Specific Heat of NaV_<b>6</b>O_<b>11</b>Single Crystals

Abstract

The specific heat of NaV 6 O 11 single crystal was investigated with an AC calorimeter. Lambda type anomalies at 64.3, 80.1 and 242.7 K were observed. It is found that the transition temperature of the P6 3 /mmc - P6 3 mc structural transition is 242.7 K, which has been reported to occur at a temperature between 200 K and room temperature. The anomalies at 64.3 and 242.7 K coincide well with the two magnetic transitions previously reported. Present specific heat study coupled with single crystal X-ray diffraction data reveals that the P6 3 mc - Cmc2 1 structural transition occurs at 80.1 K and accompanies the kink in the resistivity. Previous study reported that the P6 3 mc - Cmc2 1 structural transition occurs at 35–40 K, however no anomaly in the specific heat was observed at 35–40 K in this study.