Substitution Of Pb For Bi Research Articles

Effect of Lead substitution on LaO0.5F0.5BiS2

We examined Lead (Pb) Substitution effect on a single crystal of a layered superconductor LaO0.5F0.5BiS2. Pb concentration dependence of the lattice constant showed slight anomaly at about 8% and 9% substitution of Pb for Bi. These samples showed the enhancement of the superconducting transition temperature and the superconducting volume fraction. Furthermore, these samples showed the anomaly in the temperature dependence of the resistivity at about 150 K. These results were not observed in Pb substituted NdO0.7F0.3BiS2. Therefore, the enhancement of the superconducting properties by Pb substitution is related to the structural instability for the pale perturbation in LaO0.5F0.5BiS2.

Enhancement of Tc in BiS2-based superconductors NdO0.7F0.3BiS2 by substitution of Pb for Bi

We succeed in enhancement of a superconducting transition temperature (Tc) for NdO0.7F0.3BiS2 single crystal by partial substitution of Pb for Bi. The Tc increases with increasing Pb concentration until 6%. The maximum Tczero is 5.6 K, which is the highest value among BiS2 based superconductors synthesized under an ambient pressure. Pb substitution for Bi induces lattice shrinkage along the c axis. These results reflect that superconductivity in this system is responsive to the lattice strain.

Synthesis of the Bi-2222 Compounds of Bi–Sr–Ln(Zr)–Cu–O (Ln = Sm, Eu, Gd, and Dy)

Bi-based superconducting compounds with the 2222 structure has been already synthesized in the Bi2Sr2- (Ln1−xCex)2Cu2O10+y (Ln = Sm, Eu, and Gd) systems. One of the characteristics of these compounds is the existence of the fluorite-like (Ln1−xCex)2O2 block between two CuO5 pyramids in the crystal structure. The tetravalent ions of Ce4+ are reported to be necessary to stabilize the 2222 structure. Recently, we have discovered that the Bi-2222 phase could be composed in the Bi2Sr2(Ln2−xZrx)Cu2Oz (Ln = Sm, Eu, Gd, and Dy) systems, where Zr4+ is used as a new tetravalent ion stabilizing the 2222 structure in stead of Ce4+. In the new system, nearly single 2222 phase samples have been obtained at the nominal composition of x=0.5 (Ln = Sm, Eu, and Gd) and in the range of 0.1≤x≤0.3 (Ln = Dy). Among them, the sample with Ln = Gd has the smallest resistivity at 273 K. But it is a semiconductor, and the conduction process at low temperatures is assumed to be followed by a two-dimensional VRH. The experimental results for the Gd samples with a partial substitution of Pb for Bi in the Bi2Sr2(Gd2−xZrx)Cu2Oz system are also reported.

Synthesis, Electrical Properties, and Powder Neutron Crystal Structure Refinement of Pb1−xBixPt2O4 Compounds (0≤x≤0.3)

Substitution of Pb for Bi in the recently characterized mixed-valence lead–platinum oxide PbPt2O4 was attempted and a Pb1−xBixPt2O4 solid solution was obtained for 0≤x≤0.3. Powder X-ray diffraction study showed that all substituted compounds crystallize with similar triclinic unit cell and PbPt2O4 lattice parameters. The structural model of Pb0.7Bi0.3Pt2O4 was refined from powder X-ray diffraction data using the Rietveld method and the results indicate the same crystal structure than PbPt2O4 with one mixed Pb/Bi atomic site. Neutron diffraction realized on the two limit compositions of the solid solution (x=0 and 0.3) allowed to confirm the PbPt2O4 and Pb0.7Bi0.3Pt2O4 stoichiometries. Mean oxidation degree of Pt atoms in the [PtO4] infinite chains decreases from +3 for PbPt2O4 to +2.7 for Pb0.7Bi0.3Pt2O4. Conductivity measurements show a metallic behavior for all the compositions except the limit composition x=0.3 for which a semiconducting behavior appears.

Thermoelectric properties of Bi2.2−xPbxSr2Co2Oy system

Polycrystalline samples of Bi2.2−xPbxSr2Co2Oy (x=0, 0.4, and 0.8) with a layered structure have been prepared using a hot pressing technique and their thermoelectric properties methodically investigated. It is found that the substitution of Pb for Bi is a fairly effective means of improving the thermoelectric properties of the Bi2.2−xPbxSr2Co2Oy system owing to resistivity (ρ) decreasing and thermoelectric power (S) increasing simultaneously. The thermal conductivity (κ) at high temperature also decreases markedly with Pb substitution. As a result, for the x=0.8 sample the dimensionless figure of merit, ZT(=S2T/ρκ), increases with temperature and reaches 0.26 at 1000 K, which indicates that this material is a strong candidate as a high-temperature thermoelectric material.

Ferromagnetism and Large Negative Magnetoresistance in Pb Doped Bi–Sr–Co–O Misfit-Layer Compound

Ferromagnetism and accompanying large negative magnetoresistance in Pb-substituted Bi-Sr-Co-O misfit-layer compound are investigated in detail. Recent structural analysis of (Bi,Pb)${}_2$Sr${}_{3}$Co${}_2$O${}_9$, which has been believed to be a Co analogue of Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\delta}$, revealed that it has a more complex structure including a CoO${}_2$ hexagonal layer [T. Yamamoto {\it et al.}, Jpn. J. Appl. Phys. {\bf 39} (2000) L747]. Pb substitution for Bi not only introduces holes into the conducting CoO${}_2$ layers but also creates a certain amount of localized spins. Ferromagnetic transition appears at $T$ = 3.2 K with small spontaneous magnetization along the $c$ axis, and around the transition temperature large and anisotropic negative magnetoresistance was observed. This compound is the first example which shows ferromagnetic long-range order in a two-dimensional metallic hexagnonal CoO${}_2$ layer.

Oxygen stoichiometry and properties of Pb-substituted Bi2Sr2CaCu2O8 + δ

The effect of partial Pb substitution for Bi on the oxygen stoichiometry and superconducting properties of Bi2Sr2CaCu2O8+δ was studied. The Pb content and heat-treatment conditions were optimized to attain the highest critical parameters. The observed changes in the superconducting properties were shown not to correlate with oxygen stoichiometry. Superconducting properties were found to persist in the absence of Cu in the formal oxidation state 3+. A reduction in the concentration of excess oxygen to about the lowest possible level is accompanied by a significant increase inT c R = 0 (96 K) and critical current density. The possible mechanisms underlying the effect of Pb substitution on the properties of 2212 are discussed.

Effect of lead additive on the ferroelectric properties and microstructure of SrxPbyBi2zTa2O9 thin films

Ferroelectric thin films of bismuth-containing layered perovskite SrxPbyBi2zTa2O9 have been prepared using the metalorganic decomposition method. The effect of both Sr and Pb content on the crystal structure, microstructure, and ferroelectric properties of SrxPbyBi2.3Ta2O9 films was investigated. A maximum remanent polarization of 2Pr=19.2 μC/cm2 was obtained for the SrxPb0.2Bi2.3Ta2O9 film with 20 mol % Sr-deficient composition as prepared at 800 °C, which could be the compromising effects of Sr content on both grain growth and second phase formation of BiTaO4. The substitution of Pb for Bi is accompanied by the occurrence of oxygen vacancies to compensate the charge balance, which is responsible for grain growth mechanism in Sr0.8Pb0.2Bi2.3Ta2O9 films. Fatigue endurance of Sr0.8Bi2.3Ta2O9 films becomes problematic after 109 cycles with a decrease in remanent polarization to 85% of the original value. This phenomenon was related to electron injection and creation of electron traps due to the occupation of Sr vacancies by Bi cations. It is demonstrated that the fatigue endurance of Sr0.8Bi2.3Ta2O9 film can be improved by doping with 20 mol % PbO.

Rapid Preparation of High-Tc Superconductors of the Bi-2212 Phase Using a Domestic Microwave Oven

Single-phase samples of high-Tc superconductors of the Bi-2212 phase have been prepared using a domestic microwave oven. It is to be important for the preparation to control the temperature of the sample environment and to repeat the microwave-radiation process with intermediate grinding, because the Bi-2212 phase is stable only in a narrow temperature range and requires a long heat-treatment time for formation. The partial substitution of Pb for Bi is also to be effective for the formation of the Bi-2212 phase.

Superconductivity and structural change in the (Bi 2− yPb y)Sr 2 (Eu 2− xCe x)Cu 2O z system

Superconductivity and crystal structure change have been observed in the Bi(Pb)-2222 system of (Bi 2− y Pb y )Sr 2 (Eu 2− x Ce x )Cu 2O z . By substitution of Pb for Bi, the samples easily become superconductors without annealing under high-pressure O 2 atmosphere. Then, when the Pb content y is increasing and exceeds 0.5, the crystal structure changes from a pseudotetragonal structure to an orthorhombic one. Interestingly, with increasing of the y value, the T c value monotonously increases, while the superconducting volume fraction shows a maximum at y=0.5.

Studies on simultaneous substitution of Pb and Y in Bi 2Sr 2CaCu 2O 8+ δ single crystals

The effect of simultaneous substitution of Pb for Bi and Y for calcium in Bi 2Sr 2CaCu 2O 8+ δ has been studied. Phase pure single crystals of Bi 1.7Pb 0.3Ca 1− x Y x Cu 2O 8+ δ has been grown for x = 0 to 5. Variation in lattice parameters and the change in superconducting transition temperature for different x values has been studied. The optical micrograph revealed the layer growth mechanism and occurrence of some growth twins which are not removed even after annealing. Chemical etching with a bromide-ethanol solution revelaed elongated diamond shaped etch pits reflecting the orthorhombic symmetry of the crystal.

Negative Magnetoresistance in (Bi,Pb)2Sr3Co2O9 Layered Cobalt Oxides

ABSTRACTTransport and magnetic properties of layered cobalt oxide (BiPb)2Sr3Co2O9 are investigated in detail under magnetic field up to 8 T. Parent compound, Bi2Sr3Co2O9, is a typical band insulator with Co ions being in a low-spin 3+ state because of the well-separated dε and dγ levels possibly due to a strong crystal field. We have tried to introduce holes mainly by Pb substitution for Bi. The hole-doped sample shows metallic behavior in a resistivity measurement between 300 and 30 K. Below 30 K, however, the resisitivity increases. Under the magnetic field the resistivity is strongly suppressed in this region. We observed more than 30% resistivity drop at 2 K under H = 8 T, which is comparable to insulating (La,Sr)CoO3 system. We discuss the mechanism of hole doping and the origin of negative magnetoresistance with tranport and magnetic properties, and point out that the conventional double-exchange mechanism cannot be applied to this system. This means that some new mechanism is necessary to explain this phenomenon.

TEM study of the iodine intercalated BI 1.5PB 0.5SR 2CA 2CU 3O 10+x

The partial substitution of Pb for Bi made it possible to prepare single phase 2223 and iodide intercalated I-2223 BiSrCaCuO compounds. Both compounds were studied by TEM, HRTEM, X-ray diffraction, and electrical resistivity. A change in symmetry occurs upon intercalation, likely a Bbmb to Pbm2 transition, and the change in the stacking sequence of the perovskite blocks was directly observed by HRTEM. Low temperature electrical resistivity measurements showed a metallic type conduction with critical temperatures of 105 K and 83 K, respectively. The resistivity at room temperature was 1.6 × 10 −3 Ωcm for 2223 and 0.14 Ωcm for I-2223.

Interlayer coupling in Pb-substituted Bi 2Sr 2CaCu 2O 8+δ single crystals

We show that Pb-substitution for Bi in single crystals of highly anisotropic Bi 2Sr 2CaCu 2O 8+δ induces a decrease of the structural anisotropy. As a direct result, the out-of-plane resistivity ϱ c ( T) is reduced by four orders of magnitude and the temperature behavior changes from semiconductor-like (d ϱ c /d T < 0) to metallic (d ϱ c /d T > 0). The results can be explained by assuming that Pb-doping introduces an additional covalent type of bonding between the BiO-bilayers, which is not present in the undoped crystals. This additional bonding may be due to an enhanced overlap of atomic orbitals to such an extent that a metallic conductivity perpendicular to the CuO 2 planes becomes possible. By modeling the out-of-plane magnetoresistivity ϱ c ( T, H) with H ∥ c we show that also the strength of the interlayer Josephson coupling is significantlyl affected by the Pb-substitution.

Critical Current Densities and Irreversibility Fields in Pb-Doped and Pb-Free Bi2Sr2Ca2Cu3Oy Superconductors

From the hysteresis in DC magnetization loops, we evaluated critical current densities J c and irreversibility fields B irr of Pb-doped and Pb-free Bi-2223 superconductors which were prepared from nominal compositions Bi1.68Pb0.32Sr1.85Ca1.85Cu2.85BxOy (x=0, 0.01) and Bi2Sr1.6Ca2.4Cu3O10 by different heating processes. The intragrain J c and B irr for the Pb-doped samples were larger than those of the Pb-free one, although the superconducting volume fraction and superconducting characteristics of the three samples are almost the same. This result suggests that effective pinning centers are introduced by the partial substitution of Pb for Bi in Bi-2223.

Structural and superconducting properties of Bi 2− mPb mSr 2Ca 2Cu 3O 10−δ with 0 ≤ m ≤ 1

Substitution of Pb for Bi in polycrystalline “Bi 2− x Pb x Sr 2Ca 2Cu 3O 10−δ” (2223 phase) has been achieved up to the solubility limit of x Pb = 0.35 ± 0.03 by optimizing the annealing time and annealing temperature of each sample. Addition of Pb beyond its solubility limit results in changes of the liquidus compatibility relations. The microstructure of the samples and the chemical compositions of all phases present were studied by scanning electron microscopy (SEM), energy dispersive X-ray fluorescence (EDX) and electron probe microanalysis (EPMA). The lattice parameters of the 2223 phase determined by X-ray powder diffraction reveals also the incorporation of Pb for Bi. Single-crystal X-ray methods show a superstructure along [010] with an incommensurate modulation of q = 0.115b ∗ for x Pb = 0.36 . In spite of the drastic variations in the chemical composition of the 2223 phase, T c remains constant over the whole observed range with T c = 111.5 ± 1.5 K.

Magnetic penetration depths of (BiPb)-2212 and (TlPb)-1212 — Universal correlations revisited

A systematic study of the dependence of the critical temperature on the superconducting carrier density, as measured byμ +SR, was carried out for a variety of cuprate oxides. We have shown that substitution of Pb for Bi and La for Sr result in well pinned vortex lattices in Bi2Sr2CaCu2Ox, and studied (BiPb)-2212 from the underdoped to the slightly overdoped regime. We also found that Tl-1212 samples, which have optimal maximumT c=108 K, trace a separate line with parameters comparable to overdoped Tl-2223 at the maximum. These data, together with data on Y-124/247, Tl-2201 and other cuprates result in an larger set of “universal correlations” between Tc andσ(0) ∞n s /m * for the high temperature superconductors.

Effects of Silver and Lead on the Phase Stability of Bi2Sr2Ca1Cu2O8+x and Bi2Sr2Ca2Cu3O10+x above and below the Solidus Temperature

A solid‐state ionic technique has been used to determine the effects of Ag on the phase stability of Bi2Sr2Ca1Cu2O8+x(Bi‐2212), and Ag and Pb on the phase stability of Bi2Sr2Ca2Cu3O10+x (Bi‐2223), over a temperature range of 600° to 910°C and oxygen partial pressure range of 10–6 to 10°atm (10–1 to 105 Pa). The addition of Ag to Bi‐2212 leads to a marginal decrease in the stability of the phase above 883°± 3°C and 7 × 10–2 atm (7 kPa) oxygen, resulting in a reduction in the incongruent melting point by 15°C in air. The substitution of Pb for Bi in the (Bi,Pb)‐2223 phase leads to an increase in phase stability below the solidus, but to only a minor change in stability above the solidus. For both phases, several incongruent melting reactions have been identified over the range of reduced oxygen partial pressures studied. In addition, the phase equilibria both above and below the stability line have been determined for certain regions of the stability diagrams. From the thermo‐dynamic information obtained in this study an improved melt‐processing route for Bi‐2212 has been found which minimizes unwanted phases. In addition, the optimum precursors for the formation of more phase‐pure (Bi,Pb)‐2223 during shorter time periods have been found by determining the initial decomposition products of (Bi,Pb)‐2223, both above and below the solidus.

Synthesis of Bi-2222 compounds not containing tetravalent ions: Bi 2Sr 2−xLa 2−yLn x+yCu 2O z (Ln=Sm, Eu, Gd and Dy)

Bi-based cuprate system with the 2222 structure have been synthesized without doping of tetravalent ions such as Ce 4+ or Pr 4+ in the Bi 2Sr 2−xLa 2−yLn x+yCu 2O z (Ln=Sm, Eu, Gd and Dy) systems. The almost-single phase sample for each system was attained at a limited composition. All of the sample for each system was semiconducting, and the conduction process at low temperatures was assumed to be followed by a two-dimensional variable-range hopping. The results after partial substitution of Pb for Bi and annealing under high-pressure O 2 atmosphere are also reported.

The decomposition of edta-gel precursors in the production of BSCCO superconductors

The decomposition of EDTA gel precursors for BSCCO superconductor manufacture has been studied using STA (TG/DTA) and dilatometry in conjunction with FTIR. The thermoanalytical data are discussed in relation to the sequence of phase formation necessary for the production of the 2223 BSCCO superconducting phase. The effects of substitution of Pb for Bi on the temperatures of formation of the superconducting phases is also discussed. STA has also been carried out under varying oxygen partial pressures to determine the effects of oxygen pressure on the formation and decomposition of the phases involved in the production of the 2223 compound.