Topic
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.
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TL;DR: In this article, the results of a UV/VIS spectroscopic investigation of thin films of oxidized polypyrrole doped with p-toluenesulfonate, dodecylsulfate or copper phthalocyanine tetrasulfonates anions immediately after electrochemical synthesis and during heat treatment are presented.
Abstract: The results of a UV/VIS spectroscopic investigation of thin films of oxidized polypyrrole doped with p-toluenesulfonate, dodecylsulfate or copper phthalocyanine tetrasulfonate anions immediately after electrochemical
synthesis and during heat treatment are presented. The absorption bands in the resulting spectra were
identified with the electronic transitions of the polarons, bipolarons and transverse bipolarons as follows:
the absorption bands below ca. 1.4 and at 1.8 eV are both attributed to the sum of the polarons and transverse
bipolarons, the band at 2.44–2.5 eV to the sum of polarons, bipolarons and transverse bipolarons and the band
around 3.2–3.6 eV to the band gap transition of polypyrrole. The identity of the absorption band above
3.8 eV remains uncertain. The absorbance changes of bands in the UV/VIS spectra collected during sample aging
and heat treatment were explained as a result of the rearrangement of the polypyrrole structure. The main
processes acting during the sample aging are the interchain conversion of polarons into transverse bipolarons
and the interaction of polarons with transverse bipolarons yielding bipolarons. The spectral changes
induced by sample heating at 80 °C seem to be caused mainly by an interchain dissociation of the transverse
bipolarons to polarons and by their slower intrachain recombination into bipolarons and the polypyrrole
neutral form. The structural rearrangement induced by the sample heating is a very slow process because
the UV/VIS spectra were not stable even after 35 h. The changes taking place in the polypyrrole structure
during sample cooling are the opposite of those during the heating but they are only partially reversible
in magnitude. The polypyrrole samples doped with p-toluenesulfonate and copper phthalocyanine tetrasulfonate exhibited very similar behavior whereas dodecylsulfate doped samples exhibited an extraordinary
behavior owing their liquid-like solid-state micellar structure. The magnitudes of the polypyrrole spectra
changes showed that only a relatively small proportion
of the
species present within
the polypyrrole were influenced by these processes.
32 citations
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TL;DR: In this paper, an electron in the ground state occupies the t2g orbital of a Nb4+ ion and its orbital degeneracy is lifted by a combination of the breathing and Jahn-Teller modes where four nearest equatorial O atoms are displaced outwards and two oxygens shift inwards along the z axis.
Abstract: Quantum chemical calculations using the intermediate neglect of the differential overlap (INDO) method, combined with the large unit cell periodic model argue for an existence of the self-trapped electrons in KNbO3 and KTaO3 perovskite crystals. An electron in the ground state occupies predominantly t2g orbital of a Nb4+ ion. Its orbital degeneracy is lifted by a combination of the breathing and Jahn-Teller modes where four nearest equatorial O atoms are displaced outwards and two oxygens shift inwards along the z axis. Triplet exciton is shown to be in a good approximation of a pair of nearest Jahn-Teller electron and hole polarons (a bipolaron) which is very likely responsible for the `green' luminescence observed in these crystals.
32 citations
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TL;DR: The Holstein-Hubbard model is used to study high-temperature hopping transport when it is energetically favorable for carriers to pair as singlet small bipolarons, and the semiclassical rates for one-electron transfers involving small polarons are found to be much greater than those that only involve smallipolarons.
Abstract: The Holstein-Hubbard model is used to study high-temperature (T\ensuremath{\gtrsim}${\mathit{T}}_{\mathrm{phonon}}$/3) hopping transport when it is energetically favorable for carriers to pair as singlet small bipolarons. The semiclassical rates for one-electron transfers involving small polarons are found to be much greater than those that only involve small bipolarons. In particular, the most rapid one-electron-transfer processes have a small-polaron hopping to a vacant site and one of a small bipolaron's two carriers jumping onto the site of an adjacent small polaron. As a result, even when most carriers form small bipolarons rather than small polarons, one-electron transfers involving small polarons always dominate the dc conductivity. The energy to thermally generate small polarons from small bipolarons thus contributes to the conductivity's activation energy. This pair-breaking energy also manifests itself in a thermally activated contribution to the system's paramagnetic susceptibility. In addition, the carriers' Seebeck coefficient garners a contribution with a temperature dependence that is characterized by the pair-breaking energy. \textcopyright{} 1996 The American Physical Society.
31 citations
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TL;DR: In this article, the authors used copper phthalocyanine trisulfonate as dopant, resulting in a high concentration of bipolarons which have a high contribution from the wavefunctions of the pyrrole-nitrogen atoms.
31 citations
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TL;DR: In this paper, the dielectric function of the boron-rich solids in the FIR range is analyzed on the basis of their optical reflectivity spectra, which exhibit obviously typical, strongly increasing slopes with decreasing frequencies.
31 citations