TEMPERATURE-DEPENDENT IR REFLECTANCE INVESTIGATIONS OF THE ORGANIC SUPERCONDUCTOR (BEDO-TTF)(2)REO4(H2O)

Polarized reflectivity spectra of single crystals of (BEDO-TIF)(2)ReO4 (H2O) (BEDO-TIF = bis(ethylenedioxy) tetrathiafulvalene) were measured in the spectral range from 500 to 8500 cm(-1) at six temperatures bet ween 300 and 20 K. The polarization of the incident radiation was arra nged parallel and perpendicular to the stacking axis of the donor mole cules, The temperature-dependent reflectivity and the optical conducti vity are presented, Changes at the metal-metal phase transition at 213 K and the metal-semiconductor phase transition at 35 K are discussed, The Drude parameters of the conduction electrons were obtained by fit ting the reflectance data with a Drude-Lorentz model, indicating that both phase transitions are accompanied by an abrupt change of the rela xation constant of the free charge carriers. Both phase transitions ha ve an effect on the vibrational spectra and possible changes of the cr ystal structure at the phase transitions are discussed.