Low Temperature Behaviour of Betaine Phosphate-Betaine Arsenate Mixed Crystals

Abstract

The mixed system of betaine arsenate and betaine phosphate (BP)_x(BA)_1−x displays, at low temperatures, dielectric anomalies that have been tentatively associated to re-entrant glass phases. In this work, we report results obtained for the composition x = 0.52. The temperature dependence of the complex dielectric constant, polarization hysteresis loops and pyroelectric currents reported prove that an effective ergodicity breaking occurs in the antiferroelectric phase and show that this phase is destabilized at low temperatures. There is also evidence for a high internal bias field, in the whole temperature range studied. Infrared and Raman spectroscopy indicate that the various dielectric anomalies observed reflect structural transformations.

Keywords:

• Mixed systems
• dipolar glasses
• ferro-antiferroelectricity
• Raman and infrared spectra

Acknowledgements

The authors are grateful to A. Costa for his technical assistance. This work was supported by the project POCTI/P/FIS/14287/98.