Phase behaviour and quasi-one dimensionality of betaine arsenate/phosphate mixed crystals

Abstract

The temperature dependence (24 K < T < 300 K) of the complex permittivity in a ferroelectric mixed crystal has been studied. In order to tune the intermolecular dipolar interactions and to study the stability and kinetics of the different phases of the crystal under investigation, we performed measurements under application of hydrostatic pressures (p < 350 MPa), biasing fields , and different measurement frequencies . These experiments allowed us to depict the corresponding pressure - temperature and electric field - temperature anomaly diagrams of the crystal investigated. Furthermore, in order to analyse the changes in the dipolar system accompanying the dielectric anomalies, we performed dielectric hysteresis measurements. These measurements finally enabled us to identify the character of the phase transitions and the corresponding changes in the dipole system accompanying the dielectric anomalies. A high-temperature transition into an antiferroelectrically ordered phase followed by a re-entrant glassy phase has been found. The high-temperature antiferroelectric transition is discussed in the framework of the quasi-one-dimensional Ising model and compared to the corresponding transitions of the pure compounds, ferroelectric betaine arsenate (BA) and antiferroelectric betaine phosphate (BP), respectively. The low-temperature transition into the re-entrant glassy phase is treated according to the frequency-dependent shift of its indicating anomaly by means of an Arrhenius versus Vogel - Fulcher analysis.