Phase transitions of tetraselenafulvalene-tetracyanoquinodimethane: Acceptor-stack doping and the roles of the two kinds of stacks

The roles of the two stacks in the phase transition(s) of tetraselenafulvalene-tetracyanoquinodimethane (TSeF-TCNQ) have been further investigated by means of dc-conductivity experiments on the acceptor-doped material TSeF-(TCNQ)1-y(monomethylTCNQ)y. The temperature of the phase transition in TSeF-TCNQ seen as a peak in dlnRd(1T) at 27 K shifts only marginally with y for 0≤<y0.01. The height of the peak is strongly affected, however, being reduced to half its original value when y=0.003. From these results and earlier results of tetrathiafulvalene doping of the TSeF stacks, we conclude that if the two kinds of stacks have comparable tendencies toward a Peierls instability, then the interstack-hybridization explanation of the low Tc and its dependence on donor doping is in stronger agreement with the acceptor-doping results than is the dynamic-screening explanation. A new, weak, and unexplained resistivity anomaly is also revealed at 21 K for these small values of y, which might also be present in undoped samples. © 1982 The American Physical Society.