Effect Of Non-hydrostatic Stress Research Articles

Effects of Nonhydrostatic Stress on Structural and Optoelectronic Properties of Methylammonium Lead Bromide Perovskite.

We report synchrotron X-ray diffraction, photoconductivity, and photoluminescence investigations of methylammonium-lead-bromide (MAPbBr3) under various stress conditions, supported by density-functional-theory (DFT) calculations. The properties of MAPbBr3 show substantial dependence on the hydrostatic conditions. While nonhydrostatic compression of MAPbBr3 leads to amorphization above 2.4 GPa, under quasi-hydrostatic (Ar) and hydrostatic (He) pressure, the sample remains in crystalline phases. A sequence of phase transitions between two cubic phases and orthorhombic Pnma phase is observed when using Ar, or no pressure-transmitting-medium (PTM). In helium-PTM only transitions between the two cubic structures and a new isostructural phase transition with a large volume collapse to a third cubic-phase at 2.7 GPa was observed. The photoluminescence measurements indicate a pressure-induced band gap-narrowing in the cubic phase I, and a blue-shift in the orthorhombic structure. DFT calculations illustrate that the dynamics of the organic molecules and the inorganic lattice, coupled via the N-H···Br hydrogen-bonding interactions, affect the Pb-Br distance and the bandgap evolution under pressure.

High pressure X-ray diffraction and Raman spectroscopic studies of the phase change of D2O ice VII at approximately 11 GPa

High pressure experiments were performed on D2O ice VII using a diamond anvil cell in a pressure range of 2.0–60 GPa at room temperature. In situ X-ray diffractometry revealed that the structure changed from cubic to a low symmetry phase at approximately 11 GPa, based on the observed splitting of the cubic structure's diffraction lines. Heating treatments were added for the samples to reduce the effect of non-hydrostatic stress. After heating, splitting diffraction lines became sharp and the splitting was clearly retained. Although symmetry and structure of the transformed phase have not been determined, change in volumes vs. pressure was calculated, assuming that the low-symmetry phase had a tetragonal structure. The bulk modulus calculated for the low-symmetry phase was slightly larger than that for the cubic structure. In Raman spectroscopy, the squared vibrational frequencies of ν1 (A1g), as a function of pressure, showed a clear change in the slope at 11–13 GPa. The full width at half maxima of the O-D modes decreased with increasing pressure, reaching a minimum at approximately 11 GPa, and increased again above 11 GPa. These results evidently support the existence of phase change at approximately 11 GPa for D2O ice VII.

Ruby fluorescence pressure scale: Revisited

Effect of non-hydrostatic stress on X-ray diffraction in a diamond anvil cell (DAC) is studied. The pressure gradient in the sample chamber leads to the broadening of the diffraction peaks, which increase with the hkl index of the crystal. It is found that the difference between the determined d-spacing compressive ratio d/d0 and the real d-spacing compressive ratio dr/d0 is determined by the yield stress of the pressure transmitting media (if used) and the shear modulus of the sample. On the basis of the corrected experiment data of Mao et al. (MXB86), which was used to calibrate the most widely used ruby fluorescence scale, a new relationship of ruby fluorescence pressure scale is corrected, i.e., P = (1904/9.827)[(1 + Δλ/λ0)9.827−1].

Zircon to monazite phase transition in CeVO4: X-ray diffraction and Raman-scattering measurements

X-ray diffraction and Raman-scattering measurements on cerium vanadate have been performed up to 12 and 16 GPa, respectively. Experiments reveal that at 5.3 GPa the onset of a pressure-induced irreversible phase transition from the zircon to the monazite structure. Beyond this pressure, diffraction peaks and Raman-active modes of the monazite phase are measured. The zircon to monazite transition in CeVO4 is distinctive among the other rare-earth orthovanadates. We also observed softening of external translational Eg and internal B2g bending modes. We attributed it to mechanical instabilities of zircon phase against the pressure-induced distortion. We additionally report lattice-dynamical and total-energy calculations which are in agreement with the experimental results. Finally, the effect of non-hydrostatic stresses on the structural sequence is studied and the equations of state of different phases are reported.

Effect of nonhydrostatic stresses on solid-fluid equilibrium. II. Interface thermodynamics

We investigate thermodynamics of single-component solid-fluid interfaces when the solid phase is subject to nonhydrostatic mechanical stresses. The analysis reveals that when the solid is nonhydrostatic, the interface stress is not unique. We show the existence of several types of interface stresses, formulate them as interface excess quantities, and establish relationships between them. Using molecular dynamics simulations with an empirical potential, we compute several different interface stresses for a (110) solid-liquid interface in copper. The simulations show that biaxial tension and compression of the solid produce a strong effect on the magnitude, sign, and anisotropy of the interface stresses. The free energy of the interface was computed by thermodynamic integration along biaxial tension and compression paths. The effect of nonhydrostatic stresses on the interface free energy is much weaker than the effect on interface stresses.

Fluid–solid interaction finite element modeling of a kinetically driven growth instability in stressed solids

The kinetically driven growth instability in stressed solids has been a subject of recent investigation as there is an increasing interest in the effects of non-hydrostatic stresses on crystal growth processes. Recent experimental and modeling work using advanced numerical methods such as boundary element and level set methods have demonstrated that the effect of stress on the solid phase epitaxy (SPE) growth of crystalline silicon from the amorphous phase is responsible for the roughening of its amorphous-crystalline interface. Although our previous model (Phan et al., in Model Simul Mater Sci Eng, 9:309-325, 2001) has been able to explain the observed interfacial instability during the crystal growth of intrinsic silicon, it has not been very successful when extended to the SPE growth process of doped silicon. In an effort to identify the sources that may improve the accuracy and robustness of the previously proposed model, we present in this paper a new approach for modeling the crystal growth in stressed Si layers. The technique is based upon the coupling of a transition-state-theory-based model, a finite element model of the sequentially weak coupling analysis for fluid-solid interaction, and the marker particle method.

A sequential fluid–solid weak coupling analysis of the SPE in stressed Si layers

The kinetically driven growth instability in stressed solids has been a subject of recent investigation as there is an increasing interest in the effects of non-hydrostatic stresses on crystal growth processes. Recent experimental and modeling work have shown that the effect of stress on the solid phase epitaxy (SPE) growth of crystalline silicon from the amorphous phase is responsible for the roughening of its amorphous–crystalline interface. Although our previous model (Phan, A.-V., Kaplan, T., Gray, L.J., Adalsteinsson, D., Sethian, J.A., Barvosa-Carter, W., Aziz, M.J., 2001. Modelling a growth instability in a stressed solid. Modelling and Simulation in Materials Science and Engineering 9, 309–325.) has been able to explain the observed interfacial instability during the crystal growth of intrinsic silicon, it has not been very successful when extended to the SPE growth process of doped silicon. In an effort to identify the sources that may improve the accuracy and robustness of the previously proposed model, we present in this paper a new approach for modeling the crystal growth in stressed Si layers. The technique is based upon the coupling of finite element analysis, the sequentially weak coupling analysis for fluid–solid interaction, and the marker particle method.

Angle-dispersive diffraction under non-hydrostatic stress in diamond anvil cells

Diamond anvil cells (DAC) as opposed anvil devices produce non-hydrostatic stress state, especially in experiments at very high pressures. We develop an algorithm for analysis of the effect of non-hydrostatic stress on the shape and width of the diffraction lines acquired with an area detector in angle-dispersive powder diffraction experiments. Numerical simulations show that deviatoric stress changes d-spacings and produces broadening of all diffraction lines. Both these phenomena depend on the elastic properties of the material, value of uniaxial stress component, and orientation of the cell (loading direction) with respect to incident beam.

Effect of Non-Hydrostatic Stress on Kinetics and Interfacial Roughness During Solid Phase Epitaxial Growth in Si

AbstractWe report preliminary in-situ time-resolved measurements of the effect of uniaxial stress on solid phase epitaxial growth in pure Si (001) for the case of stress applied parallel to the amorphous-crystal interface. The growth rate is reduced by the application of uniaxial compression, in agreement with previous results. Additionally, the velocity continues to decrease with time. This is consistent with interfacial roughening during growth under stress, and is supported by both reflectivity measurements and cross-sectional TEM observations. We present a new kinetically-driven interfacial roughening mechanism which is consistent with our observations.

Questions And Answers On The Activation Strain

ABSTRACTThe activation strain tensor describes the effect of nonhydrostatic stresses on atomic or interfacial Mobilities. It has been measured for solid phase epitaxial growth of crystalline Si (001) into amorphous Si. The activation strain concept is explained and some subtle points are discussed. Implications for proposed mechanisms of solid phase epitaxy are reviewed, and new implications for combined bulk and interfacial control are presented. Questions raised during the oral presentation are answered.

Effect of Nonhydrostatic Stress on Crystal Growth Kinetics

ABSTRACTThe effect of nonhydrostatic stresses on the solid phase epitaxial growth rate of crystalline Si(100) into self-implanted amorphous surface layers has been measured. Uniaxial stresses of up to 6 kbar (0.6 GPa) were attained by bending wafers over SiO2 rods and annealing at a temperature too low for plastic deformation to relieve the stress in the crystal, but high enough for solid phase epitaxial growth to proceed. The growth rate on the tensile side was greater than that on the compressive side of the wafer, in marked contrast to the enhancement observed from hydrostatic pressure. The phenomenology of an “activation strain”, the nonhydrostatic analogue of the activation volume, has been developed to characterize the results. Combined with the measurement of the activation volume, the measurement reported here permits us to characterize to first order the entire activation strain tensor corresponding to the transition state for solid phase epitaxy of Si(lOO). We conclude that the transition state for this process is “short and fat”; that is, the fluctuation to the transition state involves an expansion in the two in-plane directions and a contraction in the direction normal to the surface large enough to make the overall volume change negative. The symmetry of the measured activation strain tensor is inconsistent with all bulk point defect mechanisms for solid phase epitaxy. The relevance of the activation strain formalism to heteroepitaxy and vapor phase epitaxy is discussed.

Behaviour of the A15 compounds under non-hydrostatic stress

The effect of non-hydrostatic stress on the cubic-to-tetragonal (C-T) transition and the superconductivity (SC) in the A15 compounds has been studied theoretically. The author has assumed that the C-T transition is driven by the band Jahn-Teller effect involving the electronic band which evolves from the doubly degenerate Gamma 12 state at the centre of the cubic Brillouin zone. The SC is also assumed to pertain to this band. He has shown that both the C-T transition and the SC should be affected by the Gamma 12 symmetry-adapted stress ( sigma 12+ sigma 22)1/2, where sigma 1=(s1-s2)/21/2, sigma 2=(2s3-s1-s2)/61/2 and si are the stress components in the Voigt notation. Apart from explaining several experimental results, he has pointed out that the origin of some seemingly different anomalies in the A15 compounds is due to the presence of stress in the samples.

Superconductivity in A15 compounds under nonhydrostatic stress.

The effect of nonhydrostatic stress on the superconducting transition temperature ${T}_{c}$ of the A15 compounds has been studied theoretically. We have assumed that the superconductivity pertains to the narrow band that evolves from the doubly degenerate ${\ensuremath{\Gamma}}_{12}$ state near the Fermi energy. Apart from explaining the existing experimental results, this analysis shows that the reduction of ${T}_{c}$ should depend only on (${\ensuremath{\sigma}}_{1}^{2}$+${\ensuremath{\sigma}}_{2}^{2}$${)}^{1/2}$, where ${\ensuremath{\sigma}}_{1}$=(${s}_{1}$-${s}_{2}$)/ \ensuremath{\surd}2 , ${\ensuremath{\sigma}}_{2}$=(2${s}_{3}$-${s}_{1}$ -${s}_{2}$)/ \ensuremath{\surd}6 , and ${s}_{i}$ are the stress components in the Voigt notation. It has also been argued that, for a given strain, the fractional reduction of ${T}_{c}$ should be inversely proportional to the residual resistivity when the crystal disorder is small. Experimental verification of these results should throw light on the electronic band structure, the origin of the high ${T}_{c}$, and the effect of crystal disorder in these compounds.

Effect of Non-Hydrostatic Stress on Chemical Processes During Diagenesis: ABSTRACT

Non-hydrostatic stress facilitates porosity reduction in sandstones at elevated temperatures. Experimental results indicate that chemical equilibrium between fluids and solids in fluid-saturated, porous rocks will not be attained under conditions of directed stress. In rocks in which pore fluid pressures are less than lithostatic (Pf < PL), downward directed stress at grain contacts can produce an inhomogeneous distribution of mineral solubilities. High strain at grain contacts causes higher solubilities of the solids and leads to dissolution (pressure solution), whereas growth may occur at solid/water interfaces with low surface strain. The driving free energy for coupled dissolution and growth reactions under non-hydrostatic loading is proportio al to PL - Pf. Consequently, the magnitude of the End_Page 917------------------------------ departure from solid/fluid equilibrium during diagenesis will increase with depth of burial if the pore fluid pressure is hydrostatic. When mineral/fluid equilibrium is not reached, the mineral assemblage developed may be controlled by kinetic rather than thermodynamic factors. Solid phases not stable at the prevailing temperature and fluid pressure may form if high local solubilities create supersaturation in the bulk fluid with respect to many solids. The growth of minerals which decreases the total supersaturation rapidly is favored. Hence, fast-growing less-stable phases (for example, clays, zeolites, and aragonite) may form or persist at the expense of more stable but more slowly forming phases (i.e., illite, feldspars, and calcite). Consequently, the influence of both kinetic factors and bulk phase equilibrium should be considered in evaluating the genesis of mineral assemblages formed during diagenesis and bur al metamorphism. End_of_Article - Last_Page 918------------

Effect of non-hydrostatic stress on the superconducting transition of A15 compounds with high critical temperature

The influence of the anomalous elastic behaviour of A15 compounds (e.g. Nb3Sn and V3Si) on its superconducting transition is investigated theoretically. The sensitive reaction of the superconducting properties to uniaxial stress is explained as a consequence of the elastic softening. In single crystals the change of the transition temperature depends strongly on the direction of the applied uniaxial stress. In polycrystals the width of the transition curve increases quadratically with the uniaxial stress. The shape of the broadened transition curve is calculated approximately. In a composite conductor the A15 layer is exerted to a non-hydrostatic stress as a result of different thermal expansion coefficients. The present model explains the observed parabolic strain dependence of superconducting properties in Nb3Sn composite conductors and allows to estimate the strain at which damage of the A15 layer occurs. Der Einfluß des anomalen elastischen Verhaltens von A15-Verbindungen (z. B. Nb3Sn und V3Si) auf den Supraleiterübergang wird theoretisch untersucht. Die empfindliche Reaktion der Supraleitereigenschaften auf einachsige Spannungen wird als Folge der elastischen Aufweichung erklärt. In Einkristallen hängt die Änderung der kritischen Temperatur stark von der Richtung der einachsigen Spannung ab. In Polykristallen wächst die Breite der Übergangskurve quadratisch mit der einachsigen Spannung. Die Form der verbreiterten Übergangskurve wird näherungsweise berechnet. In Verbundleitern wirkt auf die A15-Schicht infolge der unterschiedlichen thermischen Ausdehnungskoeffizienten eine nichthydrostatische Spannung. Die beobachtete parabolische Deformationsabhängigkeit der Supraleitereigenschaften von Nb3Sn-Verbundleitern wird erklärt, und es wird abgeschätzt, bei welcher Dehnung die A15-Schicht zerstört wird.

The Effect of Non-Hydrostatic Stress on Intergranular Water Veins and Lenses in Ice

AbstractPolycrystalline ice at the melting point has been observed in the laboratory to contain veins of water at the places where three grains meet. Under uniaxial compression lenticular water inclusions appeared at grain boundaries perpendicular to the stress, while the nearby vein began to freeze. A similar effect occurred in tension on grain boundaries parallel to the stress. When the stress on the plane of the boundary was a pure shear stress, no effect was observed. The water lenses produced by stress increased in size and decreased in number after the stress was removed. The effect under compression is explained quantitatively by the combined effects of curvature and pressure on the melting point of an ice–water interface. The rate of formation of the lenses and of their coarsening is greatly reduced by the internal pressures set up in the lenses as a result of expansion on freezing and contraction on melting; transient creep to accommodate volume changes is an essential part of the process. The effect in a grain boundary under tension may arise from pressure caused by sliding on other grain boundaries; it was absent in a bicrystal.It is concluded that internal melting and freezing at grain boundaries and veins will occur in temperate glacier ice, with some effect, not discussed here, on its permeability to water. Any pure solid at its melting point which has a dihedral angle for the liquid phase in contact with a grain boundary between 0° and 60° should show similar behaviour, in that non-hydrostatic stress should cause liquid to move away from triple junctions between grains and into grain boundaries. There may be implications for the Frank theory of the upwelling of melt fluid in the Earth’s upper mantle.

The Effect of Non-Hydrostatic Stress on Intergranular Water Veins and Lenses in Ice

AbstractPolycrystalline ice at the melting point has been observed in the laboratory to contain veins of water at the places where three grains meet. Under uniaxial compression lenticular water inclusions appeared at grain boundaries perpendicular to the stress, while the nearby vein began to freeze. A similar effect occurred in tension on grain boundaries parallel to the stress. When the stress on the plane of the boundary was a pure shear stress, no effect was observed. The water lenses produced by stress increased in size and decreased in number after the stress was removed. The effect under compression is explained quantitatively by the combined effects of curvature and pressure on the melting point of an ice–water interface. The rate of formation of the lenses and of their coarsening is greatly reduced by the internal pressures set up in the lenses as a result of expansion on freezing and contraction on melting; transient creep to accommodate volume changes is an essential part of the process. The effect in a grain boundary under tension may arise from pressure caused by sliding on other grain boundaries; it was absent in a bicrystal.It is concluded that internal melting and freezing at grain boundaries and veins will occur in temperate glacier ice, with some effect, not discussed here, on its permeability to water. Any pure solid at its melting point which has a dihedral angle for the liquid phase in contact with a grain boundary between 0° and 60° should show similar behaviour, in that non-hydrostatic stress should cause liquid to move away from triple junctions between grains and into grain boundaries. There may be implications for the Frank theory of the upwelling of melt fluid in the Earth’s upper mantle.