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Silver (Ag), not only alters the electrical and optical properties of ZnO thin films but also has the ability to enhance its ultraviolet (UV) emission. However, the mechanism for the UV emission enhancement has not been clearly understood. The study focused on optimization of the optical properties of pristine and Ag-doped ZnO films through variation of preparation and post deposition parameters. The prepared pristine and Ag-doped ZnO films were found to be polycrystalline in nature with diffraction peaks corresponding to ZnO and Ag phases. Increase in Ag and annealing temperature led to increase in the transmittance of Ag-doped ZnO films. The refractive index was found to increase with a decrease in substrate-source distance, an increase in Ag concentration, film thickness, and annealing temperature. The extinction coefficient for the analysed films was found to decrease with increase in substrate-source distance and annealing temperature, but increased with increase in film thickness. An inherent dissipation of electromagnetic energy in pristine and Ag-doped ZnO films was observed due to strong interaction between low and wide optical band gap energies of Ag and ZnO, respectively. The optical band gap energy increased with an increase in substrate-source distance, decreased with an increase in film thickness and annealing temperature at a wavelength, λ = 650 nm . The observed trends have been explained based on polarizability, reduced structural defects, thermal expansion, and lattice vibrations in pristine and Ag-doped ZnO films. The obtained optimized properties show that Ag-doped ZnO films are good candidates for optoelectronic applications. [ABSTRACT FROM AUTHOR]

The intricate relationship between electrons and the crystal lattice is a linchpin in condensed matter, traditionally described by the Fröhlich model encompassing the lowest-order lattice-electron coupling. Recently developed quantum acoustics, emphasizing the wave nature of lattice vibrations, has enabled the exploration of previously uncharted territories of electron–lattice interaction not accessible with conventional tools such as perturbation theory. In this context, our agenda here is two-fold. First, we showcase the application of machine learning methods to categorize various interaction regimes within the subtle interplay of electrons and the dynamical lattice landscape. Second, we shed light on a nebulous region of electron dynamics identified by the machine learning approach and then attribute it to transient localization, where strong lattice vibrations result in a momentary Anderson prison for electronic wavepackets, which are later released by the evolution of the lattice. Overall, our research illuminates the spectrum of dynamics within the Fröhlich model, such as transient localization, which has been suggested as a pivotal factor contributing to the mysteries surrounding strange metals. Furthermore, this paves the way for utilizing time-dependent perspectives in machine learning techniques for designing materials with tailored electron–lattice properties. [ABSTRACT FROM AUTHOR]

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We measured room‐temperature phonon Raman spectra of changchengite (IrBiS) and compared the experimental phonon wavenumbers to the theoretical ones obtained by means of the ab initio density‐functional‐theory calculations in the presence and absence of the spin‐orbit coupling effects. Combining two different excitation photon energies all the symmetry predicted Raman modes are experimentally observed. The electronic properties of IrBiS are found to be similar to the recently studied isostructural compound IrBiSe showing a large Dresselhaus spin‐orbit valence band splitting. A good agreement between the experimental and theoretically predicted Raman phonon wavenumbers is found only when the lattice parameter is constrained to the experimental value. The inclusion of the spin orbit coupling does not significantly affect the phonon wavenumbers. [ABSTRACT FROM AUTHOR]

The investigation of the Raman and Infrared phonons has been done for the tetragonal Ruddlesden-Popper compounds Barium Orthorhodate, Barium Orthoiridate, Barium Orthoplumbate, and Barium Orthostannate having phase I4/mmm and symmetry D4h17 using normal coordinate analysis. With three stretching and six bending force constants, the zone center vibrational modes have been calculated. For the first time, the assignments for the Raman and infrared wavenumbers for the tetragonal compounds Barium Orthorhodate and Barium Orthoplumbate have been reported using Wilson's GF-Matrix Method. The infrared wavenumbers for the compounds Barium Orthostannate and Barium Orthoiridate have been assigned theoretically in I4/mmm phase. A significant correlation of the cation Rhodium, Iridium, Tin, and Lead has been studied for the various vibrational modes providing insight into the structure of the investigated Barium Orthorhodate, Barium Orthoiridate, Barium Orthoplumbate, and Barium Orthostannate compounds. The force constants containing the cation Rhodium, Iridium, Tin, and Lead follow a predictable pattern and also exhibit changes in values as the atomic orbit varies. Further, as the atomic number varies, the vibrational modes that are governed by the cation Rhodium, Iridium, Tin, and Lead take on a distinct nature demonstrating that the size of the cation has a significant impact on the vibrational properties. The potential energy distribution for each normal mode in the tetragonal structure of the Ruddlesden-Popper phase of Barium Orthorhodate, Barium Orthoiridate, Barium Orthoplumbate, and Barium Orthostannate crystals have been analyzed and the contributions of stretching and bending force constants toward different vibrational modes have been calculated. [ABSTRACT FROM AUTHOR]

We study the coupled macroscopic and lattice wave propagation in anisotropic crystals seen as continua with affine microstructure (or micromorphic). In the general case, we obtain qualitative information on the frequencies and the dispersion relations. These results are then specialized to crystals of the tetragonal point group for various propagation directions: exact representation for the acoustic and optic frequencies and for the coupled vibrations modes are obtained for propagation directions along the tetragonal c -axis. [ABSTRACT FROM AUTHOR]

Mixed tin‐lead halide perovskites are promising low‐bandgap absorbers for all‐perovskite tandem solar cells that offer higher efficiencies than single‐junction devices. A significant barrier to higher performance and stability is the ready oxidation of tin, commonly mitigated by various additives whose impact is still poorly understood for mixed tin‐lead perovskites. Here, the effects of the commonly used SnF2 additive are revealed for FA0.83Cs0.17SnxPb1−xI3 perovskites across the full compositional lead‐tin range and SnF2 percentages of 0.1–20% of precursor tin content. SnF2 addition causes a significant reduction in the background hole density associated with tin vacancies, yielding longer photoluminescence lifetimes, decreased energetic disorder, reduced Burstein–Moss shifts, and higher charge‐carrier mobilities. Such effects are optimized for SnF2 addition of 1%, while for 5% SnF2 and above, additional nonradiative recombination pathways begin to appear. It is further found that the addition of SnF2 reduces a tetragonal distortion in the perovskite structure deriving from the presence of tin vacancies that cause strain, particularly for high tin content. The optical phonon response associated with inorganic lattice vibrations is further explored, exhibiting a shift to higher frequency and significant broadening with increasing tin fraction, in accordance with lower effective atomic metal masses and shorter phonon lifetimes. [ABSTRACT FROM AUTHOR]

The vibrations of a diatomic linear chain exhibit two bands, the acoustic and the optical one. In the case of equal masses and nearest‐neighbor spring constants, no gap exists. The effects of nearest, next‐nearest, and third‐nearest neighbor coupling with different spring constants are analyzed. Nearest neighbor coupling leads to two topologically different bulk states with winding numbers ν = 0 and −1. Next‐nearest neighbor coupling does not change the topological properties and introduces only a trivial "Semenov" gap. Third‐nearest neighbor coupling leads to four distinct topological bulk phases with winding numbers ν=0,±1,and−2. [ABSTRACT FROM AUTHOR]

Abstract—The effect of low-dose γ radiation on the mechanisms of low-frequency conductivity of mesoporous silicon has been studied. It has been shown that γ irradiation preserves the hopping character of conductivity at a change of the frequency of phonon lattice vibrations, a decrease in the size of the hop, and a shift of the level of the capture of traps to the Fermi level in the band gap, which makes the structure with mesoporous silicon irradiated by γ radiation promising for the creation of multifunctional resistive and capacitive devices. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we present the results of studies the Raman spectra of Ni1‐xZnxFe2O4 (x = 0, 0.25, 0.4, 0.5, 0.6, 0.75, 1.0) ferrites nanopowders at room temperature and spectral range from 50 to 2,000 cm−1. The interpretations of the Raman spectra are given. The analysis of the results showed that spectra of compositions contain of maxima interpreted by us as oscillations of magnetic sublattices. The intensities of these maxima correlated with changes of Ni and Zn concentrations in compositions and, accordingly, of total spins concentration. [ABSTRACT FROM AUTHOR]

We discuss a two‐dimensional model that leads to results which reproduce, at least qualitatively, some of the experimentally observed features of spin‐conversion compounds. The molecules of these compounds have two electronic energy levels separated by Δ. The values of the elastic constants of the springs contained in the molecules are lower in the upper level. Consequently, the phonon branches of the crystal depend on the electronic states of the molecules. The fundamental level is a low spin (LS) state and the excited one is a high spin (HS) state. We study the thermal variation of the high spin fraction, i.e., the fraction of molecules in the (HS) level by using a model of atom‐phonon coupling with a boundary effect: Δ = Δb for molecules within the bulk, and Δ = Δse < Δb for molecules on the boundary. These values are compound‐dependent, but independent of the size of the crystal. Our results qualitatively reproduce two seemingly contradictory experimental results as well as the disappearance and reappearance of the hysteresis loop that is observed when the number N of molecules of the crystal is very small. Our model explains why the width of the hysteresis loop decreases with decreasing N. We find that, for any number of molecules, the entropy of the crystal vanishes at 0 K, in accordance with the third law of thermodynamics. [ABSTRACT FROM AUTHOR]

The vibrational properties of two-dimensional phononic crystals are studied with large-scale molecular dynamics simulations and finite element method calculation. The vibrational band structure derived from the molecular dynamics simulations shows the existence of partial acoustic band gaps along the [ABSTRACT FROM AUTHOR]

A multifield theory of bodies with microstructure is developed. As the basic model we take the structural model of a Cosserat chain consisting of particles of rectangular shape. A linear complete discrete model, a linear reduced discrete model, and a nonlinear discrete model are derived and discussed. One-period and two-period solutions are obtained, describing small oscillations of particles in one direction and in different directions. Single-field and two-field, complete and reduced Cosserat models are constructed. It is shown that the singlefield model describes one-period solutions in the chain while the two-field model describes both long-wave one-period and short-wave two-period solutions. [ABSTRACT FROM AUTHOR]

The diffuse scattering pattern produced by frozen crystals of the 70S ribosome from Thermus thermophilus is as highly structured as it would be if it resulted entirely from domain-scale motions within these particles. However, the qualitative properties of the scattering pattern suggest that acoustic displacements of the crystal lattice make a major contribution to it. [ABSTRACT FROM AUTHOR]

Confocal Raman microscopy was applied in order to investigate the homogeneity of donor doping in Nb:SrTiO3 single crystals. Measurements of local Raman spectra revealed a systematic relation between the intensity of the Raman signal and the donor content of the crystals. We successfully elaborated a correspondence between the electronic structure and the intensity of the Raman lines using a crystal with macroscopic inhomogeneity as a demonstration sample. By mapping the distribution of the intensity of the Raman signal, we identified a characteristic inhomogeneous structure related to the presence of clusters with sizes of 5 µm to 20 µm, indicating inhomogeneous donor distribution caused by flaws introduced during crystal growth. Hence, we propose confocal Raman microscopy as a convenient technique for investigating the homogeneity and quality of doped perovskite surfaces, which are needed for various technological applications. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Structure and quantum effects of a Cl2molecule embedded in fcc and hcp para-hydrogen (pH2) crystals are investigated in the zero-temperature limit. The interaction is modelled in terms of Cl2–pH2and pH2–pH2pair potentials fromab initioCCSD(T) and MP2 calculations. Translational and rotational motions of the molecules are described within three-dimensional anharmonic Einstein and Devonshire models, respectively, where the crystals are either treated as rigid or allowed to relax. The pH2molecules, as well as the heavier Cl2molecule, show large translational zero-point energies (ZPEs) and undergo large-amplitude translational motions. This gives rise to substantial reductions in the cohesive energies and expansions of the lattices, in agreement with experimental results for pure hydrogen crystals. The rotational dynamics of the Cl2impurity is restricted to small-amplitude librations, again with high librational ZPEs, which are described in terms of two-dimensional non-degenerate anharmonic oscillators. The lattice relaxation causes qualitative changes of the rotational energy surfaces, which finally favour librations around the crystallographic directions pointing towards the nearest neighbours, both for fcc and hcp lattices. Implications on the reactant orientation in the experimentally observed laser-induced chemical reaction, Cl + H2→ HCl + H, are discussed. [ABSTRACT FROM AUTHOR]

The paper reports on magnetite successfully functionalized with two new molecules. The investigations, involving chemical and physical methods, provided relevant features involving cell parameters and grain sizes, or the intermingling ratio between magnetite and functionalizing molecules, as deduced from magnetic measurements. A large amount of interesting data concerning various surface and local interaction mechanisms was supplied by detailed Mössbauer measurements. The new outputs are explained in terms of material processing and intimate mixing of the involved molecules. [ABSTRACT FROM AUTHOR]

We use a lattice vibrational technique to derive thermophysical and thermochemical properties of the pure elements aluminum and iron in pressure-temperature space. This semi-empirical technique is based on either the Mie-Grüneisen-Debye (MGD) approach or an extension of Kieffer's model to incorporate details of the phonon spectrum. It includes treatment of intrinsic anharmonicity, electronic effects based on the free electron gas model, and magnetic effects based on the Calphad approach. We show that Keane's equation of state for the static lattice is better suitable to represent thermodynamic data for aluminum from 1 bar to pressures in the multi-megabar region relative to Vinet's universal and the Birch-Murnaghan equation of state. It appears that the MGD and Mie-Grüneisen-Kieffer approach produce similar results, but that the last one better represents heat capacity below room temperature. For iron we show that the high temperature behavior of thermal expansivity can be explained within the Calphad approach by a pressure-dependent Curie temperature with a slope between -1 and 0 K/GPa. [ABSTRACT FROM AUTHOR]

We report on a study of structural properties of Zn1-xCoxO by micro- and macro-Raman scattering from phonons. Bulk mixed crystals (x ≤ 0.03), grown by chemical vapour transport were investigated between 5 K and 295 K. Beside the common eigenmodes of the ZnO host lattice, we observed disorder-induced lattice vibration modes and a structure, tentatively assigned to a local vibration mode of the Co impurity. Our results are compared with literature data of other ZnO-based diluted magnetic semiconductors such as (Zn,Mn)O. [ABSTRACT FROM AUTHOR]

Terahertz spectral responses have been studied for five borate crystals Na5[B2P3O13] (NBP), Zn3BPO (ZBP), SrB4O7 (SBO), Na3La9O3(BO3)8 (NLBO) and PbB4O7 (PBO). It is found that the samples had good transmission in 0.25-1.5 THz region. Both SBO and NLBO have an absorption coefficient less than 10 cm-1. Among them, SBO has not only the smallest absorption coefficient but also a very flat dispersion in the frequency region under investigation. Distinct resonance absorption peaks are observed for ZBP at v1 = 1.4 THz, v2 = 2.0 THz and SBO at v = 2.4 THz. In the spectrum of PBO, two abnormal dispersions appear in the frequency regions 1.44-1.74 and 2.2-2.5 THz. The absorption coefficients and refraction indices of the five crystals are extracted from the THz time-domain (THz-TDS) spectra in 0.25-2.5 THz region. The properties and origins of the spectral responses are addressed. [ABSTRACT FROM AUTHOR]

During the period 1949-1961 Szigeti published four seminal papers on the dielectric behaviour of crystals. Szigeti's theory is applicable to isotropic and anisotropic, ionic and covalent crystals with different structures. Szigeti's theory connects dielectric, spectroscopic and elastic properties. An important outcome of Szigeti's theory is the concept of the effective ionic charge (s). It is pointed out that s correlates with a number of physical properties and is a measure of ionicity of the interatomic bond. Since Szigeti's work, several theoretical models have been proposed to account for the fact that s < 1. These models provide an insight into the complex polarization mechanisms in solids. This review summarizes Szigeti's work and the work that followed; the implications and applications of Szigeti's theory are discussed. Some new results are also included. [ABSTRACT FROM AUTHOR]

Inelastic nuclear resonance scattering measurements, utilizing a submilli eV monochromator, were performed on natural Dy metal, dysprosium oxide, and intermetallic Laves and Chevrel phase dysprosium compounds. The inelastic spectrum directly yields the partial phonon density of states, and thus provides a wealth of information about the modes of vibration occurring in a lattice at the Mössbauer Dy site. The extraction of the partial phonon density of states from a broad range of materials containing dysprosium demonstrates the feasibility of material science studies. [ABSTRACT FROM AUTHOR]

New experiments show that the solution of the complicated problem of Far Infrared (FIR) absorption by crystals of very low symmetry, illuminated at quasi-normal incidence, might have a simple solution, which has been suggested now that a number of spectroscopic studies on monoclinic Triglycine Sulphate (TGS) are available: i) in a first classical approximation where only the strongest bands are considered, the absorption spectrum depends only on the direction of the electric field E of the IR radiation, and Transverse Optic (TO) vibrations are directly excited with electric dipole variations dp parallel to E. ii) in a second approximation looking only at the weakest absorption bands, it depends only on the direction of the wave vector k and Longitudinal Optic (LO) vibrations are excited with dp parallel to k and extinction coefficients 3 orders of magnitude smaller. [ABSTRACT FROM AUTHOR]

Often one needs to estimate heat capacities and related properties such as the entropy for a particular material through interpolation, extrapolation, or comparison with data for related materials. A scheme is discussed to perform such estimates, focusing on the vibrational entropy. At intermediate and high temperatures, the entropy depends only on the logarithmic average over the phonon frequencies. This average can be factorized, so that the atomic masses separate from the interatomic force constants. Thus, one can account for the mass effect in the vibrational entropy and get a remaining quantity which depends only on the force constants, i.e., on the electronic structure, and shows a strong regularity when chemically similar materials are compared. In the framework of these ideas, estimates based on an additivity rule for the entropy of a complex system in terms of the entropies of the constituents, and also relations between the vibrational entropy and sound velocities, are discussed. Oxide and silicate minerals are used as examples. [ABSTRACT FROM AUTHOR]

In a crystal with a free surface the translational symmetry in one direction is raised. In this case it is possible to reduce the equation of motion of the crystal to a form which is analogous to the equation of motion of a semi-infinite generalized linear chain. In this picture the surface-phonons correspond to boundary vibrations of the chain. Methods to calculate the frequencies and the 'damping' constant of the surface-phonons are shown. If the surface exhibits a symmetric structure it is possible to classify the frequencies according to the irreducible representations of a subgroup of the surface-space-group. Model-calculations are performed for a free Si-111-surface using a six-parameter potential (fitted to dispersion curves). The change of the force constants near the surface is considered and fitted to the experiment of Ibach (ν=13.3×10 sec). With the obtained weakening of the potential near the surface, dispersion-curves for surface-phonons are calculated. [ABSTRACT FROM AUTHOR]

Zone-center optical phonons of tetrahedrally coordinated II-VI semiconductor ternary (ABC) and quaternary (ABCD) alloys display a variety of distinct multi-mode behavior patterns. A brief review of the modified random element isodisplacement model, which can satisfactorily account for the composition dependence of the frequencies of the zone-center optical phonons, is presented; in this model, one uses the macroscopic parameters of the binary end members and their LO-TO phonon frequencies. When a constituent is present in extreme dilution in a binary (or in a ternary), e.g., C in AB (or in AB D), one sees either a local or a gap mode associated with it. For higher concentrations, one can see two (three) LO-TO phonon pairs for the ternary (quaternary) in the first order Raman spectrum or in the infra-red deduced from an analysis of the reststrahlen bands, when the masses of B and C differ significantly but are lighter than that of A. We illustrate these features in the Raman spectra of CdMgTe and Cd MgMnTe. Also shown are the infra-red spectra of the local mode of Mg and Mn in Cd Te, where their isotopic nature is clearly manifested. [ABSTRACT FROM AUTHOR]

The first measurements of the depolarization ratios for low frequency Raman active rotational and translational modes of semicrystalline (melt) pyrazinamide (PA) are reported. Tentative assignments have been proposed for the lattice modes based on polarization characteristics and their experimental intensities. Intra- and inter-translational oscillations have been assigned using an isolated single-chain approximation whereas the rotational oscillations are identified by their intensities and energy-order in similar NH...N hydrogen bond system. The PA dimer symmetry based on these results has been discussed and supports the planar conformation. [ABSTRACT FROM AUTHOR]

A home-made slow-scan Fourier spectrometer was adapted in the far infrared (10-100 cm) to investigate strained-layer Si/SiGe superlattices (=SLs) with modulation periods D=120 Å, 40 Å at liquid helium temperature. The small variations of reflectivity (≤10) were detected against the large background by modulating the temperature of the sample using a chopped near infrared light emitting diode. The resulting change of sample temperature causes a variable population of the lowest acoustic phonon branch to larger q-values, and a large fraction of the zone folded phonon dispersion (∥q∥≤ π/ D) can be measured by observing difference phonon processes. The measurements outline important SL-properties (modulation periods, phonon dispersion, interface quality and strain effects). X-ray diffraction analysis confirms the FTIR-results. [ABSTRACT FROM AUTHOR]