Anomalous thermal conductivity of NaV2O5 as compared to conventional spin-Peierls system CuGeO3

A huge increase of thermal conductivity kappa is observed at the phase transition in NaV2O5. This anomaly decreases and gradually disappears with x in Na1-xV2O5 (x = 0.01, 0.02, 0.03, and 0.04). This behavior is compared with that of pure and Zn-doped CuGeO3, where only modest kinks in the kappa(T) curves are observed at the spin-Peierls transition. The change of kappa at T-c could be partially attributed to the opening of an energy gap Delta in the magnetic excitation spectrum excluding the scattering of thermal phonons on spin fluctuations. However, the reason for a strong anomaly in the kappa(T) may lie in the different character of the phase transition in NaV2O5 which can have largely a structural origin, e.g., connected with the charge ordering.