Electrocaloric effect in potassium dihydrogen phosphate

Measurements of the electrocaloric effect from 78 to 130 K were made on crystalline KH2PO4and are discussed in terms of the phenomenological theory of Devonshire and others. The predicted quadratic dependence of the electrocaloric effect upon applied field (and polarization) in the paraelectric phase was shown to occur; however, the constant of proportionality involved coincided with the value computed from Curie-Weiss law only at the highest temperatures. The electrocaloric effect in the ferroelectric phase was found to be approximately a linear function of the applied field provided the low-field irreversible region of hysteresis was ignored. Values of the spontaneous polarization were determined from the electro-caloric measurements and found to be in good agreement with the values obtained by extrapolating the hysteresis loops to zero field. If the Curie-Weiss term in the Devonshire free-energy expansion is retained when the crystal is in its ferroelectric phase, then evidently a single Devonshire function will not describe KH2PO4in both the ferroelectric and paraelectric phases.