Advanced

Donor-anion interactions at the charge localization and charge ordering transitions of (TMTTF)(2)AsF6 probed by NEXAFS

Medjanik, Katerina LU ; Chernenkaya, A.; Nepijko, S. A.; Öhrwall, Gunnar LU ; Foury-Leylekian, P.; Alemany, P.; Canadell, E.; Schoenhense, G. and Pouget, J. -P. (2015) In Physical Chemistry Chemical Physics 17(29). p.19202-19214
Abstract
High-resolution near-edge X-ray absorption fine structure (NEXAFS) measurements at the As M-edge, F K-edge and S L-edge of the Fabre salt (TMTTF)(2)AsF6 were performed from room temperature (RT) to 90 K, allowing to reach the charge localization regime below T-rho approximate to 230 K and to cross the charge ordering (CO) transition at T-CO approximate to 102 K. The F K-edge and S L-edge spectra exhibit several transitions which have been indexed on the basis of first-principles DFT calculations. Upon cooling from RT significant energy shifts up to +0.8 eV and -0.4 eV were observed in transitions exhibited by the F 1s and S 2p spectra respectively, while the As 3p doublet does not show a significant shift. Opposite energy shifts found in... (More)
High-resolution near-edge X-ray absorption fine structure (NEXAFS) measurements at the As M-edge, F K-edge and S L-edge of the Fabre salt (TMTTF)(2)AsF6 were performed from room temperature (RT) to 90 K, allowing to reach the charge localization regime below T-rho approximate to 230 K and to cross the charge ordering (CO) transition at T-CO approximate to 102 K. The F K-edge and S L-edge spectra exhibit several transitions which have been indexed on the basis of first-principles DFT calculations. Upon cooling from RT significant energy shifts up to +0.8 eV and -0.4 eV were observed in transitions exhibited by the F 1s and S 2p spectra respectively, while the As 3p doublet does not show a significant shift. Opposite energy shifts found in the F 1s and S 2p spectra reflect substantial thermal changes in the electronic environment of F atoms of the anion and S atoms of TMTTF. The changes found around the charge localization crossover suggest an increase of the participation of the S d orbitals in the empty states of TMTTF as well as an increase of the strength of donor...anion interactions. A new F 1s pre-edge signal detected upon entry into the CO phase is a clear fingerprint of the symmetry breaking occurring at TCO. We propose that this new transition is caused by a substantial mixing between the HOMO of the AsF6- anion and the unoccupied part of the TMTTF HOMO conduction band. Analysis of the whole spectra also suggests that the loss of the inversion symmetry associated with the CO is due to an anion displacement increasing the strength of S...F interactions. Our data show unambiguously that anions are not, as previously assumed, innocent spectators during the electronic modifications experienced by the Fabre salts upon cooling. In particular the interpretation of the spectra pointing out a thermally dependent mixing of anion wave functions with those of the TMTTF chains demonstrates for the first time the importance of anion-donor interactions. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Physical Chemistry Chemical Physics
volume
17
issue
29
pages
19202 - 19214
publisher
Royal Society of Chemistry
external identifiers
  • pmid:26135020
  • wos:000358207400035
  • scopus:84937231547
ISSN
1463-9084
DOI
10.1039/c5cp02902c
language
English
LU publication?
yes
id
6da5ee23-210a-4db4-a6e6-43a67138a355 (old id 7779616)
date added to LUP
2015-09-18 11:39:00
date last changed
2017-08-27 05:01:04
@article{6da5ee23-210a-4db4-a6e6-43a67138a355,
  abstract     = {High-resolution near-edge X-ray absorption fine structure (NEXAFS) measurements at the As M-edge, F K-edge and S L-edge of the Fabre salt (TMTTF)(2)AsF6 were performed from room temperature (RT) to 90 K, allowing to reach the charge localization regime below T-rho approximate to 230 K and to cross the charge ordering (CO) transition at T-CO approximate to 102 K. The F K-edge and S L-edge spectra exhibit several transitions which have been indexed on the basis of first-principles DFT calculations. Upon cooling from RT significant energy shifts up to +0.8 eV and -0.4 eV were observed in transitions exhibited by the F 1s and S 2p spectra respectively, while the As 3p doublet does not show a significant shift. Opposite energy shifts found in the F 1s and S 2p spectra reflect substantial thermal changes in the electronic environment of F atoms of the anion and S atoms of TMTTF. The changes found around the charge localization crossover suggest an increase of the participation of the S d orbitals in the empty states of TMTTF as well as an increase of the strength of donor...anion interactions. A new F 1s pre-edge signal detected upon entry into the CO phase is a clear fingerprint of the symmetry breaking occurring at TCO. We propose that this new transition is caused by a substantial mixing between the HOMO of the AsF6- anion and the unoccupied part of the TMTTF HOMO conduction band. Analysis of the whole spectra also suggests that the loss of the inversion symmetry associated with the CO is due to an anion displacement increasing the strength of S...F interactions. Our data show unambiguously that anions are not, as previously assumed, innocent spectators during the electronic modifications experienced by the Fabre salts upon cooling. In particular the interpretation of the spectra pointing out a thermally dependent mixing of anion wave functions with those of the TMTTF chains demonstrates for the first time the importance of anion-donor interactions.},
  author       = {Medjanik, Katerina and Chernenkaya, A. and Nepijko, S. A. and Öhrwall, Gunnar and Foury-Leylekian, P. and Alemany, P. and Canadell, E. and Schoenhense, G. and Pouget, J. -P.},
  issn         = {1463-9084},
  language     = {eng},
  number       = {29},
  pages        = {19202--19214},
  publisher    = {Royal Society of Chemistry},
  series       = {Physical Chemistry Chemical Physics},
  title        = {Donor-anion interactions at the charge localization and charge ordering transitions of (TMTTF)(2)AsF6 probed by NEXAFS},
  url          = {http://dx.doi.org/10.1039/c5cp02902c},
  volume       = {17},
  year         = {2015},
}