With XRD,R-T, and acχ measurements a comparative study on the doping effects of 3d elements in Bi1.5Pb0.2Sr2Ca2Cu2.8M0.8O y (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, or Zn) has been carried out. The effects of the former five members are significantly different, both on phase formed and onT c , from the latter four. It seems that the effect on phase stabilization correlates with the valency of the doped cation. In connection with the instability of the 2223 phase, the correlation has been discussed.

Materials with La2NiO4+δcomposition, δ ranging between 0 and 0.25, have been prepared either by solid state reaction or electrochemical oxidation; their electrical conductivity, thermoelectric power, and magnetic susceptibility behaviors are reported. The compounds remain semiconducting in the whole range of composition and, at low temperature, the resistivity increases with δ. The sign of the Seebeck coefficient changes for δ ≈ 0.2 and the thermal variation shows complex behavior. La2NiO4.03exhibits a thermally activated hopping and an antiferromagnetic ordering. When δ increases, variable range hopping or nearest neighbor hopping, involving at least two types of carriers, can account for the transport properties. The magnetic behavior of materials with δ ≤ 0.18 reveals either 3D or 2D magnetic correlations whereas the susceptibility of La2NiO4.25(La8Ni4O17) follows a Curie–Weiss law below 170 K; a change in the electronic configuration of the nickel ions arises beyond this temperature.

Two kinds of solid solutions exist in the La2CuO4-Nd2CuO4 system with, respectively, the T/O and T′ type structures characteristics of La2CuO4 and Nd2CuO4. When synthesized at atmospheric pressure in air, i.e., under P ≈ 20 kPa oxygen pressure, both solid solutions exhibit semiconducting properties. A treatment under oxidizing conditions either under oxygen pressure or anodic polarization of La2-xNdxCuO4 compounds causes the insertion of some oxygen species into the T/O structure and the formation of a mixed valence Cu(III)/Cu(II). The resistivity of the corresponding compounds is drastically decreased, and a bulk superconducting behavior is induced at low temperature in the compositional range 0 ≤ x ≤ 0.60. For a fixed concentration of excess oxygen, the critical temperature decreases with increasing amount of neodymium.

The thermoelectric power and Hall effect of Sn or Ge doped In2O3 semiconductors were investigated based on a comparative study. Metal-type conductivity occurs in both samples when the carrier concentration exceeds approximately 1019 cm−3. The carrier mobility is found to be higher for Ge doped samples. The relation between the “Lewis acid strength” of the dopant element and its scattering cross-section is also presented.

The intercalation of fluorine in various types of carbon fibers (PAN-based or pitch-based, asreceived or high-temperature treated) has been investigated at room temperature in the presence of gaseous HF. Stage-1 compounds with C2.5F to C4F compositions are obtained for 10 bar F2 pressures, whereas lower pressures (1 bar F2) lead to stage-2 compounds. Although in higher stages (≥2) the electrical conductivity is generally larger than in the pristine fiber, in stage-1 compounds a drastic increase of resistivity is observed, ρ being more than one order of magnitude larger than that of the starting material. Finally, fluorine-intercalated GICs have been found appropriate to investigate the effects of disorder and reduced dimensionality.

The mechanism of intercalation in high Tc superconductors is presented and the microstructure of intercalated materials is studied by Raman microspectroscopy for IBr in Bi2Sr2CaCu2O8 Presence of I2Br- is shown and the results are in agreement with a P4/mmm structure. An increasing of Tc onset of 15 K is also found.

Pure and lead doped Bi2Sr2CaCu2O8 (Bi2212) single crystals were grown and their structures were studied by several methods, especially by resistivity measurements, electron microprobe and Raman micro-spectroscopy. The microstructure and the Raman spectrum of Bi2212 were analyzed in comparison to those of Bi2201 and Bi2223 single crystals. In these structures, the existence of close, staggered and antiparallel BiO bonds leads to a Raman doublet at 653 and 627 cm−1 which corresponds to coupled motions in these bonds. The intercalation of iodine in Bi2212 suppresses this staggered configuration and gives a more homogeneous vertically aligned distribution of (Bi)O(Cu) bonds. In these intercalations, the presence of unsymmetrical I3− ion is demonstrated. Similar bond-ordering was observed on intercalation with chloranil and tetrahydrofuran. By lead doping, the staggered bonds are no longer identical and the decoupling leads to a single phonon around 623 cm−1 and confirms that Pb occupies Bi position.

We report and discuss experimental data on the electrical resistivity p, thermoelectric power S, thermal conductivity kappa, specific heat C and magnetic susceptibility chi of polycrystalline U(2)M(3)Si(5) silicides (M = Co, Rh, Ru). The magnetic and transport properties of these compounds depend strongly on the nature of the transition metal M. In U2Co3Si5, p(T) shows features that could be identified to Kondo systems while S(T) shows a two-peak structure. U2Rh3Si5 shows an antiferromagnetic ordering at T-N similar to 25 K, which is accompanied by steep changes in both p(T) and S(T). U2Ru3Si5 behaves like a nonmagnetic compound and displays distinct anomalies in the low-temperature domains of p(T, H) and S(T, H). The lattice thermal conductivity varies as T-2 at low temperatures, suggesting a dominant scattering of the phonons by the conduction electrons.

With XRD,R-T curves, and a.cϰ measurements, the doping and codoping effects of Sb and V to a Cu-deficient Pb-doped Bi system have been studied. A sample singly doped with V possesses aT c about 2 K lower than that of a sample singly doped with Sb. This is attributed to the different sites of their substitution. It was observed that for promoting 2223 phase formation, Sb and V works cooperatively, and the codoping of Sb may enhance the 2223 phase formed. With a low doping level of Sb, the optimum doping amount of V is 0.3, i.e., with a nominal composition of Bi1.5Pb0.3Sb0.06Sr2Ca2Cu2.4V0.3O y . A sample in which the 2223 phase is the dominant phase and which has a zero resistance transition temperature of 105 K has been obtained.

The transport properties of undoped and Sn-doped In2O3 (ITO) single crystals prepared by a flux method are reported. Hall measurements are detailed: they show that the mobility increases as the Sn dopant concentration increases. A maximum value of 100 cm2V−1s−1 is measured with an electron concentration of about 1.6 × 1020 cm−3. However, at high dopant concentration the mobility decreases again and the presence of neutral entities such as (SnO)x is expected to be responsible for this behavior. Some results dealing with undoped and Sn- or Pb-doped In2O3 ceramics are also presented and discussed.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Mixed-valence copper(II/III) oxide solid solutions Sr2-xNaxCuO3 (0 less-than-or-equal-to x less-than-or-equal-to 1) have been prepared by solid-state reactions in oxygen atmosphere. All solid solutions exhibit the structure of Sr2CuO3 (S.G. Immm). Electrical conductivity and thermoelectric power measurements show a semiconducting behavior in the whole composition range. The electronic structure of Sr2CuO3 is compared with that of La2CuO4 on the basis of an iono-covalent model. Interpretation of transport properties suggests the formation of small polarons. Magnetic susceptibility and EPR measurements show that the antiferromagnetic ordering of Sr2CuO3 tends to vanish as x increases, however magnetic interactions are still strong for a concentration of Cu2+ ions corresponding to x = 0.8.

The electrochemical oxidation of La2CuO4 in alkaline solution (1N KOH) has been used for preparing the superconducting phase La2CuO4+δ (δ⋍0.07). Crystallographic data show an enhanced orthorhombic distortion and an increase of the unit cell volume. The transport properties reveal a sharp transition from a metallic behaviour to a superconducting state below 44 K which is corroborated by the noteworthy magnetic properties.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The preparation of YBa2Cu3O7 ‐ δ‐based ceramics was made from a mixture of oxides taken in the molar proportions α:1:2 BaCuO2:Y2BaCuO5:CuO(0.95 α 3). The densification of the ceramics is strongly dependent on the initial amount of BaCuO2. The highest density is obtained when α= 1. All the ceramics present a superconducting transition. A sintering mechanism is proposed in which the densification is mainly governed by the appearance of a metastable BaCuO2‐based liquid at around 900°C.

Fluorine-intercalated graphite fibers have been synthesized at room temperature by direct reaction with elemental fluorine. The host materials were either vapor-grown fibers or pitch-based fibers. The CxF compounds obtained were mostly of the stage-3 type with a 12.65 Å repeat distance. The carbon-to-fluorine atomic ratio ranged from 10 to 14. Resistivity measurements carried out between 4.2 and 300 K show clearly that the fluorination reduces the resistivity values, whatever the type of pristine material. For fluorine-intercalated pitch-based fibers an anomalous increase of resistivity below 30 K may be consistent with a weak electronic localization or with two-dimensional carrier-carrier interaction effects. In fluorine-intercalated vapor-grown fibers the anomalous bump observed around 190 K could result from a phase transition. The room temperature value of the conductivity of this type of material, i.e. σ = 1.6 × 105 S cm−1, is one of the highest ever observed for fluorine-intercalated CxF fibers.

Electrical conductivity and thermoelectric power of polycrystalline solid solutions of formula Cr1−x, W1+xO4 were measured between room and liquid helium temperature. The behavior is metallic for the monoclinic WO2-type (1⩾x⩾0.80) and the tetragonal rutile-type (0.50⩾x⩾0.40) phases, whereas the monoclinic CrWO4-type phase (x⩽0.25) is a semiconductor. The metal-insulator transition is correlated to the increase of the W-W distances observed as x decreases. The evolution of the sign of the thermopower with composition confirms the band diagrams proposed by previous authors. The temperature dependence of the electrical conductivity of the rutile-type phase is interpreted based on recent theories taking into account the role of the inelastic mean free path and the long range electronic correlations in metallic disordered systems.