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Selected results of department 12

Molecular tilt induced by gold nanoparticles or clusters of nanoparticles in the liquid crystalline smectic A phase of “de Vries” type of compound

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 »

Nanocomposite of superparamagnetic maghemite nanoparticles and ferroelectric liquid crystal

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 »

Catching intermediate phases in antiferroelectric single crystals

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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Compositional behaviour of phonons in Pb(Zr1-xTix)O3 ceramics

Raman spectra of PZT ceramics were studied systematically in a broad temperature interval (10–600 K) and a broad Ti/Zr concentration range around the morphotropic phase boundary (x = 0.25–0.70) [E. Buixaderas et al., Phys. Rev. B 91, 014104 (2015)]. The whole text »

Phase transition in ferroelectric domain walls of BaTiO3

The seminal paper by Zhirnov (1958 Zh. Eksp. Teor. Fiz. 35 1175–80) explained why the structure of domain walls in ferroelectrics and ferromagnets is so different. We have recently realized that the antiparallel ferroelectric walls in rhombohedral ferroelectric BaTiO3 can be switched between the Ising-like state (typical for ferroelectrics) and a Bloch-like state (unusual for ferroelectric walls but typical for magnetic ones) [see Fig. 1] by a compressive epitaxial stress. The whole text »

Electron localization in CdS nanocrystals

Ultrafast electron dynamics and short-range electron transport in CdS nanocrystals prepared by chemical-bath deposition were investigated in terahertz regime [Z. Mics et al., Phys. Rev. B 83, 155326 (2011)]. Initially high mobility of photogenerated electrons exhibits a decrease within 1 picosecond due to the relaxation of their excess energy. Role of nanocrystal surfaces and nanocrystalline aggregates in electron transport was elucidated.

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New experimental method allowed to record dispersion curves of polar lattice modes in magnetoelectric BiFeO3

Bismuth ferrite (BiFeO3) is a prototypical multiferroic system exhibiting extraordinary properties; it is ferroelectric up to TC ~ 1100 K as well as antiferromagnetic up to TN ~ 640 K. Characterisation of polar phonon modes is essential for understanding its dielectric and electromechanical behaviour. The whole text »

Reentrancy phenomenon of a smectic A phase in chiral liquid crystalline compounds

Unique sequence of phases was discovered in a chiral smectic, namely reentrance of orthogonal paraelectric A phase below the ferroelectric C phase. This behavior was explained by non-monotonous temperature dependence of the principal coefficient in the free energy expansion and microscopically by changes of molecular conformations and intermolecular distances due to occurrence a lateral bulky group in the molecule. This phenomenon is accompanied with anomalies in dielectric, optical and switching properties. The whole text »

Magnetoelectric multiferroics

Magnetoelectric multiferroics are materials, which exhibit simultaneously magnetic and ferroelectric order. There is theoretically possible to influence magnetic or ferroelectric domains with electric or magnetic fields, respectively, therefore these materials are intensively studied for their promising potential applications in non-volatile memories. Unfortunately, there are only few multiferroics in nature and most of them work only at low temperatures. We suggested to use large mechanical strain in ultrathin films for preparation of new „artificial“ multiferroics. The whole text »

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