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Time-domain Brillouin scattering (TDBS) uses ultrashort laser pulses to (i) generate coherent acoustic pulses of picoseconds duration in a solid sample and (ii) follow their propagation in order to image material inhomogeneities with the axial resolution that can be deeply sub-optical, to nm-scale, and the lateral one down to the optical diffraction limit (half the optical wavelength of the probe laser). TDBS permits highly resolved 3D-imaging of grains in polycrystalline transparent samples with unlimited lateral sizes and thicknesses of at least 10 μ m also when samples are orientationally textured and/or located in devices permitting access along one direction and from one side only. This optical technique presents, accordingly, clear advantages compared to any x-ray based computed tomography (neither back-projection algorithm nor multiple viewpoints of the sample are needed) and classical spectroscopic methods. Here, we applied TDBS to the 3D-imaging of a sample of polycrystalline water ice containing two high-pressure phases. The imaging, accomplished via a simultaneous detection of quasi-longitudinal and quasi-shear waves, provided shape, coordinates, phase content, and crystallographic orientation of resolved crystallites in a common coordinate system. Monitoring of acoustic pulses simultaneously propagating in two neighboring grains provided a new tool for the localization of grain boundaries. [ABSTRACT FROM AUTHOR]

The analytical theory for the directivity patterns of ultrasounds emitted from laser-irradiated interface between two isotropic solids is developed. It is valid for arbitrary combinations of transparent and opaque materials. The directivity patterns are derived both in two-dimensional and in three-dimensional geometries, by accounting for the specific features of the sound generation by the photo-induced mechanical stresses distributed in the volume, essential in the laser ultrasonics. In particular, the theory accounts for the contribution to the emitted propagating acoustic fields from the converted by the interface evanescent photo-generated compression-dilatation waves. The precise analytical solutions for the profiles of longitudinal and shear acoustic pulses emitted in different directions are proposed. The developed theory can be applied for dimensional scaling, optimization, and interpretation of the high-pressure laser ultrasonics experiments in diamond anvil cell. [ABSTRACT FROM AUTHOR]

Featured Application: Evaluation of the elastic and optical parameters of any sub-micrometer-thick transparent inhomogeneous films. In the case of doped multiferroic materials, the proposed multi-technique approach is envisioned to help in designing promising films for multifunctional applications in the frame of the future information and communication technologies. Picosecond laser ultrasonics is an experimental technique for the generation and detection of ultrashort acoustic pulses using ultrafast lasers. In transparent media, it is often referred to as time-domain Brillouin scattering (TDBS). It provides the opportunity to monitor the propagation of nanometers-length acoustic pulses and to determine acoustical, optical, and acousto-optical parameters of the materials. We report on the application of TDBS for evaluating the effect of Praseodymium (Pr) substitution on the elasticity of multiferroic (Bi1−xPrx)(Fe0.95Mn0.05)O3 (BPFMO) thin films. The films were deposited on Si and LaAlO3 (LAO) substrates by a sol-gel method. X-ray diffraction and Raman spectra revealed earlier that a phase transition from rhombohedral to tetragonal structure occurs at about 15% Pr substitution and is accompanied by the maxima of remnant magnetization and polarization. Combining TDBS with optical spectral reflectometry, scanning electron microscopy, and topographic measurements by atomic force microscopy, we found that the structural transition is also characterized by the maximum optical dielectric constant and the minimum longitudinal sound velocity. Our results, together with earlier ones, suggest that BiFeO3-based films and ceramics with compositions near phase boundaries might be promising materials for multifunctional applications. [ABSTRACT FROM AUTHOR]

(C7H12N2)2[SnCl6]Cl2·1.5H2O is crystallized at room temperature in the monoclinic system (space group P21/n). The isolated molecules form organic and inorganic layers parallel to the (a, b) plane and alternate along thec-axis. The inorganic layer is built up by isolated SnCl6octahedrons. Besides, the organic layer is formed by 2,4-diammonium toluene cations, between which the spaces are filled with free Cl−ions and water molecules. The crystal packing is governed by means of the ionic N—H···Cl and Ow—H···Cl hydrogen bonds, forming a three-dimensional network. The thermal study of this compound is reported, revealing two phase transitions around 360(±3) and 412(±3) K. The electrical and dielectric measurements were reported, confirming the transition temperatures detected in the differential scanning calorimetry (DSC). The frequency dependence of ac conductivity at different temperatures indicates that the correlated barrier hopping (CBH) model is the probable mechanism for the ac conduction behavior. [ABSTRACT FROM PUBLISHER]

The Raman spectra of bis (4-acetylanilinium) tetrachloridozincate single crystals were studied in the range of 100-3500 cm-1 as a function of temperature of 298 K to 398 K. The bands mainly associated with the internal modes of the ZnCl4 anions only undergo weak changes. However, the strong evolutions of wavenumbers, widths and intensities of many lines associated with the organic cations are observed with discontinuities in the vicinity of the phase transition at 351 K. A phase transition at Tc = 351K was observed and characterized by the differential scanning calorimetry (DSC). The most important changes are observed for two lines at 3197.13 cm-1 and 3167.10 cm-1 (at room temperature) issued from asymmetric and symmetric stretching vibrations of (C-H) band and (NH3) group, respectively. The spectral characteristics of these lines are analyzed and consistently described in the framework of an order-disorder model for the phase transition. [ABSTRACT FROM AUTHOR]

Abstract: The room temperature structure of crystallized [N(C3H7)4]2Cu2Cl6 is triclinic with space group. It exhibits two sublattices made up of [Cu2Cl6]2− bitetrahedra and tetrapropylammonium N(C3H7)4 + layers. The vibrational characteristics have been measured at room temperature by infrared spectroscopy (400–4000cm−1) on polycrystalline samples, and by polarized Raman spectroscopy (30–3500cm−1) on microcrystals orientated with respect to the organic and inorganic sublattices. The strongly polarized Raman spectra at low wavenumbers are consistent with the existence of orientated [Cu2Cl6]2− bitetrahedra that exhibit a quasi C 2h symmetry. Ab initio calculations using Gaussian 98 set of quantum chemistry code are performed by DFT approach with B3LYP to predict the set of normal modes characteristics of free [Cu2Cl6]2−. The reliability of 3-21G, 6-31G(d) and LanL2DZ basis functions has been first checked in the case of [CuCl4]2− for which the results can be compared with experimental data previously reported. The low wavenumbers Raman spectra of [N(C3H7)4]2Cu2Cl6 are analysed and the lines are assigned on the basis of group theory and the ab initio calculation results. The whole vibrational characteristics of the [Cu2Cl6]2− bitetrahedra are given. [Copyright &y& Elsevier]

Ranking is a ubiquitous phenomenon in human society. On the web pages of Forbes, one may find all kinds of rankings, such as the world's most powerful people, the world's richest people, the highest-earning tennis players, and so on and so forth. Herewith, we study a specific kind-sports ranking systems in which players' scores and/or prize money are accrued based on their performances in different matches. By investigating 40 data samples which span 12 different sports, we find that the distributions of scores and/or prize money follow universal power laws, with exponents nearly identical for most sports. In order to understand the origin of this universal scaling we focus on the tennis ranking systems. By checking the data we find that, for any pair of players, the probability that the higher-ranked player tops the lower-ranked opponent is proportional to the rank difference between the pair. Such a dependence can be well fitted to a sigmoidal function. By using this feature, we propose a simple toy model which can simulate the competition of players in different matches. The simulations yield results consistent with the empirical findings. Extensive simulation studies indicate that the model is quite robust with respect to the modifications of some parameters. [ABSTRACT FROM AUTHOR]

To date, the fastest lithium ion-conducting solid electrolytes known are the perovskite-type ABO oxide, with A = Li, La and B = Ti, lithium lanthanum titanate (LLTO) ${\rm Li}_{3x} {\rm La}_{\left( {{2 \mathord{\left/ {\vphantom {2 3}} \right. \kern-\nulldelimiterspace} 3}} \right) - x} \Box_{\left( {{1 \mathord{\left/ {\vphantom {1 3}} \right. \kern-\nulldelimiterspace} 3}} \right) - x} {\rm TiO}_3 $ and its structurally related materials. In this formula, $\Box$ represents the vacancy. These materials have attracted much attention due to their application in lithium ion batteries used as energy sources in microelectronic and information technologies. In addition to the well-established simple cubic, tetragonal and orthorhombic perovskite type distorted cell structures, the hexagonal unit cell was reported in a recent study for Li La TiO, $\left( {0 \le \delta \le 0.06} \right)$. We investigated the ionic conductivity in hexagonal ${\rm La}_{0.5} {\rm Li}_{0.5}\- {\rm TiO}_3 $ by molecular dynamics. We confirmed that ionic conductivity in this compound is due to the motion of lithium ions. We show that both Arrhenius and Vogel-Tamman-Fulcher-type relationships could be used to express the high-temperature conductivity of this compound. From our results, hexagonal LLTO exhibits almost 1.7-1.9 ×10 S cm at room temperature. Thus, due to its high ionic conductivity, this compound is expected to show some advantages in comparison with the best conductors of this family, for usual applications of ionic conductors. [ABSTRACT FROM AUTHOR]

In NH 4 AlF 4 the NH 4 + molecules form a layered structure where the interlayer distance, 6.367 Å, is about twice as large as the intralayer nearest neighbours distance, 3.597 Å. There is an orientational order-disorder transition at T c = 156.9 ± 0.1 K, explained by the Ising model, with first and second neighbours and a weak interlayer coupling. Monte Carlo simulations are presented based on this model. [ABSTRACT FROM AUTHOR]

The temperature dependence of piezoelectric resonance frequency, dielectric, and piezoelectric properties of (65-x)[Pb(Mg1/3Nb2/3)O3]-xBaTiO3-35PbTiO3 (x = 0, 1, 2, 3) ceramics has been investigated. Sample compositions with x = 2 and 3 were found to exhibit a large piezoelectric response. Particularly, d31 value was nearly a constant over a temperature range from 150 to 325 K. A broad ferroelectric phase transition tuned by BaTiO3 ratio in the sample was deduced from the dielectric constant, piezoelectric resonance frequency, and Raman spectra. The temperature dependence of the Raman modes wavenumber positions and intensities provides a clear evidence for the occurrence of the phase transition. The temperature-stable piezoelectric response was attributed to the counter-balance of contributions from the dielectric and elastic responses. [ABSTRACT FROM AUTHOR]

Laser ultrasonics in a point-source-point-receiver configuration is applied for the evaluation of elastic properties of nontransparent materials in a diamond anvil cell at high pressures. Measurement of both longitudinal and shear acoustic wave velocities in an iron foil at pressures up to 23 GPa does not require any information in addition to the one obtained by all-optical pump-probe technique. [ABSTRACT FROM AUTHOR]

The time-domain Brillouin scattering technique, also known as picosecond ultrasonic interferometry, allows monitoring of the propagation of coherent acoustic pulses, having lengths ranging from nanometres to fractions of a micrometre, in samples with dimension of less than a micrometre to tens of micrometres. In this study, we applied this technique to depth-profiling of a polycrystalline aggregate of ice compressed in a diamond anvil cell to megabar pressures. The method allowed examination of the characteristic dimensions of ice texturing in the direction normal to the diamond anvil surfaces with sub-micrometre spatial resolution via time-resolved measurements of the propagation velocity of the acoustic pulses travelling in the compressed sample. The achieved imaging of ice in depth and in one of the lateral directions indicates the feasibility of three-dimensional imaging and quantitative characterisation of the acoustical, optical and acousto-optical properties of transparent polycrystalline aggregates in a diamond anvil cell with tens of nanometres in-depth resolution and a lateral spatial resolution controlled by pump laser pulses focusing, which could approach hundreds of nanometres. [ABSTRACT FROM AUTHOR]