Local and Spatial Disorder in β‘ ‘-(ET)₂SF₅RSO₃ Solid Solutions (R = CH₂CF₂, CHF, CHFCF₂)

Abstract

We report the polarized infrared reflectance spectra and optical conductivity of β‘ ‘-(ET)2SF5RSO3 superconducting (R = CH2CF2), metallic (R = CHF), and metal−insulator (R = CHFCF2) mixed crystal materials. Incorporation of chiral counterions in the superconducting matrix allows us to tune the physical and spectroscopic properties over the composition range by modulating the anion potential. We conclude that the two low-energy electronic excitations at ≈5200 and 9600 cm-1 are spectral manifestations of charge localization in the ET stack, made manifest by both local (anion pocket) and spatial (positional) disorder.

Vibrational spectra of two BEDT-TTF-based organic conductors: charge order

“…Signatures of the disorderdriven charge localization on the dimerized BEDT-TTF molecules are found both in electronic and vibrational response of β"-(BEDT-TTF) 2 SF 5 CHFCF 2 SO 3 . Thus, the disorder in the anion pocket in this material results in a metal-insulator transition at 175 K. The two disorderrelated low-energy electronic transitions are enhanced in the spectra with both spatial and local disorder [5].…”

“…In the β"-(BEDT-TTF) 2 SF 5 CH 2 CF 2 SO 3 superconductor the anion contains no chiral carbon and the anion pocket is ordered [4]. The anion pocket which comprises SF 5 CH 2 CF 2 SO − 3 ion is formed by spatial organization of the cation layers [5]. Short contacts, which determine a local order, are formed by the BEDT-TTF hydrogen atoms: four to SF 5 fluorine atoms and six to SO 3 oxygen atoms of the anions.…”

“…Electronic characteristics of the organic conductors depend strongly also on the acceptor anion which in some cases can be modified prior to the crystallization process. These effects will be exemplified by the family of organic BEDT-TTF-derived conductors of the general formula (BEDT-TTF) 2 RR'SO 3 , where R = SF 5 , CF 3 , and R' = CH 2 , CF 2 , * Presented at 2-nd International Conference on Functional Materials and Devices, ICFMD 2008, June 16-19, 2008, Kuala Lumpur, Malaysia † E-mail: graja@ifmpan.poznan.pl CHF, CHFCF 2 , CH 2 CF 2 . These salts are based not only on the organic donor but also the organic acceptor.…”

“…These salts are based not only on the organic donor but also the organic acceptor. This family contains materials from a superconductor (with R = SF 5 , and R' = CH 2 CF 2 ) to various semiconductors [1][2][3][4][5][6].…”

Solid-solution (alloying) strategies in crystalline molecular conductors

“…Organic counter-ions offer an increased degree of complexity as reported in the alloys involving Me4Sb + vs. EtMe3Sb + , 67 or SF5CH2CF2SO3 − vs. SF5CHFSO3 − . 88 In these salts, to the positional disorder of the two species on a given crystallographic site for the counter-ion is added a substitutional disorder even more difficult to characterize (see below section 2.4). A specific warning should be made here for reported solid solutions involving the pairs GaCl4 − /GaBr4 − , or FeCl4 − /FeBr4 − .…”