Specific heat capacity and thermal conductivity of NdGaO₃and LaAlO₃single crystals at low temperatures

Abstract

For single-crystalline samples of NdGaO3 and LaAlO3 the specific heat capacity cp(T) (temperature ranges 2.24-100 K and 4.35-350 K, respectively) and the thermal conductivity κ(T) (15-300 K) are determined. From an analysis of the specific heat capacity of NdGaO3 the crystalline electric field contribution and the high-temperature tail from the magnetic ordering are extracted. The thermodynamic standard values for enthalpy and entropy at 298.15 K are calculated: H° = 18.40(18) kJ mol-1, S° = 121.0(1.2) J mol-1 K-1 (NdGaO3); H° = 14.57(22) kJ mol-1, S° = 86.6(1.3) J mol-1 K-1 (LaAlO3). Significant contributions to the entropy from the magnetic ordering of the Nd3+ ions are included in the calculation. A recently published value of the standard entropy for the related NdAlO3 is re-evaluated (S° = 105.1(3) J mol-1 K-1) in this context. The thermal conductivity of NdGaO3 at low temperatures is limited by spin-wave scattering, while that of LaAlO3 in the same temperature range is lessened by the short phonon mean free path, which is due to the presence of twin domains.