Neutron-diffraction evidence for structural phase transitions in the organic conductors bis-tetramethyltetraselenafulvalenium salts [(TMTSF)2X,X=ClO4 −andBF4−

Abstract

Single-crystal neutron-diffraction experiments using the time-of-flight Laue technique establish that organic conductors, bis-tetramethyltetraselenafulvalenium salts [${(\mathrm{TMTSF})}_{2}X$, $X={\mathrm{ClO}}_{4}^{ \ensuremath{-}}$ and ${\mathrm{BF}}_{4}^{\ensuremath{-}}$], undergo crystallographic phase transitions at low temperatures. This is the first neutron-diffraction evidence for structural phase transitions in any TMTSF salts. The phase transition in the ${\mathrm{ClO}}_{4}^{\ensuremath{-}}$ salt leads to the creation of two crystallographically independent TMTSF columns with the possibility of different electrontransport properties for each column which can lead to independent low-temperature phase transitions.