Temperature-dependent IR reflectance investigations of the organic superconductor (BEDO-TTF)2 ReO4(H2O)

Polarized reflectivity spectra of single crystals of (BEDO-TTF)2ReO4(H2O) (BEDO-TTF = bis(ethylenedioxy)tetrathiafulvalene) were measured in the spectral range from 500 to 8500 cm−1 at six temperatures between 300 and 20 K. The polarization of the incident radiation was arranged parallel and perpendicular to the stacking axis of the donor molecules. The temperaturedependent reflectivity and the optical conductivity are presented. Changes at the metal-metal phase transition at 213 K and the metalsemiconductor phase transition at 35 K are discussed. The Drude parameters of the conduction electrons were obtained by fitting the reflectance data with a DrudeLorentz model, indicating that both phase transitions are accompanied by an abrupt change of the relaxation constant of the free charge carriers. Both phase transitions have an effect on the vibrational spectra and possible changes of the crystal structure at the phase transitions are discussed.