Anomalous behavior of the elastic and inelastic properties in the ferroelectric phase of single-crystal (NH4)2SO4

The anomalous changes of the low-frequency elastic and inelastic properties of single-crystal (NH₄)₂SO₄ accompanying the phase transition from the paraelectric to the ferroelectric phase have been studied by the reverse torsion-pendulum method at 223 K and in the temperature region where the spontaneous polarization changes sign. Fiz. Tverd. Tela (St. Petersburg) 40, 2202–2205 (December 1998)     

Acoustical and elastic properties of transition metal nitrides

Elastic moduli of transition metal nitrides, TiN, ZrN and HfN, have been evaluated using electrostatic and Born repulsive potentials. Acoustical dissipation due to phonon-phonon (p-p) interaction, thermoelastic mechanism and dislocation damping due to screw and edge dislocations has been evaluated in the temperature range 50-500 K along the three crystallographic directions of propagation, viz. [1 0 0], [1 1 0] and [1 1 1] for longitudinal and shear modes. Grüneisen numbers, acoustic coupling constants and their ratios have been evaluated for the longitudinal and shear waves. Results are in good agreement with available data.     

On the elastic and inelastic scattering of O

Elastic and inelastic scattering data on ¹⁷O on ⁴⁰Ca measured at E_1ab=61 MeV are analyzed using collective core contributions plus valence terms which are obtained with the microscopic single-folding model. The role of two-step transfers and reorientation processes is also assessed.     

Characterisation of the high-pressure structural transition and elastic properties in boron arsenic

This paper carries out the First principles calculation of the crystal structures (zinc blende (B3) and rocksalt (B1)) and phase transition of boron arsenic (BAs) based on the density-functional theory. Using the relation between enthalpy and pressure, it finds that the transition phase from the B3 structural to the B1 structural occurs at the pressure of 113.42GPa. Then the elastic constants C₁₁, C₁₂, C₄₄, bulk modulus, shear modulus, Young modulus, anisotropy factor, Kleinman parameter and Poisson ratio are discussed in detail for two polymorphs of BAs. The results of the structural parameters and elastic properties in B3 structure are in good agreement with the available theoretical and experimental values.     

Effect of proton and laser irradiation on the elastic and inelastic properties of a V-Ti-Cr alloy

The behavior of Young’s modulus E and the decrement of ultrasonic vibrations δ in a V-4Ti-4Cr alloy is studied during proton (8-MeV protons, dose rate 10⁴ Gy/s) or IR laser (YAG: Nd³⁺ laser, wavelength 1.06 μm, intensity up to 10² W/cm²) irradiation. Measurements are performed using the method of a composite piezoelectric oscillator (longitudinal 100-kHz resonance vibrations). The sizes of the irradiated surface regions of a sample in the proton and laser experiments are the same in order to provide the same thermal conditions in the sample-quartz transducer system. The amplitude, time, and temperature dependences of E and δ are measured before and after preliminary plastic deformation, as well as before, during, and after irradiation of a sample. The process of postdeformation aging (the kinetics of recovery of internal friction after deformation) during proton irradiation is shown to differ substantially from that during laser irradiation. The specific features detected can be explained by the more intense evolution of the defect structure during proton irradiation. Analysis shows that radiation annealing is related to the ionizing component of proton irradiation, which excites the electronic subsystem of the metallic alloy and, thus, creates hot electrons and plasmons. The electron excitations relax at lattice defects (dislocations) and increase the dislocation mobility; this results in a relatively rapid decrease in the dislocation density and in a more significant (as compared to the laser irradiation) decrease in the level of internal stresses in the material. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 8, 2004, pp. 1409–1415. Original Russian Text Copyright ? 2004 by Kardashev, Plaksin, Stepanov, Chernov.     

Acoustic study of the elastic and inelastic properties of high-pressure polyethylene samples with different irradiation histories

The influence of vibrational deformation amplitude ε on the dynamic elasticity modulus (Young’s modulus E) and internal friction (logarithmic decrement δ) of high-pressure polyethylene samples with different histories is studied. Acoustic measurements are made by a resonance method using the longitudinal vibrations of a composite piezoelectric vibrator at a frequency of ≈ 100 kHz. The dependences E(ε) and δ(ε) are taken at room temperature. From the acoustic data, the elasticity and microplasticity of the samples are estimated. It is found that the microplasticity remains almost unaffected upon irradiation and aging, while the elasticity modulus and breaking elongation per unit length considerably depend on the history and clearly correlated with each other. The observed effects are explained by the fact that atom-atom interaction and defects inside polymer macromolecules substantially influence the elastic modulus and breaking strength, while the inelastic microplastic strain is most likely associated with molecule-molecule interaction, which is affected by irradiation insignificantly.     

High pressure phase transition and elastic properties of thorium chalcogenides

The structural and elastic properties of thorium chalcogenides at high pressure, have been investigated using a suitable inter-ionic potential. The calculated equation of state, phase transition pressures for B1-B2 transition and bulk moduli for ThX (X=S,Se,Te) compounds agree well with the experimental results. ThTe, which crystallizes in the CsCl structure, does not show any structural transition up to 48 GPa. The present analysis does not show any anomalous features in elastic properties arising from ‘f’ electrons.     

Multi-step processes in high-energy elastic and inelastic nuclear scattering

Multi-step processes in elastic and inelastic nuclear scattering at intermediate and high energies are investigated using a formulation whereby a finite number of channels are explicitly treated while all the other channels are approximately accounted for through a “second-order potential matrix”. Within the framework of the eikonal approximation the problem reduces to a finite system of first-order coupled integro-differential equations with non-local potentials which depend on the two-body density matrix of the target nucleus. The relationship of the above formulation to the DWIA, the close-coupling method, and the Glauber multiple scattering model is examined. This approach is applied to the elastic and inelastic (2⁺, 4.43 MeV) scattering of 1 GeV nucleons by ¹²C. The corrections to the DWIA are sizeable, and the inelastic scattering appears to be very sensitive to the multi-step contributions and the nuclear structure.     

Peculiarities in the thermal and elastic properties of polycrystalline titanium near the electronic topological transition

Temperature dependences of the photoacoustic signal magnitude and the relative velocity variation of longitudinal ultrasound in polycrystalline titanium are measured. Anomalous behavior of these quantities is observed in the temperature region corresponding to the electronic topological transition in a titanium single crystal. The results of measurements are interpreted as an experimental verification of the possibility for the anomalies associated with the electronic topological transition to “survive” in a polycrystalline metal.     

Deformed tensor interactions in deuteron elastic and inelastic scattering

The various forms of tensor potentials present in deuteron elastic and inelastic scattering on a deformed target nucleus are derived using a folding model for the deuteron-nucleus interaction. Approximate expressions for the radial dependence of the deformed tensor interactions parametrized with the derivatives of Woods-Saxon potentials are obtained and discussed for the case of a rotational nucleus.     

Structural phase transition and elastic properties of ZnSe at high pressure

We have evolved an effective interionic interaction potential to investigate the pressure-induced phase transitions from zinc blende (B3) to rock salt (B1) structure in II-VI [ZnSe] semiconductors. The elastic constants, including the long-range Coulomb and van der Waals (vdW) interactions and the short-range repulsive interaction of up to second-neighbor ions within the Hafemeister and Flygare approach, are deduced. Keeping in mind that both of the ions are polarisable, we employed the Slater-Kirkwood variational method to estimate the vdW coefficients. The estimated value of the phase transition pressure (P _t ) is higher than in the reported data, and the magnitude of the discontinuity in volume at the transition pressure is consistent with that data. The major volume discontinuity in the pressure-volume phase diagram identifies the structural phase transition from zinc blende to rock salt structure.

The variation of second-order elastic constants with pressure resembles that observed in some binary semiconductors. It is inferred that the vdW interaction is effective in obtaining the thermodynamic parameters such as the Debye temperature, the Gruneisen parameter, the thermal expansion coefficient and the compressibility. However, the inconsistency between the thermodynamic parameters as obtained from present model calculations and their experimental values is attributed to the fact that we have derived our expressions by assuming the overlap repulsion to be significant only up to the nearest second-neighbor ions, as well as neglecting thermal effects. It is thus argued that full analysis of the many physical interactions that are essential to binary semiconductors will lead to a consistent explanation of the structural and elastic properties of II–VI semiconductors.     

Pressure-induced structural phase transformation and elastic properties of transition metal mononitrides

The high-pressure structural phase transition in six transition metal mononitrides (TMNs) (M=Ti, Mo, V, Nb, Hf, and Zr), have been studied using a two-body interionic potential theory which includes the effect of Coulomb screening due to the semi-metallic nature of these compounds. The present theoretical results have been compared with the corresponding experimental and predictions of LDA theory. These TMN compounds have been found to undergo NaCl (B₁) to CsCl (B₂) phase transition, at a pressure quite high as compared to other binary systems. We have also predicted the elastic constants. It is shown that these binary materials are partially ionic in nature and the structural transformation is analogous to several other ionic binary systems.     

Microstructure,elastic, and inelastic properties of biomorphic carbons carbonized using a Fe-containing catalyst

The microstructure and amplitude dependences of the Young’s modulus E and internal friction (logarithmic decrement δ), and microplastic properties of biocarbon matrices BE-C(Fe) obtained by beech tree carbonization at temperatures T _carb = 850–1600°C in the presence of an iron-containing catalyst are studied. By X-ray diffraction analysis and transmission electron microscopy, it is shown that the use of Fe-catalyst during carbonization with T _carb ≥ 1000°C leads to the appearance of a bulk graphite phase in the form of nanoscale bulk graphite inclusions in a quasi-amorphous matrix, whose volume fraction and size increase with T _carb. The correlation of the obtained dependences E(Т _carb) and δ(T _carb) with microstructure evolution with increasing Т _carb is revealed. It is found that E is mainly defined by a crystalline phase fraction in the amorphous matrix, i.e., a nanocrystalline phase at Т _carb < 1150°C and a bulk graphite phase at T _carb > 1300°C. Maximum values E = 10–12 GPa are achieved for samples with Т _carb ≈ 1150 and 1600°C. It is shown that the microplasticity manifest itself only in biocarbons with T _carb ≥ 1300°C (upon reaching a significant volume of the graphite phase); in this case, the conditional microyield stress decreases with increasing total volume of introduced mesoporosity (free surface area).     

High pressure phase transition and elastic properties of cerium chalcogenides and pnictides

The structural properties of Cerium mono-chalcogenides and mono-pnictides have been investigated for the first time by using a modified interionic potential theory. The calculated transition pressures are in good agreement with the experimental results. The ionic bonding is found to be more pronounced in Ce-mono-chalcogenides than mono-pnictides. The calculated values of elastic constants are also predicted for the first time.     

An analysis of pressure-induced phase transition and elastic properties of neodymium monopnictides

We have predicted the phase transition pressures and corresponding relative volume changes of two neodymium monopnictides (NdAs and NdSb) having NaCl-type structure at ambient conditions, using an improved interaction potential model (IIPM) approach. Both the compounds have been found to undergo from their initial NaCl(B1) phase to a body centered tetragonal (BCT) phase at high pressure. Our calculated results of phase transitions, volume collapses and elastic behavior of these compounds are found to be close to the experimental results. This shows that the inclusion of the three-body interaction and polarizability effect makes the present model suitable for high pressure studies.     

Three-body elastic and inelastic scattering at intermediate energies

The Faddeev equation for three-body scattering at arbitrary energies is formulated in momentum space and directly solved in terms of momentum vectors without employing a partial wave decomposition. For identical bosons this results in a three-dimensional integral equation in five variables, magnitudes of relative momenta and angles. The cross sections for both elastic and breakup processes in the intermediate energy range up to about 1 GeV are calculated based on a Malfliet-Tjon type potential, and the convergence of the multiple scattering series is investigated.