Growth from gas cavities in a molten salt and properties of superconducting Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>CaCu<Subscript>2</Subscript>O<Subscript>8+δ</Subscript> single crystals

Perfect single crystals of the high-temperature superconductor Bi₂Sr₂CaCu₂O_8+δ with the superconducting transition temperature T_C = 72–85 K (depending on the crystallization conditions) are obtained by the method of free growth in gas cavities formed in a KCl solution-melt. The specific features of the growth process are in the formation of an enclosed growth gas cavity in a (previously synthesized) blend of a specified phase composition dissolved in KCl and the free crystal growth in this cavity. The combination of growth and high-temperature annealing in the same process made it possible to obtain uniform (ΔT_C = 1.5 K) single crystals with stable superconducting properties. Annealing of the grown single crystals in oxygen or in air in the temperature range 400–850°C confirmed that the crystals with maximum values of T_C are optimally doped.     

The (Bi,Pb)4Sr3Ca3Cu4Ox glass–ceramics: Disordered metal and superconductor

The (Bi_0.8Pb_0.2)₄Sr₃Ca₃Cu₄O_x glass, annealed under proper conditions, is transformed into a granular metal and superconductor. Oxide superconductors of the bismuth family crystallize as a result of annealing: (Bi,Pb)₂Sr₂CuO_x (2201, T_c = 10 K), (Bi,Pb)₂Sr₂CaCu₂O_x (2212, T_c = 85 K) and (Bi,Pb)₂Sr₂Ca₂Cu₃O_x (2223, T_c = 100 K). (Bi_0.8Pb_0.2)₄Sr₃Ca₃Cu₄O_x glass–ceramic samples were obtained by annealing an amorphous solid at temperatures between 650 °C and 870 °C. The temperature dependence of resistivity in annealed samples was measured with the conventional four-terminal method in the temperature range from 3 K to 300 K. The (Bi_0.8Pb_0.2)₄Sr₃Ca₃Cu₄O_x glass–ceramics may be considered as a disordered metal and superconductor. The material has high resistivity and a high, usually negative, temperature coefficient of resistivity (TCR). Its granular and disordered character is also reflected in its superconducting properties. The normal-state and superconducting properties are correlated.     

Contribution to the Ti‐Bi phase diagram

The system Ti‐Bi has been investigated by solid/liquid diffusion couples at 400, 500, 600 and 700 °C. Indication that the growth rate of the diffusion layers at 500 °C is linear has been found, with a growth constant of around 5 × 10^–11 m.s^–1. The existence of the Ti₂Bi phase has been confirmed. Some formerly unknown binary phases (TiBi, Ti₂Bi₃, TiBi₂) have been observed. The phase TiBi is, probably, identical with Ti₈Bi₉ reported previously. All intermediate phases suffer air corrosion, but in various degrees. A tentative variant of the Ti‐Bi phase diagram, including the newly found compounds, has been constructed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth,structure, and superconducting properties of Bi2Sr2Ca2Cu3O10 and (Bi,Pb)2Sr2Ca2Cu3O10‐y crystals

Large and high‐quality single crystals of both Pb‐free and Pb‐doped high temperature superconducting compounds (Bi_1‐xPb_x)₂Sr₂Ca₂Cu₃O_10‐y (x = 0 and 0.3) were grown by means of a newly developed “Vapour‐Assisted Travelling Floating Zone” technique (VA‐TSFZ). This modified zone‐melting technique was realised in an image furnace and allowed for the first time to grow Pb‐doped crystals by compensating for the Pb losses occurring at high temperature. Crystals up to 3×2×0.1 mm³ were successfully grown. Post‐annealing under high pressure of O₂ (up to 10 MPa at T = 500°C) was undertaken to enhance T_c and improve the homogeneity of the crystals. Structural characterisation was performed by single‐crystal X‐ray diffraction (XRD) and the structure of the 3‐layer Bi‐based superconducting compound was refined for the first time. Structure refinement showed an incommensurate superlattice in the Pb‐free crystals. The space group is orthorhombic, A2aa, with cell parameters a = 27.105(4) Å, b = 5.4133(6) Å and c = 37.009(7) Å. Superconducting studies were carried out by A.C. and D.C. magnetic measurements. Very sharp superconducting transitions were obtained in both kinds of crystals (ΔT_c ≤ 1 K). In optimally doped Pb‐free crystals, critical temperatures up to 111 K were measured. Magnetic critical current densities of 2�10⁵ A/cm² were measured at T = 30 K and μ₀H = 0 T. A weak second peak in the magnetisation loops was observed in the temperature range 40‐50 K above which the vortex lattice becomes entangled. We have measured a portion of the irreversibility line (0.1‐5 Tesla) and fitted the expression for the melting of a vortex glass in a 2D fluctuation regime to the experimental data. Measurements of the lower critical field allowed to obtain the dependence of the penetration depth on temperature: the linear dependence of λ(T) for T < 30 K is consistent with d‐wave superconductivity in Bi‐2223. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of simultaneous doping of Tl and Bi on microstructure and critical current density of HgBa2Ca2Cu3O8+δ

It has been found that simultaneous doping of Tl and Bi at Hg site of HgBa₂Ca₂Cu₃O_8+δ HTSC phase induces interesting microstructural variants in the form of long period polytypoid (LPP) like structure embodying native defect substructures. It has been observed that the as synthesized (HgTl_0.2−xBi_x)Ba₂Ca₂Cu₃O_8+δ (with x = 0.05, 0.10, 0.15) phases have superconducting onset transition temperature (T_c) of about ∼133 K. However, the intragrain critical current density (J_c) for the various materials with different compositions varies significantly. It varies from 6.2 × 10⁶ A/cm² to 2.9 × 10⁶ A/cm² at 5 K and 1 T for (HgTl_0.10Bi₁₀)Ba₂Ca₂Cu₃O_8+δ and (HgTl_0.15Bi_0.05)Ba₂Ca₂Cu₃O_8+δ HTSC phase respectively. A correlation between the intragrain J_c and the defect substructures has been found to be present. This correlation has been described and disscussed. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and Characterization of Ml2-Intercalated Bi-2212 Cuprates (M=Mn,Fe, Co,Cu, Zn)

Abstract

A series of new layered cuprates with the composition MI_2+xBi₂Sr₂CaCu₂O_8+y (x=0.6–0.9; M=Mn, Fe, Co, Cu, Zn) have been synthesized by the reaction of Bi₂Sr₂CaCu₂O₈ with each transition metal under an atmosphere of iodine at 400°C. The new cuprates, lamellar in shape, are crystallized in a tetragonal unit cell with the lattice parameters of a = 5.393–5.402 Å and c = 43.32–43.96 Å. A structure model for these cuprates are proposed in which the monoiodide anions are intercalated in the Bi₂O₂ layer to form a bilayer accompanying 3d metal cations. All of the intercalated cuprates are non-superconducting to be as high as 0.74–2.52 MΩ · cm in resistivity at room temperature.     

On the existence of a pyrochlore-type phase in the system Bi2O3–TiO2

The existence of a bismuth titanate in the range between Bi₂Ti₄O₁₁ (Bi₂O₃ · 4 TiO₂) and Bi₄Ti₃O₁₂ (2 Bi₂O₃ 3TiO₂) has been investigated by X-ray diffraction of samples prepared by solid state reactions. For reaction temperatures above 1100 °C and a starting composition Bi₂O₃ · 2 TiO₂ there appeared additional lines which could be attributed to a cubic face-centred cell with a = 10.354 Å. A multiphase Rietveld analysis based on X-ray powder diffraction data confirmed the structural model of a pyrochlore for this compound. There is evidence that this phase belongs to the group of defect pyrochlores with a Bi³⁺-deficiency resulting in a composition of Bi_1.833Ti₂O_6.75.     

Thermal properties and glass formation in the SiO2–B2O3–Bi2O3–ZnO quaternary system

Lead-free glasses in the SiO₂–B₂O₃–Bi₂O₃–ZnO quaternary system were studied. The glass formation region, as determined by XRD patterns of bulk samples, was limited to glasses having more than 40 mol% of the glass-forming oxides SiO₂ and B₂O₃. Crystalline phases of Zn₂SiO₄ (willemite) were detected in compositions of 30SiO₂ · 10B₂O₃ · 20Bi₂O₃ · 40ZnO and 20SiO₂ · 10B₂O₃ · 25Bi₂O₃ · 45ZnO. Glass transition temperatures (T_g), dilatometric softening points (T_d) and linear coefficients of expansion in the temperatures range of 25–300 °C (α_25–300) were measured for subsystems along the B₂O₃ join of 10, 20 and 30 mol%. For these subsystems, T_g ranged from 411 to 522 °C, and T_d ranged from 453 to 563 °C, both decreasing with increasing Bi₂O₃ content. The measured α_25–300 ranged from 53 to 95 × 10⁻⁷ °C⁻¹, with values increasing with increasing Bi₂O₃ content. The ZnO content had the opposite effect to the Bi₂O₃ content. It appears that Bi³⁺ acts as a glass-modifier in this quaternary system.     

Growth and properties of layered oxycarbonate Bi2Sr4Cu2CO3O8 single crystals

Layered oxycarbonate Bi₂Sr₄Cu₂CO₃O₈ single crystals have been obtained for the first time by free growth in closed vapor-phase cavities. The morphology, structure, composition, and superconducting properties of these crystals have been investigated.     

Crystal Growth of Boron Sillenite Bi24B2O39

The Sillenite type Bi₂₄B₂O₃₉ is an incongruently melting compound at T_p = 650 °C. Single crystals have been grown from non-stoichiometric melts as well as from high temperature solutions by the Czochralski method and by a top seeded solution growth technique (TSSG), respectively. The main difficulty in the crystal growth of Bi₂₄B₂O₃₉ arises from the very small field of crystallization in the binary system Bi₂O₃–B₂O₃. Further problems are caused by the nearly simultaneous formation of the 2:1 compound Bi₄B²O₉ and the 12:1 compound Bi₂₄B₂O₃₉. Therefore, a precise thermal reinvestigation of the phase diagram was carried out using DTA-technique on the Bi₂O₃-rich side. Additionally, crystal growth runs have been started in the ternary system Bi₂O₃–B₂O₃–Li₂O in order to extend the crystallization field. Homogeneous melts were more difficult to prepare because of the high density difference between Bi₂O₃ (∂ = 9.3 g/cm³) and B₂O₃ (∂ = 2.46 g/cm³). The homogeneity of the melts were improved, using Bi₂O₃ and synthesized Bi₄B₂O₉ (∂ = 8.25 g/cm³) as starting materials. As a result of this procedure, small crystals of Bi₂₄B₂O₃₉ were grown from these starting materials and the lattice parameter were determined.     

Improved Single Crystal Growth of the Boron Sillenite “Bi24B2O39” and Investigation of the Crystal Structure

The boron sillenite, up to now known as the 12:1 compound Bi₂₄B₂O₃₉ in the system Bi₂O₃ – B₂O₃ andcrystallizing in the space group I23, melts incongruently at 655 °C only about 25 K above the eutectic tie line and corresponding to a steep liquidus line. Single crystals with dimensions larger then 1 cm ³ have been successfully grown in [100], [110], and [111] direction by an improved Top Seeded Solution Growth (TSSG) technique equipped with crucible weighing, accelerated crystal rotation technique and air‐cooled pulling rod. The structure of the boron sillenite was analyzed by X‐ray diffraction method, which was possible due to the high crystalline quality achieved. A defect‐free sublattice corresponding to a Bi‐O framework is isostructural with all sillenites, but a 2 Å environment around the origin is occupied by different cations with different population coefficients. The best calculation results in the formula Bi_24.5BO_38.25 which is more Bi‐rich than the 12:1 assumption.     

Electronic conduction in (Bi, Pb)–Sr–Ca–Cu–O glass-ceramics

Electrical properties of (Bi, Pb)₄Sr₃Ca₃Cu₄O_x granular metals and superconductors obtained by the solid state crystallization method were studied. The studied materials may be considered as 3D systems of small oval granules of the (Bi, Pb)₂Sr₂CuO_x and (Bi, Pb)₂Sr₂CaCu₂O_x phases embedded in the insulating matrix. They may by divided into two main groups: these in which the granules below the critical temperature transform into the superconducting state and those in which they remain in the normal state throughout the entire temperature range studied. The electronic transport in the (Bi, Pb)Sr–Ca–Cu–O granular system of the granules in the normal state occurs by the variable range hopping mechanism either with or without Coulomb interactions. The materials, which below the transition temperature contain the granules in the superconducting state, show different types of temperature dependence of resistivity. Those composed of very small granules (10 nm) of the superconducting phase exhibit an exponential dependence typical of the strong localization regime. In samples containing relatively large granules of the 2 2 0 1 phase (30 nm), the bulk superconducting state was achieved. The intermediate materials show unusual temperature dependence of resistivity, not compatible with the known models of electronic transport in granular materials.     

Transport and Electrochemical Properties of Bi2Sr2CaCu2O8 Superconductors

Abstract

Electrical conductivity and thermoelectric power measurements (77–300K) of both the pure and electrochemically doped with lithium Bi₂Sr₂CaCu₂O₈ system, are presented. Clear correlation between transport and electrochemical properties of Li_xBi₂Sr₂CaCu₂O₈ was shown.     

Mechanism of growth of Bi2+xSr2?yCuO6+δ single crystals in gas cavities in a KCl melt

High-quality Bi_2+x Sr_2−y CuO_6+δ single crystals in a wide range of superconducting properties, from optimally doped to strongly underdoped (including insulators), have been obtained by free growth in gas cavities formed in a KCl flux. A model of crystal growth is proposed, in which the decisive parameter is the chemical transport in a cavity at a low partial oxygen pressure and feeding of the gaseous medium from the charge heated to a higher temperature. In this case, layer-by-layer growth through the vapor-solid mechanism is implemented. This growth, as the most ordered process, makes it possible to obtain faceted plates and whiskers with specular faces, without segregation of other phases. Original Russian Text ? Yu.I. Gorina, G.A. Kalyuzhnaya, V.V. Rodin, N.N. Sentyurina, V.A. Stepanov, S.G. Chernook, 2007, published in Kristallografiya, 2007, Vol. 52, No. 4, pp. 762–766.     

Preparation and characterization of CuO doped Bi2O3–B2O3–BaO–ZnO glass system for transparent dielectric layer

The electrical, thermal, optical, and morphological properties of CUO doped Bi₂O₃–B₂O₃–BaO–ZnO glasses were studied as a PbO-free, low firing transparent dielectric layer for plasma display panels (PDP). CuO improved the transmittance of Bi₂O₃–B₂O₃–BaO–ZnO by up to 84% in the visible region, eliminating a yellowish color typical of Bi₂O₃–B₂O₃–BaO–ZnO. A slight absorption within the near infrared (NIR) region was also observed. The glass transition temperature (T_g), thermal coefficient of expansion (TCE), and root-mean square (rms) roughness of 0.005 wt% CuO doped Bi₂O₃–B₂O₃–BaO–ZnO were found to be 455 °C, 81.4 × 10⁻⁷/K, respectively, and 162 ± 14 Å, which satisfied the requirements for a transparent dielectric layer for PDP application.     

Single‐crystal growth and characterization of mullite‐type orthorhombic Bi2M4O9 (M = Al3+, Ga3+, Fe3+)

Pure and homogeneous single crystals of orthorhombic mullite‐type Bi₂M₄O₉ (M = Al³⁺, Ga³⁺, Fe³⁺), and a mixed Bi₂Fe_1.7Ga_2.3O₉ crystal from an equimolar Ga/Fe composition were grown by the top seeded solution growth (TSSG) method. All these compounds melt incongruently in the range of about 800 and 1100 °C. In case of bismuth gallate and ferrate inclusion‐free crystals with dimensions up to several cubic centimeters can be grown. Limited solubility in Bi₂O₃ and the high steepness of the liquidus curve are the reasons for getting only small imperfect bismuth aluminate crystals. In contrast to ceramic materials preparation reported in literature, divalent calcium and strontium could not be incorporated into the mullite‐type structure during the melt growth process. Several fundamental physical properties like heat capacity, thermal expansion, heat conductivity, elastic constants, high‐pressure behavior and oxygen diffusivity were determined by different research groups using single‐crystalline samples from the as‐grown materials. Furthermore, the refractive indices of Bi₂Ga₄O₉ were measured in the range of 0.430 and 0.700 μm. Such as many other bismuth containing compounds the refractive indices of Bi₂Ga₄O₉ are larger than 2, and Bi₂Ga₄O₉ is an optic biaxial positive crystal. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Glass formation and third-order optical nonlinear properties within TeO2–Bi2O3–BaO pseudo-ternary system

Tellurite glasses from TeO₂–Bi₂O₃–BaO pseudo-ternary system were prepared using a conventional melt-quenching method and its glass-forming region was determined. A series of glasses were selected and their third-order optical nonlinearities (TONL) were measured by employing the Z-scan method at a wavelength of 800 nm with femtosecond laser pulses. The results showed that glass former Te⁴⁺ ions exhibited positive influences on the TONL and glass modifiers Ba²⁺ ions behaved similarly; low concentrated Bi³⁺ ions as glass modifiers weakened the nonlinearities, but an excess amount of Bi³⁺ behaved oppositely. FTIR measurements demonstrated that chemical bonds especially Te–O_eq vibrated at a high energy level remarkably promoted the TONL susceptibility χ⁽³⁾, and the glass sample with the highest Bi₂O₃ content exhibited the largest χ⁽³⁾ value which was due to the presence of BiO₃ polyhedra.     

Crystallization of bismuth titanate and bismuth silicate grown as thin films by atomic layer deposition

Bismuth silicate and bismuth titanate thin films were deposited by atomic layer deposition (ALD). A novel approach with pulsing of two Bi-precursors was studied to control the Si/Bi atomic ratio in bismuth silicate thin films. The crystallization of compounds formed in the Bi₂O₃–SiO₂ and Bi₂O₃–TiO₂ systems was investigated. Control of the stoichiometry of Bi–Si–O thin films was studied when deposited on Si(1 0 0) and crystallization was studied for films on sapphire and MgO-, ZrO₂- and YSZ-buffered Si(1 0 0). The Bi–Ti–O thin films were deposited on Si(1 0 0) substrate. Both Bi–Si–O and Bi–Ti–O thin films were amorphous after deposition. Highly a-axis oriented Bi₂SiO₅ thin films were obtained when the Bi–Si–O thin films deposited on MgO-buffered Si(1 0 0) were annealed at 800 °C in nitrogen. The full-width half-maximum values for 200 peak were also studied. An excess of bismuth was found to improve the crystallization of Bi–Ti–O thin films and the best crystallinity was observed with Ti/Bi atomic ratio of 0.28 for films annealed at nitrogen at 1000 °C. Roughness of the thin films as well as the concentration depth distribution were also examined.     

Resistance and Current Density Studies on Plasma Sprayed Coatings of Bi(Pb)?Ca?Sr?Cu?O Superconducting Materials

Plasma spraying is a potential technique for forming flexible tapes from brittle high T_c oxides. It is possible to obtain superconducting Bi(Pb) Ca Sr Cu O coating by suitable heat treatment schedule after spraying. In an effort to get maximum transport current densities (J_c) of the coating, the content of lead and sintering time have been optimised. A J_c value of 200 Amp/cm² is obtained in Bi_1.4Pb_0.6 · Ca₂Sr_1.9Cu₃O_y specimen coated on silver sprayed Fe[(Ag)/Fe] substrate. Remarkable improvement in J_c values up to 694 Amp/cm² is obtained in the same specimen coated on Ca₂Sr_1.9Cu₃O_y sprayed Fe[Ca₂Sr_1.9Cu₃O_y)/Fe] substrate. The observed decrease in J_c(B) curves with increase in magnetic field shows the presence of weak coupling between the grains.