|Dielectric and IR spectroscopy||THz science and technology||Light and neutron scattering||
|Solid-state materials science||
Main activities of Department of Dielectrics cover experimental and theoretical investigations of high-permittivity insulators like liquid crystals, ferroelectrics, multiferroics, piezoelectrics, semiconductor nanostructures, and low-loss materials.
- Dielectric and IR spectroscopy
- THz science and technology
- Light and neutron scattering
- Theory and simulations
- Solid-state materials science
- Liquid crystals
The most significant fresh scientific results of our deparment are listed in the section Highlights.
New material for 5G mobile networks
Stanislav Kamba, Veronica Goian and Christelle Kadlec, in collaboration with Prof. D. G. Schlom from the Cornell University and other American and German colleagues, succeeded in developing a new material for mobile network of the 5th generation. Its outstanding properties were published in journal Nature Materials.
John Mangeri and Alexey Bubnov succeeded in FZU Photo Competition
John Mangeri won the second place in the FZU Photo Competition for his image of a computational simulation of a BaTiO3 nanoparticle (see Figure 1). Alexey Bubnov got the 3rd-4th place for his image of a beautiful liquid crystal texture seen under polarized light microscope (see Figure 2).
Vladimira Novotna was awarded the 2nd place in Photogenic Science Competition 2019
Photos of liquid crystals under a polarized microscope brought the second place to Vladimira Novotna in the category of ‘Photogenic Science’. The competition is organized by the Czech Academy of Sciences and by the association Science is Alive! (Věda žije! in Czech) and its aim is to evaluate photos related to science.
Organic nanotubes created from mesogenic lactic acid derivatives
We found a facile route how to prepare nanotubes from rod-like mesogens dissolved in typical organic solvents. For selected types of chiral rod-like molecules, both enantiomers as well as the racemic mixtures, the nanotubes are formed by slow evaporation from a solution, regardless the solvent, concentration or deposition type. Obtained supramolecular assemblies were studied using various experimental techniques and nanotubes of 50-60 nm diameter described. We proposed rolling-up mechanism related to the surface tension difference at the opposite layer surfaces.
Mesoscopic polarization dynamics and two ferroelectric sublattices
in the uniaxial tetragonal tungsten bronze (Sr
The high-frequency dielectric behavior of uniaxial tungsten-bronze strontium barium niobate crystals with various Sr/Ba ratios have been studied in order to thoroughly understand the evolution of the relaxation dynamics across the ferroelectric phase transition. We showed that the dielectric response along the polar axis consists of three relaxations corresponding to polarization mechanisms related to several correlation lengths of mesoscopic order and that they are closly associated with two different ferroelectric subsystems.in the structure .
Changes in spin and lattice dynamics induced by magnetic and structural phase transitions in multiferroic SrMn7O12
Upon cooling, SrMn7O12 undergoes a series of structural and magnetic phase transitions from cubic to rhombohedral symmetry, and to an incommensurately modulated crystal structure, which is connected with charge and orbital ordering of the Mn cations. We report IR, THz, and Raman spectra of SrMn7O12 ceramics reflecting corresponding changes in the phonon selection rules, including new phonons appearing in spin-order-induced ferroelectric phases .
Raman scattering yields cubic crystal grain orientation
The anisotropy of Raman scattering was applied to determine the orientation of individual microcrystal grains, as small as a few µm, of GaV4S8 polycrystalline compound. This was possible by measuring polarised Raman spectra as a function of rotation of the sample along the laser direction. On comparing the resulting set of spectra with a computer simulation for particular symmetries, the orientation of the crystal grains could of the determined with good precision.
Soft mode driven local ferroelectric transition in lead-based relaxors
Analysis of IR and THz spectra using Bruggeman effective medium approach revealed that the mesoscopic structure of Pb(Mg1/3Nb2/3)O3 and Pb(Mg1/3Ta2/3)O3 consists of dynamic randomly oriented uniaxially anisotropic polar nanoregions with harder transverse optical polar modes in the direction along the local dipoles [1,2].
Degenerate (identity) chemical reactions in ferroelastic crystals
The work points to reconsideration of degenerate chemical reactions because of the chemical reactions which take place in a solid phase where the orientation of the substituting molecules is maintained. The work points to the examples of a ferroelastic switching which is accompanied by braking and reestablisment of chemical bonds. The article suggests that the definition of the degenerate chemical reactions might distinguish the reactions where the truly identical molecules are formed from those ones where the resulting molecules are enantiomers or enatiomorphs in case of domains.