Thermodynamic properties of BaCeO3 and BaZrO3 at low temperatures

Specific heat capacities (C-p) of polycrystalline samples of BaCeO3 and BaZrO3 have been measured from about 1.6 K up to room temperature by means of adiabatic calorimetry. We provide corrected experimental data for the heat capacity of BaCeO3 in the range T < 10 K and, for the first time, contribute experimental data below 53 K for BaZrO3. Applying Debye's T-3-law for T -> 0 K, thermodynamic functions as molar entropy and enthalpy are derived by integration. We obtain C-p = 114.8 (+/- 1.0) J mol(-1) K-1, S degrees = 145.8 (+/- 0.7) J mol(-1) K-1 for BaCeO3 and C-p = 107.0 ( +/- 1.0) J mol(-1) K-1, S degrees = 125.5 (+/- 0.6) J mol(-1) K-1 for BaZrO3 at 298.15 K. These results are in overall agreement with previously reported studies but slightly deviating, in both cases. Evaluations of C-p(T) yield Debye temperatures and identify deviations from the simple Debye-theory due to extra vibrational modes as well as anharmonicity. The anharmonicity turns out to be more pronounced at elevated temperatures for BaCeO3. The characteristic Debye temperatures determined at T= 0 K are Theta(0) = 365 (+/- 6) K for BaCeO3 and Theta(0) = 402 (+/- 9) K for BaZrO3. (c) 2006 Elsevier B.V. All rights reserved.