Anomalous multi-order Raman scattering in LaMnO3: a signature of quantum lattice effects in a Jahn-Teller crystal.

The multi-order Raman scattering is studied up to fourth order for a detwinned LaMnO3 crystal. Based on a comprehensive data analysis of the polarization-dependent Raman spectra, we show that the anomalous features in the multi-order scattering could be the sidebands on the low-energy mode at about 25 cm(-1). We suggest that this low-energy mode stems from the tunneling transition between the potential energy minima arising near the Jahn-Teller Mn(3+) ion due to the lattice anharmonicity and that the multi-order scattering is activated by this low-energy electronic motion. The sidebands are dominated by the oxygen contribution to the phonon density-of-states, however, there is an admixture of an additional component, which may arise from coupling between the low-energy electronic motion and the vibrational modes.

d0 ferromagnetic interface between nonmagnetic perovskites.

We use computational and experimental methods to study d(0) ferromagnetism at a charge-imbalanced interface between two perovskites. In SrTiO(3)/KTaO(3) superlattice calculations, the charge imbalance introduces holes in the SrTiO(3) layer, inducing a d(0) ferromagnetic half-metallic 2D hole gas at the interface oxygen 2p orbitals. The charge imbalance overrides doping by vacancies at realistic concentrations. Varying the constituent materials shows ferromagnetism to be a general property of hole-type d(0) perovskite interfaces. Atomically sharp epitaxial d(0) SrTiO(3)/KTaO(3), SrTiO(3)/KNbO(3), and SrTiO(3)/NaNbO(3) interfaces are found to exhibit ferromagnetic hysteresis at room temperature. We suggest that the behavior is due to the high density of states and exchange coupling at the oxygen t(1g) band in comparison with the more studied d band t(2g) symmetry electron gas.

Evidence for strain-induced ferroelectric order in epitaxial thin-film KTaO3.

In perovskite-structure epitaxial films, it has been theoretically predicted that the polarization and the coherence of polar order can increase with increasing crystallographic strain. Experimental evidence of strain-induced long-range ferroelectric order has not been obtained thus far, posing the fundamental question of whether or not strain can induce the long-range polar order. Here we demonstrate the existence of strain-induced ferroelectric order in quantum paraelectric KTaO3 by combining experimental investigations of epitaxial KTaO3 films and density-functional-theory calculations. The long-range ferroelectric order does exist under a large enough epitaxial strain. We suggest that a region of short-range polar order might appear between paraelectric and ferroelectric states in the strain-temperature phase diagrams.

Atmospheric barrier-torch discharge deposited ZnO films: optical properties, doping and grain size effects.

Technology aspects, structure and characteristic properties of the atmospheric barrier torch discharge technique grown nominally pure and Al (0.1-5%) and Mn (0.05-0.5%) doped ZnO nanocrystalline thin films deposited on fused quartz substrates are reported. The set of films with various thicknesses in the range from 70 nm to 1000 nm were prepared for each composition. XRD and AFM analysis show well formed [001] preferably oriented hexagonal high quality films witch could be operatively fabricated in air atmosphere with controlled grain size. All films under study revealed n-type conductivity except some Mn doped films, which revealed p-type. Spectroscopic optical ellipsometry and luminescence spectroscopy studies evidenced luminescence properties typical for well formed ZnO and appreciable influence of Al doping and grain size on the optical absorption edge. Al doping shifts strongly absorption edge to the higher energies. The grain size decreasing (from 100 to 15 nm) leads to distinct diffusing of the absorption edge accompanied by increase of absorption in the near band edge region. For the smallest grains the pronounced Urbach-type absorption tail can be observed manifesting films inhomogeneity development.

Ultrathin SrTiO(3) films: epitaxy and optical properties.

Ultrathin (12-15 nm) SrTiO(3) films are grown by pulsed laser deposition on various single-crystal substrates. The crystal structure, orientation, and strain state of the films are studied by x-ray diffraction. The room-temperature optical properties of the films are experimentally determined using ellipsometric spectroscopy in the 1-6 eV spectral range. Epitaxial films with biaxial in-plane strain are obtained on LaAlO(3), DyScO(3), and KTaO(3) substrates, with the critical thickness for pseudomorphic growth being less than 10 nm. Abrupt strain relaxation has been detected. The optical properties of the films with different microstructure are compared with each other and with those of single-crystal SrTiO(3). Based on the comparison, surface effects are suggested to be dominant in the visible range, while the interband transitions are smeared and suppressed due to small film thickness and the presence of biaxial strain. The energies of gaps can increase due to strain-induced polarization. The absorption edge is affected by all the factors mentioned (surface, thickness, strain, and polarization).

SrTiO(3):Cr nanocrystalline powders: size effects and optical properties.

The crystal structure, optical absorption, and photoluminescence of chromium impurity centers were studied in nanocrystalline SrTiO(3):Cr (0.1 mol%) powders with average particle size within the range 13-100 nm prepared by the Pechini-type polymeric sol-gel method. Only the presence of a cubic perovskite phase of O(h)(1) symmetry was proved for the powders at room temperature, by means of x-ray diffraction. The lattice constant a = 3.910 Å, larger than that of bulk SrTiO(3) crystals (a = 3.905 Å), was found for nanoparticles with the size about 20 nm. The optical absorption edge and the zero-phonon R-line ([Formula: see text]) of luminescence of the octahedral Cr(3+) centers shifted to higher energies with decreasing nanoparticle size. These size effects were regarded as intrinsic to SrTiO(3). An unusual and large temperature shift of the R-line position very similar to the 'dielectric related' one of the bulk crystals was observed for all powders, evidencing their quantum paraelectric behavior. However, the powders with the average particle size about 13 and 20 nm did not reveal completely reproducible behavior of the R-line position at low temperatures. This instability was considered a possible manifestation of a low-temperature phase transition in small enough SrTiO(3) nanoparticles.

[A pharmacological analysis of the GABA-ergic system of the primordial hippocampus in the frog Rana temporaria]. / Farmakologicheskii analiz GAMK-ergicheskoi sistemy primordial'nogo gippokampa liagushki Rana temporaria.

The data on evoked potentials (EP) in the frog primordial hippocampus during the surface application of gamma-aminobutyric acid (GABA), beta-alanine and aminooxyacetic acid in the region of EP recording are presented. These results in the aggregate with the earlier described effects of picrotoxin, bicuculline, muscimol, baclofen (on EP) and GABA (on intracellular potentials) permit to suggest the presence of GABA-ergic inhibitory system and two types of GABA receptors in the frog primordial hippocampus.

[Effect of ultrasound on the membrane potential and embryonic development of sea urchin eggs]. / Vliianie ul'trazvuka na membrannyi potentsial i émbrional'noe razvitie iaitsekletok morskogo ezha.

Eggs of sea urchin Strongylocentrotus intermedius were exposed to continuous wave ultrasonic energy at a frequency of 2 MHz for 3 min. Ultrasonic treatment results in the appearance of monstrous embryos that die at the latest stages of their development. The number of dead embryos sharply grows with the increase in the spatial average intensity from 0.4 W/cm2 up to 1.6 W/cm2, when it comprises 100%. Dramatic decrease from 99% to 17% in the absolute value of transmembrane potential for both fertilized and unfertilized eggs was observed after ultrasonic treatment. These results seem to be caused by the action of stable cavitation. The given estimations show that for ultrasonic intensities more than 0.2 W/cm2 and providing the presence of gaseous bubbles in the vicinity of eggs shell the value of shear stress in an egg shell becomes great enough to cause the cytoplasmic gel fragmentation.

[The neurotropic action of kavinton]. / Issledovanie neirotropnogo deistviia kavintona.

The presence of the neurotropic component in cavinton effect was shown as a result of the analysis of the changes in evoked potentials of the frog primordial hippocamp, the surviving slices of the mouse hippocamp and the neuronal activity of the rabbit visual cortex pyramidal neurons at different routes of administration of apovincaminic acid ethyl ether (cavinton).

[2 types of GABA receptors in the intact olfactory bulb and primordial hippocampus of the frog: the pharmacological data]. / Dva tipa GAMK-retseptorov v intaktnoi oboniatel'noi lukovitse i primordial'nom gippokampe liagushki: farmakologicheskie dannye.

The in vivo effects of (+/-) baclofen (10(-6)-10(-4) M), muscimol (10(-5)-10(-4) M), and (+) bicuculline (10(-4)-10(-3) M) applications on evoked potentials in the olfactory bulb (OB) and primordial hippoccamp (PH) were studied in frogs. Baclofen was found to decrease drastically postsynaptic components of OB orthodromic potential and to slightly increase OB antidromic potential. Muscimol decreased only the second component of OB orthodromic potential and OB antidromic potential. Baclofen and muscimol decreased all the components of PH orthodromic potential, but for the first positive one. All the effects were reversible and dose-dependent. Bicuculline antagonized muscimol effects, without affecting baclofen effects in both structures under study. The results suggest the presence of two types of GABA-receptors in OB and PH of frogs. GAGAB-receptors are shown to be located on the primary olfactory afferents and to be responsible for presynaptic inhibition in OB.

[Visual projections in the forebrain of the carp Cyprinus carpio]. / Zritel'nye proektsii v perednem mozgu karpa Cyprinus carpio.

In the carp C. carpio, studies have been made on the evoked potentials (EP) in the-forebrain elicited by electrical stimulation of contralateral (with respect to the midbrain tectum) nerve. The most high-amplitude and short-latency EP were recorded in the rostro-lateral part of the forebrain at the depth of 1,000-1,500 mu. According to the topographical nomenclature of cyprinid telencephalon, this region corresponds to the area dorsalis telencephali pars lateralis, whereas according to classic comparative neuroanatomical nomenclature it may be defined as the primordium hippocamp or primordium piriform zone. Comparison of the EP in the telencephalon with those in the midbrain tectum suggests active nature of the former.