One Dimensional Electric Conduction Mechanism in Mixed-Valence Complexes

Abstract

The d.c. conductivity a along the chain of —M(II)—XM(IV)X— was observed with crystals of [M(II)(AA)₂3]·[M(IV)(AA)₂X₂]Y₄; M=Pt, Pd, Ni, X=Cl, Br, I, (AA)=(en), (tn), Y=ClO₄, BF₄. Systematic change of [sgrave] from 10⁻⁸ to 10⁻¹⁵ (Ω-cm)⁻¹ with M and X was characterized by an inter-ionic distance δ as [sgrave]∞exp [-αδ]. Its temperature change is expressed as [sgrave](T)=[sgrave]₀ exp [-ΔE/kT] with ΔE=0.4 to 1.4 eV, which is in hν>2ΔE relation for the specturm absorption. Hydrostatic pressure on single crystal induces lattice contraction and [sgrave] enhancement of 10^3±1 times only by 7 kbar, suggesting dominant role of the orbital overlapping on [sgrave]. ESR singnal of g_av=2.15±0.03 was observed for M=Pt, and its anisotropy with c-axis as gτ>g// indicates dz² band contribution. The signal intensity change down to 77 K provides the carrier activation energy Δε=12±1 meV (X=I) and scarce activation number 1 per 10⁴ Pt ion. Hence the conduction is considered as dominantly regulated by hopping process among the localized dz² states with phonon assisted tunneling.