Sequence of phase transitions in a quasi-one-dimensional β-Na _0.33V₂O₅ compound with variable valence

The thermal properties - specific heat, thermal conductivity, and thermal expansion coefficients - of a single crystal of quasi-one-dimensional variable-valence β-Na_0.33V₂O₅ compound were studied. With lowering temperature, it sequentially undergoes the structural (T_S ∼ 230 K), charge (T_C ∼ 136 K), and magnetic (T_N ∼ 22 K) phase transitions. The structural transition at T_S, resulting in the ordering of the Na ions, and the charge ordering at T_C, resulting in the charge redistribution over the positions of V ions, are accompanied by the anomalies in the temperature dependences of all the studied properties. The magnetic ordering at T _N results in the appearance of the canted antiferromagnetic structure and manifests itself only in the anomaly in the temperature dependences of the thermal expansion coefficients.