Thermal conductivity of solid parahydrogen with methane admixtures

TL;DR

This study measures the thermal conductivity of solid parahydrogen with methane admixtures at very low temperatures, revealing a broad maximum around 2.6 K and analyzing phonon scattering mechanisms.

Contribution

It provides the first detailed measurements of thermal conductivity in solid p-H2 with methane admixtures and interprets the data using the Callaway model considering multiple phonon scattering processes.

Findings

Thermal conductivity peaks at about 110 W/(m·K) near 2.6 K.

Methane admixtures cause broadening of the thermal conductivity maximum.

Solid p-H2 with CH4 is a heterogeneous solution for concentrations above 0.1 ppm.

Abstract

The thermal conductivity of solid parahydrogen crystal with methane admixtures has been measured in the temperature range 1.5 to 8 K. Solid samples were grown from the gas mixture at 13 K. Concentration of CH4 admixture molecules in the gas varied form 5 to 570 ppm. A very broad maximum of thermal conductivity with absolute value of about 110 W/(m K) is observed at 2.6 K. The data are interpreted by Callaway model considering phonons resonant scattering on quasi-local vibrations of CH4 molecules, phonon-grain boundary and phonon-phonon scattering processes. The increase of grain boundary scattering leads to the decrease of the maximum broadening. The analysis shows that the solid mixture of p-H2 and CH4 is a heterogeneous solution for CH4 concentration higher than 0.1 ppm.