INVESTIGATION OF THE INFLUENCE OF DEFECTS ON THE HEAT CONDUCTIVITY OF NON-METALLIC CRYSTALS, PARTICULARLY SUBSTITUTED ALUMINUM OXIDE (A1203).
Final technical rept., 1 Aug 62-31 Jul 63,
OXFORD UNIV (ENGLAND)
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Work has been done on gold-iron as an element for thermocouples. With spectroscopically pure gold as starting material not only is the sensitivity likely to be more reproducible from piece to piece, but also the effects of magnetic fields appear to be more nearly universal functions of the ratio of magnetic field to absolute temperature. The most complete set of heat conductivity measurements are those made on lanthanum cobalt nitrate, to study the interaction between the spin system and the lattice. At low temperatures the only energy levels occupied by the cobalt ions consist of a Kramers doublet, which is not split in the absence of a magnetic field. The thermal conductivity is then similar to that of other dielectric crystals, and for the specimens measured seems to be dominated by the presence of dislocations. In a magnetic field the ground state is split and phonons of the appropriate energy can be absorbed and emitted by transitions within the spin system. Author