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.

Polarons, Bipolarons, and Possible High-Tc Superconductivity in Metal-Ammonia Solutions

Abstract: We examine the nature of fluid metal-ammonia solutions with a special emphasis on the electronic structure and dynamics of polaronic and bipolaronic charge carriers. Importantly, we find that close to the compositionally-induced Nonmetal-to-Metal Transition in the fluid at low temperatures (ca. 240K), the vast majority (ca. 85% or above) of current carriers are highly mobile, diagmagnetic (S = 0) bipolarons. This raises the intriguing possibility, first proposed by R. A. Ogg in 1946, of a Bose–Einstein Condensation (BEC) of trapped electron pairs in vitreous, quenched metal-ammonia solutions. From a “modern” (2000) perspective we believe that there are important similarities to the situation in the crystalline layered cuprates, where we have argued elsewhere that High-T c superconductivity derives from the BEC of bipolarons in the electronically active CuO2 planes [A. S. Alexandrov and P. P. Edwards, Physica C 331, 97 (2000)]. We now propose that the search begins for high temperature superconductivity in quenched metal-ammonia and related solutions.

Electrical Conductivity and ESR Studies in Iodine-Doped Polythiophene from Semiconductor to Metallic Regime

Abstract: Dependences of electrical conductivity and ESR of iodine-doped polythiophene films, (C 4 H 2 SI y ) x , on iodine concentrations which are precisely determined by a neutron activation technique (from a dilute level of y ∼4×10 -4 to a deep level of y ∼4×10 -1 ) are reported. A drastic increase of conductivity from 10 -8 to 10 -2 S/cm is observed at the fairly narrow dopant concentration region of 2×10 3 < y <5×10 -3 , accompanied by a remarkable decrease in the activation energy of conductivity. At this transitional region, the ESR signal also changes significantly, showing a maximum spin density and a minimum linewidth. These results are discussed to understand the semiconductor-to-metal transition in iodine-doped polythiophene, taking polaron and bipolaron models into account.

Spin and spinless conductivity in polypyrrole. Evidence for mixed-valence conduction

Abstract: In-situ conductivity of polypyrrole (as tosylate) as a function of oxidative doping level attains a maximum at 3/4 the total oxidation charge and the relevant in-situ ESR signal corresponds to an equal concentration of spin-carrying (polaron) and spinless (bipolaron) species. Results are explained on the basis of mixed-valence conduction.

Doped Conductive Polymers: Modeling of Polythiophene with Explicitly Used Counterions

Abstract: The effect of counterions on the properties and structure of conducting polymers was studied by using a series of Cl 3 - doped polythiophenes (PTs) as a case example. Hybrid density functional theory (DFT) with periodic boundary conditions (PBC) at the B3LYP/6-31G(d) level has been used. This is the first theoretical study of infinitely long doped PT using DFT with counterions explicitly taken into account. The balance between charge carrier states was addressed by studying the singlet and triplet state unit cells of differently doped PTs. The relative isomer energies, density of states diagrams, bond length alternation, and charge distribution patterns were analyzed. Interestingly, the position of the counterion is flexible over the polymer chain and the electronic structure of the polymer and, consequently, optical properties are sensitive to the position of the counterion. A bipolaron electronic configuration is preferred at high dopant concentrations (one dopant per six or less thiophene rings) while a polaron pairs configuration is preferred at low dopant concentrations (one dopant per ten or more thiophene rings) which is in line with many experimental observations.