A. Klöpperpieper

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 DBP0.15 DBPI0.85 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 DBP0.15 DBPI0.85 and one of 10 K for protonated BP0.15 DBPI0.85 . 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.

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.

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.

Fractional spinon excitations in the quantum Heisenberg antiferromagnetic chain

One of the simplest quantum many-body systems is the spin-1/2 Heisenberg antiferromagnetic chain, a linear array of interacting magnetic moments. Its exact ground state is a macroscopic singlet entangling all spins in the chain. Its elementary excitations, called spinons, are fractional spin-1/2 quasiparticles created and detected in pairs by neutron scattering. Theoretical predictions show that two-spinon states exhaust only 71% of the spectral weight and higher-order spinon states, yet to be experimentally located, are predicted to participate in the remaining. Here, by accurate absolute normalization of our inelastic neutron scattering data on a spin-1/2 Heisenberg antiferromagnetic chain compound, we account for the full spectral weight to within 99(8)%. Our data thus establish and quantify the existence of higher-order spinon states. The observation that, within error bars, the experimental line shape resembles a rescaled two-spinon one with similar boundaries allows us to develop a simple picture for understanding multi-spinon excitations.

Critical 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 Betaine Phosphite (BPI), Betaine Phosphate (BP), and mixed crystals of (BPI)x(BP)1−x for x=0.05; 0.15; 0.30 and 0.60. The behaviour observed for the mixed compounds has a good resemblance to that of structural glasses.

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).

Structural phase transitions in partially deuterated betaine phosphite crystals studied by dielectric and electron paramagnetic resonance methods

Abstract Partially deuterated betaine phosphite (DBPI) crystals were investigated by measurements of the dielectric constant and by means of electron paramagnetic resonance (EPR). Two phase transitions could be detected in the temperature range from 100 K to 380 K: a high-temperature phase transition at Tc1 = (355 ± 3) K and a ferroelectric phase transition at Tc2 = (297 ± 3) K. The EPR studies show that the ferroelectric phase transition is related to the simultaneous ordering of the protons and deuterons in the O-H/D… O bonds.

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.