On the heat capacity of Ti3GeC2

In this paper, we report experimental data of the heat capacities, c, of bulk polycrystalline samples of Ti3GeC2 in the 3-260 K temperature range. The results obtained are compared with those on Ti3SiC2. The c(p) results are analyzed using the Debye and Einstein models and are compared to the heat capacities values calculated from first principles. At temperatures up to 10 K the main contributors to cp are electrons with gamma = 6.5 (mJ/mol K-2) and phonons with a Debye temperature OD of 556 K. In that temperature range only four atoms of the six in a formula unit-most likely one Ge and three Ti atoms-contribute to cp. In the 10- 120 K temperature range excellent fits were obtained using a theta(D) of 513 K and an optical mode with an Einstein temperature theta(E) of 139 K. For T > 120 K, five additional optical modes with theta(E) = 870 K are required to properly fit the experimental results. The ab initio calculations throughout the temperature range (4-1500 K) show reasonably good agreement with the experimental data obtained particularly at low temperatures. (c) 2005 Elsevier B.V. All rights reserved.