Thermal conductivity of solid NH3 and ND3▪ Discovery and investigation of libron heat transport

Results are presented of an experimental and theoretical study of the features of heat transport in solid NH3 and ND3 in the premelting temperature region. It was found that the thermal conductivity of ND3 near the triple point, as distinct from NH3, does not fall as the temperature rises, but increases. It was established that the observed anomaly is brought about by a contribution from libron modes to heat transport, associated with rotation of the molecules about the threefold axes. A theoretical analysis has been carried out of the collision processes of quasiparticles which lead to the anomalous λ(T) dependence. It is shown that the increase in thermal conductivity of ND3 is produced by a rapid softening of the libron branches carrying heat, which leads to a reduction near Ttr of the probability of phonon–libron interactions. The apparatus and the method of studying the thermal conductivity of cryocrystals in the premelting temperature region are described.

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