The Meissner effect of polysulfur nitride, (SN)x

The magnetic susceptibility of (SN)_x was measured by the a.c. method. The Meissner effect occurs at 250 ± 3 mK. The real part of the susceptibility nearly saturates at 100 mK and reaches 93 ± 7% of ?$\text{1}\text{4}\text{π}$ at 30 mK for weak field perpendicular to the polymer axis, while for the parallel direction it remains at 65 ± 10% of ?$\text{1}\text{4}\text{π}$. The susceptibility depends strongly on the a.c. magnetic field. There is a peak in the imaginary part of the susceptibility at the transition region to the superconducting state.     

The upper critical field of superconducting polysulfur nitride, (SN)x

A measurement of the temperature and angular dependence of the upper critical magnetic field H_c² in crystals of polymeric (SN)_x is reported. A large anisotropy is observed at all temperatures with H_c²6 = 8.1 ± 0.4 kOe parallel to, and H_c²⊥ = 870 ± 80 Oe perpendicular to, the polymer axis at 0°K. The results are explained in terms of the polymeric crystal structure and fibrous morphology of (SN)_x.     

AB initio energy band structure of polysulfur nitride, (SN)x

All electron energy band structure is reported for an infinite one-dimensional model of polysulfur nitride, (SN)_x, using the ab initio LCAO Hartree-Fock method. The calculated values of the effective mass and density of states at the Fermi level are ?0.72 m_e and 0.06 states/(eV spin molecule), respectively. An appreciable amount of charge transfer (0.30 e) from sulfur to nitrogen was obtained. Finally, comparison is made with the results of a semi-empirical version of the same method.     

Hall effect and magnetoresistance of (SN)x films

Hall effect and electrical conductivity have been investigated between 77 K and 300 K and the magnetoresistance at 4.2 K for a number of (SN)_x films deposited at substrate temperatures between — 10 and 50°C. The small magnitude of the Hall mobility (? 1 cm² Vsec^?1 at 300 K) and its activated temperature dependence are interpreted in terms of a heterogenous model for (SN)_x films with thin depletion layers separating highly conductive islands. The hole concentration in these islands (p ≈ 10²¹ cm^?3, the microscopic mobility (μ ≈ 500 cm² Vsec^?1 at 4.2 K) and the temperatures dependence of μ are found to be close to values for (SN)_x crystals.     

X-ray determination of the linear compressibilities of (SN)x

The linear compressibilities of (SN)_x have been determined up to 22 kbar using a hydrostatic-pressure X-ray cell: at 1 bar, k_a = 5.5;k_b = 2.2; k_c = 5.0; k_[201] = 3.8 —; all in units of 10^-12cm²/dyne. The results are compared with other chain-like solids and confirm the anisotropic three-dimensional bonding character of (SN)_x. Pressure dependence of the electrical conductivity is discussed.     

Nuclear relaxation of the water protons included in (SN)x crystals

The temperature and frequency dependences of the proton spin-lattice relaxation time in H₂O included in (SN)_x crystals have been measured and discussed. It is suggested that a significant amount of water is adsorbed on the surface of the (SN)_x fibers.     

Temperature dependences of electrical resistivity and magnetic susceptibility in (SN)x single crystal

Pauli-paramagnetism is observed in high quality (SN)x single crystal. Density of state at Fermi level is estimated to be 0.14 ± 0.06 states/(eV spin molecule) from the observed magnetic susceptibility. Curie Weiss like laws are observed in γ-ray irradiated and low quality (SN)x crystals which show the resistivity minimum at 30–40 K. The resistivity minimum is discussed in terms of carrier scattering by localized paramagnetic centers.     

Superconductivity in polymeric sulfur nitride (SN)x at high pressure

Investigations of the pressure dependence of the superconducting transition temperature T_c up to 17 kbar, and of the normal conductivity up to 50 kbar are reported. It is observed that below 8 kbar, the value of T_c increases linearly with the pressure. In addition, there is a significant drop of T_c at about 9 kbar which may be due to a phase transition.     

Band structure of polyacetylene, (CH)x

The one-electron energy bands and densities of states of polyacetylene in both cis- and trans-conformations have been investigated. The principal issue addressed is whether the itinerant picture alone is sufficient to explain the experimental properties of this material. We conclude that the one-electron model provides an excellent zeroth-order explanation of current observations of optical and transport effects in both pure and doped forms of this unusual polymer.     

Electrical transport properties of polyacetylene tetrachloroferrate - [CH(FeCl4)y]x]

Conductivity and thermopower measurements of polyacetylene doped with FeCl₄ are reported. The conductivity changes over 10 orders of magnitude and reaches the maximum value of 200 Ω^-1 cm^-1 at y = 0.07. The thermopower reveals the semiconductor to metal transition at y ? 0.002, with high and temperature independent Seebeck coefficient in the dilute limit and a metallic dependence in the heavily doped samples.     

Phototransport effects in polyacetylene, (CH)x

We have made the first comprehensive measurements of the photovoltaic and photoconductivity effects in polyacetylene in that we have extended the spectral range originally covered by Matsui and Nakamura [17] to include the visible region as well. The photovoltaic experiments were done on Schottky barrier junctions formed between AsF₅ lightly-doped p-type trans-(CH)_x and a low work function metal, the first junctions of this type to be produced in semiconducting polyacetylene. The observation of a photovoltaic response threshold at 1.48 eV provides the first definitive measurement of the single-particle band gap in trans-(CH)_x. In addition, we have found the existence of a peak at 1.35 eV in the photoconductivity spectrum of undoped trans-(CH)_x which may be due either to extrinsic sources or to thermal dissociation of a weakly bound Wannier exciton.     

Preparation of (CdO)1−x(PbO)x and (CdS)1−x(PbS)x thin films by spray pyrolysis technique and their characterization

Mixed thin films of (CdO)_1−x(PbO)_x and (CdS)_1−x(PbS)_x (x=0.25) were prepared on glass substrates by spray pyrolysis technique for various substrate temperatures 300, 320 and 340 °C. Structural and optical properties were studied. XRD studies reveal the formation of mixed films. The substrate temperature of 340 °C seems to be critical for the formation of CdO-PbO mixed films. It is observed that (CdS)_1−x(PbS)_x mixed films were formed at all the three substrate temperatures. The direct band gap value of (CdO)_1−x(PbO)_x and (CdS)_1−x(PbS)_x mixed films is about 2.6 and 2.37 eV, respectively.     

Optical and electronic properties of (GaAs)n / (InAs)n(001) superlattices: LMTO-ASA approach

The optical and electronic properties of (GaAs)_n/(InAs)_n superlattices are calculated by means of LMTO-ASA method. The too small band gap problem of bulk material and superlattices is corrected by adding to the effective potentials an additional external potential that is sharply peaked at the atomic sites. The results show that the optical properties of GaAs/InAs(001) superlattices are about average of that of two bulks of GaAs and InAs.     

The properties of acicular particles of (γ-Fe2O3)x(Fe3O4)1-x

It is known that acicular particles, initially of Fe₃O₄, which have been partially oxidised, show anomalous properties e.g. in the variation of H_c with composition. It is shown that these can be explained by considering the particles to comprise an inner core of Fe₃O₄ with an outer layer of γ-Fe₂O₃. Owing to the large change in volume which occurs on oxidation, these mutually stress each other. Over a certain range of composition, the stress field interacts with the magnetization to increase H_c, and it is also responsible for H_c increasing with time after the oxidation process. A similar situation applies to partially reduced γ-Fe₂O₃.     

Growth and X-ray studies of (NaCl)x(KCl)y−x(KBr)1−y single crystals

Ternary mixed crystals of NaCl, KCl and KBr were grown by the melt method for the first time. Densities and refractive indices of all the grown crystals were determined and also used for the estimation of the bulk composition in the crystal. Lattice parameters and thermal parameters like Debye-Waller factor, mean square amplitude of vibration, Debye temperature and Debye frequency were determined from the X-ray powder diffraction data. The observed lattice parameters showed the existence of two phases in crystals with NaCl content greater than 0.1 mole fraction. The thermal parameters show a highly non-linear composition dependence. The results are reported.     

Raman scattering from mixed crystals (HgBr2)1−x(HgI2)x

The behavior of long wavelength optic phonons in mixed system HgBr₂-HgI₂ has been investigated in Raman scattering. Different types of behavior, i.e. ‘persistent type’ and ‘amalgamation type’ were observed. Three strong Raman bands were observed for persistent type mode. These correspond to stretching vibration of HgBr₂, HgBrI, HgI₂ molecules. Intensity of these bands showed striking concentration dependence. A model based on nearly free molecular approximation have been proposed to explain the dependence. The analysis indicated that the distribution of anions on the sublattices is essentially random. For amalgamation (one-mode) type behavior, it is suggested that the intramolecular force relevant to the vibration is comparable to the intermolecular force and that the band width of the corresponding phonon branch in the parent crystal is broad enough to be degenerate with impurity mode at the low concentration limit.     

Structural, optical and magnetic properties of (ZnO)1−x(MnO2)x thin films deposited at room temperature

The structural, magnetic and optical properties of (ZnO)_1−x(MnO₂)_x (with x = 0.03 and 0.05) thin films deposited by pulsed laser deposition (PLD) were studied. The pellets used as target, sintered at different temperatures ranging from 500 °C to 900 °C, were prepared by conventional solid state method using ZnO and MnO₂ powders. The observation of non-monotonic shift in peak position of most preferred (1 0 1) ZnO diffraction plane in XRD spectra of pellets confirmed the substitution of Mn ions in ZnO lattice of the sintered targets. The as-deposited thin film samples are found to be polycrystalline with the preferred orientation mostly along (1 1 0) diffraction plane. The UV-vis spectroscopy of the thin films revealed that the energy band gap exhibit blue shift with increasing Mn content which could be attributed to Burstein-Moss shift caused by Mn doping of the ZnO. The deposited thin films exhibit room temperature ferromagnetism having effective magnetic moment per Mn atom in the range of 0.9-1.4μ_B for both compositions.     

Structural stability and magnetic properties of Bi1−xLa(Pr)xFeO3 solid solutions

In this work, X-ray diffraction data taken on Bi_1−xLa_xFeO₃ solid solutions are used to verify the following structural phase transitions: “polar rhombohedral-antipolar orthorhombic” at x≈0.16 and “commensurate-incommensurate” within the orthorhombic phase at x≈0.18. In contrast, in the Bi_1−xPr_xFeO₃ series, the polar rhombohedral phase transforms into an antipolar orthorhombic one at x≥0.13. The polar rhombohedral phase near the morphotropic phase boundary exhibits an isothermal transformation into an antipolar orthorhombic phase, though the transformation occurs much faster in the case of La-doped compounds. The incommensurate structural phase was not detected in Bi_1−xPr_xFeO₃ solid solutions. The ternary structural phase diagram is constructed for (Bi,La,Pr)FeO₃ systems. In addition, the polar rhombohedral phase exhibits a magnetic field-induced transition from the modulated antiferromagnetic state into a homogeneous weak ferromagnetic state whereas the antipolar phase is a weak ferromagnetic state in the absence of an external field.     

Photoinduced absorption in Trans-(CD)x; isotope energy shifts

Steady state photoinduced absorption in trans (CD)_x is reported for energies of 0.1–2.1 eV. All induced infrared active vibrations as well as the photoinduced electronic bands show an energy down shift compared to those of (CH)_x. The change in the induced vibrations spectrum is fully understood and it results from different bare-phonons in the two isotopes. The origin of the isotope shift observed in the electronic bands is discussed.     

On the magnetic properties of Y(FexCo1-x)2 compounds

The composition dependence of the mean magnetic moment of cobalt atoms in Y(Fe_xCo_1-x)₂ compounds is analysed in the local environment model. Cobalt has a magnetic moment of 1.56 μ_B if there are at least two Fe atoms as nearest neighbours. The maximum in the composition dependence of the transition metal moments is due to the magnetic contributions of iron atoms only. The thermal variation of reciprocal susceptibility obeys a Curie-Weiss behaviour, in addition to the Pauli paramagnetic term. Finally, the influence of the variable magnetic interactions on the transition metal moments is discussed.