High Specific Heat Dielectrics and Kapitza Resistance at Dielectric Boundaries

摘要

This program has two efforts: Kapitza and thermal properties studies. Two separate Kapitza conductance test facilities have been designed and fabricated for both solid solid and for solid liquid HE II measurements. Preliminary data has been obtained for copper to T lambda C lambda interface conductance and also for KBr and LiF thermal conductance to Helium II. For the latter two materials, the test dewars were designed to allow cleaving of the samples under liquid helium. The Kapitza conductance of both samples was very near the phonon radiation limit providing strong evidence that the anomalous Kapitza conductance is not the result of surface contamination. Thermal properties work has included the measurement of the specific heat and thermal conductivity of the CdCr2O4 spinels and of several CsC lambda structure heavy metal halides in the temperature range of 1.5 to 35K. The specific heat data for the spinels was analyzed in terms of both lattice phonons and magnetic contributions. The dependence of the spinel's thermal conductivity on magnetic fields up to 15T was studied and magnetocaloric data has been obtained. For both the Zn and Cd spinels, the lattter results showed a paramagnetic behavior with demagnetization cooling and magnetization heating. Theory has been developed to explain some of the magnetocaloric effects in the new spinels, CdCr2O4 and ZnCr2O4.