Peierls transition of perylene radical cation salts with five-eighth filled conduction band

The Peierls transition of Perylene (PE) radical cation salts (PE)2X1 · 23THF (nominal composition, X = (PF6)1−x(AsF6)x, 0 ⪯ x ⪯ 1, THF = tetrahydrofuran) was analysed by static magnetic susceptibility (χ), radiofrequency and microwave electron spin resonance (ESR), (g-factor, line width ΔB), and microwave conductivity (σ). According to crystal structure analyses, these salts have a five-eighth filled conduction band. The opening of the energy gap at 100 – 120 K (depending on x) was determined by the analysis of χ(T). Additional phase transitions were observed and analysed by the different experimental techniques (χ(T), σ(T), g(T)). Due to the narrow ESR line in the metallic phase (ΔBpp ≅ 15 mG), a reorientation of the PE-stacks at 162 K can be derived precisely via the g-anisotropy. In the low-temperature phase the angular and frequency dependence of the ESR linesʹ boardening is used in order to analyse the interaction between thermally activated conduction electrons and localized defects in these quasi-onedimensional conductors.