THERMODYNAMICS OF ELECTROCALORIC PHENOMENA IN KCL-OH . PARAELECTRIC COOLING

The thermodynamics of low-temperature electrocaloric phenomena in alkali halides doped with polar impurities is developed, making use of the models for the tunneling splitting, dielectric saturation, and dipole correlations that pertain to KCl: OH. The thermodynamic theory is in good quantitative agreement with published data on the specific heat, adiabatic-depolarization temperature changes, and electrocaloric coefficient for KCl: OH, using a dipole moment of about 3·7 debye (D). The calculated hydroxyl concentrations, however, are consistently somewhat larger than the experimental concentrations. The observed concentration dependences of the final depolarization temperature and of the electrocaloric coefficient are explained quantitatively as arising from the dipole-dipole interactions contribution to the specific heat. The lowest temperature achievable in KCl: OH by the process of adiabatic depolarization is estimated to be 0·205°K (consistent with a tunneling splitting of 0·30°K), starting from an initial temperature of 1·27°K. © 1969.