Electronic Structure and Piezoelectric Properties of SbSI Crystals

The SbSI crystals are investigated in the paraelectric and ferroelectric phases. The calculations have been performed to find the symmetry and normal coordinates of vibrational modes. We have observed that potential energy with double well create the soft mode of B1u symmetry in the microwave range and semisoft modes in the IR range. The Au and Bg symmetry, top electronic levels of the highest valence band, are degenerate in the paraelectric phase. It is shown that the Jahn-Teller effect is caused by Au symmetry normal mode interacting with the degenerate Au symmetry electronic states in the valence band top. The pseudo-Jahn-Teller effect is induced due to the same mode interacting with Au symmetry electronic states in the valence band and Bg symmetry states in the conduction band bottom. Concerning these two effects, the normal mode force constant K decreases and vibrational constants undergo changes during the phase transition. The theoretical deformation along the crystallographic—x(a), y(b), and z(c)—axes were studied for Sb atoms. The major change of piezoelectric modulus takes place in the ferroelectric phase near the phase transition temperature. At lower temperatures piezoelectric modulus changes become slow. The value as well as anomalous temperature dependence of piezoelectric modulus and Δz(T) is influenced by the change of mean potential energy V¯pz of Sb atoms in soft mode

Raccoon dog rabies surveillance and post-vaccination monitoring in Lithuania 2006 to 2010

<p>Abstract</p> <p>Background</p> <p>Oral rabies vaccination (ORV) in rabies infected regions should target the primary rabies vector species, which in Lithuania includes raccoon dogs as well as red foxes. Specific investigations on ORV in raccoon dogs are needed e.g. evaluation of vaccine effectiveness under field conditions. The objective of the current study was to investigate the efficacy of the ORV programme 2006-2010 in Lithuania by examining the number of rabies cases and estimating the prevalences of a tetracycline biomarker (TTC) and rabies virus antibodies in raccoon dogs.</p> <p>Methods</p> <p>From 2006 to 2010, 12.5 million rabies vaccine-baits were distributed by aircraft. Baiting occurred twice per year (spring and autumn), targeting raccoon dogs and red foxes in a 63,000 km²area of Lithuania. The mandibles of raccoon dogs found dead or killed in the vaccination area were analyzed by fluorescence microscopy for the presence of the TTC. Rabies virus sera neutralizing anti-glycoprotein antibody titres were determined using an indirect ELISA method and seroconversion (> 0.5 EU/ml) rates were estimated.</p> <p>Results</p> <p>During the study period, 51.5% of raccoon dog mandibles were positive for TTC. 1688 of 3260 tested adults and 69 of 175 tested cubs were TTC positive. Forty-seven percent of raccoon dog serum samples were positive for rabies virus antibodies. 302 of 621 investigated adults and 33 of 95 investigated cubs were seropositive. In the same time 302 of 684 and 43 of 124 tested samples were TTC and ELISA positive in spring; whereas 1455 of 2751 and 292 of 592 tested samples were TTC and ELISA positive in autumn. There was a positive correlation between the number of TTC and antibody positive animals for both adult and cub groups.</p> <p>Conclusions</p> <p>ORV was effective in reducing the prevalence of rabies in the raccoon dog population in Lithuania. The prevalence of rabies cases in raccoon dogs in Lithuania decreased from 60.7% in 2006-2007 to 6.5% in 2009-2010.</p

Prolonged mixed phase induced by high pressure in MnRuP

Hexagonally structured MnRuP was studied under high pressure up to 35 GPa from 5 to 300 K using synchrotron X-ray diffraction. We observed that a partial phase transition from hexagonal to orthorhombic symmetry started at 11 GPa. The new and denser orthorhombic phase coexisted with its parent phase for an unusually long pressure range, {\Delta}P ~ 50 GPa. We attribute this structural transformation to a magnetic origin, where a decisive criterion for the boundary of the mixed phase lays in the different distances between the Mn-Mn atoms. In addition, our theoretical study shows that the orthorhombic phase of MnRuP remains steady even at very high pressures up to ~ 250 GPa, when it should transform to a new tetragonal phase.Comment: 15 pages, 5 figures, supplementary materia

The Hidden Hydroxide in BaNiO3 Single Crystals Grown from a KOH Flux

Hexagonal oxide perovskites with one-dimensional chains of face-sharing MO6 octahedra are of enduring interest. Specifically, the hexagonal perovskite BaNiO3, prepared via non-ceramic approaches, acts as a highly functional catalyst for the oxygen-evolution reaction (OER) in alkaline media, with numerous studies focusing on this behavior, while its fundamental structural and physical properties have been somewhat overlooked. The current work is intiated by the observation of contrasting magnetic properties of BaNiO3 synthesized via KOH flux growth and high O2 pressure ceramic synthesis. To shed light on this difference, we have performed a series of rigorous analyses and found that the KOH flux-grown crystals made in open-air are actually a wet form of BaNiO3 that can be dried upon annealing in O2 flow but will then slowly degrade if stored under a condition where the O2 partial pressure is not high enough. Therefore, the present work not only provides insightful information to unveil a previously unknown aspect of the OER catalyst BaNiO3, but also rings a bell that the hidden hydroxide principle described here may also be applied to other hexagonal perovskite oxides prepared in wet conditions.Comment: 21 pages, 6 figure

Experimental and theoretical investigation of electronic properties of semiconductors with Schottky barrier in strong electric field

Magistriniame darbe tyrinėjamos elektroninės savybės įvairioms puslaidininkinėms medžiagoms. Tarp jų eksperimentiškai ir teoriškai tirti SbSI - tipo kristalai. Išmatuotos jų voltamperinės charakteristikos įvairiose temperatūrose bei srovės temperatūrinės priklausomybės esant skirtingai įtampai. Iš matavimų paskaičiuotas tarp metalo ir puslaidininkio susidarantis barjero aukštis, kuris vėliau buvo panaudotas teorinių – eksperimentinių rezultatų palyginimui. Eksperimentiniams elektrinio laidumo matavimams paaiškinti remtasi įvairiomis fononais stimuliuoto tuneliavimo teorijomis, kurių taikymui papildomai apskaičiuota elektronų ir fononų sąveikos konstanta esant skirtingoms temperatūroms. Taip pat įvertinti kiti, nemažiau elektriniame laidume svarbius, parametrai. Darbe parodyta, kad fononais stimulioto tuneliavimo teorijos efektyviai aprašo elektrinį laidumą tirtose medžiagose prijungiant prie jų metalo kontaktus.In this work experimental and theoretical investigations of the high electric field electrical properties in semiconductors with Schottky barrier are presented. Experimental research is given for SbSI – type crystals. Theoretical calculations and comparison with experimental data were made using electrical phonon-assisted tunnelling model (PhAT), which is usable for explanation of temperature-field dependent conductivity in wide branch of materials: semiconductors, dielectrics, inorganic, organic and other materials. PhAT model were used including well determined parameters: effective mass of the charge carrier, participating phonon energy, barrier height and electron-phonon interaction. Barrier height was experimentally measured and found for SbSI, SbSe0.2S0.8I, SbSe0.5S0.5I, SbSeI crystals. The results of the temperature dependence of electron–phonon (e–ph) interaction in the inquiring semiconductors were also calculated. It is shown that these semiconductors have kin e–ph interaction. It varies nearly for about ~ 2.6. It has been shown that the temperature dependent I-V characteristics of SbSeI crystals can be explained by the phonon-assisted tunnelling of charge carriers from the states located in the high electric field region at the electrode-crystal junction. The electron tunnelling probability W(E, T) from traps of the apparent depth to the conduction band was computed using evaluated electron-phonon interaction constant and effective mass of the polaron. The theoretical W-E curves in all the range of electric field strength and temperature fit well to the measured data I-V of Ag/SbSexS1-xI/Ag Schottky diodes. Also it has been shown that equation of electron tunnelling probability from the states in the high electric field region at the electrode-crystal junction to the conduction band in the case of assisting phonons is valid in the analysed range electric field strengths and temperatures.Švietimo akademijaVytauto Didžiojo universiteta

Temperature dependence of electron-phonon interaction in paraelectric and ferroelectric semiconductors

The results of (he temperature dependence of clcctron-phonon (c-ph) interaction in paraclcctric and ferroelectric semiconductors arc presented. Investigation performed for SbScI and SbSI crystals in the temperature ranges 80-325K and 275-335K respectively. It is shown that both types of semiconductors have kin c-ph interaction a. It varies nearly for about a ~ 2.7 and increases by sly degrees with the temperature increase. A mild increment of c-ph interaction at the temperature near ferroelectric phase transition for SbSI crystals is observed. Estimated Huang-Rhys parameter S was rather smaller for the SbSI than for SbSel crystalsVytauto Didžiojo universitetasŠvietimo akademij

AVBVICVII tipo junginių elektroninės struktūros, optinių ir dinaminių savybių tyrimas

In the dissertation AVBVICVII type compounds are analyzed theoretically and experimentally. Theoretical studies were carried out using Density Functional Theory (DFT), along with the Full Potential Linearized Augmented Plane Wave (FP-LAPW) method and the Generalized Gradient Approximation (GGA). For calculations Wien2k and PHONON comp. packages were used. Experimental studies were performed using spectroscopic ellipsometry method and measuring permittivity (electrical capacitance) as a function of temperature. The study discusses AVBVICVII type compounds’ inter-atomic chemical bonding, the electronic structure, optical properties, lattice dynamics, vibrational thermodynamic functions and dielectric properties in the paraelectric, ferroelectric and antiferroelectric phases