Concerning the first-order phase transition in the low-dimensional organic superconductor (BEDO—TTF)2ReO4 · H2O. Crystal and electronic band structures below the phase transition (T = 170 K)

The effect of the first-order phase transition occurring around 220 K on the crystal and electronic structure of the molecular superconductor (BEDO-TTF) has been studied. The crystal structure at 170 K has been determined and it is found that the main structural change resulting from the phase transition is connected with a rotation of the anions. This rotation leads to changes in the SS and SO intermolecular contacts within the BEDO-TTF donor layers. How these structural changes affect the electronic structure of the salt is studied by comparing the transfer integrals for the different donordonor intermolecular interactions calculated for the room temperature and 170 K crystal structures. It is shown that Fermi surfaces for the 170 K and room temperature structures are very similar, do not exhibit nesting properties, and can be described as resulting from the hybridization of superposing ellipses. Received: 4 September 1997 / Received in final form: 2 December 1997 / Accepted: 3 December 1997