Elastic neutron-scattering study of the three low-temperature transitions in tetrathiafulvalenium-tetracyanoquinodimethanide

Elastic neutron-scattering measurements of the satellite structure of tetrathiafulvalenium-tetracyanoquinodimethanide show the existence of phase transition points at 38, 48.5, and 54 K. All of the low-temperature phases are incommensurate with a 0.295 component along $b^{*}$ but differ as to their modulation along the $a^{*}$ axis. These results are interpreted within the framework of a theory by Bak and Emery. An unusual hysteresis behavior in the intermediate phase between 38.5 and 48.5 K is reported. Measurements on satellites with a component of 0.59 along $b^{*}$ for the lowest temperature phase are also discussed.