Anomalous Thermal Conductivity ofNaV2O5as Compared to Conventional Spin-Peierls SystemCuGeO3

A huge increase of thermal conductivity $\kappa$ is observed at the phase transition in ${\mathrm{NaV}}_2{\mathrm{O}}_5$. This anomaly decreases and gradually disappears with x in ${\mathrm{Na}}_{1-x}{\mathrm{V}}_2{\mathrm{O}}_5$ ( $x=0.01\mathrm{}$, $0.02$, $0.03$, and $0.04$). This behavior is compared with that of pure and Zn-doped ${\mathrm{CuGeO}}_3$, where only modest kinks in the $\kappa \left(T\right)$ 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 $\kappa \left(T\right)$ may lie in the different character of the phase transition in ${\mathrm{NaV}}_2{\mathrm{O}}_5$ which can have largely a structural origin, e.g., connected with the charge ordering.