Determination of in‐plane thermal conductivity of Na x Co 2 O 4 single crystals via a parallel thermal conductance (PTC) technique

A novel parallel thermal conductance (“PTC”) system was specifically developed to conduct the steady state thermal conductivity measurement on small size samples such as single crystals of Na x Co 2 O 4 as reported here. The accuracy and reproducibility of the PTC system has been confirmed by measuring several standard reference materials. The in‐plane thermal conductivity κ of Na x Co 2 O 4 single crystals grown by a NaCl flux method was measured from 10 K to 300 K and κ was found to be ∼5 W m –1 K –1 at 300 K. The phonon mean free path (MFP) is estimated to be l ph ∼ 9 Å at 300 K, which is comparable to the lattice constant but much smaller than the reported MFP of conducting carriers. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)