Determination of electronic structure by impedance spectroscopy

Niklasson, Gunnar A.; Malmgren, Sara; Green, Sara; Backholm, Jonas

doi:10.1016/j.jnoncrysol.2009.06.053

Cited by 13 publications

(11 citation statements)

References 18 publications

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“…Other capacitive processes, perhaps connected with the interfaces in the WE, might be superimposed on the chemical capacitance at low frequencies. However, the shape of the EDOS, apart from a multiplicative factor, is in good agreement with the computed DOS up to 1 eV from the band edge, as shown before [10]. At higher energies (lower potentials), the intercalation process is not reversible and the EIS experiment indicates reaction or trapping processes, probably the formation of Li compounds [10].…”

Section: Resultssupporting

confidence: 83%

“…However, the shape of the EDOS, apart from a multiplicative factor, is in good agreement with the computed DOS up to 1 eV from the band edge, as shown before [10]. At higher energies (lower potentials), the intercalation process is not reversible and the EIS experiment indicates reaction or trapping processes, probably the formation of Li compounds [10]. It is clear that the EDOS is not reliable in the presence of strong side reactions.…”

Section: Resultssupporting

confidence: 70%

“…Measurements discussed below used a 10 mV amplitude ac signal with frequencies from 10 mHz to 1 MHz [10]. This was done for a number of bias potentials between 3.2 V and 1 V vs. Li.…”

Section: Experimental Techniquesmentioning

confidence: 99%

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Electrochemical measurements of the electronic density of states

Niklasson

2015

Phys. Scr.

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PostprintThis is the accepted version of a paper published in Physica Scripta. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination.Citation for the original published paper (version of record):Niklasson, G A. (2015) Electrochemical measurements of the electronic density of states.Physica Scripta, 90 (9) AbstractWe present a simple electrochemical method, called intercalation spectroscopy, to study the electronic density-of-states of intercalation materials. It is based on the realization that electrochemical quasi-steady state potential curves of a number of materials exhibit fine structure in good agreement with features in the density of electronic states. Different electrochemical techniques are able to give this information, but chronopotentiometry appears to have advantages from an experimental viewpoint. In this paper we compare the so called "electrochemical density-of-states" of amorphous and crystalline structures. We also address the limitations of intercalation spectroscopy due to kinetic effects, i.e. very slow relaxations of the charge carriers. Intercalation spectroscopy is in principle very sensitive, although in limited energy ranges, and is able to give information complementary to electron and X-ray spectroscopies for a number of materials.

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Section: Resultssupporting

confidence: 83%

Section: Resultssupporting

confidence: 70%

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Electrochemical measurements of the electronic density of states

Niklasson

2015

Phys. Scr.

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“…Li/Li + , ( ref. 10). The physical and chemical bases of the irreversibility remain poorly known, experimentally as well as theoretically.…”

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confidence: 99%

Eliminating degradation and uncovering ion-trapping dynamics in electrochromic WO3 thin films

2015

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Amorphous WO3 thin films are of keen interest as cathodic electrodes in transmittance-modulating electrochromic devices. However, these films suffer from ion-trapping-induced degradation of optical modulation and reversibility upon extended Li+-ion exchange. Here, we demonstrate that ion-trapping-induced degradation, which is commonly believed to be irreversible, can be successfully eliminated by constant-current-driven de-trapping, i.e., WO3 films can be rejuvenated and regain their initial highly reversible electrochromic performance. Pronounced ion-trapping occurs when x exceeds ~0.65 in LixWO3 during ion insertion. We find two main kinds of Li+-ion trapping sites (intermediate and deep) in WO3, where the intermediate ones are most prevalent. Li+-ions can be completely removed from intermediate traps but are irreversibly bound in deep traps. Our results provide a general framework for developing and designing superior electrochromic materials and devices.

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“…A previous study of aWO 3 , employing the same electrolyte and similar samples to those used in the present work, approximated the position of the conduction band edge at about 3.05 V vs. Li/Li + . 31 Therefore, the features at potentials above this value in Fig. 5(b) occur at electron energies below the conduction band edge.…”

Section: Resultsmentioning

confidence: 84%

Differential coloration efficiency of electrochromic amorphous tungsten oxide as a function of intercalation level: Comparison between theory and experiment

Rojas-González,

Niklasson

2020

Preprint

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Optical absorption in amorphous tungsten oxide (aWO 3 ), for photon energies below that of the band gap, can be rationalized in terms of electronic transitions between localized states. For the study of this phenomenon, we employed the differential coloration efficiency concept, defined as the derivative of the optical density with respect to the inserted charge. We also made use of its extension to a complex quantity in the context of frequency-resolved studies. Combined in situ electrochemical and optical experiments were performed on electrochromic aWO 3 thin films for a wide lithium intercalation range using an optical wavelength of 810 nm (1.53 eV). Quasi-equilibrium measurements were made by chronopotentiometry (CP). Dynamic frequency-dependent measurements were carried out by simultaneous electrochemical and color impedance spectroscopy (SECIS). The differential coloration efficiency obtained from CP changes sign at a critical intercalation level. Its response exhibits an excellent agreement with a theoretical model that considers electronic transitions between W 4+ , W 5+ , and W 6+ sites. For the SECIS experiment, the low-frequency limit of the differential coloration efficiency shows a general trend similar to that from CP. However, it does not change sign at a critical ion insertion level. This discrepancy could be due to degradation effects occurring in the films at high Li + insertion levels. The methodology and results presented in this work can be of great interest both for the study of optical absorption in disordered materials and for applications in electrochromism.

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Determination of electronic structure by impedance spectroscopy

Cited by 13 publications

References 18 publications

Electrochemical measurements of the electronic density of states

Electrochemical measurements of the electronic density of states

Eliminating degradation and uncovering ion-trapping dynamics in electrochromic WO3 thin films

Differential coloration efficiency of electrochromic amorphous tungsten oxide as a function of intercalation level: Comparison between theory and experiment

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