Bipolaron

About: Bipolaron is a research topic. Over the lifetime, 1335 publications have been published within this topic receiving 29154 citations. The topic is also known as: bipolarons.

Polaron lattice in highly conducting polyaniline: Theoretical and optical studies.

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.

High-density electron anions in a nanoporous single crystal: [Ca24Al28O64]4+(4e-).

Abstract: We removed approximately 100% of clathrated oxygen ions from the crystallographic cages in a single crystal of 12CaO.7Al2O3, leading to the formation of high-density (approximately 2 x 10(21) cm-3) electrons highly localized in the cages. The resulting electron forms a structure that we interpret as an F+ center and migrates throughout the crystal by hopping to a neighboring cage with conductivity approximately 100 siemens per centimeter, demonstrating that the encaged electron behaves as an anion. The electron anions couple antiferromagnetically with each other, forming a diamagnetic pair or singlet bipolaron. The resulting [Ca24Al28O64]4+(4e-) may be regarded as a thermally and chemically stable single crystalline "electride."

Highly conducting polyparaphenylene, polypyrrole, and polythiophene chains: An ab initio study of the geometry and electronic-structure modifications upon doping

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.

Polarons and bipolarons in polypyrrole: Evolution of the band structure and optical spectrum upon doing

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

Charge storage in doped poly(thiophene): Optical and electrochemical studies

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.