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Showing papers on "Bipolaron published in 1987"


Journal ArticleDOI
TL;DR: In this paper, the authors present optical-absorption data together with band-structure calculations for the polaron lattice and bipolaron lattice for the highly conducting form of polyaniline, proton-doped polyemeraldine.
Abstract: We present optical-absorption data together with band-structure calculations for the polaron lattice and bipolaron lattice for the highly conducting form of polyaniline, proton-doped polyemeraldine. We show that the polaron-lattice band structure fully accounts for the observed optical transitions. These results are in marked contrast with the electronic structure of other doped conducting polymers, in that only one single broad polaron band appears deep in the gap together with a very narrow band nearly degenerate with the conduction-band edge.

770 citations


Journal ArticleDOI
TL;DR: In this paper, the in situ spectra in the visible region are presented as a function of the potential of the electrode, which can determine the level of doping of the polyaniline polymer.

156 citations


Journal ArticleDOI
TL;DR: In this article, the amplitude mode model was modified to include an additive extrinsic component Δe to obtain a ld gap 2 Δ = 2.2 eV and 2 Δe = 0.22 eV.

95 citations


Journal ArticleDOI
TL;DR: In this paper, electron spin resonance measurements and spectroscopic data on the doped poly(3-hexylthienylene) macromolecules in solution were used to determine the nature of the charge storage configurations.

83 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present the results of tight-binding band structure calculations performed in the framework of the adiabatic Su-Schrieffer-Heeger Hamiltonian.

83 citations


Journal ArticleDOI
TL;DR: In this paper, peroxide bonding of the typeO - Cu + O - occur readily in the high temperature superconductive oxides and may be responsible for its superconductivity.

76 citations


Journal ArticleDOI
TL;DR: In this article, an energetic study of the excitation spectrum in doped polythiophene is presented within the framework of the Huckel approximation, and it is shown that localized states like polarons and bipolarons are produced by doping, the formation of doubly charged bipolarons being energetically more favorable than two polarons charged singly.
Abstract: An energetic study of the excitation spectrum in doped polythiophene is presented within the framework of the H\"uckel approximation. The calculations show that localized states like polarons and bipolarons are produced by doping, the formation of doubly charged bipolarons being energetically more favorable than the formation of two polarons charged singly. It is then shown from the analysis of available magnetic and optical data that the bipolarons are the dominant charge states while the features due to the polarons appear under certain circumstances at low doping levels.

70 citations



Journal ArticleDOI
01 Sep 1987
TL;DR: In this article, it was shown that the current response in the whole accessible potential range of conventional conducting polymers is mainly caused by faradaic charge transfer reactions rather than capacitive effects.
Abstract: Voltammetric measurements on selected polypyrrole (PPy) films and defined soluble oligomers belonging to the oligo-p-phenylene and the oligo-p-phenylenevinylene series provide new insights into the charging/discharging properties of conducting polymers. It turns out that the current response in the whole accessible potential range of conventional conducting polymers is mainly caused by faradaic charge transfer reactions rather than capacitive effects. This is supported by digital simulations which are based on a model of n-fold electron transfers within a finite layer. In addition, from the data of defined oligomers it becomes clear that the number and energies of accessible redox states in such materials depend on the extension of conjugation in the monomeric unit and on the chain length of the polymer. In general, in systems such as PPy up to a charging level of approximately 20 – 25 mol% all redox states are degenerated. Then, the successive redox states are gradually shifted to higher energies in accordance with increasing Coulomb repulsion between the charges. The results show that the bipolaron model must be amended. Nevertheless, experimental data reveal that the charging steps in conducting polymers are coupled with structural relaxation processes; but they occur, in contrast to the theoretical predictions, already on the polaron state.

67 citations


Journal ArticleDOI
01 Nov 1987-EPL
TL;DR: In this paper, it was shown that the change of the optical absorption of reduced undoped LiNbO3 under heating can be explained as the dissociation of Nb4+-Nb4 + bipolarons.
Abstract: It is shown that the change of the optical absorption of reduced undoped LiNbO3 under heating can be explained as the dissociation of Nb4+-Nb4+ bipolarons. By this treatment the well-known absorption band of the material at 500 nm decreases in favour of a new band at 760 nm, attributed to Nb4+ small polarons. The bipolaron dissociation energy is determined to be 0.27 eV. Also other properties of reduced LiNbO3 are consistent with the model.

65 citations



Journal ArticleDOI
TL;DR: In this article, a possible occurrence of cooperative Jahn-Teller distortion in La2CuO4 is suggested, which is related to the superexchange between the spins of d holes in |z2> orbital and suggested not to exceed the Neel temperature.
Abstract: A possible occurrence of cooperative Jahn-Teller distortion in La2CuO4 is suggested. In doped (La1-xMx)2CuO4 the d holes in Cu2+ ions in |x2-y2> orbitals tend to form a polaron pair in the Cu2+-O2--Cu2+ form, and consequently extra d holes in |z2> orbitals in Cu3+ ions also form a polaron pair in a less distorted situation. Then the coherent tunneling of an extra bipolaron occurs through all the Cu2+-O2--Cu2+ sites, and the extra bipolarons make a Bose condensation at the zero wavevector state. This causes high Tc superconductivity. Tc is related to the superexchange between the spins of d holes in |z2> orbital and suggested not to exceed the Neel temperature of La2CuO4.

Journal ArticleDOI
TL;DR: In this paper, in situ ESR-electrochemical experiments in conducting polymers are presented, where spin concentration has been measured as a function of doping level, and quantitative data are presented for the case of polypyrrole.

Journal ArticleDOI
TL;DR: It is established within this model that small-bipolaron formation will be energetically favored in the boron carbides.
Abstract: Small-bipolaron hopping has been proposed as the mechanism of electrical transport in the boron carbides, compounds composed of boron-rich icosahedra linked by carbon-containing chains. We present a simple model of small-bipolaron formation and of the small-bipolaron hopping activation energy. We then consider, by means of a molecular-orbital calculational technique, a cluster model of bipolaron formation in a boron icosahedron set in charge-neutral surroundings. A lower limit of 3.7 eV is calculated for the bipolaron formation energy, of which 1.0 eV is related to site distortion and 2.7 eV to filling of icosahedral bonding orbitals. We have therefore established within our model that small-bipolaron formation will be energetically favored in the boron carbides.

Book ChapterDOI
01 Jan 1987
TL;DR: In this paper, it was shown that the polaron pairing is hindered by potential barriers and, consequently, polarons and bipolarons are not in thermodynamical equilibrium, and the spin susceptibility does not decrease at low temperature.
Abstract: Spin concentration has been measured as a function of charge injection in polypyrrole, polyaniline, and polydithiophene. Analysis of the data in terms of polarons and bipolarons in thermodynamical equilibrium leads to polarons and bipolarons nearly degenerate for polypyrrole and polyaniline. In the case of polydithiophene the data support the bipolarons as the fundamental charged species. However, the spin susceptibility does not decrease at low temperature as expected for fundamental spinless species. We propose that the polaron pairing is hindered by potential barriers and, consequently, polarons and bipolarons are not in thermodynamical equilibrium.

Journal ArticleDOI
TL;DR: In this paper, the Coulomb interactions in conjugated polymers are studied under the influence of Coulomb interaction and the results are compared with recent experiments in polythiophene and good agreement is found.

Journal ArticleDOI
TL;DR: In this article, the Su-Schrieffer-Heeger model has been applied to a trans-polyacetylene chain with two holes at the top of the valence band.

Journal ArticleDOI
TL;DR: In this paper, the Mott's Variable Range Hopping (VRH) model is extended to a system of mobile localized states, referred to those localized on polarons and bipolarons.

Journal ArticleDOI
TL;DR: In this paper, photo-induced electronic and vibrational absorption of polydiacetylene (10H) in the infrared (400-4000 cm-1) was found to be consistent with photo-generation of bipolarons.
Abstract: Photo-induced electronic and vibrational absorption of polydiacetylene (10H) in the infrared (400-4000 cm-1) is found to be consistent with photo-generation of bipolarons Overlap of electronic and vibrational transitions occurs due to strong electron correlation effects which reduce the electronic transition energies Electron-phonon interaction produces anti-resonances in the bipolaron electronic absorption

Journal ArticleDOI
TL;DR: In this article, the frequency and temperature dependence of electrical conductivity σ(f, T) in lightly doped polypyrrole is investigated, and it is shown that σac changes with √ f 0.7.
Abstract: Frequency (f) and temperature (T) dependence of electrical conductivity σ(f, T) in lightly doped polypyrrole is presented. The behavior of σ(f, T) is different from those of disordered semiconductors and insulating polymers, with considerably strong temperature and frequency dependence of σac.σac changes with ∝f0.7. These results can be described by slightly modified Kivelson's model, that is, the interpolaron hopping process between the polaron and bipolaron states.

Journal ArticleDOI
TL;DR: In this paper, the optical properties of electrochemically polymerized poly(terthiophene) (PTT), poly(bithiophene), and polypyrrole (PP) were studied.

Journal ArticleDOI
TL;DR: In this paper, the relation between electrical conductivity and ESR characteristics in polythiophene upon doping has been studied by utilizing (I) a neutron activation technique and (II) a radiation-induced doping technique.

Journal ArticleDOI
TL;DR: In this article, photoinduced negative polaron (or electron) trapped at dopant-induced bipolaron is predominantly observed in photoinduced absorption spectra of lightly doped poly(3-methylthiophene) films.


Journal ArticleDOI
TL;DR: A theory of the bipolaron lattice in the Peierls-distorted system with nondegenerate ground states is presented and a possible first-order phase transition to a metallic phase consisting of an array of polaronlike distortions from a lattice of charged bipolarons is described.
Abstract: We present a theory of the bipolaron lattice in the Peierls-distorted system with nondegenerate ground states. First, we obtain an exact solution for the order parameter of a bipolaron lattice in terms of the Weierstrass \ensuremath{\zeta} function for the continuum model of Brazovskii and Kirova. Making use of the exact solution, we determine the complete band structure of a bipolaron lattice. In addition to the conduction and valence bands, we find two bipolaron bands symmetrically located about the middle of the Peierls energy gap. We also calculate the electronic density of states and the energy of formation of a bipolaron lattice as a function of the bipolaron density ${n}_{b}$. The chemical potential of a bipolaron determines the domain of stability of the lattice as a function of the confinement parameter \ensuremath{\gamma}. In the weak-coupling limit (infinite momentum cutoff \ensuremath{\Lambda}) the bipolaron-bipolaron interaction decays as a repulsive exponential while for finite \ensuremath{\Lambda} it decays inversely proportional to the distance and is attractive. This yields the possibility of phase separation in doped quasi-one-dimensional conducting polymers with nondegenerate ground states. For higher dopant concentrations we describe a possible first-order phase transition to a metallic phase consisting of an array of polaronlike distortions from a lattice of charged bipolarons. As well, the optical absorption spectrum of a bipolaron lattice is briefly discussed. Our results apply to cis-polyacetylene as well as to a class of heterocyclic compound polymers, namely, polypyrroles, polythiophenes, and their derivatives. Finally, we make contact with recent experiments which study the evolution of ordered phases during the electrochemical doping of polyparaphenylene by alkali atoms and indicate the possibility of a bipolaron lattice.

Journal ArticleDOI
TL;DR: In this article, the changes in energy, atomic positlions and charge distribution when a pair of electrons is added to the isoelectronic icosahedral clusters B12 and (B11C)+ were calculated.
Abstract: Boron carbides, B1-xCx with 0.085 ≤ × ≤ 0.200, generally contain both B12 and B11C icosahedra. However, the electronic transport with 0.1 ≤ × ≤ 0.2 is believed to occur by means of bipolaron hopping between only B11 C icosahedra [i]. We have calculated the changes in energy, atomic positlions and charge distribution when a pair of electrons is added to the isoelectronic icosahedral clusters B12 and (B11C)+. We simulate an icosahedron in a neutral lattice by bonding the icosahedral atoms to hydrogenic atoms which we constrain to be neutral. The computations are performed with a self-consistent molecular-orbital method, PRDDO. We find a total energy reduction of -3.7 eV for two electrons added to a B12 icosahedron. Of this, -2.7 eV arises from the electrons filling the icosahedron’s bonding orbitals. The remaining -1.0 eV comes from the contraction of the icosahedron’s radius by -0.09 A. For two electrons added to a (B11C)+ icosahedron we find a total energy reduction of -18.2 eV. Of this, -16.5 eV arises from filling the icosahedron’s bonding orbitals. The remainder arises frop a -0.09 A contraction of the icosahedron’s radius. Thus, we find (B11C) icosahedra to be strongly energetically favored over B12 icosahedra as bipolaron sites. The positive charge associated with a (B11C)+ icosahedron is distributed over the eleven boron atoms. Concomitantly, we find the added two electrons of the bipolaron to be distributed over all twelve sites of the B11C icosahedron. We find the energy difference between an electron pair added to B12 and (B11C)+ icosahedra to arise principally from the increased Coulomic attraction provided by the extra positive charge of the (B11C) icosahedron.

Journal ArticleDOI
D. K. Ray1
TL;DR: In this paper, a microscopic theory based on hybridization-induced wide-band bipolarons is proposed to explain the occurrence of high-temperature superconductors such as La2−x-BaxCuO4, and La 2−xSrxCuO 4.
Abstract: A microscopic theory based on the idea of hybridization-induced wide-band bipolarons is proposed to explain the occurrence of high-temperature superconductors such as La2−x-BaxCuO4, and La2−xSrxCuO4. In our view, these are such that bipolarons are formed whose singlet ground state possesses a large binding energy (Δ) with bandwidth W (>Δ) as a result of two distinct electron-phonon mechanisms and two types of hybridization between Cu2+ d electrons and other electrons. This wide-band bipolaron gas has features similar to Cooper pairs and leads to a superconducting state with high Tc in which all occupied electron states participate. The large electron-phonon coupling and a large W both cause the transition temperature Tc, to rise spectacularly.

Journal ArticleDOI
TL;DR: In this paper, the structural phase transition of V4+ ions in β-Ag0.40V2O5 was investigated by NMR and EPR, and the 51V Knight shift results showed that the spin-singlet ground state of pairs is realized as bipolaron.
Abstract: The electronic states of V4+ ions in β-Ag0.40V2O5 are investigated by NMR and EPR. The structural phase transition is observed between 170 and 210 K. The 51V Knight shift results show that the spin-singlet ground state of V4+ ion pairs is realized as bipolaron. Nous avons etudie el etat electronique des V4+ ion dans β-Ag0.40V2O5 avec des measures de RMN et RPE. On trouve que il exist le transition de phase structural pendent 170 et 210 K. Le deplacement de Knight du 51V montre que l'on a un etat de base spin-singlet pour des paires d'ions V4+ en bipolaron.

Journal ArticleDOI
TL;DR: In this article, the spectral properties of conducting polymer, poly(3-methylthiophene), were investigated for a wide spectral range of 30 − 45000 cm −1, and strong electronic transition was found in the far-i.r. reflectance of the heavily doped film.

Journal ArticleDOI
TL;DR: In this paper, it is proposed that the electron pairs responsible for high Tc superconductivity in Ba (or Sr)LaCuO compounds fall in the crossover region from bipolarons to Cooper pairs.