X-ray scattering study of charge-density waves in K3Cu8S6.

Abstract

Two phase transitions have previously been identified in K/sub 3/Cu/sub 8/S/sub 6/, a second-order transition at 153 K and a first-order transition at 55 K. In this x-ray scattering study we show that the 153-K transition, which is associated with a decrease in the conductivity, corresponds to the onset of an incommensurate charge-density wave (CDW) with a wave vector of q = (0,(1-delta)/2,0). The 55 K transition, which is accompanied by an increase in the conductivity, results in a significant modification of the host structure and the creation of a superlattice with a commensurate periodicity given by q = ((1/2),(1/2),0). The temperature dependence of the CDW order parameter is unusual. First, at temperatures just above the first-order transition, oscillations in the order parameter as a function of temperature are observed. Similar oscillations have previously been observed in the conductivity and the magnetic susceptibility. Second, like the transport properties, the order parameter shows a large hysteresis (approx.60 K) as the temperature is scanned through the first-order transition.