Ideal Paraelectric Refrigeration in KCl: OH and RbCl: CN

Abstract

The Carnot‐cycle refrigeration characteristics of two probable paraelectric refrigerators KCl: OH and RbCl: CN are studied, according to a thermodynamic model which appears to be basically correct for describing electrocaloric phenomena in these doped salts. A high‐temperature reservoir at 1.11°K is assumed for comparison with actual magnetic and He‐dilution refrigerators, and the operating characteristics of the paraelectric refrigerators are optimized with respect to the dopant concentration. Published values for the zero‐field splitting, dipole moment, specific‐heat coefficient, and dielectric constant of these salts are employed. The lowest calculated temperatures achievable with these model refrigerators are 0.19° and 0.03°K for KCl: OH and RbCl: CN, respectively; and the estimated maximum power obtainable places the RbCl: CN model refrigerator between the He‐dilution and magnetic (iron‐ammonium‐alum) refrigerators in refrigerating capacity. It is shown that, although the zero‐field splitting determines the lowest achievable temperature, the dipole correlations limit the refrigeration capacity.