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Experimental studies of the shock wave properties of two epoxy resins with the same composition but different curing temperatures (160 and 200 °C) at up to 330 GPa pressure have been carried out. Laser interferometry was used to record particle velocity profiles at up to 73 GPa pressure while measuring the shock wave velocity. The release sound velocity was experimentally determined in the 3–73 GPa pressure range. Cumulative explosive shock wave generators were used to study the shock Hugoniot of epoxy resins at pressures above 100 GPa. It was shown that the shock compressibility data of both samples are approximated by a single shock Hugoniot within the experimental error. A kink on Hugoniot recorded close to 25 GPa pressure indicates a chemical decomposition in epoxy resin. Above this kink, a change in the shock wave front structure was recorded. Hugoniots of epoxy resin and unidirectional carbon/epoxy composite were compared at up to 370 GPa pressure. [ABSTRACT FROM AUTHOR]

This Tutorial focuses on the physics of layered compounds under high pressure. We have chosen h-BN and III–VI layered materials as representative materials. h-BN layers are strictly two-dimensional. Layers in III–VI compounds are more complex, and subtle details in their structural behavior play an important role in the evolution of high pressure properties. They are also interesting because they contain a different number of layers in their primitive unit cell and/or have a different ionic character. We begin describing the structural evolution. We discuss the experimental challenges encountered as well as the main findings related to intra- and interlayer compressibility, polytype influence, and geometrical modifications induced by pressure inside the layers. We then describe lattice vibrations. The origin of the modes is reviewed, paying attention to the relationships between atom motions in different layers. We discuss the convenience of redefining the Grüneisen parameter and describe the behavior of rigid layer modes, soft modes, and Davidov pairs. The last section is devoted to the electronic properties. We show that the changes observed when passing from a single layer to a three-dimensional BN are qualitatively similar to those induced by high pressure. The pressure behavior of electronic transitions in III–VI layered compounds is very rich, revealing the subtle balance between intra- and inter-layer interactions. Finally, we take advantage of high pressure studies to explain the formation of the Mexican hat type of valence band at ambient conditions in single layers of InSe and GaSe, but not in three-dimensional compounds. [ABSTRACT FROM AUTHOR]

In this work, we report a high-pressure study on fergusonite-type LaNbO4. Powder x-ray diffraction and Raman spectroscopic experiments support the occurrence of a phase transition between 11 and 14 GPa. The transition takes place from a monoclinic fergusonite-type structure (space group I2/a) to another monoclinic structure (space group P21/c). The phase transition is reversible, and the high-pressure phase is isomorphic to the high-pressure phase of HoNbO4. The high-pressure phase remains stable up to 33.3 GPa, the highest pressure reached in the present measurements. Density-functional theory calculations found that in the pressure range of the studies; the high-pressure phase has a higher enthalpy than the low-pressure fergusonite phase. We propose that the high-pressure phase is metastable and it is observed because of non-hydrostatic conditions in the experiments. The pressure dependence of unit-cell parameters of the low-pressure phase and the room-temperature equation of state are reported. The pressure dependence of various Raman and IR frequencies as obtained from experiment and theory is also reported. For the fergusonite phase, we have also obtained the isothermal compressibility tensor, elastics constants, and elastic moduli. [ABSTRACT FROM AUTHOR]

This study examines the high-pressure structural properties of nanocrystalline Fe confined by single-walled carbon nanohorns (SWCNHs) and SWCNHs (filled with Fe nanoparticles) named Fe-filled SWCNHs up to a pressure of 21.8 GPa. In detail, the Fe-filled SWCNHs did not undergo a special structural transformation at up to 21.8 GPa, except the partial irreversible amorphization of graphene sheets forming the core part above ∼18 GPa. Cubic Fe (bcc Fe) and Fe3O4 coexisted simultaneously in the Fe-filled SWCNHs. The Fe encapsulated by the SWCNH underwent a reversible transformation from bcc Fe to a hexagonal Fe (hcp Fe) at 11.7 GPa and reversed to bcc Fe at 6.2 GPa with a width of the domain of coexistence of bcc hcp of the order of 5 GPa. Due to the effect of the special tubular confinement of the SWCNHs, the high-pressure behavior of Fe confined by them exhibited a sharp contrast to that of Fe confined by carbon nanotubes. In comparison to the bulk bcc Fe, hcp Fe, and Fe3O4, these nanocrystallines confined by SWCNHs had higher compressibility than their bulk phases. Fe3O4 did not exhibit any phase transformation until 21.8 GPa, where this was similar to the results of bulk Fe3O4. [ABSTRACT FROM AUTHOR]

We study the deformation of tantalum under extreme loading conditions. Experimental velocity data are drawn from both ramp loading experiments on Sandia's Z-machine and gas gun compression experiments. The drive conditions enable the study of materials under pressures greater than 100 GPa. We provide a detailed forward model of the experiments including a model of the magnetic drive for the Z-machine. Utilizing these experiments, we simultaneously infer several different types of physically motivated parameters describing equation of state, plasticity, and anelasticity via the computational device of Bayesian model calibration. Characteristics of the resulting calculated posterior distributions illustrate relationships among the parameters of interest via the degree of cross correlation. The calibrated velocity traces display good agreement with the experiments up to experimental uncertainty as well as improvement over previous calibrations. Examining the Z-shots and gun-shots together and separately reveals a trade-off between accuracy and transferability across different experimental conditions. Implications for model calibration, limitations from model form, and suggestions for improvements are discussed. [ABSTRACT FROM AUTHOR]

Lasing is a well-established field in optics with several applications. Yet, having lasing or huge amplification in other wave systems remains an elusive goal. Here, we utilize the concept of coherent perfect absorber-laser to realize an acoustic analog of laser with a proven amplification of more than 10 4 in terms of the scattered acoustic signal at a frequency of a few kHz. The obtained acoustic laser (or the coherent perfect absorber-laser) is shown to possess extremely high sensitivity and figure of merit with regard to ultra-small variations of the pressure (density and compressibility) and suggests its evident potential to build future acoustic pressure devices such as precise sensors. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) have attracted a great deal of scholarly attention in the last few decades due to their unique properties and potential for photovoltaic and optoelectronic applications. The mechanical and electrical properties of MHPs are substantially affected by altering pressure and/or temperature. Near the phase transition pressure, these properties alter dramatically and a discontinuity in the Raman frequencies is observed. In this study, the Raman frequencies of the modes were calculated as a function of pressure (at room temperature) through the isothermal mode Grüneisen parameter for these modes by using the experimental volume data from the literature for CsPbI3. Moreover, I calculated the isothermal compressibility and the bulk modulus through the calculated Raman frequency shifts and isothermal Grüneisen parameter as a function of pressure for the orthorhombic and monoclinic phases of CsPbI3 at room temperature. The predicted Raman frequencies, isothermal Grüneisen parameter, isothermal compressibility, and the bulk modulus for the studied modes were compared with the experimental measurements below and above the orthorhombic and monoclinic phases. [ABSTRACT FROM AUTHOR]

A series of planar impact tests were performed aiming at measuring the compressibility of the paraffin–poly-methylmethacrylate (PMMA) mixture up to a pressure of 2.5 GPa. It was found that compressive waves in the mixture consist of the initial part, characterized by a virtually linear increase of parameters, followed by the part associated with their relaxation. The dependence of the maximum strain rate of compression of the mixture on the final shock pressure was found to be much weaker than observed in metals and liquids. This inconsistency was explained by the difference of the viscosity mechanisms in these media. Based on an assumption of additivity of volumes of the mixture constituents, the estimates of bulk PMMA compressibility were obtained. [ABSTRACT FROM AUTHOR]

In this work, the structure, elastic, and electronic properties of the recently synthesized MAX phase Lu 2 SnC under pressure were studied by the first-principle calculation. The effect of high pressures, up to 20 GPa, on the structure shows that the compressibility along the a -axis was higher than that along the c -axis, which indicates that the Lu–C bonds are more resistant than Lu–Sn bonds. Meanwhile, we derived the elastic modulus (B, G, Y), Pugh's ratio (G / B), Poisson's ratio (ν), and averaged compressibility (β). The value of bulk moduli, Young's moduli, and shear moduli increases under pressure, which means that the pressure can enhance the ability of resisting to shape change and improve the stiffness and hardness of Lu 2 SnC. Poisson's ratio change from 0.184 to 0.246 in the 0–20 Gpa pressure range, which means that Lu 2 SnC is brittle in nature, this result is consistent with that obtained from the Cauchy pressure and Pugh's ratio. In addition, we calculated the shear anisotropy factor (A), A i (i = 1,2,3), A B , and A G. We found that the elastic anisotropy increases with increasing pressure. Finally, the electronic properties of Lu 2 SnC were calculated. As the pressure increases, a pseudo-gap appears in the energy range of − 2 eV to − 3 eV. The total density of state at the Fermi level remains virtually unchanged with the increasing pressure. We hope that our study can complement the future experimental and theoretical work, which can lead to further insights. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) are a broad and interesting class of materials known for their mechanical flexibility. As such, their response to pressure is usually extreme and often counterintuitive. This tutorial review surveys the structural response of MOFs to pressure as observed experimentally. It describes the experimental tools exploited in high-pressure crystallographic measurements and highlights some of the experiment design choices that influence the actual physics probed in these measurements. The main focus of the review is a description of the key pressure-driven structural responses exhibited by MOFs: isosymmetric compression, including negative compressibility; symmetry-lowering transitions; changes in connectivity; amorphization; and inclusion of the pressure-transmitting medium within the MOF pores. The review concludes both by highlighting some functional implications of these responses and by flagging some future directions for the field. [ABSTRACT FROM AUTHOR]

In contrast to cubic ZrW2O8 and ZrMo2O8, which have isotropic negative thermal expansion, the compounds Sc2(WO4)3 and Sc2(MoO4)3 with the orthorhombic structure show anisotropic thermal expansion that is negative along the b and c axes. Using ab initio density functional theory calculations of lattice dynamics, we identify that the anisotropic expansion is not due to anisotropic elasticity or negative linear compressibility, which is the case in several compounds; instead, it is due to anisotropic Grüneisen parameters of specific phonons, mostly of energy around 6 meV. Such a behavior not involving anomalous elasticity is unusual. The phonon eigenvectors show that these phonons have a rather complex vibrational character of MoO4/WO4 and ScO6 polyhedral units that involve translational, librational, and internal distortion dynamics. [ABSTRACT FROM AUTHOR]

In contrast to cubic ZrW2O8 and ZrMo2O8, which have isotropic negative thermal expansion, the compounds Sc2(WO4)3 and Sc2(MoO4)3 with the orthorhombic structure show anisotropic thermal expansion that is negative along the b and c axes. Using ab initio density functional theory calculations of lattice dynamics, we identify that the anisotropic expansion is not due to anisotropic elasticity or negative linear compressibility, which is the case in several compounds; instead, it is due to anisotropic Grüneisen parameters of specific phonons, mostly of energy around 6 meV. Such a behavior not involving anomalous elasticity is unusual. The phonon eigenvectors show that these phonons have a rather complex vibrational character of MoO4/WO4 and ScO6 polyhedral units that involve translational, librational, and internal distortion dynamics. [ABSTRACT FROM AUTHOR]

Dynamic compaction of granular materials is a complex process, wherein the material response at the continuum scale arises from fracture, comminution, and fragment flow at the grain scale. Granular materials have heterogeneity due to variation in grain properties as well as variation in local packing density and structure. These heterogeneities may affect the dynamic compaction response, producing a structured and time-varying compaction front. The methodology used to characterize the shock behavior in solid materials may be inappropriate for granular materials because of this unsteady behavior and interactions between the granular material and measurement surfaces. To observe the compaction front heterogeneity, in situ x-ray imaging of granular compaction is conducted at a scale between the grain- and continuum scales. To allow for sufficient x-ray transmission, a thin sample geometry is used, for which boundary affects may result in a significantly different load path than would occur in a 1-D compaction configuration. Numerical simulations of the experimental geometry support the analysis of the results so that the feature of the compaction front can be distinguished from artifacts of the experimental configuration. The results suggest that compaction front heterogeneity may have structure with a length scale of tens of particle diameters and demonstrate that finite grain size can inhibit the formation of shear-induced features that would arise in a homogenized representation of the same material. [ABSTRACT FROM AUTHOR]

The equation of state and principal shock Hugoniot of the elemental technetium to 285 GPa were predicted from ab initio molecular dynamics simulations using Erpenbeck's approach based on the Rankine-Hugoniot jump conditions. The phase space was sampled by carrying out NVT simulations for isotherms between 300 and 4500 K and densities ranging from ρ ≃ 11.4 to 16.7 g/cm3. A temperature-driven hcp → fcc reverse-martensitic phase transformation is predicted to occur at T ≃ 2800 K in Tc bulk subjected to shock loading. The results from dynamic compression were compared to recent diamond-anvil-cell hydrostatic compression data and cold-curve predictions using the density functional theory. The melting curve of Tc is predicted from Lindemann's criterion. [ABSTRACT FROM AUTHOR]

Rare-earth orthoniobates constitute a class of materials that has been exploited due to their interesting physical properties depending on the lanthanide element. Besides paramagnetism, ferroelasticity, and negative compressibility, these materials are known by their interesting optical properties and mixed types of conduction processes (protonic, ionic, and electronic). In this work, two types of SmNbO4 samples were studied: polycrystalline samples, prepared by a sol-gel route using the Pechini method, and single crystalline fibres grown by the Laser Floating Zone technique. These samples were structurally characterized based on powder and single-crystal X-ray diffraction studies. A metastable tetragonal phase, stabilized by grain size, was identified in the synthesized powders. After a sintering process of such powders, a single monoclinic phase was obtained. Complementarily, scanning electron microscopy and Raman spectroscopy analyses were performed to these samples. Photoluminescence and photoluminescence excitation spectroscopic studies allowed identifying more than one optically active centre of the trivalent samarium ion in the analysed material. Impedance spectroscopy measurements have shown a large variation of the ac conductivity as a function of temperature, assigned to a protonic conduction and to native ionic conduction mechanisms. [ABSTRACT FROM AUTHOR]

Rare-earth orthoniobates constitute a class of materials that has been exploited due to their interesting physical properties depending on the lanthanide element. Besides paramagnetism, ferroelasticity, and negative compressibility, these materials are known by their interesting optical properties and mixed types of conduction processes (protonic, ionic, and electronic). In this work, two types of SmNbO4 samples were studied: polycrystalline samples, prepared by a sol-gel route using the Pechini method, and single crystalline fibres grown by the Laser Floating Zone technique. These samples were structurally characterized based on powder and single-crystal X-ray diffraction studies. A metastable tetragonal phase, stabilized by grain size, was identified in the synthesized powders. After a sintering process of such powders, a single monoclinic phase was obtained. Complementarily, scanning electron microscopy and Raman spectroscopy analyses were performed to these samples. Photoluminescence and photoluminescence excitation spectroscopic studies allowed identifying more than one optically active centre of the trivalent samarium ion in the analysed material. Impedance spectroscopy measurements have shown a large variation of the ac conductivity as a function of temperature, assigned to a protonic conduction and to native ionic conduction mechanisms. [ABSTRACT FROM AUTHOR]

In this work, we develop a full wave solution for the acoustic scattering by inhomogeneous compressibility spheres having an impenetrable core. The solution is developed by following two alternative mathematical formulations: one through a volume integral equation where a modified Green's function is needed to describe the scattering by the impenetrable core, and one through a surface-volume integral equation where the equivalent surface sources due to the impenetrable core are described via a surface integral. We prove analytically that these two alternative paths lead to the same set of nonhomogeneous equations for the evaluation of the total acoustic field. We investigate both Dirichlet and Neumann boundary conditions. Our developed method is then numerically validated by comparison with other techniques, including the exact solution for core-mantle spheres with constant compressibility function. Furthermore, we construct a solution which is valid for a special inhomogeneous compressibility profile based on the Nomura-Takaku distribution, which allows to construct the solution based on the separation of variables. Thus, the proposed method is further validated for inhomogeneous functions. New numerical results are presented for the interior and scattered acoustic fields for various inhomogeneous profiles. [ABSTRACT FROM AUTHOR]

High temperature mechanical and thermodynamic properties of TiB2 are important to its applications as ultrahigh temperature ceramic, which were not well understood. In this study, the thermodynamic and mechanical properties of TiB2 were investigated by the combination of first principle and phonon dispersion calculations. The thermal expansion of TiB2 was anisotropic, αc/αa is nearly constant (1.46) from 300K to 1500 K, theoretically. The origination of this anisotropy is the anisotropic compressibility. The heat capacity at constant pressure was estimated from the theoretical entropy and fitted the experimental result quite well when higher-order anharmonic effects were considered. Theoretical isentropic elastic constants and mechanical properties were calculated and their temperature dependence agreed with the existed experiments. From room temperature to 1500 K, the theoretical slope is -0.0211 GPa·K-1, -0.0155 GPa·K-1, and -0.0384 GPa·K-1 for B, G, and E, respectively. Our theoretical results highlight the suitability of this method in predicting temperature dependent properties of ultrahigh temperature ceramics and show ability in selecting and designing of novel ultrahigh temperature ceramics. [ABSTRACT FROM AUTHOR]

Boron carbide ceramics have been particularly problematic in attempts to develop adequate constitutive model descriptions for purposes of analysis of dynamic response in the shock and impact environment. Dynamic strength properties of boron carbide ceramic differ uniquely from comparable ceramics. Furthermore, boron carbide is suspected, but not definitely shown, to undergoing polymorphic phase transformation under shock compression. In the present paper, shock-wave compression measurements conducted over the past 40 years are assessed for the purpose of achieving improved understanding of the dynamic equation of state and strength of boron carbide. In particular, attention is focused on the often ignored Los Alamos National Laboratory (LANL) Hugoniot measurements performed on porous sintered boron carbide ceramic. The LANL data are shown to exhibit two compression anomalies on the shock Hugoniot within the range of 20-60 GPa that may relate to crystallographic structure transitions. More recent molecular dynamics simulations on the compressibility of the boron carbide crystal lattice reveal compression transitions that bear similarities to the LANL Hugoniot results. The same Hugoniot data are complemented with dynamic isentropic compression data for boron carbide extracted from Hugoniot measurements on boron carbide and copper granular mixtures. Other Hugoniot measurements, however, performed on near-full-density boron carbide ceramic differ markedly from the LANL Hugoniot data. These later data exhibit markedly less compressibility and tend not to show comparable anomalies in compressibility. Alternative Hugoniot anomalies, however, are exhibited by the near-full-density data. Experimental uncertainty, Hugoniot strength, and phase transformation physics are all possible explanations for the observed discrepancies. It is reasoned that experimental uncertainty and Hugoniot strength are not likely explanations for the observed differences. The notable mechanistic difference in the processes of shock compression between the LANL data and that of the other studies is the markedly larger inelastic deformation and dissipation experienced in the shock event brought about by compaction of the substantially larger porosity LANL test ceramics. High-pressure diamond anvil cell experiments reveal extensive amorphization, reasoned to be a reversion product of a higher-pressure crystallographic phase, which is a consequence of application of both high pressure and shear deformation to the boron carbide crystal structure. A dependence of shock-induced high-pressure phase transformation in boron carbide on the extent of shear deformation experienced in the shock process offers a plausible explanation for the differences observed in the LANL Hugoniot data on porous ceramic and that of other shock data on near-full-density boron carbide. [ABSTRACT FROM AUTHOR]

Novel analytical models have been proposed in this study which extends current available fluid-structure interaction (FSI) theories for explosion induced shock loading on monolithic and laminated composite plates to sandwich composite panels, featuring core compression. The proposed models have been asymptotically validated against other FSI existing theories in low pressure range. A qualitative comparative analysis of the proposed models has been made with other existing FSI theories from the viewpoint of energy conservation. Core compression as predicted by the proposed models can be utilized for more economical, robust design of blast resistant sandwich composite structures. [ABSTRACT FROM AUTHOR]

Scandium fluoride displays isotropic negative thermal expansion (NTE) from at least 10 to 1100 K and retains a cubic ReO3-type structure over this range; the NTE is most pronounced at low temperatures. Control of thermal expansion was explored by forming Sc1-xYxF3 (x≤0.25), which were characterized with synchrotron powder diffraction at ambient pressure from 100 to 800 K. The behavior of the solid solutions under pressure (≤0.276 GPa) was also examined while heating from 298 to 523 K. Insertion of the relatively large Y3+ ion into ScF3 results in a cubic-to-rhombohedral phase transition upon cooling from ambient temperature to 100 K, even at low substitution levels (5%). The coefficient of thermal expansion (CTE) of the solid solutions in the rhombohedral phase is strongly dependent on both composition and temperature; however, above 400 K, where all samples are cubic, the CTE appears to be largely independent of composition. The isothermal bulk modulus and CTE of ScF3, but not those of the solid solutions, are independent of temperature and pressure, respectively. Yttrium substitution lowers the bulk modulus, even at temperatures where the samples are cubic. Finally, the solid solutions stiffen upon heating. [ABSTRACT FROM AUTHOR]

A model framework for predicting the dynamic shock-compression response of heterogeneous powder mixtures using readily obtained measurements from quasi-static tests is presented. Low-strain-rate compression data are first analyzed to determine the region of the bulk response over which particle rearrangement does not contribute to compaction. This region is then fit to determine the densification modulus of the mixture, σD, an newly defined parameter describing the resistance of the mixture to yielding. The measured densification modulus, reflective of the diverse yielding phenomena that occur at the meso-scale, is implemented into a rate-independent formulation of the P-α model, which is combined with an isobaric equation of state to predict the low and high stress dynamic compression response of heterogeneous powder mixtures. The framework is applied to two metal + metal-oxide (thermite) powder mixtures, and good agreement between the model and experiment is obtained for all mixtures at stresses near and above those required to reach full density. At lower stresses, rate-dependencies of the constituents, and specifically those of the matrix constituent, determine the ability of the model to predict the measured response in the incomplete compaction regime. [ABSTRACT FROM AUTHOR]

A new fluid-structure interaction model that considers high gas compressibility is developed using the Rankine-Hugoniot relations. The impulse conservation between the gas and structure is utilized to determine the reflected pressure profile from the known incident pressure profile. The physical parameters of the gas such as the shock front velocity, gas density, local sound velocity, and gas particle velocity as well as the impulse transmitted onto the structure are also evaluated. A series of one-dimensional shock loading experiments on free standing monolithic aluminum plates were conducted using a shock tube to validate the proposed model. The momentum was evaluated using high speed digital imagery. The experimental peak reflected pressure, the reflected pressure profile, and the momentum transmitted onto the plate were compared with the predicted results. The comparisons show that the gas's compressibility significantly affects the fluid structure interaction behavior, and the new model can predict more accurate results than existing models. The effect of factors, such as the areal density of a plate and the peak incident pressure on momentum transfer are also discussed using the present model. Moreover, the maximum achievable momentum and the fluid structure interaction time are defined and calculated. [ABSTRACT FROM AUTHOR]

We conducted comparison of the original experimental data of the temperature dependences of thermal expansion in crystals with layered crystalline structure. It is shown that in most crystals with layered structure (graphite, boron nitride, GaSe, GaS, and InSe) the effect of negative thermal expansion can be explained by the specific character of the phonon spectra. It was shown, that in contrast to other crystals with layered structure, negative thermal expansion in the layers' plane of TlGaSe2 is the result of negative area compressibility. We demonstrate that the thermal expansion of TlGaSe2 crystals can be controlled by illumination, external electric field, and thermal annealing. The nature of observed effects and a special mechanism of the negative area compressibility in TlGaSe2 crystals are discussed. [ABSTRACT FROM AUTHOR]

The dynamics of microcantilever beams can be strongly affected by immersion in fluid. While the importance of viscosity for devices of microscale dimensions is well established, the significance of fluid compressibility has not been investigated in detail. Here, we present a rigorous theoretical model for the frequency response of a rectangular cantilever beam that is executing normal and torsional oscillations, and is immersed in a compressible fluid. Both the viscous case and the inviscid limit are considered, and the model is valid for arbitrary mode number. We find that compressibility becomes increasingly important as the mode number rises. This is particularly relevant for gases, where compressibility is found to be important for high mode numbers of practical interest. [ABSTRACT FROM AUTHOR]

The effect of oxygen flooding during ultralow energy SIMS depth profiling of silicon with Cs+ primary ions is presented. New experimental data show the effective sputtering yield of silicon in the presence of oxygen, as well as the energy distribution of the secondary Si- ions. It is found that the component sputtering yield of Si is very sensitive to minute amounts of oxygen in the proximity of the sputtered surface. At these very low flooding pressures (in the 10-9–10-8 mbar range), one cannot account for a full oxidation in the time frame of a typical measurement; it is concluded that in this particular case, which is technologically very relevant, small traces of oxygen will change the desorption characteristics of cesium as well as silicon. It shows that oxygen that is adsorbed to the silicon surface provides an attachment site for impinging cesium ions and thereby increases the retention capacity of cesium tremendously. Also, oxygen changes the secondary ion yield and can even promote the desorption of Si from the analysis surface. [ABSTRACT FROM AUTHOR]

Hugoniot measurements have been performed on high-purity cubic boron nitride polycrystals in the pressure range up to 296 GPa using a two-stage light-gas gun. Hugoniot parameters have been measured by a line reflection method and Fabry–Pérot velocimetry. The Hugoniot elastic limit (HEL) is determined to be 44.3 GPa, which is the second highest value after that of diamond. Above the HEL, the Hugoniot compression curve shows a considerable offset from its hydrodynamic compression curve, which is calculated from static-compression data. This result shows that cubic boron nitride preserves its shear strength in the plastic region. Hugoniot data indicate that the cubic phase of boron nitride is stable in the pressure range up to 296 GPa. [ABSTRACT FROM AUTHOR]

A noncoplanar mesh design that enables electronic systems to achieve large, reversible levels stretchability (>100%) is studied theoretically and experimentally. The design uses semiconductor device islands and buckled thin interconnects on elastometric substrates. A mechanics model is established to understand the underlying physics and to guide the design of such systems. The predicted buckle amplitude agrees well with experiments within 5.5% error without any parameter fitting. The results also give the maximum strains in the interconnects and the islands, as well as the overall system stretchability and compressibility. [ABSTRACT FROM AUTHOR]

We studied the compressibility of monolithic fully dense electrodeposited nanocrystalline Ni (∼29 nm grain size) under both quasihydrostatic and nonhydrostatic conditions up to a nominal pressure of 50 GPa using angle-dispersive x-ray diffraction. We obtained an equation of state consistently and unambiguously from each measured reflection. The apparent bulk modulus measured under nonhydrostatic conditions is larger than that of the corresponding coarse-grained material under either type of compression, but is nearly the same when measured under quasihydrostatic conditions. These results may be consistent with a strength, but not necessarily a bulk modulus, that is enhanced in the nanomaterial relative to its coarse-grained counterparts. [ABSTRACT FROM AUTHOR]

We describe experiments and numerical simulations on high-density energy conversion using a compact closed-cycle magnetohydrodynamic electrical power generator, where shock-tube-based experiments and quasi-three-dimensional numerical simulations are fully coupled. The temporal plasma-fluid behavior, the one- and two-dimensional plasma-fluid structures, the enthalpy-entropy diagram, the Hall voltage-Hall current characteristics, and the quality of the energy conversion efficiency are investigated. The slightly divergent channel configuration, the application of high- and uniform-density magnetic flux to the entire generator, the high electrical conductivity, the symmetric plasma structure and stable plasma behavior, and the sufficient pressure gradient used to drive the fluid overcome the disadvantages of the generator due to its compactness, and markedly improve its energy conversion performance, namely, a power density of 0.76 GW/m3, an isentropic efficiency of 51%, and an enthalpy extraction ratio of 17.0%. [ABSTRACT FROM AUTHOR]

X-ray diffraction measurements on the sphalerite-derivatives ZnGa2Se4 and CdGa2S4 have been performed upon compression up to 23 GPa in a diamond-anvil cell. ZnGa2Se4 exhibits a defect tetragonal stannite-type structure (I42m) up to 15.5 GPa and in the range from 15.5 to 18.5 GPa the low-pressure phase coexists with a high-pressure phase, which remains stable up to 23 GPa. In CdGa2S4, we find that the defect tetragonal chalcopyrite-type structure (I4) is stable up to 17 GPa. Beyond this pressure a pressure-induced phase transition takes place. In both materials, the high-pressure phase has been characterized as a defect-cubic NaCl-type structure (Fm3m). The occurrence of the pressure-induced phase transitions is apparently related with an increase in the cation disorder on the semiconductors investigated. In addition, the results allow the evaluation of the axial compressibility and the determination of the equation of state for each compound. The obtained results are compared to those previously reported for isomorphic digallium sellenides. Finally, a systematic study of the pressure-induced phase transition in 23 different sphalerite-related ABX2 and AB2X4 compounds indicates that the transition pressure increases as the ratio of the cationic radii and anionic radii of the compounds increases. [ABSTRACT FROM AUTHOR]

X-ray diffraction measurements on the sphalerite-derivatives ZnGa2Se4 and CdGa2S4 have been performed upon compression up to 23 GPa in a diamond-anvil cell. ZnGa2Se4 exhibits a defect tetragonal stannite-type structure (I42m) up to 15.5 GPa and in the range from 15.5 to 18.5 GPa the low-pressure phase coexists with a high-pressure phase, which remains stable up to 23 GPa. In CdGa2S4, we find that the defect tetragonal chalcopyrite-type structure (I4) is stable up to 17 GPa. Beyond this pressure a pressure-induced phase transition takes place. In both materials, the high-pressure phase has been characterized as a defect-cubic NaCl-type structure (Fm3m). The occurrence of the pressure-induced phase transitions is apparently related with an increase in the cation disorder on the semiconductors investigated. In addition, the results allow the evaluation of the axial compressibility and the determination of the equation of state for each compound. The obtained results are compared to those previously reported for isomorphic digallium sellenides. Finally, a systematic study of the pressure-induced phase transition in 23 different sphalerite-related ABX2 and AB2X4 compounds indicates that the transition pressure increases as the ratio of the cationic radii and anionic radii of the compounds increases. [ABSTRACT FROM AUTHOR]

A constitutive relationship for modeling of shock wave propagation in orthotropic materials is proposed for nonlinear explicit transient large deformation computer codes (hydrocodes). A procedure for separation of material volumetric compression (compressibility effects equation of state) from deviatoric strain effects is formulated, which allows for the consistent calculation of stresses in the elastic regime as well as in the presence of shock waves. According to this procedure the pressure is defined as the state of stress that results in only volumetric deformation, and consequently is a diagonal second order tensor. As reported by Anderson et al. [Comput. Mech. 15, 201 (1994)], the shock response of an orthotropic material cannot be accurately predicted using the conventional decomposition of the stress tensor into isotropic and deviatoric parts. This paper presents two different stress decompositions based on the assumption that the stress tensor is split into two components: one component is due to volumetric strain and the other is due to deviatoric strain. Both decompositions are rigorously derived. In order to test their ability to describe shock propagation in orthotropic materials, both algorithms were implemented in a hydrocode and their predictions were compared to experimental plate impact data. The material considered was a carbon fiber reinforced epoxy material, which was tested in both the through-thickness and longitudinal directions. The ψ decomposition showed good agreement with the physical behavior of the considered material, while the ζ decomposition significantly overestimated the longitudinal stresses. [ABSTRACT FROM AUTHOR]

At Lawrence Livermore National Laboratory, we are developing a new type of accelerator, known as a dielectric wall accelerator, in which compact pulse-forming lines directly apply an accelerating field to the beam through an insulating vacuum boundary. The electrical strength of this insulator may define the maximum gradient achievable in these machines. To increase the system gradient, we use “high-gradient insulators” composed of alternating layers of dielectric and metal for the vacuum insulator. In this paper, we present our recent results from experiment and simulation, including successful testing of a high-gradient insulator in a functioning dielectric wall accelerator cell. Our results indicate that proper high-voltage conditioning of the insulators can delay the onset of flashover, that the observed conditioning consists of both a permanent and a temporary part, and that the insulators’ voltage-holding capability increases with increasing dielectric layer thickness. [ABSTRACT FROM AUTHOR]

At the microscale level, it is impossible to obtain a completely smooth wall surface, and the effect of surface roughness may be a main factor responsible for some different characteristics between fluid flow in the microchannels and that in conventional size channels. In the present work, the lattice Boltzmann method is applied to investigate the gaseous flow in a microchannel with surface roughness which is modeled by an array of rectangular modules. The effects of relative surface roughness, roughness distribution, and rarefaction on gaseous flow are studied, but the compressibility effect is neglected since the Mach number is less than 0.2. It was shown that the surface roughness had an important influence on friction factor and mass flow rate. In particular, this effect becomes more significant with the decrease of the Knudsen number. This is because the rarefaction reduces the interaction between the gas molecules and the channel walls, which results in reduction of the surface roughness effect. [ABSTRACT FROM AUTHOR]

The reactive flow analysis of high energy material is performed using hydro shock compression of condensed matter (SCCM) tool that is being developed for handling complex multimaterial dynamics involving energetic and inert matters. Typically, the reacting flows of high energy materials such as fires and explosions give rise to strong nonlinear shock waves and high strain rate deformation of metallic confinements at unusually high pressure and temperature. In order to address difficulties associated with analyzing such complex systems, we have developed a suite of modeling capabilities for elegantly handling large gradients and high strain rates in solids as well as reactive shock waves present in gaseous phase. Mathematical formulation of explosive dynamics involving condensed matter is explained with an emphasis on validating and application of hydro-SCCM to a series of problems of high-speed multimaterial dynamics in nature. A detailed numerical description of a level-set based reactive ghost fluid approach is reported in a separate paper. [ABSTRACT FROM AUTHOR]

The growth of multiphased binary and ternary mixed crystals by the melt method using the miscible alkali halides, viz., NaBr and KCl, along with the experimental determination of their compressibility, have been recently reported. These materials are particularly useful for the construction of laser optical windows. Here, we suggest a theoretical model that enables the estimation of the compressibility of the multiphased mixed crystals in terms of the elastic data of the end members alone. The calculated values are in reasonable agreement with the experimental ones. The model makes use of an early suggestion that interconnects the Gibbs energy for the formation and migration of defects in solids, with bulk properties, and has been found of value in a large variety of solids. [ABSTRACT FROM AUTHOR]

This paper presents a compact electrical equivalent circuit which describes the dark current-voltage characteristics of nonideal p-n junction solar cells in a wide range of temperatures. The model clearly separates the voltage drop in the junction and bulk regions. It is based on the combination of two exponential mechanisms, shunt and series resistances and space-charge limited current. In order to increase the accuracy of the parameter extraction process, both ln(I-V) and its derivative plots are fitted simultaneously. From the temperature dependence of the extracted parameters, the conduction mechanisms governing the I-V characteristics can be obtained without assuming dominating terms. In addition, the extracted parameters can be related to other electrical magnitudes obtained from such independent measurements as capacitance-voltage measurements (diffusion potential) and illuminated current-voltage characteristics (series resistance and open-circuit voltage). To exemplify the application, a p+ a-SiC:H/n c-Si solar cell is studied and a number of major physical aspects derived from the analysis of the fitting values are discussed. [ABSTRACT FROM AUTHOR]

The impulse imparted by a blast wave to a freestanding solid plate is studied analytically and numerically focusing on the case in which nonlinear compressibility effects in the fluid are important, as is the case for explosions in air. The analysis furnishes, in effect, an extension of Taylor’s pioneering contribution to the understanding of the influence of fluid-structure interaction (FSI) on the blast loading of structures [The Scientific Papers of Sir Geoffrey Ingram Taylor, edited by G. K. Batchelor (Cambridge University Press, Cambridge, 1963), Vol. III, pp. 287–303] to the nonlinear range. The limiting cases of extremely heavy and extremely light plates are explored analytically for arbitrary blast intensity, from where it is concluded that a modified nondimensional parameter representing the mass of compressed fluid relative to the mass of the plate governs the FSI. The intermediate asymptotic FSI regime is studied using a numerical method based on a Lagrangian formulation of the Euler equations of compressible flow and conventional shock-capturing techniques. Based on the analytical and numerical results, an approximate formula describing the entire range of relevant FSI conditions is proposed. The main conclusion of this work is that nonlinear fluid compressibility further enhances the beneficial effects of FSI in reducing the impulse transmitted to the structure. More specifically, it is found that transmitted impulse reductions due to FSI when compared to those obtained ignoring FSI effects are more significant than in the acoustic limit. This result can be advantageously exploited in the design and optimization of structures with increased blast resistance. [ABSTRACT FROM AUTHOR]

Single crystals of cyclotetramethylene tetranitramine (HMX) were isentropically compressed perpendicular to (010) and (011) faces at the Sandia Z-Machine. A 50 GPa ramped magnetic pressure load of about 200 ns rise time loaded four specimens of each orientation. HMX specimens were from 300–600 μm thick. Velocity histories at the rear of each crystal were measured by Doppler velocimetry. Although a phase change in HMX at 27 GPa has been proposed based upon isothermal data, no evidence of this change is seen in our analyses between 5 and 50 GPa along the isentrope. Previous isentropic loading experiments on HMX had not shown evidence of a phase change either, but those experiments were complicated by the use of NaCl interferometer windows that have a phase change near the pressure of interest. The experiments described in this paper employed LiF interferometer windows that are known to be absent phase changes in the regime of application. Accurate determination of isentropic compressibility for HMX was not possible using data from these experiments owing to uncertainty in the very large compressibility at low pressures. [ABSTRACT FROM AUTHOR]

Hugoniot equation-of-state data of shock compressed β-Si4Al2O2N6 have been determined to a pressure of 120 GPa. The relationship between shock velocity (Us) and particle velocity (Up) is expressed by a linear equation Us(km/s)=5.62+0.96Up(km/s) above a pressure of ∼40 GPa beyond the Hugoniot elastic limit (15–16 GPa). A phase transition to spinel is observed at the onset pressure of 32 GPa. According to the systematics of high-pressure phase transitions of spinels that indicate a phase transition to CaTi2O4-type phases at high pressures, β-Si4Al2O2N6 may also be transformed into a CaTi2O4-type phase with further increasing pressure. The previous recovery experiments on β-SiAlON indicated the formation of spinel and amorphous phases at shock pressures of 41–63 GPa. A comparison of the Hugoniot data and recovered samples suggests that the high-pressure CaTi2O4-type phase is not quenchable and quenched as an amorphous phase although a large hysteresis is detected in the release path. [ABSTRACT FROM AUTHOR]

A piston impacting a granular bed will cause the material to compact; the strength of a granular bed is significant during weak impact relating to piston speeds of 100 m/s. The strength associated with the granular structure is described as the intergranular stress; this is the resistance of a granular bed to compaction which can be measured by carefully constructing experiments. The compaction process may then be modeled by solving a hyperbolic system of equations that utilizes these data to close the system. The compaction behavior of a porous material is particle-size dependent; to accurately describe the response of two granular beds that may be of different particle sizes and distributions, it is essential that the intergranular stress is derived for each particle bed. This work uses recent compaction experiments to derive intergranular stress curves for prepressed conventional HMX material that is of nonuniform distribution with a mean diameter of 40 μm and a microfine HMX of more uniform distribution of mean diameter <5 μm. Steady-state compaction waves in the solid material are analyzed: initially the solid is assumed to behave as an incompressible medium. The speed and extent of compaction can be simply determined through the solution of a quadratic equation. Following this, the assumption is relaxed allowing changes in solid-phase density; a complicated equation of state makes the use of numerical methods mandatory. The speed of steady-state waves in HMX due to low impact compaction can be determined within 2% accuracy using the simple closed solution based on solid incompressibility, which is a function of the initial material porosity and density, piston speed, and the intergranular stress of the granular bed. This analysis reveals the difference between the weak impact response of a coarse nonuniform bed and a fine almost uniform granular bed that are initially loaded to 75% of the theoretical maximum density. The fine particle beds have increased resistance to compaction meaning that the extent of compaction is reduced and the speed of compaction waves are faster. The long-term objective of this research is the study of combustion and detonation in granular beds; a two-phase flow capability is required to simulate this type of problem. A multiphase flow model is utilized to simulate the complete low impact response of HMX that includes gas-phase effects. The time-dependent flow rapidly attains steady-state conditions; these solutions agree with the steady-state solutions of the reduced problem described above. Dissipation due to compaction is analyzed and compared with other dissipative processes within the system. [ABSTRACT FROM AUTHOR]

Isothermal pressure-volume equations of state of beta HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) at temperatures of 30, 100, and 140 °C under both hydrostatic and nonhydrostatic compressions have been obtained using synchrotron angle-dispersive x-ray diffraction experiments. The samples were heated to the isotherm temperature and compressed up to 5.8 GPa. At all temperatures HMX remained in the beta phase up to 5.8 GPa. However, at 140 °C upon decompression to ambient from nonhydrostatic pressures above 4 GPa, HMX underwent a phase transition to the delta phase. The same transition was seen upon decompression to ambient from hydrostatic compression; however, parts of the sample remain in the β phase, resulting in a mixed-phase sample. The diffraction data were analyzed to yield unit-cell dimensions at each pressure, and further analyzed to yield thermal expansion, bulk modulus, and the pressure derivative of the bulk modulus. [ABSTRACT FROM AUTHOR]

This paper studies the pressure effect on radial breathing modes (RBMs) of multiwall carbon nanotubes (MWNTs). The analysis is based on a multiple-elastic shell model which assumes that each of the concentric tubes of a MWNT is an individual elastic shell and coupled with adjacent tubes through van der Waals interaction. The pressure effect on RBMs of MWNTs is mainly attributed to the pressure-induced reduction of interlayer spacing and the increase of the interlayer vdW interaction coefficient defined by the second derivative of the energy-interlayer spacing relation of MWNTs. In the absence of external pressure, the RBM frequencies and vibration modes predicted by the present shell model are found to agree very well with the available experimental and molecular-dynamics simulation results. In the presence of an external pressure, our results show that high external pressure considerably raises the vdW interaction coefficients especially between the outermost few layers of MWNTs. As a result, some of the RBM frequencies of MWNTs increase significantly with increasing external pressure. The most significant pressure effect occurs for the highest-frequency mode of large-diameter MWNTs (with the innermost diameter greater than 2 nm) or an intermediate-frequency mode of small-diameter MWNTs (with the innermost diameter less than 2 nm), and is always associated with those RBMs in which adjacent outermost layers vibrate in opposite directions with significant change in interlayer spacing. [ABSTRACT FROM AUTHOR]

Samples of silver and gold have been compressed together in a diamond anvil cell up to ∼150 GPa and the x-ray diffraction patterns recorded using a synchrotron radiation source. The parameters αt for silver and gold, where α is a factor that determines the relative weights of iso-stress and iso-strain conditions and t is the difference between the axial and radial stress components, are estimated from the analysis of the diffraction data. The αt-values are small and increase with pressure reaching 2 GPa and 0.5 GPa at 150 GPa for silver and gold, respectively. The effects of varying α between 1 and 0.5 on the hydrostatic volume compression derived from the measured data and the pressures computed therefrom are discussed. The compression data for silver and gold, corrected for nonhydrostatic compression effects assuming iso-stress condition (α=1), fit the relation (V/V0)Ag=1.5946(V/V0)Au3-3.0024(V/V0)Au2+2.8285(V/V0)Au-0.4207. The pressures computed from (V/V0)Ag and (V/V0)Au using equations of state from different sources have been compared. A fit of the Vinet equation to (V/V0)Ag data and pressures derived from the (V/V0)Au data using a recently proposed equation of state gives 5.47(2) for the pressure derivative of bulk modulus if the bulk modulus is constrained at 98.0 GPa, a value obtained from the ultrasonic measurements. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The present work studies the effects of absorption and desorption on the chemical stress field in a membrane during permeation or both-side charging of a diffusing species. The permeation and both-side charging processes are analyzed with the consideration of the absorption and desorption processes, wherein the flux continuity boundary conditions are adopted. The results show that the chemical stresses are compressive near the surfaces and tensile in the center of the membrane. The maximum magnitude of stress occurs at the entry surface for the permeation process and at both surfaces for the both-side charging process. For the permeation process, the compressive stress at the entry surface increases with time to a maximum and then decreases with time gradually to zero. A similar phenomenon is found at both surfaces in the both-side charging process. In both processes, the stress magnitude depends upon the ratio of the drift velocity through surface to the drift velocity through bulk. When this ratio approaches infinity, the flux continuity boundary conditions reduce to the concentration boundary condition and the highest chemical stress field will be produced. Therefore, reducing the drift velocity through surface would be an efficient means to reduce the strength of the chemical stress. In general, designed surface alloying can introduce diffusing species traps at the surfaces of a membrane, which may efficiently decrease the drift velocity through surface. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents a study which examined the magnetovolume effects and magnetic anisotropy of Ce[sub3](FeTi)[sub29] and Ce(FeCr)[sub29] compounds. Description of the linear thermal expansion of the compounds; Values of compressibility observed in the ferromagnetic and paramagnetic states of Ce[sub3](FeTi)[sub29]; Information on the anisotropy fields detected in Ce[sub3](FeTi)[sub29] associated with saturation.

Shock-compression experiments were performed on 50% by volume ceramic-metal mixtures of silicon carbide and copper at pressures of 15–30 GPa. The objective of these experiments was to determine the hydrodynamic compressibility (dynamic pressure-volume response) of silicon carbide through shock measurements on the ceramic-metal composite and the application of analytic mixture theory. Compression states inferred for silicon carbide above 20 GPa appear consistent with hydrodynamic behavior and are in agreement with compression curves extrapolated from ultrasonic data. Dynamic strength or viscosity effects apparently complicate shock compression of the ceramic-metal composite at the lower shock pressures. Shock release experiments on the composites provide further high-pressure equation-of-state data for the ceramic-metal mixture. [ABSTRACT FROM AUTHOR]

High-pressure x-ray diffraction studies have been carried out on the two group IV transition metals-based bulk metallic glasses (BMGs) Zr57Cu15.4Ni12.6Al10Nb5 and Ti42Zr24Cu15.5Ni14.5Be4 to a pressure of 30 GPa at ambient temperature in a diamond anvil cell. Image plate x-ray diffraction studies under high pressure were carried out at a synchrotron source and the two BMG diffraction bands can be followed to the highest pressure using an internal copper pressure standard. The amorphous phase is observed to be stable to the highest static pressure of 30 GPa suggesting that the phase change observed in dynamical pressure experiments is related to an increase in temperature. The measured bulk modulus (B0) and its pressure derivative (B′) are 118 GPa and 3.11 for Zr-based BMG and 116 GPa and 2.84 for Ti-based BMG. The measured bulk modulus for BMG’s by x-ray diffraction technique is consistent with the ultrasonic measurements. The decompression data reveal an increase in density by 3%–4% at ambient condition after pressure cycling to 30 GPa indicating reduction in excess free volume. [ABSTRACT FROM AUTHOR]