Showing papers on "Bipolaron published in 1984"
TL;DR: In this paper, the effect of charge transfer on conjugated polymers was investigated at the ab initio level with explicit consideration of the doping agents, and three systems were chosen for study as prototypical examples of polymers with nondegenerate ground states: polyparaphenylene, polypyrrole, and polythiophene.
Abstract: The effect of charge-transfer doping on the geometric and electronic structures of conjugated polymers has been investigated at the ab initio level with explicit consideration of the doping agents. Three systems were chosen for study as prototypical examples of conjugated polymers with nondegenerate ground states: polyparaphenylene, polypyrrole, and polythiophene. As a result of charge transfer with electron-donating dopants, extra charges appear on the polymer chains and induce strong geometry modifications. The lattice evolves from an aromatic structure towards a quinoid-like structure. Charged defects associated with lattice deformations such as spinless bipolarons are formed. The influence on the electronic structure of the polymer chains is such that with respect to the undoped case, new states appear within the gap. For the maximum doping levels experimentally achieved, band-structure calculations demonstrate that the states in the gap overlap to form bipolaron bands, a few tenths of an electron volt wide. The presence of these bipolaron bands is consistent with optical data as well as with magnetic data which suggest that the charge carriers in the highly conducting regime are spinless.
627 citations
IBM1
TL;DR: This article presented des resultats de calculs de structure de bandes en liaison forte pour une chaine polypyrrole deformable, en fonction du dopage.
Abstract: Presentation des resultats de calculs de structure de bandes en liaison forte pour une chaine polypyrrole deformable, en fonction du dopage. Les etats qui sont produits sont des polarons et des bipolarons dont le spectre d'excitation explique les donnees d'absorption optique
579 citations
TL;DR: In this paper, the authors present a new method of electrochemical polymerization of poly(thiophene) using dithiophene as the starting material, from which they obtain a high-quality film with a sharp interband absorption edge.
Abstract: We present a new method of electrochemical polymerization of poly(thiophene) using dithiophene as the starting material, from which we obtain a high-quality film with a sharp interband absorption edge. An in situ study of the absorption spectrum during the electrochemical doping process has been carried out. In the dilute regime, the results are in detailed agreement with charge storage via bipolarons; weakly confined soliton pairs with confinement parameter $\ensuremath{\gamma}\ensuremath{\cong}0.1\ensuremath{-}0.2$. At the highest doping levels, the data are characteristic of the free-carrier absorption expected for a metal. From a parallel electrochemical voltage spectroscopy study, we find evidence of charge injection near the band edge and charge removal from the bipolaron gap states. In the dilute regime, the position of the chemical potential is consistent with charge storage in weakly confined bipolarons. The high Coulombic recovery over a charge-discharge cycle indicates that poly (thiophene) may be an excellent cathode-active material in battery applications.
550 citations
TL;DR: In this article, an interchain hopping mechanism for spinless conductivity in doped polyacetylene, doped $\math{poly}(p\ensuremath{-}\mathrm{p}{h}\mathm{e}n}\math m{n}m{y}\math l{l{l}m \math m{\math m}n}{e}\math n{n}\m{m}m}{n{e})$ was proposed, which can account for the observed dopant-concentration dependence of
Abstract: Interchain hopping of bipolarons (doubly charged defects) is discussed as a mechanism for spinless conductivity in doped polyacetylene, doped $\mathrm{poly}(p\ensuremath{-}\mathrm{p}\mathrm{h}\mathrm{e}\mathrm{n}\mathrm{y}\mathrm{l}\mathrm{e}\mathrm{n}\mathrm{e})$, and other doped polymers. It is shown that this mechanism can account for the observed dopant-concentration dependence of the conductivity in trans-polyacetylene and the observation of anomalously low magnetic susceptibilities in the highly conducting regime of several doped polymers.
159 citations
IBM1
TL;DR: In this paper, experimental data and theoretocal studies support the hypothesis that bipolarons are the charge carriers responsible for the conductivity of polypyrrole, and a consistent model emerges from consideration of earlier transport, ESR, photoelectron spectroscopy and optical absorption results.
125 citations
TL;DR: In this article, the formation of charged defects such as solitons, polarons and bipolarons in doped conjugated polymers is discussed and the results of ab initio quality calculations on the modifications of geometric and electronic structures occurring upon doping are presented.
107 citations
TL;DR: In this paper, a self-consistent numerical study was performed to investigate the formation of the polaron, soliton, and soliton lattice in the framework of Su-Schrieffer-Heeger model.
Abstract: We have performed a self-consistent numerical study, which allows each CH group in a finite polyacetylene chain to relax to its equilibrium position, in order to investigate the formation of the polaron, soliton, and soliton lattice in the framework of Su-Schrieffer-Heeger model. The bondalternation order parameter, the delocalization of the gap states, the polaron-formation energy, the soliton-formation energy, the Peierls gap, and the gap separating the valence (or condition) band and the impurity band are calculated as functions of dopant level. The effect of electron-electron interaction is then examined in the Hartree approximation. Our results are compared with those derived by other authors. Although our approach simulates a doping process, further calculation based on the decaying of an electron-hole pair into a soliton-antisoliton pair gives exactly the same results as those shown in this paper. In particular, our finding clearly demonstrates the singlecharge injection via polarons which subsequently combine to form soliton-antisoliton pairs, in agreement with the recent experimental discovery.
50 citations
35 citations
TL;DR: In this paper, an explicit solution for the Brazovskii-kirova continuum model of cis-polyacetylene is presented for the following three configurations: two polarons, two bipolarons, and a polaron and a bipolaron coexisting on a single chain.
Abstract: Explicit solutions for the Brazovskii-Kirova continuum model of cis-polyacetylene are presented for the following three configurations: two polarons, two bipolarons, and a polaron and a bipolaron coexisting on a single chain. The results show that two polarons attract each other with a long-range potential reflecting large spatial extension of the polarons and that the attracted polarons form a bipolaron; two bipolarons repel each other; and polarons and bipolarons can freely pass through each other without attractive or repulsive interactions.
34 citations
TL;DR: In this paper, the correlation energy U between two holes in the valence band is shown to be caused by a dynamic bipolaron effect, and the authors suggest that the negative U is caused by the large admixture of 3D states in this band.
Abstract: Presents Auger electron spectra of Si, Ti and compounds of Ca, Sc, Ti and Cr. From a combination with photoelectron spectra the correlation energy U for the various two-hole states was deduced. For Sc, Ti, TiSe2 and CrSe2 the correlation energy U between two holes in the valence band is negative. The authors suggest that the negative U is caused by a dynamic bipolaron effect. They found that Auger decay involving valence states is strong for TiSe2 and CrSe2, due to a large admixture of 3d states in the valence band. Other features in the spectra are discussed in terms of multiplet splitting and satellites.
28 citations
TL;DR: In this article, the gap between bonding and antibonding was shown to be closed at the highest doping level and a metallic state was observed at the lowest doping level, consistent with the bipolaron model showing two defect states in the gap.
Abstract: Electron-energy-loss spectroscopy has been used to investigate the electronic structure of Li-doped polyparaphenylene. For low doping concentration the results are consistent with the bipolaron model showing two defect states in the gap. At the highest doping level, the gap between bonding and antibonding $\ensuremath{\pi}$ electrons is closed and a metallic state is observed.
TL;DR: In this article, the optical conductivity spectra of the conducting and insulating forms of poly(β, β)-dimethylpyrrole perchlorate (PβDMP-ClO4) films have been determined by the Kramers-Kronig transformation of the transmittance spectra from 0.074 to 6.25 eV.
Abstract: The optical conductivity spectra of the conducting and insulating forms of the poly‐β, β′‐dimethylpyrrole perchlorate (PβDMP–ClO4) films have been determined by the Kramers–Kronig transformation of the transmittance spectra from 0.074 to 6.25 eV. The optical spectrum of the conducting form is not consistent with Drude‐like free carriers. Absorption spectra have been measured on PβDMP‐ClO4 films with various concentrations of perchlorate anions obtained using an electrochemical technique. Compared to those of polypyrrole perchlorate, the absorption spectra of PβDMP–ClO4 show some significant differences, especially in the low energy region of the almost neutral forms. Evolution of the PβDMP–ClO4 absorption spectra as a function of doping level is inconsistent with a rigid band model and is interpreted in terms of bipolaron formation on the chains.
TL;DR: In this article, the oxidative doping of thin films of poly(p-phenylene sulphide) by arsenic pentafluoride has been followed by transmission absorption spectroscopy (near i.r. to u.v.) and transitions are assigned involving cationic states, poloran and bipolaron, formed within the π-π* band gap.
Abstract: The oxidative doping of thin films of poly(p-phenylene sulphide) by arsenic pentafluoride has been followed by transmission absorption spectroscopy (near i.r. to u.v.) and transitions are assigned involving cationic states, poloran and bipolaron, formed within the π–π* band gap.
TL;DR: In this article, an electrical conductivity and a thermopower of sintered Li 1.1 Ti 1.9 O 4 were measured and the Seebeck coefficient is proportional to temperature.
Abstract: An electrical conductivity and a thermopower of sintered Li 1.1 Ti 1.9 O 4 were measured. The Seebeck coefficient is proportional to temperature. The conductivity becomes larger with increasing temperature but it does not fit to the T 1/4 relation of a variable range hopping model nor to the relation for a small polaron hopping model at lower temperatures. To explain the transport, magnetic and thermal properties of Li 1+ x Ti 2- x O 4 , it is proposed a bipolaron state in a random field.
TL;DR: In this paper, structural changes were found by an X-ray scattering study in β-vanadium bronze compounds, having a localized one-dimensional electron system, which were attributed to a possible ordering of the bipolarons which are expected to be formed on vanadium chains by strong electron-phonon coupling.
06 Jan 1984
TL;DR: In this paper, the authors present a new method of electrochemical polymerization of poly(thiophene) using dithiphene as the starting material, from which a high quality film with a sharp interband absorption edge is obtained.
Abstract: : This paper presents a new method of electrochemical polymerization of poly(thiophene) using dithiphene as the starting material, from which a high quality film with a sharp interband absorption edge is obtained. An in situ study of the absorption spectrum during the electrochemical doping process has been carried out. In the dilute regime, the results are in detailed agreement with charge storage via bipolarons; weakly confined soliton pairs with confinement parameter gamma = 0.1-0.2. At the highest doping levels, the data are characteristic of the free carrier absorption expected for a metal. From a parallel electrochemical voltage spectroscopy (EVS) study, we find evidence of charge injection near the band edge and charge removal from the bipolaron gap states. In the dilute regime, the position of the chemical potential is consistent with charge storage in weakly confined bipolarons. the high Coulombic recovery over a charge-discharge cycle indicates that poly(thiphene) may be an excellent cathode-active material in battery applications.
TL;DR: In this paper, it was shown that the ac transport in the single-polaron tunneling model could be dominated by correlated barrier hopping (CBH) of single polarons.
Abstract: It is again shown that the ac transport in $a\ensuremath{-}\mathrm{S}\mathrm{i}{\mathrm{O}}_{2}$ could be dominated by the correlated barrier hopping (CBH) of single polarons. It is concluded that there are difficulties in interpreting the experimental data using the bipolaron CBH and single-polaron tunneling model proposed by Meaudre and Meaudre.
TL;DR: In this paper, the authors compared the models proposed to explain the ac conduction in rf sputtered Si${\mathrm{O}}_{2}$ films and showed that the ac conductivity observed in the (77-570)-K range is well explained when considered as the sum of two contributions: the first dominating at low temperatures, arising from bipolaron correlated barrier hopping, and the second dominating at high temperatures arising from quantum-mechanical tunneling of holelike polarons.
Abstract: The models proposed to explain the ac conduction in our rf sputtered Si${\mathrm{O}}_{2}$ films are compared. The ac conductivity observed in the (77-570)-K range is well explained when considered as the sum of two contributions: the first dominating at low temperatures, arising from bipolaron correlated barrier hopping, and the second dominating at high temperatures, arising from quantum-mechanical tunneling of holelike polarons. It is emphasized that correlated barrier hopping of one or two types of carriers cannot render an account of the entire range of experimental results. It is shown that this ac transport is controlled by ${D}^{\ensuremath{-}},{D}^{+},{D}^{0}$ defects and that a different choice of defects is unfounded.
TL;DR: In this article, the perturbation theory was used to calculate the energy bands of the bipolaron and the free-polaron, in order to investigate the stabilities of the singlet and the triplet bipolaron states.
Abstract: We have used the perturbation theory to calculate the energy bands of the bipolaron and the free-polaron, in order to investigate the stabilities of the singlet and the triplet bipolaron states. By analyzing the specific heat and the magnetic susceptibility, we illustrate the importance of the triplet bipolaron state in understanding the experimental data.
01 Jan 1984
TL;DR: In this article, the authors describe the derniers resultats sur le polythiophene and describe du polyisothianaphtalene, and describe polyheterocycles.
Abstract: Breve revue des polyheterocycles; description des derniers resultats sur le polythiophene; description du polyisothianaphtalene
TL;DR: In this article, the ground states in the extended Hubbard model are obtained taking into account polaron effects, with both, intrasite repulsion and intra-site attraction, and it is shown that the function fq, characterizing the degree of lattice polarization due to the electron-phonon interaction depends on the type of the ground state and on the electron concentration.
Abstract: The ground states in the extended Hubbard model are obtained taking into account polaron effects, with both, intrasite repulsion and intrasite attraction. It is shown that the function fq, characterizing the degree of lattice polarization due to the electron—phonon interaction depends on the type of the ground state and on the electron concentration. Depending on the interaction parameters, the hopping energy (the bandwidth), and the electron concentration the crystals can be in the following ground states: 1. the polaron charge-ordered state; 2. the bipolaron chargeordered state; 3. the bipolaron state with a homogeneous electron distribution over the lattice; 4. the state with an intersite bipolaron.