Phase diagram of the betaine arsenate–betaine phosphate mixed-crystal system by dielectric hysteresis and current curves

Abstract

The ferroelectric (FE) betaine arsenate (BA) and the antiferroelectric (AF) betaine phosphate (BP) are structurally very closely related and mixed crystals of BA(x)BP(1-x) can be grown over the whole concentration range. The concentration (x)-temperature (T)-pressure (P) phase diagram of the system is characterized by a transition from an AF to a FE phase along with the appearance of some mixed regions upon changing concentration. Depending on concentration, one or two relaxation processes appear in the low-temperature region of the phase diagram. Measurement of the hysteresis loops and the current curves have been carried out along the (x-T-P)-phase diagram of this system. Multiple loops have been observed in various regions of the phase diagram. The correlation of the different contributions of the polarization and the temperature behavior of their critical fields with the main features of the temperature- and frequency-dependent dielectric constant enables clarification of the rich phase diagram obtained in this mixed compound in terms of the ferro- and/or antiferroelectric interactions.