Low thermal conductivity of the negative thermal expansion material, HfMo2O8

Abstract

The thermal conductivity of the cubic polymorph of hafnium molybdate, HfMo2O8, was determined over the temperature range of 2-400 K. The values of thermal conductivity were low (0.64 +/- 0.15 W m(-1) K-1 at T=300 K for a fully dense sample), with a positive temperature coefficient throughout the temperature range examined. Calculations of the theoretical minimum thermal conductivity and the effective phonon mean free path show that the heat-carrying phonons are nearly fully coupled in HfMo2O8, consistent with the rather large magnitude of its Gruneisen parameter. The low-frequency optic modes which lead to negative thermal expansion in HfMo2O8 are likely responsible for the low thermal conductivity. (c) 2007 American Institute of Physics.