Electrical and Thermal Transport Properties of the beta-Pyrochlore Oxide CsW2O6

TL;DR

This study investigates the electrical, thermal, and thermoelectric properties of CsW2O6, revealing incoherent electron conduction in Phase I and a transition to semiconducting behavior with a band gap in Phase II.

Contribution

It provides detailed measurements of transport properties of CsW2O6, highlighting phase-dependent conduction mechanisms and low thermal conductivity due to lattice rattling.

Findings

In Phase I, electron conduction is incoherent and hopping-like.

Thermal conductivity is low in both phases, possibly due to Cs+ rattling.

A phase transition at 215 K leads to semiconducting behavior with a band gap.

Abstract

We report the electrical resistivity, thermoelectric power, and thermal conductivity of single-crystalline and sintered samples of the 5d pyrochlore oxide CsW2O6. The electrical resistivity of the single crystal is 3 mohm cm at 295 K and gradually increases with decreasing temperature above 215 K (Phase I). The thermoelectric power of the single-crystalline and sintered samples shows a constant value of approximately -60 uV K-1 in Phase I. These results reflect that the electron conduction by W 5d electrons in Phase I is incoherent and in the hopping regime, although a band gap does not open at the Fermi level. The thermal conductivity in Phase I of both samples is considerably low, which might be due to the rattling of Cs+ ions. In Phase II below 215 K, the electrical resistivity and the absolute value of thermoelectric power of both samples strongly increase with decreasing temperature, corresponding to a transition to a semiconducting state with a band gap open at the Fermi level, while the thermal conductivity in Phase II is smaller than that in Phase I.