The Influence of Neutron Irradiation on (B0.65C0.35)Ba1.4Sr0.6Ca2Cu3Oz Superconducting Phase: The Role of the Grain Edge

Using the transport and magnetization measurements, the influence of neutron irradiation at a fluence of 5 × 10¹⁷ n cm⁻² on (B_0.65C_0.35)Ba_1.4Sr_0.6Ca₂Cu₃O _z has been investigated. The neutron irradiation was found to decrease critical temperature and transport critical current density, increase the residual and normal state resistivity, and improve the intragranular critical current density with 1.6 × 10⁵ A/cm² (at 77.3 K and in the applied field up to 160 kA m) and ΔM _irr/ΔM _nonirr ratio (up to factor of 3) at highest field used for investigation. The field dependence of this ratio, which is below the unity at very low field but higher than 1 at high fields, correlated with the shape of the hysteretic loops as well as with the change of the transport parameters after irradiation suggests the role of the irradiation-induced effects on the grain edges. We discuss these effects in the framework of the Bean-Livingstone surface barriers and geometrical barriers.     

Evidence for Irradiation Triggered Nonuniform Defects Distribution in Multiharmonic Magnetic Susceptibility of Neutron Irradiated YBa2Cu3O7?δ

Multiharmonic ac-magnetic susceptibility χ₁, χ₂, χ₃, of neutron irradiated Li-doped YBa₂Cu₃O_{7− x} has revealed a nonmonotonic dependence of all harmonics on the neutron fluence. The irradiation has a strongly depressive influence on the intergrain connection suggesting an increase of the effective thickness of the intergranular Josephson junction at a neutron fluence of 0.98 × 10¹⁷ cm⁻². Less damaged are the intragrain properties. A spectacular enhancement of the superconducting intragranular properties reflected in the characteristics of all harmonics was observed at highest fluence Φ = 9.98 × 10¹⁷ cm⁻². We assume that this effect results from the development of a space inhomogeneous distribution with alternating defectless and defect-rich regions.     

Influence of different synthesizing steps on the multiferroic properties of Bi5Fe1Ti3O15 and Bi5Fe0.5Co0.5Ti3O15 ceramics

The compounds Bi₅FeTi₃O₁₅ (BFTO) and Bi₅Fe_0.5Co_0.5Ti₃O₁₅ (BFCT) were prepared by incorporating BiFeO₃ (BFO) and BiFe_0.5Co_0.5O₃ (BFCO) into the host Bi₄Ti₃O₁₂ (abbreviated as BFTO-1 and BFCT-1) and by the conventional solid-state reaction method (abbreviated as BFTO-2 and BFCT-2). X-ray analysis indicates a four-layer Aurivillius phases with an orthorhombic symmetry. At room temperature, the remnant polarization (2P _r) of BFTO-1, BFTO-2, BFCT-1, and BFCT-2 samples are measured to be 11.0, 3.5, 13, and 6.3 μC/cm², respectively, and the corresponding remnant magnetization (2M _r) are about 2.72 × 10⁻³ memu/g, 1.51 × 10⁻³ memu/g, 7.6 and 2.1 memu/g, respectively. Both BFTO-1 and BFCT-1 samples exhibit the dielectric peaks at around 755 and 772 °C in their ε–T curves, respectively.     

Detailed Physical Characterizations of Cu-rich and Ru-poor (Ru0.9Cu0.1)Sr2YCu2O7.9

The optimized nominal composition, (Ru_0.9Cu_0.1) Sr₂YCu₂O_7.9 sample, has been prepared through high-pressure and high-temperature solid-state densification method. The obtained material has been studied by X-ray (laboratory) diffraction powder technique, magnetization and detailed magneto-transport measurements. The title compound indicates bulk magneto-superconducting properties under field strengths of H=10, 100, 500 and 1000 Oe. It shows diamagnetic transition at T _d=54, 38, 20 and 8 K for H=10, 100, 500 and 1000 Oe, respectively, in the zero-field-cooled susceptibility measurements. The high-field (H=5 and 10 kOe) molar susceptibility measurements show sharp ferromagnetic transition at ∼150 K with reduced molar susceptibility values. The various field dependence of magnetization, M(H), isotherm curves recorded at constant temperatures (5, 10, 25, 50, 100 and 150 K) indicate ferromagnetic saturation, whereas the MH curves measured at 200 and 300 K conditions reveal the paramagnetic state of the compound. Though the sample showed onset transition temperature, T_c^onsetT_{\mathrm{c}}^{\mathrm{onset}}, at ∼34 K under different field strengths (H=0, 10, 30, 50, 70 and 90 kOe), no T_c^R=0T_{\mathrm{c}}^{R=0} is seen down to 2 K. Even under relatively low applied field (ΔH=10 kOe) the title compound shows large negative magnetoresistance (MR) of about 68% at 2 K and increases with increasing the field strength up to ΔH=90 kOe (MR=77% at 2 K). This value is amazing and probably higher than other 1212 type ruthenocuprates. The title compound which shows little negative MR (about 1%) in the high temperature regions (125–300 K) is not affected much by different field strengths. Among the different fixed temperature MR(H) isotherms, the MR(H) curve measured at 5 K shows maximum negative MR of about 47% at 90 kOe compared to other four (T=50, 100, 200 and 300 K) MR(H) curves.     

Nonmonotonous Variation of the Superconducting Parameters of Neutron Irradiated Li-Doped YBa2Cu3O7?x

The effect of thermal and epithermal neutron irradiation on the superconducting critical temperature and critical current density of some Li-doped YBa₂Cu₃O_7–x samples was studied. The critical temperature exhibits a peak and the critical current density a valley in their dependence on neutron fluence, for moderate dose. A simple model, based on the Van Hove scenario and the kinetics of the defect production, is used to describe both phenomena.     

Evidence for Irradiation Triggered Nonuniform Defects Distribution in Multiharmonic Magnetic Susceptibility of Neutron Irradiated YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7−</Subscript><Subscript><Emphasis Type="Italic">δ</Emphasis></Subscript>

Multiharmonic ac-magnetic susceptibilityx ₁,x ₂,x ₃, of neutron irradiated Li-doped YBa₂Cu₃O_7−x has revealed a nonmonotonic dependence of all harmonics on the neutron fluence. The irradiation has a strongly depressive influence on the intergrain connection suggesting an increase of the effective thickness of the intergranular Josephson junction at a neutron fluence of 0.98 × 10¹⁷ cm⁻². Less damaged are the intragrain properties. A spectacular enhancement of the superconducting intragranular properties reflected in the characteristics of all harmonics was observed at highest fluence φ=9.98 × 10¹⁷ cm⁻². We assume that this effect results from the development of a space inhomogeneous distribution with alternating defectless and defect-rich regions.     

Ferroelectric and dielectric properties of Bi4-xNdxTi3O12 thin films prepared by sol–gel method

Bi_4-xNd_xTi₃O₁₂ (BNT-x, x = 0, 0.25, 0.50, 0.75 and 1.0) thin films were prepared on Pt/Ti/SiO₂/Si substrates by a sol–gel method. The microstructure, ferroelectric and dielectric properties of BNT-x thin films were investigated. The single-phase BNT-x thin films were obtained. With increasing Nd content, the preferred orientation changed from random to (117) and surface morphologies changed from the mixture of rod- and plate-like grains to rod-like grains. The Nd substitution improved the ferroelectric and dielectric properties of BTO films. BNT-x films showed better electrical properties at x = 0.50—1.0. BNT-0.75 film exhibited the best electrical properties with remanent polarization (2P _r) of 26.6 μC/cm², dielectric constant (ε _r) of 366 (at 1 MHz), dielectric loss (tanδ) of 0.034 (at 1 MHz), leakage current density (J) of ±3.0 × 10⁻⁶ A/cm² (at ± 5 V) and fatigue-free characteristics.     

Annealing temperature dependence of effective piezoelectric coefficients for Bi3.15Eu0.85Ti3O12 thin films

The effects of annealing temperatures 600, 650, 700, and 750 °C on microstructure, chemical composition, leakage current, ferroelectric, dielectric, and piezoelectric properties of Bi_3.15Eu_0.85Ti₃O₁₂ (BET) thin films prepared by metal–organic decomposition were studied in detail. The largest spontaneous polarization 2P _s (98.7 μC/cm² under 300 kV/cm), remnant polarization 2P _r (81.7 μC/cm² under 300 kV/cm), dielectric constant ε_r (889.4 at 100 kHz), effective piezoelectric coefficient d ₃₃ (46.7 pm/V under 260 kV/cm), and lowest leakage current (1.3 × 10⁻⁶ A/cm² under 125 kV/cm) of BET thin film were obtained with annealing at 700 °C. The mechanisms concerning the dependence of the enhancement d ₃₃ are discussed according to the phenomenological equation, and the improved piezoelectric performance could make BET thin film a promising candidate for piezoelectric thin film devices.     

The comparative influences of structural ordering, grain size, Li-content, and bulk density on the Li+-conductivity of Li0.29La0.57TiO3

The lattice and total Li⁺-ionic conductivity of Li_0.29La_0.57TiO₃ ceramic (LLTO) sintered at 1200 °C were determined as functions of powder calcination temperature and sintering duration, and these results were correlated with the relative degrees of Li⁺-ordering, Li-content, grain size, and bulk density to assess the relative impact of these parameters on material performance. Under all conditions, LLTO formed with a high degree of tetragonal superstructure to its perovskite related framework, and the lattice conductivity closely followed the relative amounts of the superstructure, as evaluated via determination of the sample ordering parameter from X-ray diffraction data. LLTO powders that were calcined at 900 °C for 1 h and sintered at 1200 °C for 6 h gave lattice conductivity values (~1.14 × 10⁻³ S cm⁻¹) comparable within the highest ranges reported in the literature. This coincided with the lowest degree of tetragonal superstructure formation, and it was also found to be largely independent of the values of Li-content measured on sintered ceramic despite significant Li₂O volatilization at longer sintering times (up to 23 % after 12 h at 1200 °C). Samples of LLTO powder that were calcined at 1100 °C and sintered at 1200 °C for 12 h resulted in the highest total Li-ion conductivity value ~6.30 × 10⁻⁵ S cm⁻¹. The total conductivity of LLTO varied inversely with grain size when the grains were <20 μm but was insensitive to that parameter above that size threshold. The strongest influence on total conductivity was primarily the bulk ceramic density. It was estimated from measured values that as the bulk ceramic density approached the full theoretical value for LLTO the total conductivity could near the lattice conductivity of ~1.2 × 10⁻³ S cm⁻¹.     

Characterization of NaPO3–SnO–WO3 glasses prepared by microwave heating

Phosphate glasses containing tin and tungsten oxides were produced by microwave heating under a nitrogen protective atmosphere. Microwaves permit to heat the raw materials at temperatures close to 1000 °C in short time and to obtain homogeneous glasses in less than 10 min. All samples were characterized from thermal and mechanical point of view as function of metal oxide proportions. The equimolar addition of SnO and WO₃ in sodium phosphate matrix involves a linear evolution of the different properties (T _g, CTE, density, mechanical properties, and durability). Thus, we have shown a progressive strengthening of the network. The glass transition temperature does not exceed 405 °C, and the chemical durability is improved to four orders of magnitude. The dissolution rate is equal to 3.4 × 10⁻⁷ g cm⁻² min⁻¹ for 40NaPO₃–30SnO–30WO₃ glass composition and is comparable with those of the window glass.     

The orthobaric liquid and vapor densities of tetramethylsilane and of 2,2-dimethylpropane

The orthobaric densities of tetramethylsilane and 2,2-dimethylpropane have been measured by means of a hydrostatic density balance. For tetramethylsilane the liquid density has been determined from 289.73 K to the critical point 448.60 K and the vapor density from 353.55 K to the critical point, while for 2,2-dimethylpropane the liquid density has been measured from 290.88 K to the critical point 433.71 K and the vapor density from 349.01 K to the critical point. The results are represented well by the extended-scaling equation of Wegner with three correction terms and the critical indices α,β, andΔ ₁, obtained from renormalization-group theory. The fit is not improved by a term expressing an anomaly in the diameter using either of the exponents (1−α) or 2β. The critical density for tetramethylsilane is estimated as (0.2436±0.0001) g·cm⁻³ and that for 2,2-dimethylpropane as (0.2318±0.0001) g·cm⁻³.     

Epitaxial Growth of CeO2/YSZ/CeO2 Buffer Layers on Textured Ni Substrates for YBCO Conductors

CeO₂/YSZ/CeO₂ buffer layers were deposited on textured Ni substrates by in situ pulsed laser deposition. The out-of-plane texture and in-plane texture of the buffer layers were characterized by X-ray diffraction ω-scans and ϕ-scans. Using this CeO₂/YSZ/CeO₂ architecture as the buffer layers, high quality YBCO films with a zero-resistance T _c about 90 K and a self-field critical current densities J _c above 10⁶ A/cm² at 77 K can be obtained on Ni substrates.     

Transport Properties under Magnetic Field and J c (H) Peak Effect on Single-Crystal Bi-2212 Whiskers

In this study, 50 nm–18 mm in length superconducting single-crystal Bi-2212 whiskers have been fabricated using glass-ceramic BSCCO material. The microstructure, transport and magnetic properties were characterized by XRD, SEM-EDX, R–T, I–V and M–H analysis. Highly c-axis oriented single-crystal whiskers were produced without any grain boundaries in any crystallographic direction. T _c and T _zero were obtained to be 94.8 K and 92.8 K, respectively, and decreased with increasing the magnetic field. Magnetic properties, M–H curves of the whiskers, were investigated at 3 different constant temperatures up to 5 T. Symmetric hysteresis loops for all temperature and field cases were obtained and maximum J _c ^mag value was calculated to be 4.58×10⁶ A cm⁻² at 10 K for 0 T but dropped to 1.61×10⁶ A cm⁻² at 30 K for 0 T. Transport critical current density, J _c ^trans, of the whiskers in low magnetic field (between 0 and 270 Oe) and in a wide temperature region (5–75 K) was investigated. It was obtained that initially J _c ^trans increased with increasing the magnetic field but then started to decrease with further increase on the magnetic field at all temperature values. We have investigated this problem in terms of the Bulk pinning model, the Geometrical barrier model and the Bean–Livingston surface barrier model. We have noticed that all these models were not fitted well to our data. However, we have modified the Bean–Livingstone model by adding a new parameter. It was found that this modified formula fitted well to the data obtained in this work and can give successful explanations to the other results obtained by other groups.     

Effect of Zn2TiO4 and ZnB2O4 additions on the microstructure and dielectric properties of AgNb1 ? xTaxO3 solid solutions

We report the preparation and characterization of AgNb_0.6Ta_0.4O₃ (ANT) based materials. The addition of Zn₂TiO₄ and ZnB₂O₄ influences the sintering temperature, phase composition, and microstructure of ANT ceramics. ANT doped with 1 wt % Zn₂TiO₄ or ZnB₂O₄ has high dielectric permittivity (400–470), low dielectric losses (tanδ ∼ 10⁻³), and a nonlinearity coefficient n _R ≅ 3–9% (at a field strength E = 3 × 10⁶ V/m).     

Magnetic transitions and magnetocaloric effects in Fe0.75Mn1.35As

In Fe_0.75Mn_1.35As compound, a metamagnetic transition from an antiferromagnetic phase to a ferrimagnetic phase can be induced above its phase transition temperature T _s = 165 K by an external magnetic field, which leads to large magnetocaloric effects around T _s. The sign of the magnetic entropy change ΔS _M in the Fe_0.75Mn_1.35As compound is negative, not as expected as an inverse magnetocaloric effect, and the maximum value of ΔS _M is 4.2 J/kg K at 167.5 K for a magnetic field change of 5 T. Although it induces an irreversible lattice expansion, the cycling of a magnetic field does not induce an irreversible change in the magnetic transitions and magnetocaloric behaviors. The antiferromagnetism-related metamagnetic transitions with a large magnetic entropy change may provide with an opportunity in searching novel materials for magnetic refrigeration.     

Neutron dosimetry using activation of thermoluminescent CaSO4

Sulfur activation in calcium sulfate doped with dysprosium (CaSO₄:Dy) thermoluminescent powder, which is bound in pure sulfur, has been used to measure the fast neutron dose at the tangential beam port of a Triga Mark III reactor. After a post-irradiation time of 3 d, the dosimeters were annealed at 600°C for 30 min in order to erase all the thermoluminescence acquired during the irradiation. The dosimeters were then stored to allow self-irradiation by betas from ³²P produced by sulfur activation. The thermoluminescent signal accumulated during a post-irradiation time of 20 d due to a neutron fluence of 2.2 × 10¹¹ n/cm² was equivalent to an absorbed dose of 10 mGy of ⁶⁰Co gamma rays. The thermoluminescence as a function of fast neutron dose fitted to a straight line on a log-log scale from 1 Gy to 10⁴Gy.     

Photo-electronic properties of InAs0.07Sb0.93 films

The temperature dependent photoconductive and surface barrier photovoltaic spectral responses of InAs_0.07Sb_0.93 films with an impurity density ～5.5×10¹⁵ cm^-3, grown by liquid phase microzone crystallization, are shown to be a function of their fundamental energy bandgaps shifted to values lower than those of InSb. From charge carrier transport measurements their absolute zero bandgap is calculated as ε_g0=0.197 eV, in good agreement with theory. In contrast with previously reported data on InAs_xSb_1-x solid solution bulk and single crystal layers, the electron mobility of InAs_0.07Sb_0.93 films increases with decreasing temperature reaching a value of ～1.32×10⁵ cm²/Vs at 77 K.     

Ion irradiation effects in EuBa2Cu3Oy thin film

The effect of He ion irradiation on the pinning potential in EuBa₂Cu₃O _y , thin film was investigated by measuring the temperature dependence of resistivity in magnetic fields. The pinning potential decreased as the ion fluence increased. A slower decrease of pinning potential was observed in higher magnetic field in the fluence region <3.5×10¹⁵ cm^–2.     

Direct Peritectic Growth of c-Axis Textured YBa2Cu3Ox on a Flexible Metallic Substrate

Previous work in the development of YBa₂Cu₃O _x (YBCO) superconducting wires and tapes has been focused on the deposition of YBCO on buffered metallic substrates. Although such an approach has proved successful in terms of achieving grain texturing and high transport current density, critical issues involving continuous processing of long-length conductors and stabilization of the superconductor have not yet been entirely settled. We have developed a novel process, the so-called direct peritectic growth (DPG), in which textured YBCO thick films have been successfully deposited directly onto a silver alloy substrate. No buffer layer is employed in the film deposition process. The textured YBCO grains have been obtained through peritectic solidification over a wide range of temperatures and times. The substrate materials have not demonstrated any observable reaction with the YBCO melt at the maximum processing temperature near 1010°C. The transport J _c has reached a respectable value of 10⁴ A/cm² at 77 K and zero magnetic field. Based on the experimental results in this work, we show that the DPG method offers an effective alternative for the fabrication of long-length YBCO conductors. Also reported is a physical explanation of the texturing mechanism on the metal substrate.     

Investigation of the temperature dependence of electron and phonon Raman scattering in single crystal YBa2Cu3O6.952

Detailed Raman-scattering measurements have been performed on high-quality YBa₂Cu₃O_6.952 single crystal (T _c =93 K, T _c =0.3 K). A sharp (FWHM 7.2 cm^–1 at 70 K and 10.0 cm^–1 at 110 K) 340 cm^–1phonon mode has been observed inB _1g polarization. An electronic scattering peak at 500 cm^–1 in theB _1g polarization extends down to 250 cm^–1. These FWHM values determine the upper limit of the homogeneous linewidth of the phonon and electronic excitations. The start of the electronic spectral function renormalization and of the 340 cm^–1 mode anomalies (frequency softening, linewidth sharpening, and intensity increase) have been observed to occur approximately 40 K aboveT _c . The 340 cm^–1 mode Fano shape analysis has been performed and the temperature dependences of the Fano shape parameters have been estimated. All 340 cm^–1 mode anomalies have been explained by the electronic spectral function renormalization.This work was supported by Swedish Natural Sciences Research Council (G.B. and L.B.) and by the National Science Foundation (DMR 91-20000) through the Science and Technology Center for Superconductivity (G.B. and M.V.K.).