Ferroelectric Properties of Stable and Metastable Phase-III KNO3

Abstract

The ferroelectric properties of stable phase-III polycrystalline and single-crystal KNO3 have been studied at temperatures up to 150°C and hydrostatic pressures up to 20 000 psi. Results obtained show phase III has two Curie points, the upper increasing and the lower decreasing with pressure. At constant temperature near the center of phase III, the polarization increases linearily with pressure at 0.007 μC/cm2/atm. Within the stable phase-III region, KNO3 suffers no shelf or excitation decay, has a significant t* effect with a power-law E dependence, and has its switching speed decrease exponentially (τ≃10 sec) as the time between reversals increases. Disturb-pulse measurements show that the exponential high-E dependence of the switching time continues down to low E with an eventual reduction of α. Switching times as long as 10 min have been observed at low E. For typical matrix memory operation, only about 103 disturb pulses can be tolerated. The indications of a threshold field seen in metastable phase-III KNO3 appear to be due to field-induced ferroelectricity.