2Cu 3O 7− y (YBaCuO) thick films on polycrystalline MgO substrates were synthesized and networked grains were systematically made less disordered in order to probe the crossover from strong to weak inter-grain disorder. Grain boundary passivation was achieved by metallic inclusions of different forms. We have shown that the normal state of samples exhibit a semiconducting behavior and changes to ‘metallic’ with sharper transitions to the superconducting state as we reduce grain-interfaces disorder, i.e. increase metallic inclusion content. On the basis of electron localization mechanisms, the normal state conductivity is thus shown to undergo a dimensional crossover from 3D to 2D in the frame of the variable-range hopping (VRH) regime. The transition threshold was found to depend on the form of metallic inclusions.

PLD growth of La 0.7Sr 0.3MnO 3 tilted nanocolumn boundaries on constricted step-edged GaAs substrates and MR properties

In this study, PLD growth of La 0.7Sr 0.3MnO 3 (LSMO) tilted nanocolumn boundaries and their magnetoresistance (MR) properties at 77 K were examined. All LSMO films were grown on polycrystalline MgO substrates and step-edged (1 0 0) GaAs substrates (step-edge angles ranged from 0° to 100°) by Ar–F excimer laser ablation (pulsed laser deposition) method. Grains were made up in the shape of the nanocolumns standing normal to the substrates surfaces. The intergrain magnetoresistances (IMRs) showed marked reduction against the magnetic field application below 100 mT, followed by a gradual change for further increase in the field. They clearly showed the nanocolumn boundary angle dependence in accordance with the extended Julliere’s model.

Effect of Ag admixture on the electron localization mechanism in the normal state of dip-coated YBa 2Cu 3O 7− δ thick films

The effects of superconducting grain boundary disorder on the normal-state transport properties of cuprate films was investigated. Dip-coated granular YBa 2Cu 3O 7− δ (YBaCuO) thick films on polycrystalline MgO substrates were synthesized and networked grains were systematically made less disordered in order to probe the cross-over from strong to weak inter-grain (between grains) disorder. Grain boundary passivation was achieved by AgNO 3 metallic inclusions. The normal state of samples was shown to exhibit a semi-conducting behaviour and then changes to metallic with sharper transitions to the superconducting state as the grain-interfaces disorder is decreased, i.e. increase metallic inclusion content. The normal-state conductivity is thus shown to undergo a dimensional cross-over from 3D to 2D in the frame of the variable range-hopping regime.

Potentiometric imaging of (La0.7Sr0.3)MnO3 thin films

Scanning tunneling potentiometry has been used to simultaneously image the surface topography and map the potential distribution on films of (La0.7Sr0.3)MnO3 deposited on polycrystalline and single crystal MgO substrates. Potential steps in the polycrystalline films coincide with the crystallite boundaries in the film. The grain boundary resistivity varies in the range 3×10−7–3×10−5 Ω cm2, with a typical value of 6×10−6 Ω cm2.

Melt processing of Bi-2212 on MgO and MgO-buffered substrates

Bi-2212 thick films have been prepared by full and partial melt processing to investigate the suitability of MgO substrates in polycrystalline, single crystal and buffer layer formats. There is a marked difference in microstructural and electrical properties between thick films on polycrystalline and single crystal MgO substrates. This is attributed to the degree of interaction between the liquid phase and substrate during melting. The thickness of films on single crystal MgO substrates is an important consideration in the optimization of the superconducting transport properties.

Thick films of the Tl-based superconductor fabricated via the sol-gel technique

Superconducting thick films of Tl-based cuprate were grown via the sol-gel technique with a two-step method: deposition of a Tl-free precursor film followed by Tl-vapor annealing. A zero resistance superconducting transition temperature ( T c) of 120 K on polycrystalline MgO substrates for Tl-1223 films and of 124 K on (100) LaAlO 3 substrates and polycrystalline MgO substrates for Tl-2223 films was obtained. The intragranular critical current density at 5 K of these films is greater than 10 6 A/cm 2 for Tl-1223 and Tl-2223. The microstructure of these films was examined with X-ray diffraction and scanning electron microscopy.

Pulsed laser deposition of Bi 4Cu 2 xV 2(1- x) O 11 thin films

The growth of Bi 4Cu 2 x V 2(1- x) O 11 thin films by pulsed laser deposition (PLD) is reported for the first time. Samples with x = 0.1 are grown on polycrystalline BeO and (100) MgO substrates. Films show lattice parameters a = b = 3.926 Å and c = 15.491 Å. Films deposited on BeO are unoriented, whereas on (100) MgO they are oriented with the c-axis perpendicular to the substrate surface irrespective of the growth temperature from 773 to 873 K. At 873 K, atomic force microscopy (AFM) evidences very low surface roughness associated with spiral growth terraces having 9 Å steps.

Growth of c-axis-oriented films of YbBa 2Cu 3O 7− δ on single and polycrystalline MgO substrates by oxidation of a liquid alloy precursor

Textured superconducting films of YbBa 2Cu 3O 7–δ supported on both single and polycrystalline MgO substrates were prepared by oxidation of a liquid precursor alloy. The substrates were coated by dipping them into the molten alloy (YbBa 2Cu 3, melting point ≈870°C). After withdrawal from the melt, the adhering metal was oxidized to the corresponding oxide phase, i.e., Y YbBa 2Cu 3O 7−δ, which exhibited a superconducting transition at ≈80 K following annealing in pure O 2 at 500°C. With MgO(1 0 0) substrates, evidence was seen for the epitaxial growth of YbBa 2Cu 3O 7−δ crystals having their c-axis parallel to the [1 0 0] direction of the substrate. For polycrystalline MgO, X-ray diffraction and microstructural examination showed that the high- T c crystallites in the films were also oriented with their c-axis perpendicular to the substrate surface, but the directions of the a and b axes were disordered rather than epitaxial. The superconducting properties of as-prepared films are discussed together with the effects of key processing parameters on composition and microstructure.

High-quality Y1Ba2Cu3O7−x thin films on polycrystalline MgO by temperature-controlled chemical vapor deposition

Y1Ba2Cu3O7−x superconducting thin films were grown in situ on polycrystalline MgO substrates by a chemical vapor deposition process that closely couples the sublimation temperatures of the elemental sources to that of the substrate during deposition. It was found that the best quality films were achieved with a controlled ramping of the substrate temperature from 850 °C, at the onset of deposition, down to 750 °C at the end of deposition. The films were analyzed by Rutherford backscattering (RBS), scanning electron microscopy (SEM), x-ray diffractometry (XRD), and four-point resistivity probe. The results of these studies showed that the films were highly c-axis oriented, had near-stoichiometric composition, and exhibited Tc,onset=90 K, Tco=85 K, and had a Jc=2×105 A/cm2 at 77 K in zero magnetic field. A model is proposed for the effect of such temperature control on the CVD growth mechanism of high-quality YBCO films.

Growth and properties of YBa/sub 2/Cu/sub 3/O/sub 7/ thin films on non-lattice-matched and polycrystalline substrates

The authors have investigated the nature of the in-situ growth of c-axis normal YBa/sub 2/Cu/sub 3/O/sub 7/ thin films on non-lattice-matched, vicinal, and polycrystalline MgO substrates and on buffer layers of MgO. It is found that the preparation of the MgO surface determines the structural and transport properties of the films. In particular, the authors were able to reproducibly grow films exhibiting either weak link behavior or very high critical current densities. The variation of the thin-film microstructure, oxygen content, and superconductive properties with the changes in the thin-film crystal structure that result from the different growth situations is discussed. The structural and transport measurements of YBCO films grown on various MgO surfaces clearly indicate the importance of obtaining a nucleation stage which will result in high-quality YBCO on non-lattice-matched substrates. Such considerations are of prime importance when the low-temperature growth of the cuprate superconductors is required in order to obtain a morphology which facilitates the use of lithographic processing and the growth of multilayer structures.

Superconducting thin films of Bi-Pb-Sr-Ca-Cu-O synthesized by the spray-inductively coupled plasma technique

Superconducting thin films of Bi-Pb-Sr-Ca-Cu-O were synthesized on polycrystalline MgO substrates by injecting atomized aqueous solutions of appropriate nitrates into an inductively coupled r.f. plasma (ICP) under atmospheric pressure (the spray-ICP technique). 1–2 μm thick films composed ofc-axis oriented phases (c=2.4 and 3.0 nm) could be synthesized in runs of 15–20 min. The phase compositions of the films were varied fromc=2.4 nm phase toc=3.0 nm phase through their mixed phases by increasing the distance of the substrates from the ICP. In some cases the mixed phases contained a small amount ofc=3.7 nm phase. Annealing in air (850 °C for 10 min and then 800 °C for 5 h) convertedc=2.4 nm phase toc=3.0 nm phase. The best as-deposited film showedTc (resistance = 0) at 55 K, and after annealing its resistance began to drop around 110 K and reached zero at 75 K.

Growth and properties of YBa2Cu3O7 thin films on vicinal and polycrystalline MgO substrates

We discuss the results of a study on the growth by laser ablation of YBa2Cu3O7 thin films on polycrystalline and annealed vicinal (001) MgO substrates. In both instances the films were found to grow predominantly with the c axis normal to the plane of the substrate, regardless of the orientation of the MgO surface. In the case of the vicinal substrates the films were found to have superconducting properties comparable to those obtained with films grown on (001) oriented, annealed single-crystal substrates.

Phase formation and crystallization in Bi-Sr-Ca-Cu-O thick films

Thick films of Bi2Sr2CaCu2Ox superconducting at 84 K have been prepared on polycrystalline MgO substrates. The effect of heat treatment on phases formed at various stages of the film preparation is studied. Investigations show that a thin layer at the top is highly oriented while the bulk of the 212 phase material beneath it consists of randomly oriented grains. This appears to be the main reason for the low critical current densities obtained in practice.

Oriented BSCCO thick film coatings on polycrystalline MgO

Highly oriented 2212 BSCCO thick films were prepared on polycrystalline MgO substrates using a melt/crystallization technique. Results compare very favorably with those on single crystal materials.1,2 The melting, quenching, and annealing processes were all found to be important in the development of a good microstructure and good superconducting properties. The best results (Jc ∼ 2000 A/cm2 at 64 K and 6000 A/cm2 at 4.2 K) were obtained on films which had been melted, quenched to room temperature, heated to 860°C where they were annealed before slow cooling to room temperature in oxygen, lightly polished, and reannealed at 860°C.

Preparation of MgO substrates for superconducting films

Preparation and properties of polycrystalline MgO substrates for superconducting films have been studied. Seven hours heat treatment at 950°C was sufficient to obtain proper hardness, crystallinity and to remove ionic impurities from as-prepared MgO pellets. Effect of heat treatment and other conditions have been discussed. Fluorine doped tin oxide coated MgO substrates have also been prepared for deposition of superconducting films by electrodeposition technique.

Spray-on films of superconducting BiSrCaCuO on polycrystalline and single-crystal MgO

A procedure is described for producing dense, oriented films of the two-layer copper oxide superconductor Bi 2Sr 2CaCu 2O 8+δ on either polycrystalline or single-crystal MgO substrates. Zero resistance is at 80 K, and the critical currents are 7× 10 3 A cm −2 at 70 K. and > 3 × 10 4 A cm −2 at 50 K.

Post‐deposition annealing and crystallisation of Y-Ba-Cu-O thin films deposited on polycrystalline substrates

Abstract Superconducting thin films of Y-Ba-Cu-O have been prepared by 50 Hz ac sputtering on polycrystalline SrTiO3, yttria-stabilized-ZrO2, and MgO substrates. Films deposited on different substrate materials are required to be annealed at different temperatures to induce superconductivity. The optimum annealing temperature for a film depends on the reaction between the film and its substrate material. It appears that a correlation exists between the process of crystallisation and substrate-film reaction.

DC-sputter deposition of BiPbSrCaCuO films with superconductivity above 100 K

Superconducting thin films of Bi-Pb-Sr-Ca-Cu-O have been prepared on polycrystalline MgO substrates by dc-sputtering from a single sintered target and subsequent annealing. The as-sputtered films were amorphous and non-conducting. By annealing in air for 12 hours at 854 °C these films became superconducting with an onset temperature of 120 K and zero resistance at 104.5 K.