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Abstract: The present work reports an experimental investigation on the influence of glycine (NH2CH2COOH) substitution in the polar properties and the critical dynamics of the molecular ferroelectric betaine arsenate, (CH3)3NCH2COO·H3AsO4. The dielectric dispersion (20Hz<ν<3MHz) and the thermally induced displacement currents are investigated in detail over the extended Curie region of the system (130K

Temperature dependences of the dielectric permittivity of betaine phosphite crystals are studied both without and under application of an electric bias. It is shown that, in view of the fact that the high-temperature improper ferroelastic (antiferrodistorsive) phase transition at T[sub c1] = 355 K is nearly tricritical, the nonlinear temperature dependence of inverse dielectric permittivity in the paraelectric phase and the effect of the field on the dielectric permittivity can be described within a phenomenological model containing two coupled (polar and nonpolar) order parameters with a negative coupling coefficient. An analysis of the model revealed that, in the case where two phase transitions, a nonpolar and a ferroelectric one, can occur in the crystal, all of its dielectric properties, including the polarization response in a field, can be described by one dimensionless parameter a. For the crystal under study, we have a = -2.5. This value of the parameter corresponds to a second-order ferroelectric transition far from the tricritical point, at which a = -1. It is shown that the polarization response in the paraelectric phase in an electric field calculated within this model differs radically from that in the ferroelectric phase-transition model for which the Curie-Weiss law holds in the paraelectric phase. [ABSTRACT FROM AUTHOR]

We have attempted to understand the low temperature microscopic structure and dipolar ordering of the (BP)x(BA)1 -x mixed system in a previous work, by performing detailed pyroelectric, dielectric and polarization reversal measurements, complemented with Raman and infrared spectroscopic investigations. Whenever the same experimental techniques are used, our experimental results agree extremely well with those reported in the literature. However, our use of slightly different methods disclosed new aspects of the phase sequence, which allowed us to trace an alternative phase diagram for the (BP)x(BA)1-x mixed system. The present paper is aimed at emphasising the most relevant of these previous results. Particular attention will be paid to the role of ferro-antiferroelectric competitions in the mixed system (BP)x(BA)1 -x. [ABSTRACT FROM AUTHOR]

In this work we present a detailed study of the temperature evolution (290 K–20 K) of the polarized Raman spectra in a single crystal of glycinium phosphite. The phase transition manifests itself by the activation of new Raman bands and by the occurrence of anomalies in the temperature dependence of the wavenumber of some external and internal modes. The results show that occurring deformations in molecular units contribute relevantly to the spontaneous polarization in GPI. The anomalous behaviour of the wavenumber and of the damping constant of some bands is in good agreement with a theoretical model based in a pseudospin-phonon interaction. [ABSTRACT FROM AUTHOR]

Betaine calcium perchlorate monohydrate (here designate by BCPM) is a new compound of the amino acid betaine with a triclinic symmetry and with the space group P..., at room temperature. In this work we present a detailed study of dielectric properties and of Raman scattering spectra of BCPM, which disclose interesting structural changes in the temperature range 20 K-300 K. [ABSTRACT FROM AUTHOR]

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]

Betaine potassium bromide dihydrate: (CH 3 ) 3 N + CH 2 COO - ·KBr·2H 2 O, for short BKBr, is a compound of the aminoacid betaine with an orthorhombic symmetry and the space group Pbcm at room temperature. The study of the dielectric properties of this compound, in the temperature range 20-300K, provides a clear evidence for the existence of a structural phase transition occurring around 160K. This phase transition is related to the freezing of water molecules degrees of freedom. [ABSTRACT FROM AUTHOR]