Ferroelectric Betaine Arsenate Research Articles

Dielectric and structural properties of ferroelectric betaine arsenate films

Ferroelectric films of betaine arsenate and partially deuterated betaine arsenate have been grown by evaporation on LiNbO3, α-Al2O3, and NdGaO3 substrates with a preliminarily deposited structure of interdigitated electrodes, as well as on the Al/glass substrate. This paper presents the results of the examination of the block structure of the films in a polarizing microscope, the X-ray diffraction analysis of their crystal structure, and the investigation of the dielectric properties in a measuring field oriented both parallel and perpendicular to the plane of the film. The transition of the films to the ferroelectric state at T = T c is accompanied by anomalies of the capacitance of the structure, an increase in the dielectric loss, and the appearance of dielectric hysteresis loops. The growth of the films from a solution of betaine arsenate in a heavy water leads to an increase in the ferroelectric transition temperature from T c = 119 K in the films without deuterium to T c = 149 K, which corresponds to the degree of deuteration of approximately 60–70%. The dielectric and structural properties of the films are compared with those of the betaine arsenate single crystals and the previously studied films of betaine phosphite and glycine phosphite.

Effect of glycine substitution on the ferroelectric phase of betaine arsenate [(CH 3) 3NCH 2COO·H 3AsO 4

The present work reports an experimental investigation on the influence of glycine (NH 2CH 2COOH) substitution in the polar properties and the critical dynamics of the molecular ferroelectric betaine arsenate, (CH 3) 3NCH 2COO·H 3AsO 4. The dielectric dispersion (20 Hz<ν<3 MHz) and the thermally induced displacement currents are investigated in detail over the extended Curie region of the system (130 K< T<100 K). The results obtained for a single crystal with nominal glycine content of 20% are analyzed, compared with those obtained for pure betaine arsenate and discussed within the scope of a phenomenological Landau model previously used to describe a system with competing ferroelectric and structural instabilities.

Alternative phase diagram for the betaine phosphate-betaine arsenate mixed system

The mixed solid solutions of ferroelectric betaine arsenate (BA) and antiferroelectric betaine phosphate (BP) are known examples of H-bonded materials with competing ferro and antiferro interactions. Dispersive anomalies detected in the dielectric loss at low temperatures have been tentatively associated with the stabilization of disordered phases such as re-entrant dipolarlike glassy phases. Despite extensive experimental studies of $(\mathrm{BP}{)}_{\mathrm{x}}(\mathrm{BA}{)}_{1\ensuremath{-}\mathrm{x}}$ mixed systems, the existence of such phases is doubtful so far. In an attempt to clarify the nature of the low temperature phase transition sequence of $(\mathrm{BP}{)}_{\mathrm{x}}(\mathrm{BA}{)}_{1\ensuremath{-}\mathrm{x}}$, we have undertaken detailed pyroelectric, dielectric, polarization reversal, Raman, and infrared studies as a function of temperature. In this work we shall present the experimental results for $x=0.25$ (BP25) and compare them with the ones previously reported for the two other intermediate compositions. We shall then propose a phase diagram alternative to the one already published for this system; moreover, we shall tentatively identify the possible underlying mechanisms, and discuss how such mechanisms evolve as a function of the BP concentration.

Review of experimental and theoretical results for the betaine arsenate/phosphate mixed crystals system

Ferroelectric betaine arsenate (BA) and antiferroelectric betaine phosphate (BP) are structurally very closely related and mixed crystals BA x BP1−x can be grown over the full concentration range. The phase diagrams of several concentrations 0 ⩽ x ⩽ 1 have been established by investigating dielectric and structural properties by changing external parameters like temperature, hydrostatic pressure, electric bias field, and frequency. This system exhibits interesting pressure-temperature-concentration phase diagrams in which the transition in concentration from an AF to a FE phase can be observed with the appearance of some mixed regions and a probably incommensurate phase in the intermediate concentration range. At low temperatures the transition in concentration from a domain to an orientational glass state can be observed besides the appearance of some mixed phases in which different phases coexist. The experimental results were compared with some theoretical models. The high temperature transition into the ordered phase was discussed in the framework of the quasi-1D Ising, the tunnel, and a phenomenological models. The low temperature transition into the reentrant glassy phase is treated according to the frequency dependent shift of its indicating anomaly by means of an Arrhenius versus Vogel-Fulcher analysis.

Dimensionality crossover and the nonlinear dielectric response in betaine phosphate/arsenate mixed crystals

Dielectric properties of quasi-one-dimensional hydrogen-bonded chains are studied for mixed crystals of antiferroelectric betaine phosphate and ferroelectric betaine arsenate at three different mixing concentrations, x = 0.1, 0.3, and 0.4 (x being the concentration of arsenate). For mixed crystals with x = 0.3 and 0.4 dielectric study revealed dimensionality crossover at around 82 K, where the quasi-one-dimensional nature was turned into three-dimensional Curie - Weiss behaviour on lowering the temperature, well above the antiferroelectric transition point. For x = 0.1 mixed crystal, on the other hand, the crossover point was almost coincident with the antiferroelectric transition point, showing still too-weak interchain coupling and strong one-dimensionality, almost to the point of antiferroelectric transition. For this system, the electric bias field effect revealed temperature-dependent nonlinearity of the dielectric constant, which may be ascribed to a development of competition between antiferroelectric and ferroelectric interchain couplings, the latter growing with increasing bias field and lowering temperature.

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

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.

Electric field effect on the phase transitions in betaine phosphates and arsenates

Abstract Optical and dielectric study of the electric field effect on the low-temperature phase transitions in betaine phosphate (abbreviated as BP), betaine arsenate (BA) and their deuterated analogs (DBP and DBA, resp.) is reported. In the ferroelectric BA the effect of the electric bias (shift of T c ) follows the predictions of the Landau theory. In the other compounds with antiferroelectric phases, including the deuterated BA, the phase diagrams are more complex because of the appearance of a field-induced ferroelectric phase. Strong dielectric dispersion takes place in the polar field-induced phases below 100 kHz but no glassy behaviour has been found even in the (partially) deuterated betaine arsenate.

Dieelectric properties of the mixed crystals of ferroelectric betaine arsenate and antiferroelectric betaine phosphate

Abstract Mixed crystals of the system BP1−xAx were grown in the entire concentration region and their dielectric properties were investigated in detail. For compositions with 0≤x≤0.4, the crystal undergoes an antiferroelectric phase transition, whereas for 0.9≤x≤1.0, a ferroelectric phase trsansition is observed. For in-between compositions, i.e., 0.5≤x≤0.85, proton-glass like behavior is observed.

X-ray study on a binary system of antiferroelectric betaine phosphate and ferroelectric betaine arsenate

Abstract X-ray diffraction measurements in antiferroelectric betaine phosphate (BP), ferroelectric betaine arsenate (BA) and random mixtures (BP)1 –x (BA) x were carefully carried out. Antiferrodistortive nature in BP and ferroelastic one in BA were also detected clearly. It is found that in (BP)1 –x (BA) x crystal the antiferroelectric ordering decreases with increasing x. It was not clear, however, that there exists a glassy phase in the mixed crystal.

Phase transitions in mixed crystals of ferroelectric betaine arsenate and antiferroelectric betaine phosphate

Abstract Phase transitions in the mixed crystals system of ferroelectric betaine arsenate (BA) and antiferroelectric betaine phosphate (BP) are investigated by X-ray, dielectric and thermal measurements. The phase diagram of the system BP(1–x)BA x in the whole concentration region is given; an antiferroelectric phase transition occurs in the region 0 ≤ x ≤ 0.4, the structural-glass like behavior is observed in the region 0.5 ≤ x ≤ 0.85, and a ferroelectric phase transition takes place in the region 0.9 ≤ x ≤ 1.0.

Elastic,Dielectric and Optical Properties of Ferroelectric Betaine Arsenate

Successive phase transitions in betaine arsenate (BA) have been investigated around its ferroelastic phase transition at 411 K ( T 1 ) and ferroelectric transition at 119 K ( T 2 ). Temperature dependence of elastic compliances s 11 , s 22 and s 33 and the frequency dependence of e a , were measured around the ferroelectric transition. Clear elastic anomalies at T 2 are observed in s 11 and s 33 and marked frequency dependence of e a is found in the ferroelectric phase. Temperature dependence of the domain pattern and the rotation angle of indicatrix in the ferroelastic phase are observed. Brief discussion on the successive phase transitions of BA is made.

Critical behavior of betaine arsenate

The critical exponents β, γ and δ of undeuterated and partially deuterated ferroelectric betaine arsenate are estimated. Small but remarkable deviations from the tricritical values are observed. The obtained values are tested via scaling of the isothermals.

The elastic properties of betaine arsenate and betaine phosphate determined by brillouin spectroscopy

Abstract Brillouin spectroscopy has been used to determine the complete elastic stiffness tensors of the monoclinic room temperature phases of ferroelectric Betaine Arsenate and anti-ferroelectric Betaine Phosphate.

Ferroelectricity and Antiferroelectricity in Partially Deuterated Betaine Arsenate

Ferroelectric betaine arsenate (BA) becomes antiferroelectric by deuteration. Complete miscibility of BA and deuterated betaine arsenate (DBA) allows the growth of crystals in which the effective interaction, deciding about the transition to a ferroelectric or to an antiferroelectric state, goes to zero. Tc, however, shifts monotonically with the Dcontent, indicating that this interaction is not responsible for the transition itself. Dielectric and caloric data of some crystals with different deuteration degrees are presented.

Heat capacity of the ferroelectric betaine arsenate

Abstract The heat capacity of a betaine arsenate single crystal was measured near Tc2 by an automatic adiabatic calorimeter. A typical second order phase transition γ-anomaly is observed. The transition entropy is Δ = 0.65 J/mol/K. the heat capacity jump at TC2 Δ = 21 J/mol/K. The relation between Δ(T) and Ps (T) given by the Landau theory is roughly satisfied.