The roles of the donor (tetrathiafulvalene, TTF) and acceptor (tetracyanoquinodimethane, TCNQ) stacks in the 53- and 38-K phase transitions of TTF-TCNQ and in the phases below each transition are determined by a systematic study of the effects of selectively doping the donor stacks and the acceptor stacks with impurities of similar perturbation strength. Both the magnetic susceptibility and the electrical conductivity of these doped materials were measured as a function of temperature. The experiments indicate that the 53-K transition is a quasi-one-dimensional Peierls transition driven by the acceptor stacks, and that the 38-K transition involves both kinds of stacks but results from long-range order developing on the donor stacks.

• Received 3 June 1976

DOI:https://doi.org/10.1103/PhysRevB.15.3643