  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.

Materials Science