J. Albers

Betaine compounds–a new family with ferroelectric and incommensurate phases

Abstract Several addition compounds of the amino acid betaine and inorganic acids were found in the last years to possess structural, ferroelastic, ferroelectric or antiferroelectric phase transitions. As well commensurate as incommensurate phases are observed. The materials are betaine phosphate (antiferroelectric), betaine arsenate (ferroelectric, but antiferroelectric if deuterated), betaine borate (ferroelastic), betaine phosphite (ferroelectric), and betaine calcium chloride dihydrate (several commensurate and incommensurate phases with soft mode behavior, ferroelectric in its lowest phase).

Ferroelectricity in betaine phosphite

Abstract Betaine phosphite, an addition compound of the amino acid betaine and phosphorous acid, can be grown in single crystal form from aqueous solutions. Structural, optical, dielectric, and caloric data of this new material are reported. At least two phase transitions are observed in (CH3)3NCH2COO˙H3PO3. The lower one, around 216 K, leads to a ferroelectric phase with a spontaneous polarization of about 1.7 μC/cm2.

Phase transitions, critical dielectric phenomena and hysteresis effects in betaine calcium chloride dihydrate

Abstract Single crystals of betaine calcium chloride dihydrate ((CH3)3NCH2COO*CaCl2*2H20) are grown from aqueous solutions. The dielectric constant shows several distinct anomalies with the highest values of about 20000 near 125 K. Below this temperature complex dielectric hysteresis loops are observed. Their shape strongly depends on temperature, field and frequency. Below 51 K only single loops can be obtained which probably indicate a ferroelectric phase.

Quenching of lamellar ordering in an n-alkane embedded in nanopores

We present an X-ray diffraction study of the normal alkane nonadecane C19H40 embedded in nanoporous Vycor glass. The confined molecular crystal accomplishes a close-packed structure by alignment of the rod-like molecules parallel to the pore axis while sacrificing one basic ordering principle known from the bulk state, i.e. the lamellar ordering of the molecules. Despite this disorder, the phase transitions observed in the confined solid mimic the phase behavior of the 3D unconfined crystal, though enriched by the appearance of a true rotator phase known only from longer alkane chains.

Ferroelectric and antiferroelectric properties of deuterated betaine arsenate and betaine phosphate

Abstract The dielectric and thermal behaviour of deuterated betaine phosphate is similar to that of the undeuterated anti-ferroelectric material, but Tc is increased by 69 deg. In deuterated betaine arsenate, however, the low temperature phase is not ferroelectric, as in the undeuterated compound, but anti-ferroelectric.

Ferroelasticity and ferroelectricity in betaine arsenate

Abstract Single crystals of betaine arsenate. an addition compound of the amino acid betaine with H3 As04, were investigated by dielectric, optical, caloric, and X-ray methods. At room temperature betaine arsenate is ferroelastic with two different monoclinic domains. This state seems to disappear at 411 K. Below Tc = 119 K the ferroelastic domains show a ferro2 electric behaviour with a spontaneous polarization Ps = 2μmlC/cm2 at T = Tc—35 deg

Dielectric and pyroelectric behaviour in (BPI)x (BP)1−x

Abstract Measurements of dielectric constant, dielectric loss and pyroelectric coefficient as a function of temperature have been performed in mixed crystals of Betaine Phosphite (BPI) and Betaine Phosphate (BP) ((BPI)x (BP)1−x), for x = 0.80, 0.90, 0.94 and 0.97. The obtained results are compared with the ones previously reported for x = 0.00, 0.05, 0.15, 0.30, 0.60 and 1.00. Three regions are apparent: one where the ferroelectric properties are dominant (x > 0.90), another which can be related to a glassy phase (0.30< x <0.90) and a third one mainly associated with an antiferroelectric behaviour of BP (x < 0.30).

Inelastic neutron scattering study of the soft phonon branch in deuterated BCCD

Abstract Inelastic neutron scattering on deuterated BCCD revealed a transverse acoustic branch of Λ3 symmetry coupled to a soft polarisation branch Py(k) of same symmetry. As the transition to the incommensurate state is approached from above (T>T1 = 164 K), the lowest-frequency branch develops a broad dispersion minimum near k =0.32c ∗ . The soft mode is observed as an underdamped excitation down to 170K. The present results establish the displacive nature of the phase transition at T1 and the P y- symmetry of the primary order parameter. A semi-quantitative scheme for the 14 lowest phonon branches along the c∗ direction, in the normal phase, is suggested, based on the available neutron-scattering, infrared, Raman, and acoustic data.

Anomalous elastic properties of betaine calcium chloride dihydrate, (CH3)3NCH2COO·CaCl2·2H2O

The elastic constants of orthorhombic betaine calcium chloride dihydrate have been investigated by ultrasonic methods in the range between 300 and 100 K. The phase transition at 169 K is accompanied by a sharp softening of all ultrasonic waves having longitudinal components of the displacement vector, similar to the effects observed at the α-β transition of Li2Ge7O15 and at the V–IV transition of thiourea. The transition at 129 K shows only very weak anomalies like those found in the α-β transition of Te(OH)6·2NH4H2PO4·(NH4)2HPO4. The transitions at 169 K and 129 K are of second order.

Elastic and thermoelastic constants of triglycine sulphate (TGS) in the paraelectric phase

All elastic and thermoelastic constants of triglycine sulphate, point group 2/m, have been measured by ultrasonic methods between 55° and 75°C. The elastic properties in the paraelectric and in the ferroelectric phases do not differ a great deal. The elastic as well as the thermoelastic properties of the paraelectric phase are highly anisotropic.