Electronic Studies of KH2PO4

The results of electrocaloric studies of the electrical equation of state of K${\mathrm{H}}_2$P${\mathrm{O}}_4$ in the temperature region within 1 K of the ferroelectric transition are reported. Chief emphasis is given to determination of the spontaneous polarization. A discontinuous polarization jump of 1.87 ± 0.09 μC/${\mathrm{cm}}^2$ is found at $T_c$. Several tests of the validity of the phenomenological theory of ferroelectricity, including a noncalorimetric determination of the heat capacity, are made. It is shown that the phenomenological theory provides a good and consistent description of the thermodynamic behavior of K${\mathrm{H}}_2$P${\mathrm{O}}_4$. No major discrepancies which might be linked to behavior near a phase transition are found. Any possible discrepancies are minor and confined to the temperature region $T_c-T<\mathrm{}0.1\mathrm{}$ K. It is shown that a term proportional to $P^8$ dominates the saturation behavior. Evidence is presented that a portion of the calorimetric anomaly near $T_c$ is not directly related to the temperature dependence of the polarization.