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Selected results of department 12

The former head of the Department of Dielectrics, Dr. Jan Petzelt, was awarded a prestigious award of the scientific community. The whole text »

Phase-field simulations demonstrate that the polarization order-parameter field in the Ginzburg-Landau-Devonshire model of rhombohedral ferroelectric BaTiO3 allows for an interesting linear defect, stable under simple periodic boundary conditions. This linear defect, here called the Ising line, can be described as an about 2-nm-thick intrinsic paraelectric nanorod acting as a highly mobile borderline between finite portions of Bloch-like domain walls of opposite helicity. The whole text »

BZT and NBT have become recently the most studied lead-free relaxor materials for their attractive piezoelectric and interesting physical properties. The whole text »

The ultra-broadband dielectric spectroscopy is particularly useful for studying dielectric–conductor nanocomposites, particularly near the electrical percolation threshold. Theoretically, we have studied the spectra of effective dielectric response of such composites using several models within the effective medium approximation [1]. The whole text »

Variety of multiferroic materials is prepared in our department. One of them was CaMn7O12 which exhibits strong magnetoelectric coupling. Small crystals (~ 0.1 mm) were prepared from high temperature solution of CaCl2 and MnO2, but they contained 9% of undesirable admixtures. An alternative method – modified sol-gel synthesis using water solutions of Ca and Mn nitrates and malic acid – produced pure CaMn7O12 powder with less than 1% admixtures. However, this method was not reproducible. The whole text »

Time-resolved terahertz spectroscopy provides a useful insight into charge carrier motion in nanostructured semiconductors: it provides a contact-free access to local response of charge carriers inside nanostructures averaged over macroscopic volume of a sample. This is a very pertinent quantity for many applications of disordered materials which still have a larger potential than perfectly aligned nanostructures.

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We found a unique effect of the applied electric field for new chiral liquid crystalline compound, namely lactic acid derivative. We observed reversible transformation of the planar TGBA texture to the homeotropic one, homogeneously dark in crossed polarizers. The transformation is an analogy of the Frederiks transition known in nematics and only rarely can be found for smectics. The whole text »

For the first time a tilt of molecules around the gold nanoparticles or their clusters has been observed in the liquid crystalline smectic A phase. We have shown the tilt is a consequence of interaction of the molecules with the surface of nanoparticle leading to a local smectic A-smectic C transition. Nanoparticles attracted to edge dislocations enable to visualize them under an optical polarizing microscope. The whole text »

We present a novel type of hybrid nanocomposite prepared by mixing maghemite nanoparticles (MNPs) and a chiral liquid crystalline compound. The multiferroic system exhibits the ferroelectricity as well as superparamagnetic (SPM) properties. The impact of nanoparticles and effect of applied magnetic field on ferroelectric liquid crystalline properties were established. The magnetic behavior is typical for a system of SPM nanoparticles with inter-particle dipolar interactions and surface spin disorder. The whole text »

Ferroelectric and antiferroelectric single crystals show phase transitions that can be evidence by different experimental methods. In this work we investigated single crystals of antiferroelectric PbZrO3 substituted with 1% of Ti (PZT 99/1) by means of optical microscopy, micro-Raman scattering, second harmonic generation and dielectric spectroscopy, on heating to and cooling from its cubic phase.

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