Antiferroelectric Betaine Phosphate Research Articles

Disorder in condensed matter systems: proton spin lattice relaxation study of the mixed systems of betaine phosphate and glycine phosphite, BPxGPI(1−x)

Proton NMR relaxation measurements have been carried out in the mixed system of antiferroelectric (AFE) betaine phosphate (BP) and ferroelectric (FE) glycine phosphite (GPI), BPxGPI(1-x), at 11.4 and 23.3 MHz from 300 to 100 K for x=0.3, 0.4, 0.5, 0.6, 0.7 and 0.8. The temperature dependence of spin lattice relaxation (SLR) time follows the BPP model in the parent compounds, while the Larmor frequency dependence of T1 in the mixed system is rather unusual. The T1 curve exhibits different slopes for the low-temperature wings at the two frequencies, which is a clear experimental evidence of the presence of different methyl groups with different activation energies (Ea), indicating disorder. For x=0.3 and 0.4, biexponential recovery of magnetization has been observed below 190 K, showing that the degree of disorder varies with the concentration. The temperature dependence of relaxation time data has been interpreted in terms of NH3, trimethyl ammonium and methyl group reorientations.

NMR relaxation study of disorder in condensed matter: solid solutions of betaine phosphate and phosphite

Proton NMR relaxation measurements have been carried out in anti-ferroelectric Betaine phosphate (BP), ferroelectric Betaine phosphite (BPI) and the mixed system BPI(1− x )BP x , at 11.4 MHz and 23.3 MHz from 300 K to 80 K for x = 0.0, 0.25, 0.45, 0.85, and 1.0. The temperature dependence of spin lattice relaxation time T 1 exhibits two minima as expected from the BPP model in BP and BPI. The Larmor frequency dependence of T 1 in the mixed system is rather unusual and exhibits different slopes for the low temperature wings at the two frequencies, which is a clear experimental evidence of the presence of different methyl groups with different activation energies (Ea ) indicating disorder.

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.

Phase diagram of the betaine arsenate–betaine phosphate mixed-crystal system by dielectric hysteresis and current curves

The ferroelectric (FE) betaine arsenate (BA) and the antiferroelectric (AF) betaine phosphate (BP) are structurally very closely related and mixed crystals of ${\mathrm{BA}}_{x}{\mathrm{BP}}_{1\ensuremath{-}x}$ can be grown over the whole concentration range. The concentration $(x)$-temperature $(T)$-pressure $(P)$ phase diagram of the system is characterized by a transition from an AF to a FE phase along with the appearance of some mixed regions upon changing concentration. Depending on concentration, one or two relaxation processes appear in the low-temperature region of the phase diagram. Measurement of the hysteresis loops and the current curves have been carried out along the $(x\text{\ensuremath{-}}T\text{\ensuremath{-}}P)$-phase diagram of this system. Multiple loops have been observed in various regions of the phase diagram. The correlation of the different contributions of the polarization and the temperature behavior of their critical fields with the main features of the temperature- and frequency-dependent dielectric constant enables clarification of the rich phase diagram obtained in this mixed compound in terms of the ferro- and/or antiferroelectric interactions.

Ferroelectric/Antiferroelectric Phase Coexistence in the Intermediate Concentration Regions of the BA x BP1–x Phase Diagram

Temperature and frequency dependent hysteresis loop measurements have been carried out along the phase diagram of ferroelectric (FE) betaine arsenate (BA) and antiferroelectric (AF) betaine phosphate (BP) mixed crystal system (BA x BP1 -x ). Coexistence regions characterized by competing ferro- and/or antiferroelectric interactions are detected by multiple hysteresis loops.

Raman and infrared study of the quasi-one-dimensional betaine arsenate-phosphate mixed-crystal system

Ferroelectric (FE) betaine arsenate (BA) and antiferroelectric (AF) betaine phosphate (BP) are structurally very closely related and mixed crystals ${\mathrm{BA}}_{x}{\mathrm{BP}}_{1\ensuremath{-}x}$ can be grown over the full concentration range. 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 a concentration-dependent appearance of some mixed regions. At low temperatures different relaxation processes have been observed that might be related to the transition from a domain state to an orientational glass depending on concentration. In some regions of the phase diagram different phases coexist. The origin of the different transitions and relaxation processes is still unclear and recent x-ray-diffraction studies reveal that the peculiar behavior of the mixed crystals cannot be explained from the structural point of view. We have performed Raman and infrared investigation of samples across the whole (x, T) phase diagram, at various hydrostatic pressures, in order to shed light on the structural origin of the different processes. It is concluded that the FE or AF character of the ordered phase is related to the degrees of freedom of the ${\mathrm{AsO}}_{4}$ and ${\mathrm{PO}}_{4}$ tetrahedra. In the same way these units determine the type and the modes triggering the phase transitions for each concentration. The latter seems to occur together with a participation of the betaine molecule, especially of the methyl and buthyl groups.

Glass behaviour in the solid solution of deuterated betaine phosphate0.15 betaine phosphite0.85

For a deuterated solid solution of 15% antiferroelectric betaine phosphate (BP) and 85% ferroelectric betaine phosphite (BPI), measurements of the dielectric permittivity at frequencies 20 Hz<<1 MHz are reported. The freezing phenomena in DBP0.15DBPI0.85 reveal the characteristics of a transition into a dipolar glass state with peculiarities due to the quasi-one-dimensional structure. Using the Kutnjak model a glass temperature of 25 K is estimated for deuterated DBP0.15DBPI0.85 and one of 10 K for protonated BP0.15DBPI0.85. The relaxation time distribution extracted from the experimental data by means of Tikhonov regularization and calculated in the region of the dielectric dispersion shows an asymmetric behaviour especially at lower temperatures, which is interpreted as being caused by a Gaussian distribution of activation energy and double-well potential asymmetry as well.

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.

Conductivity processes in deuterated betaine betaine mixed crystals

Studies of the electrical conductivity in solid solutions of the mixed crystal system of deuterated antiferroelectric betaine phosphate (DBP) and ferroelectric betaine phosphite (DBPI) were performed. The dc-conductivity in the temperature interval between 280 and 400 K is obtained from measurements of the complex dielectric permittivity at frequencies between . For all crystals studied an anisotropy of with respect to two crystallographic directions is found. Moreover, we find a clear dependence of the absolute values of on the phosphite percentage x, whereas the activation energies calculated from an Arrhenius plot of the quantity against the inverse temperature differ only slightly. For the system the conductivity results are related to data on the microscopic behaviour of the deuteron exchange derived from two dimensional nuclear magnetic resonance (NMR) exchange spectroscopic measurements. An effective charge carrier density is estimated and discussed with respect to the differences between the conductivity and the exchange behaviour for pure deuterated substances.

Indications of an intermediate phase in single crystals of betaine phosphate/phosphite solid solutions

The solid solution of ferroelectric betaine phosphite and antiferroelectric betaine phosphate shows an interesting phase diagram with a transition from a high temperature prototype phase to a common nonpolar antiferrodistortive phase followed towards lower temperatures by transitions into ferroelectric, antiferroelectric or orientaional glass phases in dependence on its composition. Using magnetic resonance techniques such as electron nuclear double resonance (ENDOR) and electron spin-lattice relaxation measurements we are able to show that an intermediate phase exists between the antiferrodistortive and the orientational glass phase at intermediate compositions. This new phase shows a regular proton order within the phosphate-phosphite chains and is supposed to be of quasiferroic or clusterlike nature.

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.

Random fields versus random bond effects in betaine arsenate/phosphate mixed crystals

Abstract Ferroelectric (F) betaine arsenate (BA) and antiferroelectric (AF) 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 F 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. Together with a small review of the most striking features of the system we shall study in...

Phase diagrams and structural order in mixed crystals BAxBP1−xfor x &gt; 0.80

Abstract In order to complete the pressure-temperature-concentration phase diagrams we have extended earlier measurements made on mixed crystals of ferroelectric (f) betaine arsenate (BA) and antiferroelectric (af) betaine phosphate (BP), BA, BAxBP1−x, by observing the anomalies in the real and imaginary parts of the dielectric function (e) and the dissipation factor (tan δ) at various temperatures (23 <T < 300 K) and hydrostatic pressures(p < 300 MPa) at frequencies v = 0.1, 0.5, 1, 5, 10, 50, 100 kHz for x = 0.86, 0.94, and 1.00. With increasing pressure the transition into the f phase at Tc2 shifts to lower temperatures; the ordered phase is destabilized. The anomalous behavior found in tan δ and e” point out the existence of a distribution of relaxation times and competing interactions. A low temperature glassy phase is supposed to exist in this system.

X‐Ray Study of the System BP1−xBPIx

AbstractAccurate X‐ray diffraction measurements are carried out as function of temperature in antiferroelectric betaine phosphate (BP), ferroelectric betaine phosphite (BPI), and mixed compounds of BP1−xBPIx. In agreement with previous studies, the phases which derive from a high‐temperature phase with P21/c symmetry are clearly detected. However, in contrast with previous assignments, for 0.90 &lt; x ≦ 1.0 a transition occurs to the P21 ferroelectric phase. For 0 ≦ x &lt; 0.20, the two successive transitions are to a P21, phase and subsequently to a Pc phase with a simultaneous doubling of the unit cell. For 0.9 ≦ x &lt; 1.0 the results confirm previous assignments of a single transition to a P21 phase. In the intermediate region 0.20 &lt; x &lt; 0.90 a clear evidence of an isomorphous transition to a glass phase is obtained, where the relative dominance of the ferroelectric or antiferroelectric interaction depends on the concentration values. Furthermore an orientational glass phase near x = 0.80 is identified. The existence of a strong anisotropy in all the studied elements of the family and of a weak coupling between the ordering of the dipoles and the lattice is evidenced. The role of the absent oxygen in the behaviour of the lattice parameters as well as its subsequent influence on the competitive interactions between dipoles are discussed.

Proton-glass behavior in a solid solution of (betaine phosphate)0.15 (betaine phosphite)0.85.

Measurements of the dielectric permittivity are reported for a solid solution of antiferroelectric (betaine phosphate${)}_{0.15}$ and ferroelectric (betaine phosphite${)}_{0.85}$ at frequencies 20 Hz 1 MHz. The freezing phenomena in ${\mathrm{BP}}_{0.15}$${\mathrm{BPI}}_{0.85}$ reveal the characteristics of a transition into a dipolar glass state. The activation energy was found to be ${\mathit{E}}_{\mathit{b}}$=518 K and the external bias field lowers this value up to 488 K.

Competing interactions and phase transitions in betaine arsenate-betaine phosphate (BAxBP1-x)

Abstract We have studied mixed crystals of ferroelectric (f) betaine arsenate (BA) and antiferroelectric (af) betaine phosphate (BP), BAxBP1-x, x=0.07, 0.24, 0.39 by observing the anomalies in the real part of the dielectric function (ϵ) and the dissipation factor (tan δ) at various temperatures (23 < T < 300 K) and hydrostatic pressures (p<300 MPa) at frequencies F=0.5, 1, 5, 10, 50, 100 kHz. For x=0.24 and x=0.39, ϵ exhibits a double peak structure near Tc mirrored in the tanδ behavior of each substance. The transition into the af phase at Tc2 shifts to lower temperatures, the ordered phase is destabilized. Interesting phase diagrams are obtained with a probable glassy state preceded by some mixed phase. The frustrated interactions af-f seem to play the major role in this behavior.

Dielectric dispersion associated with the dc-electric-field-enforced ferroelectric phase transition in the antiferroelectric betaine phosphate

Abstract The dc-electric field dependence of the dielectric properties (complex permittivity and relaxation time) of the antiferroelectric betaine phosphate was investigated under various frequencies. The strong dielectric dispersion along the b-axis associated with the field-enforced ferroelectric phase transition was observed. The slowing-down of the relaxation time toward a critical electric field Ecr, which induces the forced transition to the ferroelectric phase, was observed. The frequency dependence of the complex relative permittivity obeys the Cole-Cole are law. The relaxation time is of the order of 10−5s near Ecr.

Slowing down of the dielectric relaxation time toward the critical electric field in the antiferroelectric betaine phosphate

The frequency dependence of the complex permittivity of the antiferroelectric betaine phosphate was investigated under various dc electric fields. The strong dielectric relaxation along the b-axis associated with the field-enforced ferroelectric phase transition was observed. The slowing down of the relaxation time toward a critical electric field E cr , which induces the forced transition to the ferroelectric phase, was observed.

Proton glass behavior and hopping conductivity in solid solutions of antiferroelectric betaine phosphate and ferroelectric betaine phosphite.

Measurements of the dielectric permittivity are reported for solid solutions of antiferroelectric betaine phosphate and ferroelectric betaine phosphite at frequencies 10 −2 Hz T c the dielectric response is dominated by ac and dc conduction. The 40% sample exhibits pure relational behavior indicative of a transition into an orientational glass state