UBC Theses and Dissertations
Thermal conductivity of solid helium mixtures in the phase separation region Burgess, Arthur Edwin
The thermal conductivities of four solid helium mixtures have been measured in the temperature range between 0.15 K and 0.6 K. These are the first measurements of the transport properties of solid helium mixtures in the phase separation region. A dilution refrigerator and a novel temperature controller were constructed to obtain the necessary temperatures and temperature stability. The thermal conductivity measurements above the phase separation were consistent with present theories of conduction in isotopic mixtures. Just below the phase separation temperature the conductivity decreased rapidly with decreasing temperature. Below the phase separation, the conductivity was limited by boundary scattering and is interpreted in terms of a model of phonon scattering by domains rich in one isotope embedded in a matrix rich in the other isotope. Phonon scattering by metastable domains of one crystal structure embedded in a matrix of another crystal structure has been observed above the phase separation.
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