Quadrupolar interactions in non-cubic crystal and related extra heat capacities. Possible effects on a sapphire bolometer

It is shown that in a non-cubic crystal, the extra heat capacity due to quadrupolar interaction of nuclear spins >12 could be much bigger than the phonon heat capacity when the temperature decreases. The possible coupling between quadrupolar and phonon heat reservoir via paramagnetic impurities is stressed. A NMR experiment done on sapphire is presented with an evaluation of the coupling between the two reservoirs and its consequence on the performance of the bolometer.