Ferroelectric Betaine Research Articles

Phase diagrams and structural order in mixed crystals BAxBP1−xfor x > 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.

Electron spin relaxation of the PO 32− radical in ferroelectric betaine phosphite and in the proton glass betaine phosphate/betaine phosphite

Measurements of the electron spin-lattice relaxation time T 1 and the phase memory time T M of the PO 3 2− radical in γ-irradiated betaine phosphite and betaine phosphate/betaine phosphite are presented. The temperature dependence of T 1 indicates the interaction of the electron spin with two groups of optical branches via Raman processes in both crystals. An additional relaxation path due to the interaction with two-level local tunneling states has been observed in the mixed crystal confirming glassy behaviour. The T M temperature dependence reflects thermally activated local motional effects of the PO 3 group in both crystals.

Far-infrared spectroscopy of modulated and ferroelectric betaine calcium chloride dihydrate

Far-infrared and near-millimetre transmission and reflectivity measurements of betaine calcium chloride dihydrate were carried out between 300 and 15 K. All modes below 300 cm-1 were classified according to symmetry and their wavevectors q using selection rules for mode activation in the modulated phases. Almost all activated modes with q not=0 can be assigned assuming condensation of the single order parameter of Lambda 3 symmetry (Py(k) wave). In the low-temperature homogeneous ferroelectric phase, traces of modulated phases are observed depending on the sample clamping. On the basis of the authors' assignment the dispersion curves of the eight lowest phonon branches along the modulation direction were constructed for the four main modulated phases (incommensurate and commensurate with delta =1/4, 1/5, 1/6). The behaviour of amplitudons and pseudophasons is discussed. The E//y mode below 10 cm-1 in the incommensurate phase has been assigned to the inhomogeneous Lambda 2(c*-2k) mode (c* is the reciprocal-lattice vector and k the modulation wavevector).

Critical Dielectric Relaxation in Ferroelectric Betaine Phosphite in the Microwave Region

The dielectric behaviour of ferroelectric hydrogen-bonded betaine phosphite crystals is investigated in the frequency range up to 77 GHz. The dielectric dynamics of Debye-type shows a critical slowing-down of the polarization fluctuations. The frequency of the relaxational soft mode in the paraelectric phase varies according to vs = 0.36(T-218) GHz and decreases to 2.4 GHz at Tc = 224 K. The calulated activation energy for flipping proton motion ΔU = 2.7kTc shows the order-disorder character of the proper ferroelectric phase transition. Betainphosphit ist ein Ferroelektrikum mit Wasserstoffbrückenbindungen. Im Frequenzbereich bis 77 GHz wird das dielektrische Verhalten eines Einkristalls untersucht. Die dielektrische Dynamik zeigt ein Debye-Verhalten mit einem kritischen “slowing-down” der Polarisationsfluktuationen. In der paraelektrischen Phase folgt die Frequenz der Relaxations-Softmode der Beziehung vs = 0,36 (T-218) GHz und nimmt bis zu 2,4 GHz ab. Die berechnete Aktivierungsenergie ΔU = 2,7kTc für die Protonen-Bewegung belegt, daß es sich um einen eigentlichen ferroelektrischen Phasenübergang vom Ordnung-Unordnungstyp handelt.

Far‐infrared spectrum and the soft mode of ferroelectric betaine phosphite

AbstractThe far‐infrared reflection spectra of betaine phosphite single crystals in the three crystallographic directions are investigated in the range from 5 to 600 cm−1 at temperatures between 203 and 323 K using a dispersive Fourier spectrometer. The dielectric function is evaluated from the complex amplitude reflection coefficient measured. In the spectrum polarized along the ferroelectric direction a soft mode of relaxation type is observed which accounts for a large part of the relevant static dielectric constant at Tc = 210 K. Among the oscillator modes, which generally exhibit normal temperature dependence, there is a heavily overdamped mode at 58 cm−1, polarized along the crystallographia a1 axis, with anomalous damping behaviour. The damping constant decreases nearly linearly with temperature up to 323 K which is close to T = 355 K where a second phase transition is known to exist.

Esr–investigations on γ–irradiated ferroelectric betaine compounds

Abstract Part of this work was supported by the BMFT. Valuable support by J. Huttermann and J. Albers, Universitat des Saarlandes, are gratefully acknowledged.

Relaxational dynamics at the class transition in orientational and canonical glasses investigated by dielectric spectroscopy

Measurements of the dielectric permittivity are reported for the canonical glass glycerol and for solid solutions of ferroelectric betaine phosphite and ferroelectric betaine phosphate, which can be viewed as protype systems of orientational glasses. In this latter system long range dipolar order is suppressed by the competing ferroelectric and antiferroelectric interactions and the dipolar moments freeze-in devoid of long range order. In both systems the relaxation dynamics is studied for frequencies 10 −2Hz≤ν≤10 6Hz, close to the glass transition temperature. The relaxation dynamics is characterized according to Angell's classification scheme of strong and fragile glass-formers.

Hopping Conductivity in Hydrogen‐Bonded Antiferroelectric Compounds

AbstractAntiferroelectric betaine phosphate (BP: (CH3)3NCH2COO · H3PO4) and ferroelectric betaine phosphite (BPI: (CH3)3NCH2COO · H3PO3) are molecular crystals of the amino acid betaine and the phosphoric or phosphorous acids, respectively. In both compounds the inorganic components are linked by hydrogen bonds to one‐dimensional chains. The two isostructural compounds form solid solutions BPxBPI1‐x at any concentration. Here we report measurements of the dielectric permittivity for concentrations 0.85 ≤ × ≤ 1 at frequencies 10−2 ≤ v ≤ 109 Hz and temperatures 2 K ≤ T ≤ 300 K. The dielectric response in BP:BPI (x = 0.95) is dominated by contributions from pure hopping conductivity which we ascribe to the motion of the protons along the one‐dimensional chains. The onset of electric order supresses the a.c. conductivity. It will also be seen that BP:BPI (x = 0.95) shows dc conductivity in addition to the observed ac conductivity. These results are contrasted to BP and BP:BPI (x = 0.85) which reveal pure relaxational behavior.

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

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.

Specific heat of betaine calcium chloride dihydrate

Abstract The molar heat capacity of the ferroelectric betaine calcium chloride dihydrate (BCCD), (CH3)3NCH2COO·CaCl2·2H2O, was measured between 2 K and 300 K and the different phase transitions are investigated. The transition from normal to incommensurate phase shows a typical second-order anomaly at T i = 164 K. At the incommensurate-commensurate transition (lock-in transition) at 116 K a sharp anomaly in the heat capacity was observed indicating a first order transition. The sequence of the phase transitions is characterized by their entropies and enthalpies of transition. A possible relation between the modulation vector Δq* and the entropy change ΔS is discussed.

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.

Far-infrared spectroscopic investigation of the incommensurate and commensurate phases in ferroelectric betaine calcium chloride dihydrate (BCCD)

Abstract We have measured the far-infrared transmission spectra of BCCD, ((CH3)3NCH2 COO CaCl2 2H2O), polarized in the (ferroelectric) y-axis in the wavenumber interval 10 cm−1≤ ν ≤ 110 cm−1 and in the temperature range 20 K≤ T ≤300 K. The temperature dependence of new bands arising in the various commensurate phases and of hard-core modes have been studied. The spectra are compared with Raman spectra. A type of symmetry for the soft mode has been proposed based on the obvious selection rules obeyed by the spectra.

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.

Dielectric behaviour of betaine arsenate

Abstract Dielectric constant measurements of the ferroelectric material Betaine Arsenate showed a maximum value of 1.057∗106 (tan δ = 1.73∗10−2). The dielectric constant is compared with hysteresis loops. It is shown that close below Tc, a small signal of 1.3 V/m is sufficient to switch the spontaneous polarization.