Specific heat capacity and thermal conductivity ofNdGaO3 and LaAlO3 single crystals at low temperatures

Abstract

For single-crystalline samples of NdGaO3 and LaAlO3 thespecific heat capacity cp(T) (temperature ranges 2.24-100 K and4.35-350 K, respectively) and the thermal conductivity κ(T)(15-300 K) are determined. From an analysis of the specific heat capacityof NdGaO3 the crystalline electric field contribution and thehigh-temperature tail from the magnetic ordering are extracted. Thethermodynamic standard values for enthalpy and entropy at 298.15 K arecalculated: 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 magneticordering of the Nd3+ ions are included in the calculation. A recentlypublished value of the standard entropy for the related NdAlO3 isre-evaluated (S° = 105.1(3) J mol-1 K-1) in this context.The thermal conductivity of NdGaO3 at low temperatures is limited byspin-wave scattering, while that of LaAlO3 in the same temperaturerange is lessened by the short phonon mean free path, which is due to thepresence of twin domains.