Precision PAC measurements in Er2O3 and Ho2O3 single crystals and structure refinement

The structure of C-form Ho₂O₃ and Er₂O₃ single crystals and powder samples was investigated by the electric quadrupole hyperfine interaction of¹¹¹In(EC)¹¹¹Cd probe ions using the perturbed - angular correlation method (PAC). The resulting set of refined atomic coordinates is compared to X-ray data and used to calculate the orientations of the electric field gradients (EFG) which are reproduced by the PAC measurements in single crystals. The temperature dependence of the coordinates was measured for both substances.     

Obtaining and characterizing modified tannins by physical-chemical methods

After oxidation of tannins (Tannins 1–3) extracted from grape seeds, Tanoxil compounds with increased solubility and enhanced antioxidant activities were synthesized. In this research, ABTS^+· assay and a chemiluminescence method were used for antioxidant measurement of hydrophilic compounds (Tanoxils 1–3).

It was observed that the antioxidant activity (AA, %) is very similar for the three samples, while at the same time AA is quite high (93.16%–96.48%). The percentage of inhibition by ABTS^+· is higher for Tanoxil 2 (96.4%) as compared to Tannin 2 compound (14.34%). Moreover, the total content (T_CF) of carboxyl and phenolic groups was investigated. T_CF values, determined for Tanoxil products, revealed a double (Tanoxil 1) or triple (Tanoxil 2) increase as compared to the value of the T_CF of Tannin 1. Tanoxil products represent an interest for future research as they have a high AA (96.4%) and the content of acidic groups is significant (T_CF, 0.191 meq g^?1).

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Computational characterization of magneto-electric composites: the role of ferroelectric pre-polarization

The interaction between electric and magnetic fields enables smart devices which can find applications in sensor technology and data storage. Materials showing magneto-electric (ME) coupling combine different ferroic characteristics. In the present contribution we focus on composites, which combine ferroelectric and ferromagnetic phases due to strain couplings, such that they generate a strain-induced ME coupling. We derive a two-scale homogenization approach for the determination of effective properties in consideration of microscopic morphologies. Furthermore, we demonstrate the strong influence of ferroelectric polarization states on the ME-coefficient by modeling the switching of remanent polarizations on the microscale. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

An optical method to assess electromechanical coupling in ferroelectric ceramics

A new technique is described, which allows the assessment of elastic and inelastic regions around a macroscopic defect in ferroelectric-ferroelastic ceramics. The accuracy and robustness of the method are demonstrated on a PZT plate with a centered hole subjected to uni-axial compressive stresses. From the electrical potential distribution on the sample surface, the mechanical response of the material is obtained at different load levels.     

PAC-studies of Sn-doped In2O3: electronic defect relaxation following the 111In(EC)111Cd-decay

Perturbed γ-angular correlation measurements as function of the measuring temperature and the Sn-content have been performed in Sn-doped cubic In₂O₃ using ¹¹¹In(EC)¹¹¹Cd and ^111m Cd probes. By comparing the spectra of both isotopes, electronic relaxation phenomena, socalled decay after-effects, following the electron capture radioactive decay of ¹¹¹In, were established. A time independent loss of the static quadrupole interaction amplitudes was found to be characteristic for the electronic relaxation, and its temperature and doping dependence were measured. The high statistical accuracy of the PAC-data allowed a separation between structural and dynamic effects and the observation of each lattice site’s behaviour. Relaxation rates were extracted from numerical simulations based on Blume’s theory and related to the predominant electron transport mechanisms in In₂O₃, especially, with rising Sn-content, to the transition to metallic conduction.     

Doping of sapphire single crystals with 111In and 111Cd detected by perturbed angular correlation

The electric hyperfine interaction of ion beam implanted ¹¹¹In and ¹¹¹Cd probe atoms in sapphire (Al₂O₃) single crystals has been investigated using perturbed angular correlation spectroscopy. For both probe atoms the same distinctive electric field gradient was found, indicating that nearly all the implanted probe atoms form a stable substitutional configuration in the temperature range between 77 K and 873 K on the aluminum sublattice. A comparative study between ¹¹¹In and ¹¹¹Cd-measurements points to a dynamic interaction initiated by the electron-capture of ¹¹¹In(EC)¹¹¹Cd similar to In₂O₃ and La₂O₃. Size and orientation of the EFG are discussed in comparison to experimental results in Cr₂O₃ single crystals. This revised version was published online in August 2006 with corrections to the Cover Date.     

The isotropic-nematic interface of colloidal goethite in an external magnetic field

Polarization microscopy was used to study the behavior around the isotropic-nematic interface of colloidal goethite dispersions in a magnetic field. It has been found before that the nematic phase is favored in an external field. In the case of goethite this was also observed; nematic droplets formed inside the isotropic phase and coalesced with the nematic phase. However, the behavior was found to be much richer because of the particle rotation around a certain critical field strength. The simultaneous occurrence of (parallel)nematic-(perpendicular)nematic phase separation under the influence of a magnetic field also plays a role here.     

Application of Thermal Analysis to the Study of Some Waste Agricultural Products for the Preparation of Active Carbons

TG, DTG and DTA methods were used for the investigation of some waste agricultural products, such as grape seeds, walnut shells, plum and peach stones, which can serve as raw materials for the production of active carbons. It was demonstrated that thermo analytical methods are appropriate to study the thermal characteristics of the above wastes and the data obtained can be applied to the technological processes of active carbon preparation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Moduli of simple holomorphic pairs and effective divisors

In this note we identify two complex structures (one is given by algebraic geometry, the other by gauge theory) on the set of isomorphism classes of holomorphic bundles with section on a given compact complex manifold. In the case ofline bundles, these complex spaces are shown to be isomorphic to a space of effective divisors on the manifold. The second author was partially supported by SNF, nr. 2000-055290.98/1.