Dynamic charge disproportionation in the 1D chain material PdTeI

Abstract

PdTeI features quasi-1D –Pd–Te–Pd–Te– chains with palladium formally in the 3+ oxidation state. Using pair distribution function analysis of X-ray and neutron total scattering data, we find that there is a local charge-density wave arising from the disproportionation of Pd³⁺ towards Pd²⁺ in pseudo-square planar, and Pd⁴⁺ in pseudo-octahedral, coordination. The magnitude and coherence length for this distortion is small, such that the average structure determined by Bragg diffraction techniques possesses higher symmetry than the local structure at all temperatures. Temperature-dependent resistivity measurements show a transport anomaly at T_CDW = 50 K, corresponding to the reduced fluctuations of the charge separated Pd²⁺ and Pd⁴⁺ sites. At higher temperatures, the charge separation is dynamic, with local Pd²⁺/Pd⁴⁺ pairs persisting up to room temperature.