S. Haussühl

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.

The existence of light-induced long-lived metastable states in different Xn[Fe(CN)5NO]·yH2O crystals, powders and solutions

Abstract Irradiation-induced metastable states similar to those reported earlier in Na2[Fe(CN)5NO]·2H2O and Ba[Fe(CN)5NO]· 3H2O were observed in single crystals, crystalline powders and solutions of nitrosylpentacyanoferrates of different cations, including alkali metals, alkaline earth metals and the bivalent ions of the iron group. Such states can be generated in all nitrosylpentacyanoferrate-containing substances. The decay temperatures of the metastable states were determined using differential scanning calorimetry and appear to be positively correlated to the lattice energy.

Paraelectric and ferroelectric phases of betaine phosphite: structural, thermodynamic, and dielectric properties

Abstract The paraelectric and ferroelectric phases of betaine phosphite [BPI: (CH3)3 NCH2COO H3PO3] single crystals have been studied. The structure of BPI was determined at room temperature using x-ray and elastic neutron diffraction. Details of the ferroelectric transition and various low temperature properties were investigated using broad-band dielectric spectroscopy and calorimetric experiments. We compare the results obtained for single crystals of different origin which exhibit different ferroelectric phase transition temperatures.

Raman-spectroscopic and differential scanning calorimetric studies of the light induced metastable states in K2[RuCl5NO]

Abstract In K 2 [RuCl 5 NO] light-induced long-living metastable states can be generated similar to those in Na 2 [Fe(CN) 5 NO] · 2H 2 O and other nitrosylprussides revealing the decisive role of the NO ligand for the formation of the new states. With Raman spectroscopy intramolecular and lattice vibrations were investigated during the population process and in the state of saturation. Only the frequencies of the internal modes are shifted. The thermally induced decay was investigated by differential scanning calorimetry, yielding information about the decay temperature, the activation energy, the frequency factor and the order of reaction.

Population dynamics of the two light induced metastable states in Na2[Fe(CN)5NO]·2H2O single crystals

The dependence of the population dynamics on intensity, time, wavelength and polarisation of the illuminating light and on the temperature of both metastable states in Na2 [Fe(CN)5NO]·2H2O single crystals is investigated by differential scanning calorimetry. The population and depopulation behaviour can be described by exponential functions. The wavelength dependence shows the spectral range in which both states can be excited and the existence of a transfer process from state II into state I. Further, light of the near infrared region, transfers state I into state II.

Light-induced structural changes in sodiumnitroprusside (Na2(Fe(CN)5NO)·2D2O) at 80 K

Groundstate and electronic excited state (MSI) of deuterated sodiumnitroprusside (Na2(Fe(CN)5NO)·2D2O) have been investigated by neutron diffraction as well as by optical and Mössbauer techniques. Significant structural changes occur predominantly in the O−N−Fe−C-bond. It has been shown, that the N−O bond-length is not the order parameter, as expected from other studies. We found an increase in the bond lengths Fe−N4 of 0.019(2) Å and N−O of 0.004(4) Å respectively, which is in qualitative agreement with changes determined by Raman spectroscopy and predictions based on diatomic correlations (Badger/Herschbach/Laurie). Additionally we observed a change in the Fe−C1 bond length of 0.012(3) Å in agreement with Raman meaurements.

Mössbauer parameters of the two long-lived metastable states in Na2[Fe(CN)5NO]·2H2O single crystals

We have measured the quadrupole splitting, isomer shift and line broadening of the ground and two metastable states in Na2[Fe(CN)5NO]·2H2O single crystals. Pure state II could be observed by Mössbauer spectroscopy after irradiation of state I with light in the near infrared spectral region. The difference between the two nearly infinitely long-lived electronic states is shown. A possible change of the Fe(3d, 4s, 4p) electron densities is discussed on the basis of the Mössbauer parameters and thev(FeN) andv(NO) stretching vibrations. The resulting new orbital population allows to explain the observed properties of state I. A rearrangement of the electron density due to state II would lead to a contradiction with the vibrational behaviour of the molecule. The larger line width of both metastable states could not yet be interpreted.

Pressure-temperature phase diagrams of betaine-arsenate, -phosphate, and -phosphite

Abstract Betaine arsenate (BA), betaine phosphate (BP), and betaine phosphite (BPI) are paraelectric materials at ambient temperature, displaying structural phase transitions to ferro- or antiferroelectrically ordered low-temperature states. The crystals are closely related with respect to their chemical compositions, their crystal structures, and due to the types of intermolecular chemical bonds. Hydrogen bonds play a decisive role. By measuring the dielectric constant e(p, T) in the temperature interval 40 K ≤ T ≤ 250 K we have observed linear shifts of the transition temperatures Tc on applying hydrostatic pressure p in the range p ≤ 450 MPa. In all three materials the low temperature ordered phase is destabilized with increasing p, dTc/dp 8 MPa, i.e., the cell...

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.