Electrical conductivity and photoconductivity of polymer composites containing Cu(II)/Cr(III) heteropolynuclear complexes

The electrical conductivity and photoconductivity of films of composites based on electrically neutral poly(vinyl butyral) with additions of Cu(II)/Cr(III) heteropolynuclear complexes introduced in the form of solutions or mechanically ground polycrystalline powders are studied. Photocurrents in samples prepared in different ways differ no more than tenfold. The photoconductivity of the composite films increases with decreasing distance between the metal centers in the complexes. A phenomenological model of carrier photogeneration and transport in films of polymer composites with embedded particles of heteropolynuclear complexes prepared from a solution or by grinding is proposed. The slight difference in photocurrents between samples containing the same complexes but prepared by different methods can be accounted for by the close geometric sizes of particles of the complexes.     

Electrooptical effect in polymeric composites containing heterometallic Cu(II)/Mn(II) complexes

We studied the effect of an electric field on the transmission of linearly polarized light through films of composites based on polyvinylbutyral doped with particles of Cu(II)/Mn(II) complexes with “skeleton” and “planar” structures. The action of an electrostatic field causes light absorption to become anisotropic. The effect increases with increasing distance between the cation and anion. Its sign reverses if the spatial structure of the complex is changed. A phenomenological model is proposed according to which the electrooptical properties of the composites are due to a change in the mutual orientation of complex building blocks on exposure to an external electric field. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 4, pp. 481–484, July–August, 2007.     

Specific features of the internal photoelectric effect of the Cu(II)/Fe(III) oxalate complex with ethylenediamine in an insulating polymer film

Physics of the Solid State - The electrical and photoconductive properties of films of the composites based on poly(vinyl alcohol) with additions of the (NH4)[Cu(en)2Fe(C2O4)3] · 2DMSO...     

Specific features of the electrical conductivity of V6O11

A study has been made of the electrical conductivity of V₆O₁₁ single crystals over a broad range of temperatures covering the regions of the metal phase, metal-insulator phase transition, and insulator phase. It has been shown that the electrical conductivity of the metal phase correlates with the Mott limit of minimum conductivity. To explain the temperature dependence of the electrical conductivity of the V₆O₁₁ insulator phase, the theory of hopping conduction taking into account the effect of thermal vibration of atoms on the resonance integral has been invoked.     

Modelling the DC electrical conductivity of polymer/carbon black composites

Several DC electrical conductivity models have been proposed to explain the properties of composite materials. In particular, generalized effective medium model was used, but, in many cases, the obtained parameters do not fit accurately the data. In this paper, we extended the study to Mamunya model, with adjustable parameters. Using different carbon black nanocomposites, we obtained a good agreement with the experimental results, but only for concentrations above the percolation critical concentration. Below this point, the fit is not accurate.     

Specific features of spectra of cyclometalated Pt(II) and Pd(II) complexes in polyvinyl alcohol

The absorption spectra and luminescent properties of ethylenediamine complexes of Pt(II) and Pd(II) with cyclometalating ligands (2-phenylpyridinate and 2-2’-thienyl)pyridinate) in polyvinyl alcohol are studied. It is ascertained that, upon an increase in temperature, the nonradiative degradation of energy in palladium complexes occurs according to the mechanism of strong vibronic coupling, whereas platinum complexes show weak vibronic coupling.     

Specific features in the synthesis, crystal structure and electrical conductivity of BICUTIVOX

The formation of solid solutions Bi₄V_2 − xCu_x/2Ti_x/2O_11 − x (0.025 ≤ x ≤ 0.5) known as BICUTIVOX, synthesized by three different methods (a conventional solid-state synthesis, solid-state synthesis enhanced by mechanical activation, and through liquid precursors), has been studied. Based on crystal structure investigations carried out at different temperatures, ranges of stability and temperatures of phase transitions for different polymorphous modifications have been defined. The morphology and the local chemical composition of the ceramic samples obtained have been studied. Thermal expansion coefficients have been measured. The electrical conductivity of ceramic samples has been investigated in a wide range of temperatures and partial oxygen pressures.     

Luminescence spectra of Cr(III)-glycine complexes

The reaction of Cr(III) with glycine yields four products, fac- and mer- Cr(gly)₃, the dimeric species di-μ-hydroxotetragly cinatodichromium(III) and a series of complexes involving singly bonded glycinate ligands. ²E → ⁴A₂ (in 0 symmetry) luminescence spectra have been recorded for these species from 4 K to room temperature. The emission spectra are much more indicative of the type of complex being considered than are the corresponding absorption spectra. The concept of a weighted nephalauxetic effect is introduced to explain the energies of the emission in the various types of complexes. The monodentate gly cinate complexes are shown to be N bonded. The fac-Cr(gly)₃ species crystallized under different conditions with varying numbers of waters of hydration, the ²E splitting being dependent on the degree of hydration.     

Liquid-crystalline dendrimer Cu(II) complexes and Cu(0) nanoclusters based on the Cu(II) complexes: An electron paramagnetic resonance investigation

New nanostructured materials, namely, the liquid-crystalline copper(II) complexes that contain poly(propylene imine) dendrimer ligands of the first (ligand 1) and second (ligand 2) generations and which have a columnar mesophase and different copper contents (x = Cu/L), are investigated by EPR spectroscopy. The influence of water molecules and nitrate counterions on the magnetic properties of complex 2 (x = 7.3) is studied. It is demonstrated that water molecules can extract some of the copper ions from dendrimer complexes and form hexaaqua copper complexes with free ions. The dimer spectra of fully hydrated complex 2 (x = 7.3) are observed at temperatures T < 10 K. For this complex, the structure is identified and the distance between the copper ions is determined. It is shown that the nitrate counterion plays the role of a bridge between the hexaaqua copper(II) complex and the dendrimer copper(II) complex. The temperature-induced valence tautomerism attended by electron transport is revealed for the first time in blue dendrimer complexes 1 (x = 1.9) with a dimer structure. The activation energy for electron transport is estimated to be 0.35 meV. The coordination of the copper ion site (NO₄) and the structural arrangement of green complexes 1 (x = 1.9) in the columnar mesophase are determined. Complexes of this type form linear chains in which nitrate counterions serve as bridges between copper centers. It is revealed that green complexes 1 (x = 1.9) dissolved in isotropic inert solvents can be oriented in the magnetic field (B ₀ = 8000 G). The degree of orientation of these complexes is rather high (S _z = 0.76) and close to that of systems with a complete ordering (S _z = 1) in the magnetic field. Copper(0) nanoclusters prepared by reduction of complex 2 (x = 7.3) in two reducing agents (NaBH₄, N₂H₄ · H₂O) are examined. A model is proposed for a possible location of Cu(0) nanoclusters in a dendrimer matrix.     

Effect of mechanical activation on thermal and electrical conductivity of sintered Cu,Cr, and Cu/Cr composite powders

The results of measurement of electric resistivity and thermal conductivity of materials obtained by spark plasma sintering from powders of Cu, Cr, and their mixtures in the range of 300–600 K are presented. It is shown that the grinding of powders in planetary mills results in a reasonably substantial change in the electric and thermal properties of materials: to increasing electric resistivity and decreasing thermal conductivity and temperature coefficients of electric resistivity. The possible causes of these effects are considered.     

Specific features of spectra of cyclometalated Pt(II) complexes in polystyrene and polymethyl methacrylate

A method of obtaining polystyrene and polymethyl methacrylate films containing cyclometalated complexes of Pt(II) with 2-phenylpyridinate and 2-(2′-thienyl)pyridinate is described. The spectral and luminescent properties of these films at 77 and 298 K are studied. It is ascertained that the Pt(II) complexes in the films are in a monomolecular state.     

Dispersion of dielectric characteristics of polymer structures based on the Cu(II) complex

The results of the study of the dielectric response of thin-layer polymer films based on [Cum-Salpn-1,3] monomers and the H₂mSalpn-1,3 ligand synthesized by electrochemical polymerization are presented. A frequency dispersion of dielectric characteristics that corresponds to the distribution of a set of relaxors is revealed. The role of a metal center, i.e., divalent copper, and the azomethine group during dielectric polarization is discussed.     

Theoretical approach to the magnetic properties of Mn(II), Cr(III), and Cu(II) complexes in the newly reported 12- and 15-membered macrocyclic ligands

The magnetic properties of Cu²⁺, Cr³⁺, and Mn²⁺ ions in the newly reported 12- and 15-membered macrocyclic complexes are analysed by a theoretical approach. The calculated magnetic moment and magnetic anisotropy for various situations, especially for Cu(II) ion, suggest that the magnetic properties may lead to a better interpretation about the geometry. It is also suggested that the zero-field splitting Hamiltonian may be used for magnetic properties of some metal ions, which have orbital singlet ground term in these complexes.      

High oxygen pressures and the stabilization of a new mixed valence Cu(III)/Cu(IV)

Abstract

The Cu(III) oxides were investigated first for the unusual copper oxidation state and then for the high-Tc superconductivity. In the last case this property is observed when a mixed copper valence is stabilized : Cu(I)/Cu(II) or Cu(II)/Cu(III). A new mixed valence Cu(III)/Cu(IV) has been stabilized in the three dimensional lattice of the perovskite-type oxide Lal_-xSr_xCuO₃ (0 ≥ ′ ≥ 0,25). Chemical analysis and XPS study confirm the mixed valence. This compound shows metallic properties with an broadening of the conduction band compared to LaCu0₃. Such a behaviour can be explained either by the increase of the covalence of the average Cu-0 bond or by the decrease of the structural distortion induced by the substitution of Sr(II) for La(III). No superconducting property has been detected down to 4K.     

Specific features of electrical conductivity of the insulating phase of vanadium dioxide doped with niobium

The electrical conductivity of V_{1 – x}Nb_xO₂ single crystals have been investigated over a wide temperature range covering regions of the existence of the metallic and insulating phases. It has been shown that, with an increase in the niobium concentration, the electrical conductivity of the metallic phase becomes below the Mott limit for the minimum metallic conductivity. Immediately after the metal–insulator transition, the electrical conductivity is determined by a large amount of free electrons that gradually localized with a decrease in the temperature. The temperature dependence of the electrical conductivity in the insulating phase of V_{1 – x}Nb_xO₂ has been explained in the framework of the hopping conductivity model that takes into account the effect of thermal vibrations of atoms on the resonance integral.     

Spectral and luminescent specific features of phenylpyridine ethylenediamine complexes of Pt(II), Pd(II), and Au(III)

The orbital nature and basic photophysical parameters of phenylpyridine ethylenediamine complexes of Pt(II), Pd(II), and Au(III) are found from the comparative analysis of absorption and luminescence spectra and the luminescence decay kinetics. The orbital nature and properties of the lowest excited states responsible for luminescence are shown to depend on the type of metal and the energy of singlet-triplet splitting.     

ESR study of some Cu(II)-oxazepam complexes

The CuL₂X₂ (L = 7-chlor-l,3-dihydro-3-hydroxi-5-phenyl-2H-l,4-benzodiazepin-2-one, also known as oxazepam, X = Cl, Br) complexes were prepared and investigated by ESR (electron spin resonance) method. Powder ESR spectra of CuL₂X₂ compounds at room temperature show the presence of monomeric species having an axial symmetry with a small rhombic distortion. In case of compounds with Cl there is a superposition of two nonequivalent mononuclear species, one with ad_{x² - y²} d_{x^2 - y^2 } ground state and another with ad_z² d_{z^2 } ground state. In pyridine (Py) and dimethylformamide (DMF) solutions the monomeric species prevail. Two different monomeric species, one with pseudotetrahedral (T_d) and the other with elongated tetrahedral-octahedral symmetry, were evidenced in DMF solutions adsorbed on NaY zeolite. In Py-DMF solutions two monomeric species were also identified. Dimeric species appear in DMF and Py solutions adsorbed on NaY zeolite through the coordination of two Cu(II) ions at the same keto-oxygen from one oxazepam molecule.     

X-ray diffractometry and electrical conductivity of the ceramics LaSrAl(Cu,Ni)O4

A continuous series of solid solutions LaSrAL_1−x Me_xO₄ (Me = Cu, Ni) has been investigated by x-ray diffractometry and by electrical conductivity measurements. The results are of interest from the standpoint of the theory of close-packing, percolation theory, and the theory of the cooperative Jahn-Teller effect. Fiz. Tverd. Tela (St. Petersburg) 39, 985–990 (June 1997)     

Specific features of electrical conduction of the poly-[NiSalen] metal-containing polymer thin-film structure

The charge transfer in the oxidized and reduced forms of poly-[NiSalen] metal-containing polymer films is investigated. It is established that the voltage dependence of the differential conductivity for the polymer in the oxidized form exhibits a nonlinear behavior, which indicates a high electrical activity of this state. The microscopic parameters characterizing the charge transfer are calculated within the space-charge-limited current theory. Differences in the surface morphology of two forms of the poly-[NiSalen] films are revealed using atomic-force microscopy.