Large Electrical Resistivity Research Articles

Quartz Nanopore Membranes for Suspended Bilayer Ion Channel Recordings

A method is described for fabricating 25-75 mum thick fused quartz membranes containing a single conical shaped nanopore (orifice radius ranging from 10 to 1000 nm). The quartz nanopore membrane (QNM) provides an excellent solid support structure for lipid bilayers in ion channel recordings due to the large electrical resistivity of fused quartz. Electrical measurements demonstrate that the leakage current through 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) bilayers suspended across a 500-1000 nm radius QNM orifice is immeasurably small, corresponding to a bilayer resistance greater than 10(12) ohms. Translocation of single-stranded DNA oligomers (poly dA 50-mer and poly dA 20-mer) through a protein ion channel (alpha-hemolysin) reconstituted in a DPhPC bilayer suspended across the QNM orifice is demonstrated.

Large electrical resistivity and high saturation magnetization nanocrystalline Fe 86B 13Cu 1 alloy prepared by hot isothermal pressing

The effects of hot isothermal pressing (HIP) on the microstructures and magnetic properties of nanocrystalline Fe 86B 13Cu 1 ribbons were studied. It is shown that the precipitation of Fe 3B phase is suppressed and the grain size of α-Fe phase decreases to 13.2 nm when amorphous Fe 86B 13Cu 1 ribbons are annealed by HIP under the pressure of 150 MPa. A high electrical resistivity and high saturation magnetization nanocrystalline soft magnetic material is prepared by HIP owing to the suppression of the precipitation of Fe 3B phase and a marked decrease in the grain size of α-Fe phase. The prepared sample exhibits a large electrical resistivity of 183 μΩ cm, a high saturation magnetization of 1.94 T and a low coercive force of 12 A/m.

Change in piezoelectric boundary acoustic wave characteristics with overlay and metal grating materials

This paper describes how the characteristics of shear-horizontal type piezoelectric boundary acoustic waves (PBAWs) change with combination of different overlay and metal grating materials. It is shown that PBAWs are supported in various structures provided that highly piezoelectric material(s) are employed as structural member(s). For verification, numerical simulation of different material combinations is done. The results are in good agreement with the qualitative prediction. That is, large electromechanical coupling factor K(2) is obtainable when materials having small mass densities shear modulus c(44) and shear velocity VBS; and materials having extremely large shear modulus c(44) are chosen, respectively, for overlay and metallic grating. When YX-LiNbO(3) is assumed as a substrate, for example, the best choice seems to be SiO(2) and Au for overlay and metallic grating, respectively. Although metals with extremely large rho and c(44) such as W and Ta offer large K(2), they may not be acceptable for practical PBAW applications because of their large electric resistivity.

Magnetic properties and spin-glass-like behavior in stoichiometric Mn3In compound

Magnetic and transport properties of stoichiometric Mn3In compound are extensively studied by means of dc magnetization, ac susceptibility, magnetic relaxation, and electrical resistivity measurements. It is found that Mn3In is a ferrimagnet with Curie temperature of 80 K and that a metallic spin-glass-like (SGL) state exists below 45 K, which is indicated by the difference between zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves, invariable FC moments, large remanence effect, magnetic relaxation, and electrical resistivity abnormality. Moreover, the SGL state in Mn3In exhibits some anomalous behaviors, such as no cusp in the ZFC curve at the frozen temperature Tf, a remarkable high-field irreversibility, and a high-field relaxation process. The presence of the SGL state in the Mn3In compound without doping or substitution is discussed in terms of magnetic cluster mode.

Effect of Ag on the sintering and dielectric properties behavior of Bi1.5ZnNb1.5O7 ceramics

Abstract Bi1.5ZnNb1.5O7–Ag composites were prepared by solid state method. The sintering temperature was lowered to 900 °C for the Bi1.5ZnNb1.5O7 ceramics with 3 wt% silver doping. The microstructures, surface morphologies, and dielectric properties of the composites were investigated. A small amount of silver doping is shown to promote grain growth. The grain size of the composites sintered at 950 °C increased from 2 to 6 μm with the silver content increasing from 1 to 4 wt%. The composites with 4 wt% silver sintered at 950 °C had the relative permittivity of 215, and dielectric loss of 10−4 ranging from 100 Hz to 1 MHz. The silver doping in composites also improves the electrical resistivity of Bi1.5ZnNb1.5O7–Ag composites, and increases the electrical resistivity value from 1013 to 1015 Ω cm for the samples sintered at 900 or 950 °C by increasing the silver content from 1 to 4 wt%. The Bi1.5ZnNb1.5O7–Ag composites with lower loss and larger electrical resistivity would be useful for electronic devices in RF application.

Three-dimensional electrical resistivity model of a nuclear waste disposal site

Abstract A three-dimensional (3D) modeling study was completed on a very large electrical resistivity survey conducted at a nuclear waste site in eastern Washington. The acquisition included 47 pole–pole two-dimensional (2D) resistivity profiles collected along parallel and orthogonal lines over an area of 850 m × 570 m. The data were geo-referenced and inverted using EarthImager3D (EI3D). EI3D runs on a Microsoft 32-bit operating system (e.g. WIN-2K, XP) with a maximum usable memory of 2 GB. The memory limits the size of the domain for the inversion model to 200 m × 200 m, based on the survey electrode density. Therefore, a series of increasing overlapping models were run to evaluate the effectiveness of dividing the survey area into smaller subdomains. The results of the smaller subdomains were compared to the inversion results of a single domain over a larger area using an upgraded form of EI3D that incorporates multi-processing capabilities and 32 GB of RAM memory. The contours from the smaller subdomains showed discontinuity at the boundaries between the adjacent models, which do not match the hydrogeologic expectations given the nature of disposal at the site. At several boundaries, the contours of the low resistivity areas close, leaving the appearance of disconnected plumes or open contours at boundaries are not met with a continuance of the low resistivity plume into the adjacent subdomain. The model results of the single large domain show a continuous monolithic plume within the central and western portion of the site, directly beneath the elongated trenches. It is recommended that where possible, the domain not be subdivided, but instead include as much of the domain as possible given the memory of available computing resources.

Preparation, Characterization and Scanned Conductance Microscopy Studies of DNA-Templated One-Dimensional Copper Nanostructures

The synthesis of one-dimensional metal nanostructures can be achieved through the use of DNA molecules as templates to control and direct metal deposition. Copper nanostructures have been fabricated using this strategy, through association of Cu(2+) ions to DNA templates and reduced with ascorbic acid. Due to the possibility that the reduction of the Cu(2+) can result in the preferential formation of Cu(2)O over metallic Cu(0), X-ray photoelectron spectroscopy and X-ray diffraction have been carried out to establish the chemical identity of the nanostructures. Conclusive evidence is found that reduction of the Cu(2+) ions does result in the formation of the desired metallic Cu(0) structures. The morphology of the nanostructured Cu(0) material has also been observed by atomic force microscopy, showing the structures to have a "beads-on-a-string" appearance and being 3.0-5.5 nm in height. The electrical properties of the structures have been investigated by scanned conductance microscopy, showing the Cu(0) structures exhibit much larger electrical resistance than expected for a metallic nanowire. This is thought to be a consequence of their "beads-on-a-string" morphology and small lateral dimensions (sub-10 nm); both these factors would be expected to increase the electron scattering rate, and, further, there are likely to be significant tunneling barriers at the Cu(0) particle-particle junctions.

Signature of checkerboard fluctuations in the phonon spectra of a possible polaronic metal La1.2Sr1.8Mn2O7

Charge carriers in low-doped semiconductors may distort the atomic lattice around them and through this interaction form so-called small polarons. High carrier concentrations on the other hand can lead to short-range ordered polarons (large polarons) and even to a long-range charge and orbital order. These ordered systems should be insulating with a large electrical resistivity. However, recently a polaronic pseudogap was found in a metallic phase of La(2-2x)Sr(1+2x)Mn(2)O(7) (ref. 7). This layered manganite is famous for colossal magnetoresistance associated with a phase transition from this low-temperature metallic phase to a high-temperature insulating phase. Broad charge-order peaks due to large polarons in the insulating phase disappear when La(2-2x)Sr(1+2x)Mn(2)O(7) becomes metallic. Investigating how polaronic features survive in the metallic phase, here we report the results of inelastic neutron scattering measurements showing that inside the metallic phase polarons remain as fluctuations that strongly broaden and soften certain phonons near the wavevectors where the charge-order peaks appeared in the insulating phase. Our findings imply that polaronic signatures in metals may generally come from a competing insulating charge-ordered phase. Our findings are highly relevant to cuprate superconductors with both a pseudogap and a similar phonon effect associated with a competing stripe order.

Growth of Pb(Ti,Zr)O 3 thin films by metal-organic molecular beam epitaxy

Single-crystal Pb(Zr x Ti 1− x )O 3 thin films have been grown on (0 0 1) SrTiO 3 and SrTiO 3:Nb substrates by molecular beam epitaxy using metal-organic source of Zr and two different sources of reactive oxygen—RF plasma and hydrogen-peroxide sources. The same growth modes and comparable structural properties were observed for the films grown with both oxygen sources, while the plasma source allowed higher growth rates. The films with x up to 0.4 were single phase, while attempts to increase x beyond gave rise to the ZrO 2 second phase. The effects of growth conditions on growth modes, Zr incorporation, and phase composition of the Pb(Zr x Ti 1− x )O 3 films are discussed. Electrical and ferroelectric properties of the Pb(Zr x Ti 1− x )O 3 films of ~100 nm in thickness grown on SrTiO 3:Nb were studied using current–voltage, capacitance–voltage, and polarization–field measurements. The single-phase films show low leakage currents and large breakdown fields, while the values of remanent polarization are low (around 5 μC/cm 2). It was found that, at high sweep fields, the contribution of the leakage current to the apparent values of remanent polarization can be large, even for the films with large electrical resistivity (∼10 8–10 9 Ω cm at an electric filed of 1 MV/cm). The measured dielectric constant ranges from 410 to 260 for Pb(Zr 0.33Ti 0.67)O 3 and from 313 to 213 for Pb(Zr 0.2Ti 0.8)O 3 in the frequency range from 100 to 1 MHz.

CaMn1−x NbxO3 (x ≤ 0.08) Perovskite-Type Phases As Promising New High-Temperature n-Type Thermoelectric Materials

Perovskite-type CaMn(1-x)Nb(x)O(3+/-delta) (x = 0.02, 0.05, and 0.08) compounds were synthesized by applying both a "chimie douce" (SC) synthesis and a classical solid state reaction (SSR) method. The crystallographic parameters of the resulting phases were determined from X-ray, electron, and neutron diffraction data. The manganese oxidations states (Mn(4+)/Mn(3+)) were investigated by X-ray photoemission spectroscopy. The orthorhombic CaMn(1-x)Nb(x)O(3+/-delta) (x = 0.02, 0.05, and 0.08) phases were studied in terms of their high-temperature thermoelectric properties (Seebeck coefficient, electrical resistivity, and thermal conductivity). Differences in electrical transport and thermal properties can be correlated with different microstructures obtained by the two synthesis methods. In the high-temperature range, the electron-doped manganate phases exhibit large absolute Seebeck coefficient and low electrical resistivity values, resulting in a high power factor, PF (e.g., for x = 0.05, S(1000K) = -180 microV K(-1), rho(1000K) = 16.8 mohms cm, and PF > 1.90 x 10(-4) W m(-1) K(-2) for 450 K < T < 1070 K). Furthermore, lower thermal conductivity values are achieved for the SC-derived phases (kappa < 1 W m(-1) K(-1)) compared to the SSR compounds. High power factors combined with low thermal conductivity (leading to ZT values > 0.3) make these phases the best perovskitic candidates as n-type polycrystalline thermoelectric materials operating in air at high temperatures.

Investigation of SnSe, SnSe2, and Sn2Se3 alloys for phase change memory applications

SnSe, SnSe2, and Sn2Se3 alloys have been studied to explore their suitability as new phase change alloys for electronic memory applications. The temperature dependence of the structural and electrical properties of these alloys has been determined and compared with that of GeTe. A large electrical resistance contrast of more than five orders of magnitude is achieved for SnSe2 and Sn2Se3 alloys upon crystallization. X-ray diffraction measurements show that the transition in sheet resistance is accompanied by crystallization. The activation energy for crystallization of SnSe, SnSe2, and Sn2Se3 has been determined. The microstructure of these alloys has been investigated by atomic force microscopy measurements. X-ray reflection measurements reveal density increases of 5.0%, 17.0%, and 9.1% upon crystallization for the different alloys.

Structural and physical properties of Mg 3−xZn xSb 2 ( x=0–1.34)

The Mg 3− x Zn x Sb 2 phases with x=0–1.34 were prepared by direct reactions of the elements in tantalum tubes. According to the X-ray single crystal and powder diffraction, the Mg 3− x Zn x Sb 2 phases crystallize in the same P3¯ m1 space group as the parent Mg 3Sb 2 phase. The Mg 3− x Zn x Sb 2 structure is different from the other substituted structures of Mg 3Sb 2, such as (Ca, Sr, Ba) Mg 2Sb 2 or Mg 5.23Sm 0.77Sb 4, in a way that in Mg 3− x Zn x Sb 2 the Mg atoms on the tetrahedral sites are replaced, while in the other structures Mg on the octahedral sites is replaced. Thermoelectric performance for the two members of the series, Mg 3Sb 2 and Mg 2.36Zn 0.64Sb 2, was evaluated from low to room temperatures through resistivity, Seebeck coefficient and thermal conductivity measurements. In contrast to Mg 3Sb 2 which is a semiconductor, Mg 2.36Zn 0.64Sb 2 is metallic and exhibits an 18-times larger dimensionless figure-of-merit, ZT, at room temperature. However, thermoelectric performance of Mg 2.36Zn 0.64Sb 2 is still poor and it is mostly due to its large electrical resistivity.

The Development of the Composite Materials for the Bipolar Plate of the Fuel Cell

The paper was to investigate the development of the graphite/phenolic resin composite materials that were fabricated by compression molding for the bipolar plate of the fuel cell. Effect of the different amounts of resin and the graphite powder size on the porosity, density, bending strength, and electrical resistance of the composites would be analyzed. In addition, the composites of the bipolar plates would be machined into the groove channel using high speed milling, which then assembles into single fuel cell. The I-V performance of the single fuel cell would be also discussed. The experimental results showed that when the larger amount of resin was employed, the resulting composites had a lower porosity, a larger electrical resistance, and a higher bending strength. The graphite/resin composites showed a good machinability during the high-speed milling. Finally, the graphite/resin composites of bipolar plates containing 25-30 vol. % phenolic resins were fabricated into a single fuel cell, which displays a relatively better I-V performance.

Revisiting the Sr–Cr(IV)–O system at high pressure and temperature with special reference to Sr 3Cr 2O 7

High pressure and temperature are used to synthesise perovskite related phases in the Sr–Cr(IV)–O system. The n = 1, 2 and ∞ members of the Sr n +1Cr n O 3 n+1 family have been obtained. Another new member, n = 3 as well as an hexagonal layered perovskite have also been observed by transmission electron microscopy and electron diffraction. The average structure of Sr 3Cr 2O 7 as determined by XRD has space group I4/ mmm, whereas its microstructure includes a large amount of defects both in the layer stacking and within the layers. 2D magnetism and a large electrical resistance in Sr 3Cr 2O 7 are observed as opposed to the nonlocalized electronic behaviour of SrCrO 3.

準結晶研究の最近の展開 ４．準結晶のはたらき（準結晶の物性と応用）Ａｌ基準結晶と近似結晶の熱電物性

Al-based icosahedral quasicrystals and their corresponding approximants are characterized by large electrical resistivity, large thermoelectric power, and very small thermal conductivity. The factors leading to these characteristics were investigated by use of their crystalline approximants, which allow us to employ the structure analysis, band calculation, and phonon calculation well developed for crystalline materials. It is found that the quasiperiodic order does not play an exclusive role in providing the characteristic thermoelectric properties, while the icosahedral-symmetry and the characteristic quasi-Bllirouin-zone significantly contribute to these properties by deepening pseudogap at the Fermi level, reducing the mumber of acoustic phonons, and enhancing Umklapp scattering of phonons.

The performance of electric double layer capacitors using particulate porous carbons derived from PAN fiber and phenol-formaldehyde resin

Activated carbon fibers are known to contain pores with a small resistance for electrolyte migration while possessing a large electrical resistance between the fibers. A carbon powder derived from pulverization of PAN-based carbon fibers was examined as an electrode for electric double layer capacitors using H 2SO 4 as the electrolyte solution. The performance of conventional-type activated carbon powders derived from phenol-formaldehyde resin char was also measured for comparison. The fiber-derived carbon exhibited an electrical resistance comparable to that of the conventional carbons while showed a larger specific capacitance as well as a lesser extent of capacitance decrease at high currents due to a smaller pore resistance. An ultimate capacitance as high as 290 F g −1 can be reached for this fiber-derived carbon powder (with a BET surface area of ≈1300 m 2 g −1). This large capacitance value was suggested to be associated with the high activity feature of the pore wall.

Nano-Granular Co-Fe-AI-O Soft Ferromagnetic Thin Films for GHz Magnetic Device Applications

Co-Fe-Al-O nanogranular thin films were fabricated by RF-magnetron sputtering under an Ar+O₂ atmosphere. High resolution transmission electron microscopy revealed that the Co-Fe-Al-O films are composed of bcc (Co, Fe) nanograins finer than 5 nm and an Al-O amorphous phase. A very large electrical resistivity of 374 μΩcm was obtained, together with a large uniaxial anisotropy field of 50 Oe, a hard axis coercivity of 1.25 Oe, and a saturation magnetization of 12.9 kG. The actual part of the relative permeability was measured to be 260 at low frequencies and this value was maintained up to 1.3 GHz. The ferromagnetic resonance frequency was 2.24 GHz. The resulting Co-Fe-Al-O nanogranular thin films with a high electrical resistivity and high resonance frequency are considered to be suitable for GHz magnetic device applications.

Magnetic and Electrical Properties of NpTGa5 (T=Fe, Rh and Ni)

We grew high-quality single crystals of NpTGa 5 (T = Fe, Rh, and Ni) with a tetragonal structure by the Ga-flux method and measured their electrical resistivity, specific heat, magnetic susceptibility, and magnetization. All the investigated compounds undergo magnetic ordering. NpFeGa 5 orders antiferromagnetically at T N =118 K and shows another magnetic transition at T * =78 K. A relatively large electrical resistivity indicates that NpFeGa 5 might be a low-carrier compound. NpRhGa 5 also orders antiferromagnetically at T N1 =36 K. Below another magnetic transition at T N2 =32 K, the antiferromagnetic easy-axis is most likely changed from [001] to the (001) plane. On the other hand, NpNiGa 5 undergoes ferromagnetic ordering at T C =30 K, where the magnetic moment of Np is directed along the [001] direction. Furthermore, below another magnetic transition at T * =18 K, the ordered moment is discontinuously enlarged and a change of the magnetic structure occurs. The electronic specific heat coefficients are approximately determined as 30, 52, and 100 mJ/K 2 ·mol for NpFeGa 5 , NpRhGa 5 , and NpNiGa 5 , respectively. The magnetic susceptibility approximately follows the Curie–Weiss law at high temperatures (250 < T < 300 K) with effective magnetic moments ranging from 2.4 to 2.6 µ B /Np for NpRhGa 5 and NpNiGa 5 , indicating that the localized 5 f 4 electronic states are most likely applicable to these compounds at high temperatures.

Dielectric and Piezoelectric Properties of Niobium-modified BiInO3–PbTiO3 Perovskite Ceramics with High Curie Temperatures

Piezoelectric ceramics with TC &gt; 500 °C were projected in the perovskite BiInO3–PbTiO3 (BIPT) system based on their low tolerance factor (∼0.884). However, a stable perovskite phase could be synthesized only when the PbTiO3 (PT) content was greater than 75%. Furthermore, the large tetragonality (c/a &gt; 1.08) and low electrical resistivity made the ceramics difficult to pole. Niobium-modified BIPT ceramics with PT contents of 80% and 85% were found to possess significantly lower dielectric loss at elevated temperatures, making it possible to polarize the materials. Piezoelectric properties were measured for a BIPT85–1.5 mol% Nb composition with a Curie temperature of 542 °C; the longitudinal piezoelectric coefficient and coercive field were found to be 60 pC/N and 125 kV/cm, respectively.

Nanoscale structural correlations in magnetoresistive manganites

The colossal magnetoresistance (CMR) effect in perovskite manganites is a magnetic-field-induced transition from a paramagnetic insulating (PI) to a ferromagnetic metallic state. The large electrical resistivity of the PI state lies at the heart of the CMR effect. This enhanced resistivity stems, in part, from strong electron–lattice coupling and the associated local lattice distortions. Both uncorrelated local distortions (Jahn–Teller polarons) and correlated distortions are present in the PI state. The latter are believed to signal the presence of nanoscale orbital correlations. In this paper, we describe recent x-ray and neutron-scattering studies of the orbital correlations in pseudocubic manganites Ln1−xBxMnO3. Possible microscopic structures giving rise to these correlations are discussed. It is found that the correlations are ubiquitous in the orthorhombic PI phase of hole-doped manganites, and that their properties are defined by a single parameter—the doping level x. The correlations, however, are absent in the other paramagnetic phase exhibited by the manganites—the rhombohedral phase. The latter phase is metallic in the doping range in which the CMR effect is observed. Since the uncorrelated lattice distortions are present in both these phases, the insulating character of the PI state in CMR manganites results from the presence of the correlated lattice distortions. The orbital correlations, therefore, play the key role in the CMR effect.