LATTICE-DISTORTIONS IN TETRATHIOFULVALINIUM BROMIDE [(TTF)BR0.74-0.79]

The crystal structure of tetrathiafulvalene bromide [(TTF)Br0.74-0.79] consists of incommensurate cation and anion sublattices. Each of the sublattices experiences a periodic potential due to the presence of the other sublattice. We find that the TTF sublattice experiences the largest potential, with an amplitude of 75 meV for (TTF)Br0.787. The resultant distortion of the TTF lattice consists of periodic modulation of the positions and angles of the TTF molecules, with the same period as that of the bromine chains. The amplitude of the translational modulation is estimated to be 0.08 for (TTF)Br0.787, and the gap in the TTF phonon spectrum is calculated to be 1.3 meV. © 1979 The American Physical Society.