Fyzikální ústav Akademie věd ČR

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Physical Review Focus, 4/9/ 2009.

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Selected results of department 12

Theoretically predicted ferroelectric phase induced by tensile stress was confirmed in SrTiO3 epitaxial films and SrTiO3/DyScO3 heterostructures on DyScO3 substrates, prepared in top world laboratories. It occurs near 270 K and it is drive by a soft phonon mode in the THz range which couples to a low-frequency overdamped excitation (at ~ 10 cm–1) in the whole measured temperature range of 20-300 K.

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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.

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Computer simulations based on Ginzburg-Landau-Devonshire theory have been used to investigate piezoelectric properties of tetragonal BaTiO3 crystals. We have shown that piezoelectric response of twinned BaTiO3 increases with increasing density of 90° domain walls. A considerable enhancement of the longitudinal piezoelectric coefficient is predicted for domain sizes below 50 nm.

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A new series of new multifunctional materials with the azo-group in the molecular core has been prepared, which exhibit ferroelectric properties and are photosensitive. With these materials (known as photoferroelectrics) the illumination by visible light can change their electric and optical properties. After the light is switched off their properties are restored to the original state. Such materials offer a series of applications in optoelectronics or photonics.  The full text >>

Dye-sensitized nanostructured semiconductors represent a new generation of prospective materials for solar cell fabrication. Their operation relies on a cascade of complex physical processes. The efficiency of solar cells crucially depends on the speed of long-range charge carrier transport and the character of this transport constitutes the key knowledge for its improvements. Here we are interested in processes occurring on the sub-nanosecond time scale which include namely the electron injection into the semiconductor and the initial phase of the electron transport towards the anode (see Fig. 1). We use time-resolved terahertz spectroscopy as a contact-free probe of ultrafast carrier transport complemented with numerical simulations.

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