Thermal conductivity of solid parahydrogen with methane admixtures

The thermal conductivity of a solid parahydrogen crystal with methane admixtures was measured in the temperature range 1.5 to 8 K. Solid samples were grown from the gas mixtures at 13 K. The concentration of CH4 admixture molecules in the gas varied from 5 to 570 ppm. A very broad thermal conductivity peak with an absolute value of about 110 W/(m⋅K) was observed at 2.6 K. The data were interpreted using Callaway’s model with resonance scattering of phonons by quasilocal vibrations of CH4 molecules and phonon–grain boundary and phonon–phonon scattering. As grain boundary scattering increases, the broadening of the peak decreases. The analysis shows that a solid mixture of p-H2 and CH4 is a heterogeneous solution for CH4 concentration higher than 0.1 ppm.