Electrocaloric Effect in Doped Alkali Halides

Electric cooling with the polarizable impurities ${\mathrm{Li}}^{+}$ and ${\mathrm{OH}}^{-}$ in KCl and ${\mathrm{CN}}^{-}$ in RbCl has been measured in the temperature region where the tunnel splitting of the motional ground states of these impurities becomes the limiting factor. In KCl:Li, quantitative agreement with the theoretically expected cooling is demonstrated. The cooling in KCl:OH and RbCl:CN also agrees with the models based on the known tunnel splitting and polarizability. The possibility of using these impurities for practical cooling is discussed.