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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. [ABSTRACT FROM AUTHOR]

Betaine arsenate (BA) and betaine phosphate (BP) are addition compounds of the amino acid betaine [(CH 3 ) 3 N + CH 2 COO - ] and arsenic and phosphoric acids, respectively. The mixed system (BP) x (BA) 1 - x displays, at low temperatures, dielectric anomalies that have been interpreted as due to additional transitions to re-entrant glass phases originated by frustrated FE and AF interactions. In this work, Raman and infrared spectroscopic data are analysed and compared with results of complex dielectric constant, pyroelectric measurements performed during thermal cycles under different bias electric fields and low frequency polarization hysteresis loops. The results obtained for the x = 0.75 composition do not give any evidence for the stabilisation of a re-entrant glass phase or a non-ergodic regime, and a long-range order seems to prevail in the whole temperature range studied. The inclusion of BA is however capable of destabilising the AF order, giving rise to a slightly polar ferroelectric phase at low temperatures. Moreover spectroscopic results reveal that methyl groups of the betaine molecules act as excellent probes for the detailed study of the phase transition sequence in this system. [ABSTRACT FROM AUTHOR]