X‐ray diffraction studies have been carried out on carbon monoxide in the temperature range of 8 to 63 °K. The analysis of the Bragg reflection intensity has shown that the α‐CO structure belongs to the space group Pa3. From the data of the temperature dependence of the lattice parameter the molar volume thermal expansion coefficient has been calculated and the heat capacity Cv and Grüneisen coefficient γ were found. The heat capacity component Cvlib due to angular vibrations of the molecules has been separated. The temperature dependence found for Cvlib and γ is in good agreement with that calculated in the molecular field approximation for a libron subsystem of the crystal, where anharmonic librations and lattice thermal expansion are taken into account.
X-ray (300 K) and ultrasonic (77–270 K) studies and measurements of the thermal conductivity (30–300 K) are carried out on single-crystal samples of NdGaO3 in different crystallographic directions. The values of the lattice parameters of NdGaO3 are refined. The sound velocities in the principal crystallographic directions are measured, and the elastic constants and Debye temperature are calculated. The observed anisotropy of the thermal conductivity is described in the framework of a gaskinetic model and is linked to the anisotropy of the interaction parameters of the acoustical and optical phonons.
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