Dependence of the specific heat of NaxCoO2 center dot yH(2)O/D2O on sodium and water concentrations

作者：Jin R^*; Sales BC; Li S; Mandrus D

来源：Physical Review B, 2005, 72(6): 060512.

DOI：10.1103/PyhsRevB.72.060512

We report specific heat measurements down to 0.4 K on the layered oxide Na(x)CoO(2)center dot yH(2)O/D2O with 0 <= x <= 0.74 and y=0 and 1.4. For the nonhydrated system (y=0), the electronic specific heat coefficient gamma(N) and the Debye temperature Theta(D) vary nonmonotonically with x, both displaying minima when x is close to 0.5. This indicates a systematic change of the electronic and vibrational structures with Na content. For both hydrated and deuterated systems (x=0.35 and y=1.4), the specific heat reveals a sharp peak with Delta C(p)similar to 45.5 mJ/mol K at T (mid)(c)similar to 4.7 K and an anomaly at T(x)similar to 0.8 K. While the origin of the latter is not clear, the former corresponds to the superconducting transition. With the application of magnetic fields up to 14 Tesla, T-c decreases gradually but T-x remains more or less unchanged. The implication of these results is discussed.

• 出版日期2005-8