Landau-Placzek Ratio Research Articles

Temperature dependence of spatial nanoheterogeneities of shear modulus in supercooled glycerol.

The boson peak in the terahertz vibrational spectrum carries information about nano-heterogeneities in the shear modulus in glass formers. Its evolution upon heating or cooling in a supercooled liquid state may shed light on the temperature dependence of heterogeneities. For this purpose, an analysis of the light scattering spectra of supercooled glycerol in the spectral range of the boson peak and fast relaxation was carried out and the parameters of the boson peak in the temperature range 180-330K were determined. The temperature dependent frequency of the boson peak was then expressed in terms of the mean-square amplitude of the shear modulus fluctuations. This was done using the heterogeneous elasticity theory in combination with the perturbation theory on small fluctuations and Ioffe-Regel criterion for transverse vibrations in glass formers. The contribution of structural relaxation effects to phonon damping becomes significant with increasing temperature. It is shown here that structural relaxation largely determines the temperature dependence of the mean-square fluctuations of the shear modulus at high temperatures. By solving the inverse problem, the temperature dependence of shear modulus fluctuations was obtained. It shows a rapid decrease above ∼250K with a linear extrapolation going to zero at the so-called Arrhenius temperature TA = 350K. Comparison with literature data on the Landau-Placzek ratio shows that they have a similar temperature dependence at T < TA, which is explained by the appearance of nanometer scale spatial heterogeneities below TA. This is confirmed by the temperature dependence of the amplitude of the boson peak.

The coloration of smalt produced at Ust-Ruditsa glass factory from 1753 to 1768

The Ust-Ruditsa glass factory, founded in 1753 by the Russian scientist Mikhail Lomonosov has produced a variety of smalt glasses for mosaics and bijouterie. Lomonosov, which was the glass-technologist of the factory, by using a limited number of glass colorants elaborated the glass receipts with the aim to obtain colored glasses. At that site several hundred colored glasses were prepared, investigated and employed. We report and discuss here the use of copper as colorant in the preparation of glasses having the same composition of selected Ust-Ruditsa glasses. A series of K2O-PbO-SiO2 glasses (KPS) doped with copper 9.5K2O·xPbO·(90-x)SiO2·0.5CuO (x = 10.1, 19.0, 27.0, 38.0, 47.3, 52.1, 56.8, 61.4 % in mass) has been prepared by melt-quenching technique. The Brillouin and Rayleigh scattering was measured with a 532 nm laser by using the calculated glasses refraction indexes. We found that the color changes due to the bathochromic shift of charge transfer band with increasing lead concentration. The copper center coordination environment is always a distorted octahedron. Upon reduction of copper by carbon the melt glass changes to an opaque orange smalt coloration due to the presence of Cu2O dendrimers. The calculation of Landau-Placzek ratio shows a non-monotonic change with increasing lead concentration. The nano-heterogeneous structure of glasses, characterized by an elevated Landau-Placzek ratio, is confirmed by TEM.

Температурные и концентрационные зависимости соотношения Ландау-Плачека в водных растворах &amp;gamma;-пиколина

In aqueous solutions of -picoline we investigated intensity relations in components of the fine structure spectrum of molecular light scattering – Landau-Placzek ratio – in dependence on temperature and concentration. Complex dependence of the fine structure spectrum intensity distribution was observed on temperature and concentration, which is due to structural processes in aqueous solutions.

Distributed Optical Fiber Sensor Allowing Temperature and Strain Discrimination in Radiation Environments

We evaluate the potential of a new architecture of distributed optical fiber sensor (DOFS) to discriminate between the temperature and strain changes along a single optical fiber exposed to radiation. This DOFS exploits the measurements of both the Landau–Placzek ratio (LPR) and the Brillouin frequency shift (BFS) to achieve the discrimination between the two parameters on up to 10 km of fiber with a spatial resolution of 1 m. We demonstrate that the LPR remains unaffected up to MGy(SiO2) dose levels, whereas the BFS is only slightly shifted by the radiation. The measured radiation-induced BFS is strongly reduced in radiation-hardened fluorine-doped single-mode optical fibers. Combining the DOFS architecture and the fiber allows discriminating temperature and strain using a single optical fiber up to megagray dose levels.

Acoustics velocity of liquid argon at high pressure: A classical molecular dynamics study

The adiabatic sound velocity of liquid argon is calculated by means of classical molecular dynamics simulations via the COMPASS force field, at the temperature of 388 K and the pressure range of 0.5–2.0 GPa. The isothermal sound velocity of liquid argon is obtained from the fluctuations of the supercell volume via Fluctuation Formula. Then, the adiabatic sound velocity is calculated from isothermal sound velocity by the Landau–Placzek ratio derived from the dynamic structure factor of the system. The calculated adiabatic sound velocities of liquid argon are in good agreement with the former Brillouin scattering measurements.

Hydrodynamic relaxations in dissipative particle dynamics.

This paper studies the dynamics of relaxation phenomena in the standard dissipative particle dynamics (DPD) model [R. D. Groot and P. B. Warren, J. Chem. Phys. 107, 4423 (1997)]. Using fluctuating hydrodynamics as the framework of the investigation, we focus on the collective transverse and longitudinal dynamics. It is shown that classical hydrodynamic theory predicts the transverse dynamics at relatively low temperatures very well when compared to simulation data; however, the theory predictions are, on the same length scale, less accurate for higher temperatures. The agreement with hydrodynamics depends on the definition of the viscosity, and here we find that the transverse dynamics are independent of the dissipative and random shear force contributions to the stress. For high temperatures, the spectrum for the longitudinal dynamics is dominated by the Brillouin peak for large length scales and the relaxation is therefore governed by sound wave propagation and is athermal. This contrasts the results at lower temperatures and small length scale, where the thermal process is clearly present in the spectra. The DPD model, at least qualitatively, re-captures the underlying hydrodynamical mechanisms, and quantitative agreement is excellent at intermediate temperatures for the transverse dynamics.

Landau–Placzek ratio in viscous liquids

The Landau–Placzek ratio (LPR) is measured in glycerol and triacetin in a wide temperature (viscosity) range. It is attempted to explain a sharp change in the LPR based on the Isakovich and Chaban theory [1] which assumes a two-component structure of viscous liquid. It is shown that the LPR strongly depends on the cluster concentration, and their sizes remain unchanged.

Temperature dependence of the Landau-Placzek ratio in liquid water.

Rayleigh-Brillouin light scattering is studied in liquid water over the range from 249 to 365 K. Experiments are carried out with a high spectral resolution (0.1 GHz), eliminating any contribution of the structural relaxation to the elastic line. The Landau-Placzek ratio is found as the ratio of the Rayleigh and Brillouin intensities. In the whole temperature range, the Landau-Placzek ratio is found to be in good agreement with a prediction of the theory with a pair of independent thermodynamic variables, pressure and entropy. This description is usually used for single-component homogeneous liquids. An excess of the Landau-Placzek ratio above the prediction is expected for inhomogeneous liquids and is observed, for example, in glass-forming liquids below a certain temperature. In contrast to glass-forming liquids, no excess of elastically scattered light increasing at low temperatures is observed for the Landau-Placzek ratio of water. This suggests that the Landau-Placzek ratio of liquid water can be described by a homogeneous structure, and the idea of the water structure consisting of two structural motifs may not be necessary to explain the experimental ratio.

Inelastic light scattering study of hydrogen-bonded glass formers: Glycerol and ethanol

Temperature dependences of the structural relaxation time τα(T) of two hydrogen-bonded glass formers, glycerol and ethanol, were investigated by depolarized light scattering technique. τα(T) of glycerol demonstrates a transition from the Arrhenius law at high temperatures to a non-Arrhenius behavior at TA~366K. Combination of derivative analysis results for τα(T) from light scattering and dielectric spectroscopes reveals this transition near ~200K in the case of ethanol. The obtained values of TA are close to the temperatures below which the excess of the Landau-Placzek ratio, associated with the appearance of locally favored structures, was observed earlier.

Landau-Placzek ratio of an inorganic glass with PbS quantum dots

The first example of application of the Rayleigh and Mandel'shtam-Brillouin scattering (RMBS) spectroscopy to a study of glass containing quantum dots (QDs) is presented. PbS QDs were precipitated in sodiumzincaluminosilicate glass doped with lead sulfide during successive heat treatment in several steps. After each step of the heat treatment, RMBS and absorbance spectra were measured. As a result, the Landau-Placzek ratio and QDs radii were evaluated as functions of heat treatment time. It was found that the Landau-Placzek ratio rises in the course of heat treatment by an order of magnitude. We connect this rise with an increase in Rayleigh scattering caused by increase of radii and number density of QDs. To confirm this assumption, the theoretical expression for the contribution of light scattering by QDs to the Landau-Placzek ratio was derived. The theoretical dependence of the QDs Landau-Placzek ratio on radius and number density of QDs is confirmed by the experiment. For calculation of this Landau-Placzek ratio, optical constants for PbS taken from different literature sources were used. Only the use of data from [S. Adachi (1999) Optical Constants of Crystalline and Amorphous Semiconductors] gives a good agreement between the calculated and measured values.

Brillouin distributed strain sensor performance improvement using FourWaRD algorithm

Abstract This paper presents an improvement of dynamic range as well as the strain resolution of the proposed 70 km Brillouin distributed sensor using Fourier wavelet regularised deconvolution (FourWaRD) algorithm. We have investigated the deconvolution algorithms such as: Fourier deconvolution (FourD), Fourier regularised deconvolution (FourRD) and (FourWaRD) in this paper. The Landau–Placzek ratio (LPR) is used for extracting the strain profile of the proposed sensing system with the interrogating technique based on optical time domain reflectometry (OTDR). Numerical simulation result shows that the strain resolution is enhanced about eighteen times at 70 km distance using FourWaRD algorithm compared to FourD algorithm. Similarly, the dynamic range of 49.1 dB is achieved using FourWaRD algorithm whereas 32.77 dB and 45 dB are observed using FourD and FourRD algorithms respectively. The proposed system exhibits a spatial resolution of 10 m using 10 mW launched power for 70 km sensing range.

The scattering of visible radiation in glasses with lead sulfide nanocrystals

This paper discusses the light scattering of multicomponent silicate glass doped with lead sulfide, which results from secondary heat treatment when a two-phase system consisting of a glassy matrix and a nanostructured semiconductor phase of PbS is formed. The Rayleigh–Brillouin scattering spectra are obtained in this system. It is established that the Landau–Placzek ratio monotonically increases from 170 to 850 s as the heat-treatment time is increased, because the radius of the PbS crystals in the range 2.0–2.5 nm and their concentration increase.

Analysis of Variation of Brillouin and Rayleigh Scattering Coefficients with Thermal Strain in Landau-Placzek Ratio Based Optical Fiber Distributed Sensing for XLPE Insulated Power Cables

The optical fiber distributed sensing method based on Landau-Placzek Ratio (LPR), where Rayleigh and Brillouin scattering coefficients are utilized, is widely used for detecting thermal strain formations in XLPE insulated power cables. In this study, using strain dependence of material characteristics in XLPE cable insulation, i.e. Young and Shear moduli and the Poisson ratio, variations of Rayleigh and Brillouin scattering coefficients with thermal strain and their thermal strain sensitivities have been analyzed. Using Matlab R2008a, behaviour of the sensing fiber integrated to a 64/110 kV power cable has been obtained with simulations for 318 oK – 339 oK temperature range and 668  - 1231  thermal strain range. For thermal strain variations in 668  - 1231  range, while thermal strain sensitivity of Rayleigh scattering coefficient is changing from 1.8286 × 10-4 % to 1.8267 × 10-4 % , that of Brillouin scattering coefficient changes from – 7.9727 × 10-4 % to - 8.0086 × 10-4 % . Using simulation results, thermal strain sensitivity variations of Rayleigh and Brillouin scattering coefficients have been computed as  - 3.27 × 10-10 %/ and  - 6.38 × 10-9 %/ , respectively. In 668  - 1231  range, it has been observed that thermal strain sensitivity of LPR changes from 9.7439 × 10-4 % to 9.7068 × 10-4 %. Using LPR simulation results, strain-dependent LPR formula derived with the analytical method has been simplified and expressed with a linear equation

Temperature of nanometer-scale structure appearance in glasses

The structural network of glass is known to be partitioned into quasiordered nanometer regions (clusters). It is considered that the formation of nanometer-scale inhomogeneities occurs still in a liquid state in the process of cooling and substantially affects the ability of the substance to glass transition. In this work, we discuss the problem of determining the temperature at which a glass nanometer-scale structure is formed. Based on the analysis of the inhomogeneous broadening of Raman spectrum lines and the Landau-Placzek ratio, we show that the formation of an inhomogeneous structure starts near the temperature of the transition from the Arrhenius behavior of the relaxation time (viscosity) to non-Arrhenius behavior. This temperature can be determined using the derivative analysis.

Landau-Placzek ratio for heat density dynamics and its application to heat capacity of liquids

Exact relation for contributions to heat capacity of liquids is obtained from hydrodynamic theory. It is shown from analysis of the long-wavelength limit of heat density autocorrelation functions that the heat capacity of simple liquids is represented as a sum of two contributions due to "phonon-like" collective excitations and heat relaxation. The ratio of both contributions being the analogy of Landau-Placzek ratio for heat processes depends on the specific heats ratio. The theory of heat density autocorrelation functions in liquids is verified by computer simulations. Molecular dynamics simulations for six liquids having the ratio of specific heats γ in the range 1.1-2.3, were used for evaluation of the heat density autocorrelation functions and predicted Landau-Placzek ratio for heat processes. The dependence of contributions from collective excitations and heat relaxation process to specific heat on γ is shown to be in excellent agreement with the theory.

Long-lived submicrometric bubbles in very diluted alkali halide water solutions

Solutions of LiCl and of NaCl in ultrapure water were studied through Rayleigh/Brillouin scattering as a function of the concentration (molarity, M) of dissolved salt from 0.2 M to extremely low concentration (2 × 10(-17) M). The Landau-Placzek ratio, R/B, of the Rayleigh scattering intensity over the total Brillouin was measured thanks to the dynamically controlled stability of the used Fabry-Perot interferometer. It was observed that the R/B ratio follows two stages as a function of increasing dilution rate: after a strong decrease between 0.2 M and 2 × 10(-5) M, it increases to reach a maximum between 10(-9) M and 10(-16) M. The first stage corresponds to the decrease of the Rayleigh scattering by the ion concentration fluctuations with the decrease of salt concentration. The second stage, at lower concentrations, is consistent with the increase of the Rayleigh scattering by long-lived sub-microscopic bubbles with the decrease of ion concentration. The origin of these sub-microscopic bubbles is the shaking of the solutions, which was carried out after each centesimal dilution. The very long lifetime of the sub-microscopic bubbles and the effects of aging originate in the electric charge of bubbles. The increase of R/B with the decrease of the low salt concentration corresponds to the increase of the sub-microscopic bubble size with the decrease of concentration, which is imposed by the bubble stability due to the covering of the surface bubble by negative ions.

Origin of large Landau-Placzek ratio in a liquid metallic alloy

Dynamic structure factors for Na(c)K(1-c) liquid metallic alloys and pure components are studied by molecular dynamics simulations. Large values of Landau-Placzek ratio for four compositions of the liquid alloy are analyzed by wave-number dependent contributions from relaxation and propagating processes within the generalized collective modes method. The origin of the large Landau-Placzek ratio for liquid alloys is discussed.

Temperature dependence of the Landau-Placzek ratio in glass forming liquids

Here, we studied Rayleigh-Brillouin light scattering in ten different glass-forming liquids (α-picoline, toluene, o-toluidine, ethanol, salol, glycerol, dibutyl phthalate, o-terphenyl, propylene carbonate, and propylene glycol). For each of these liquids it was found that the Landau-Placzek ratio is in a good agreement with the theory at high temperatures and significantly exceeds the theoretical prediction below a certain temperature. Transition between the two temperature regimes occurs near T(A), where T(A) is crossover point from an Arrhenius-like to a non-Arrhenius behavior for the α-relaxation time dependence on temperature. Increase of the Landau-Placzek ratio relative to the theoretical prediction below T(A) seems to be the universal feature of glass-formers. We suggest that formation of locally favored structures in liquids below T(A) causes observed excess of the Landau-Placzek ratio.

Critical opalescence in fluids: 1.5-Scattering effects and the Landau–Placzek ratio

We adduce new arguments for the significance of so-called 1.5- (or sesquialteral) molecular light scattering in one-component fluids. For this purpose, we analyze its effect on the Landau–Placzek ratio for the critical opalescence spectrum. The results obtained are used to reveal experimental data which can be interpreted as evidence for its existence and to evaluate both the relative magnitude and the sign of the 1.5 scattering contribution.

Structural heterogeneity and pressure-relaxation in compressed borosilicate glasses by in situ small angle X-ray scattering

We report on Brillouin and in situ small angle X-ray scattering (SAXS) analyses of topological heterogeneity in compressed sodium borosilicate glasses. SAXS intensity extrapolated to very low angular regimes, I(q = 0), is related to compressibility. From Brillouin scattering and analyses of the elastic properties of the glass, the Landau-Placzek ratio is determined and taken as a direct reflection of the amplitude of frozen-in density fluctuations. It is demonstrated that with increasing fictive pressure, topological (mid- and long-range) homogeneity of the glass increases significantly. Heating and cooling as well as isothermal scans were performed to follow the evolution of density fluctuations upon pressure recovery. For a sample with a fictive pressure p(f) of 470 MPa, complete recovery to p(f) = 0.1 MPa was observed to occur close to the glass transition temperature. The values of fictive and apparent fictive temperature, respectively, as obtained via the intersection method from plots of I(q = 0) vs. temperature were found in good agreement with previous calorimetric analyses. Isothermal scans suggest that mid- and long-range recovery govern macroscopic density relaxation.