The doping effect of altervalent cations on the thermal decomposition and electrical conduction properties of manganese(II) carbonate

The electrical conductivities of pure and doped manganese(II) carbonate with 10 mol% Li⁺ or Al³⁺ ions were measured. The effect of doping on the observed kinetic parameters of decomposition were measured. Doping with Li⁺ or Al³⁺ ions enhances the decomposition. The enhanced promotion effect is ascribed to the generation of hole defects which are concentrated at the reaction interface. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Electrical conduction in a nonconjugated polymer doped with SnCl4 and SbCl5

The electrical and optical properties of 1,4-cis-polyisoprene before and after doping with SnCl₄ and SbCl₅ were investigated. The material becomes reddish brown and black upon doping with SnCl₄ and SbCl₅, respectively, and the conductivity increases by about 11 orders of magnitude. The optical absorption, infrared spectra, elemental analyses, and the studies of reversibility upon compensation indicate that radical cation formation is the most likely mechanism for electrical conduction in these complexes. The results are consistent with previously published articles involving iodine doping. © 1994 © John Wiley & Sons, Inc.     

Compensation effect as a consequence of vibrational energy transfer in homogeneous and isotropic heat field

By kinetics of decomposition of solids in both isothermal and non-isothermal conditions, the compensation effect (CE) is rather a rule. The topic of this work is to suggest an activation mechanism which leads to the dependences similar with CE. The solid is assimilated to a system of the harmonic oscillator with a Bose-Einstein energy distribution. Considering an activation process due to a vibrational energy transfer from a homogeneous and isotropic field of thermic oscillators to the solid-state oscillator, the thermodynamic functions are in the relationship

Approximate symmetry-breaking in the independent particle model of monocyclic completely conjugated polyenes

We examine the singlet stability of symmetry adapted, restricted Hartree-Fock (RHF) solutions and the implied symmetry breaking for various planar, π-electron systems with conjugated double bonds as described by the semiempirical Pariser-Parr-Pople Hamiltonian. In particular, we explore the energy and charge- density waves (CDWs) in various real and hypothetical structures that result by a systematic deformation of the nuclear framework: we start with a highly symmetric cyclic polyene C _N H _N having a nondegenerate ground state (N = 2n = 4ν + 2, ν = 1, 2,...), whose sites form a regular N-gon (D _Nh point group), and proceed to structures with lower symmetry (D _6h , D _3h , D _2h point groups), or with only the planar symmetry of the conjugated π-electron system (C _1h ). The objective of this study is to explore the phenomenon that could be referred to as a breaking of an approximate symmetry or an implied symmetry breaking.     

Electrical conduction in composites containing copper core-copper oxide shell nanostructure in silica gel

Composites of nanometre-sized copper core-copper oxide shell with diameters in the range 6.1 to 7.3 nm dispersed in a silica gel were synthesised by a technique comprising reduction followed by oxidation of a suitably chosen precursor gel. The hot pressed gel powders mixed with nanometre-sized copper particles dispersed in silica gel showed electrical resistivities several orders of magnitude lower than that of the precursor gel. Electrical resistivities of the different specimens were measured over the temperature range 30 to 300°C. Activation energies for the coreshell nanostructured composites were found to be a fraction of that of the precursor gel. Such dramatic changes are ascribed to the presence of an interfacial amorphous phase. The resistivity variation as a function of temperature was analysed on the basis of Mott’s small polaron hopping conduction model. The effective dielectric constant of the interfacial phase as extracted from the data analysis was found to be much higher than that of the precursor glass. This has been explained as arising from the generation of very high pressure at the interface due to the oxidation step to which the copper nanoparticles are subjected. Dedicated to Professor C N R Rao on his 70th birthday     

On the Compensation Effect at the Form of the Differential Conversion Function

From the general form of the rate equation under non-isothermal conditions, some relationships showing the existence of a compensation effect due to the change of the analytical form of the differential conversion function were derived. These relationships were checked for some simulated TG curves, as well as thermogravimetric data corresponding to the degradation of some polymers and to the decomposition of calcium carbonate. This revised version was published online in July 2006 with corrections to the Cover Date.     

RuO4-promoted oxidative polycyclization of isoprenoid polyenes. A further insight into the stereochemistry of the process

Further studies on the RuO₄-catalyzed oxidative polycyclization of isoprenoid polyenes have been carried out. The configuration of the tris-THF product from the oxidation of geranylgeranyl acetate has been determined by a combination of spectral and chemical correlation methods. The oxidation of (E,Z)-farnesyl acetate, synthesized from nerol, has been carried out. This process stops at the first cyclization indicating that an E configuration of the Δ⁶ double bond is needed for the second cyclization to occur. The results are discussed in comparison with previous knowledge on the related Re(VII) polycyclization of polyenic bis-homoallylic alcohols.     

Asymptotic behavior of the RHF energy of the PPP model of alternant cyclic polyenes

The large N expansion of the restricted Hartree–Fock (RHF) exchange energy per atom E(N) of the Pariser–Parr–Pople (PPP) model of cyclic polyenes (annulenes) C_NH_N is derived in detail. We explicitly derive the coefficients E₀ and E₁ of the asymptotic expansion: E(N)=E₀+E₁ ln N/N²+O(N⁻²), N→∞, in the very simple case of half-filling and no bond alternation. The exchange energy per atom in the infinite chain can be written as E_ex=(2/π²)∑^∞_j=1{[γ_∞(2j−1)]/[(2j−1)²]}, where γ_∞ is the two-electron repulsion integral in the infinite chain. On the other hand, the second coefficient E₁ giving a finite-size correction is found to be 1/2b, where b is the bond length. This value of E₁ differs slightly from that of a linear chain with periodic boundary conditions because the distance between sites depends upon the radius of the ring, i.e., upon N. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 66 : 397–407, 1998     

Compensation Effect in the Kinetics of Spatially Hindered Phenols

This paper reports a linear relationship between kinetic characteristics from the Arrhenius equation describing a decomposition process found when studying the kinetics of thermolysis of spatially hindered phenols. This relationship between the coefficients is known in the literature as a 'compensation effect'. The existence of the compensation effect permits some conclusions concerning the decomposition mechanism and thermal characteristics of the compounds under investigation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis,structure, and conduction of solid solutions BIMEVOX (Me = Cu,Ti)

Conditions for synthesizing single-phase solid solutions Bi₄V_{2 ? x} Cu _x/2Ti _x/2O_{11 ? x} and Bi_{4 ? x/2}V_{2 ? x/2}Cu _x/2Ti _x/2O_{11 ? x/2} are studied. The sequence of phase transformations is determined. Possible domains of stability of polymorphic modifications and the overall conductivity as a function of temperature and composition are studied. The structure of the γ-modification is refined using Rietveld’s full-profile analysis.     

MCSCF study of polaron- and bipolaron-like defects in smallall-trans conjugated polyenes

Summary A Multiconfigurational Self-Consistent Field study of neutral, singly and doubly ionized C₄H₆, C₆H₈, C₈H₁₀, and C₁₀H₁₂ as model systems for polaron and bipolaron defects in polyacetylene has been carried out. In all computations a double zeta quality basis set was used. The post-Hartree-Fock computations were carried out in the complete active subspace and the fully optimized structures are reported. Comparison with SCF results reveals that the inclusion of electron correlation attenuates the double bond/single bond alternancy in conjugated polyenes as well as the charge waves associated with the cations.Dedicated to Prof. Klaus Ruedenberg     

Evidence for a compensation effect during the temperature-programmed reduction of copper oxide in hydrogen

The reduction of copper oxide derived from basic Cu-carbonate in hydrogen has been studied under temperature-programmed conditions (TPR) and the TPR patterns were analyzed by means of Arrhenius plots at constant conversion (Friedman plots). These plots indicate that the reduction process cannot be described on the basis of constant kinetic parameters and reveal the presence of isokinetic temperatures. These suggest the presence of a compensation effect requiring a modification of the rate equation.     

On the Apparent Compensation Effect Found for Two Consecutive Reactions

A critical analysis of the use of an overall single rate reaction equation instead of the true rate equation corresponding to a complex process consisting in two consecutive reactions is presented. In accordance with this approximation, often used in the kinetic analysis of the system in which several reactions take place, the overall process is described by the apparent activation parameters (the apparent activation energy, E _ap, and the apparent pre-exponential factor, A _ap) and the apparent conversion function. The theoretical isotherms (α=α(t), where a is the conversion degree and t is the time) have been simulated for a system in which two consecutive reactions occur. In this case, the apparent activation parameters depends on: (a) the considered range of the temperature; (b) the temperature, for a given conversion degree. It is shown that the apparent activation parameters are corrrelated by the compensation effect relationship: lnA _ap=α*+β*E _ap where α* and β* are the parameters of the linear regression. The possibility of using the apparent kinetic parameters to predict the isotherms α=α(t) for temperatures lower than those for which these parameters were evaluated, is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the Apparent Compensation Effect Observed for Two Consecutive Reactions

A critical analysis is presented of the use of an overall single rate reaction equation instead of the true rate equation corresponding to a complex process consisting of two consecutive reactions. In accordance with this approximation, which is often used in the kinetic analysis of systems in which several reactions take place, the overall process is described by apparent activation parameters (the apparent activation energy E_ap and the apparent pre-exponential factor A_ap) and an apparent conversion function. The theoretical isotherms (α=α(t), where α is the conversion degree and t is time) were simulated for a system in which two consecutive reactions occur. In this case, the apparent activation parameters depend on (a) the considered range of temperature; and (b) the temperature for a given conversion degree. It is shown that the apparent activation parameters are correlated by the compensation effect relationship: ln A_ap = α^* + β^*E_ap where α^* and β^* are the linear regression parameters. The possibility of using the apparent kinetic parameters to predict the isotherms α=α(t) for temperatures lower than those for which these parameters were evaluated is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electronic energy levels in all-trans long linear polyenes: the case of the 3,20-di(tert-butyl)-2,2,21,21-tetramethyl-all-trans-3,5,7,9,11,13,15,17,19-docosanonaen (ttbp9) conforming to Kasha's rule

The absorption, fluorescence and fluorescence excitation spectra for 3,20-di(tert-butyl)-2,2,21,21-tetramethyl-all-trans-3,5,7,9,11,13,15,17,19-docosanonaen (ttbP9) in dilute solutions of 2-methylbutane were recorded at temperatures over the range 120-280 K. The high photostability of this nonaene allows us to assert that it exhibits a single fluorescence and that this can be unequivocally assigned to emission from its 1(1)B(u) excited state, it being the first excited electronic state. Available photophysical data for this polyene and the wealth of information reported for shorter all-trans polyenes allow us to conclude that if the first excited electronic state for the chromophore possessed 2(1)A(g) symmetry, then the energy of such a state might have been so close to that of the 1(1)B(u) state that: 1) the radiationless internal conversion mechanism would preclude the observation of the emission from the 1(1)B(u) state reported in this work and 2) the 2(1)A(g) state reached through internal conversion would be vibrationally coupled to 1(1)B(u) and would facilitate the detection of the emission from 2(1)A(g), which was not observed in any of the solvents used in this work. The spectroscopic and photochemical implications of these findings for other polyenes are discussed.     

Development of the activation process model: Compensation effect

In this article, an attempt was made to develop an activation process model. The average energy of the translational motion of the atoms, taking part in the elementary activation process and being in the thermodynamic equilibrium with thermal radiation, was obtained using the quantum canonical Gibbs distribution and the model principles of elementary activation. The degeneracy and exclusion of some excited vibrational levels were taken into consideration, the result being a strong dependence of the probability of surmounting the activation barrier on the behavior of the excited vibrational states of the quantum subsystems. As an application of the development model, the formulas of the preexponential factor for solid-state atomic diffusivity and first-order chemical reaction rate constants were derived. Quantitative analysis of the atomic diffusion in solids in the framework of our model has made it possible to describe the diffusion processes in metals, covalent semiconductors, as well as diffusion anomalies, connected with the “nonclassical” behavior of the empirical Arrhenius dependence. A possible physical essence of a kinetic compensation effect is discussed. It was shown that compensation may be caused by only changing the degeneracy of the vibrational levels of the quantum subsystems. © 1996 John Wiley & Sons, Inc.     

Water droplet charging process in water-in-oil microemulsions: an electrical conductivity study

 The electrical conductivity σ of water-in-oil microemulsions formulated with AOT in pentane, heptane, decane and carbon tetrachloride was investigated in a wide range of composition and temperature. Assuming an Arrhenius-type temperature dependence of the conductivity, from the slopes of the linear portions of the plots ln(σ) vs. 1/T, the equilibrium constant K of the overall kinetic reaction yielding the droplet ionization has been evaluated as a function of the water-to-surfactant molar ratio, W. The activation energies of the whole conductivity process lie in the range 25–40 kJ mol^-1, depending on the characteristics of the oil phase. These values suggest that the ionization of the water droplets, responsible of the observed conductivity, is caused by the exchange of the droplet content (Na⁺ ions in aqueous solution, deriving from surfactant molecule dissociation), when droplets coalesce and then redisperse. Received: 12 December 1997 Accepted: 16 June 1998     

Ionic conduction in the solid state

Solid state ionic conductors are important from an industrial viewpoint. A variety of such conductors have been found. In order to understand the reasons for high ionic conductivity in these solids, there have been a number of experimental, theoretical and computational studies in the literature. We provide here a survey of these investigations with focus on what is known and elaborate on issues that still remain unresolved. Conductivity depends on a number of factors such as presence of interstitial sites, ion size, temperature, crystal structure etc. We discuss the recent results from atomistic computer simulations on the dependence of conductivity in NASICONs as a function of composition, temperature, phase change and cation among others. A new potential for modelling of NASICON structure that has been proposed is also discussed. Dedicated to Prof J Gopalakrishnan on his 62nd birthday.     

O-Trimethylsilylenol ethers as versatile building blocks in a modular preparation of polyenic backbone

Versatility and synthetic potential of 1-(trimethylsilyloxy)-1,3-butadiene, 1-(trimethylsilyloxy)penta-1,3-diene, and their methyl substituted derivatives have been demonstrated in a modular synthetic methodology of stereodefined π-conjugated unsymmetrical, symmetrical two-dimensional, and octupolar polyenal structure.     

Wide-range regulation of polyaniline conduction by interphase doping of a polyaniline film

The not-sufficient-enough conductance of semioxidized protonated polyaniline (PANI) is usually attributed to the presence of ordered quasi-metallic domains surrounded by a poorly conducting amorphous phase. The paper presents experimental results testifying to the existence, in semioxidized PANI, of multilevel redox heterogeneity that crucially effects the conductance magnitude in view of specific topology at which higher-oxidized (conducting) domains are surrounded by less oxidized (poorly conducting) domains and because the PANI conduction is extremely sensitive to the oxidation degree. It is shown experimentally that the interphase doping with metals and degenerate semiconductors of a semioxidized salt of PANI and poly(2-acrylamide-2-methyl-1-propanesulfonic acid) (PAMPSA) with a 1: 2 ratio between PANI and PAMPSA raises the PANI-PAMPSA conductivity by 3–8 orders of magnitude due to the formation near the interface of thin layers whose conductance depends on the work function of the material in contact with PANI-PAMPSA and in extreme cases substantially exceeds the conductance of gold and copper at room temperature.