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

TL;DR

This paper investigates the significant anomaly in thermal conductivity at the phase transition in NaV2O5, contrasting it with the modest effects observed in CuGeO3, and explores the underlying structural and magnetic factors involved.

Contribution

It reveals the anomalously large thermal conductivity change in NaV2O5 and compares it with CuGeO3, highlighting the role of structural and charge ordering effects.

Findings

Large thermal conductivity increase at phase transition in NaV2O5

Anomaly diminishes with deviation from stoichiometry

Different phase transition mechanisms in NaV2O5 and CuGeO3

Abstract

A huge increase of thermal conductivity k is observed at the phase transition in stoichiometric NaV2O5. This anomaly decreases and gradually disappears with deviation from stoichiometry in Na(1-x}V2O5 (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 k(T) curves are observed at the spin-Peierls transition. The change of k at critical temperature Tc could be partially attributed to the opening of an energy gap in the magnetic excitation spectrum excluding the scattering of thermal phonons on spin fluctuations. However, the reason for such a strong anomaly in the k(T) may lie not only in the different energy scales of CuGeO3 and NaV2O5, but also in the different character of the phase transition in NaV2O5 which can have largely a structural origin, e.g. connected with the charge ordering.