scholarly journals Properties of Dislocation Drag from Phonon Wind at Ambient Conditions

Materials ◽  
2019 ◽  
Vol 12 (6) ◽  
pp. 948 ◽  
Author(s):  
Daniel Blaschke
Keyword(s):  
Crystal Structure ◽  
Plastic Deformation ◽  
Sound Speed ◽  
Room Temperature ◽  
Functional Form ◽  
Functional Dependence ◽  
High Stress ◽  
Slip Systems ◽  
Ambient Conditions ◽  
Transverse Sound

It is well known that, under plastic deformation, dislocations are not only created but also move through the crystal, and their mobility is impeded by their interaction with the crystal structure. At high stress and temperature, this “drag” is dominated by phonon wind, i.e., phonons scattering off dislocations. Employing the semi-isotropic approach discussed in detail in a previous paper (J. Phys. Chem. Solids 2019, 124, 24–35), we discuss here the approximate functional dependence of dislocation drag B on dislocation velocity in various regimes between a few percent of transverse sound speed c T and c T (where c T is the effective average transverse sound speed of the polycrystal). In doing so, we find an effective functional form for dislocation drag B ( v ) for different slip systems and dislocation characters at fixed (room) temperature and low pressure.

Deformation Twinning, Slip, Martensite Formation and Crack Inhibition in the B2-Type Zr50Pd35Ru15 Alloy

1991 ◽  
Vol 246 ◽  
Author(s):  
R.M. Waterstrat ◽  
L.A. Bendersky ◽  
R. Kuentzler
Keyword(s):  
Crystal Structure ◽  
Plastic Deformation ◽  
Room Temperature ◽  
Deformation Mode ◽  
Deformation Twinning ◽  
Mechanical Twinning ◽  
Dislocation Slip ◽  
Slip Mode ◽  
Martensite Formation ◽  
Additional Mode

AbstractEnhanced room temperature toughness of the Zr50Pd35Ru15B2 phase alloy was found to be a result of the activation of an additional deformation mode besides the b=[001] dislocation slip mode - {114}-type mechanical twinning. The twinning is a true one, i.e. there is no change in the ordered crystal structure. Another additional mode of plastic deformation, expected for more Pd rich alloys, is the formation of stress-induced martensite. The martensite was found to have a CrBtype structure.

A positron study of plastic deformation of silicon

1983 ◽  
Vol 61 (3) ◽  
pp. 451-459 ◽  
Author(s):  
S. Dannefaer ◽  
N. Fruensgaard ◽  
S. Kupca ◽  
B. Hogg ◽  
D. Kerr
Keyword(s):  
Plastic Deformation ◽  
Room Temperature ◽  
Functional Form ◽  
Isothermal Annealing ◽  
Positron Lifetime ◽  
Activation Enthalpy ◽  
Isochronal Annealing ◽  
Doppler Broadening ◽  
Trapping Rate ◽  
Vacancy Clusters

Positron lifetime and Doppler broadening experiments have been conducted in silicon which was subjected to various degrees of plastic deformation. With increasing plastic deformation (from 2.5 to 38%) the trapping rate per unit dislocation concentration decreased from about 8 × 1015 to 4.5 × 1015 s−1 as measured at room temperature. Two annealing stages were identified by isochronal annealing, one of which had an activation enthalpy of 3.2 to 3.8 eV as determined by isothermal annealing. Measurements in the temperature range 15 to 673 K show that the positron annihiliation parameters (lifetimes, intensities, and S-parameters) depend strongly on temperature and that the functional form of these dependencies is related to the state of annealing of the deformed samples. These results are disscussed in terms of the presence of vacancy clusters and dislocations, and evidence is presented indicating the existence of the hexavacancy.

Electron microscope studies of the plastic deformation of ternary alloys based on GaAs

1990 ◽  
Vol 48 (4) ◽  
pp. 1120-1120
Author(s):  
R. Haswell ◽  
U. Bangert ◽  
P. Charsley
Keyword(s):  
Plastic Deformation ◽  
Electron Microscope ◽  
Room Temperature ◽  
Stacking Faults ◽  
The Other ◽  
Ternary Alloys ◽  
Dislocation Mobility ◽  
Semiconducting Materials ◽  
Micro Indentation

A knowledge of the behaviour of dislocations in semiconducting materials is essential to the understanding of devices which use them . This work is concerned with dislocations in alloys related to the semiconductor GaAs . Previous work on GaAs has shown that microtwinning occurs on one of the <110> rosette arms after indentation in preference to the other . We have shown that the effect of replacing some of the Ga atoms by Al results in microtwinning in both of the rosette arms.In the work to be reported dislocations in specimens of different compositions of Gax Al(1-x) As and Gax In(1-x) As have been studied by using micro indentation on a (001) face at room temperature . A range of electron microscope techniques have been used to investigate the type of dislocations and stacking faults/microtwins in the rosette arms , which are parallel to the [110] and [10] , as a function of composition for both alloys . Under certain conditions microtwinning occurs in both directions . This will be discussed in terms of the dislocation mobility.

Single Crystal Growth of High-Pressure Phases of Ice and Salt Hydrate Far Below the Original Melting Point by Mixing Alcohol: Crystal Structure Determination of Magnesium Chloride Heptahydrate

2020 ◽  
Author(s):  
Keishiro Yamashita ◽  
Kazuki Komatsu ◽  
Hiroyuki Kagi
Keyword(s):  
Crystal Structure ◽  
High Pressure ◽  
Crystal Growth ◽  
Single Crystal ◽  
Room Temperature ◽  
Growth Technique ◽  
Salt Hydrate ◽  
X Ray

An crystal-growth technique for single crystal x-ray structure analysis of high-pressure forms of hydrogen-bonded crystals is proposed. We used alcohol mixture (methanol: ethanol = 4:1 in volumetric ratio), which is a widely used pressure transmitting medium, inhibiting the nucleation and growth of unwanted crystals. In this paper, two kinds of single crystals which have not been obtained using a conventional experimental technique were obtained using this technique: ice VI at 1.99 GPa and MgCl<sub>2</sub>·7H<sub>2</sub>O at 2.50 GPa at room temperature. Here we first report the crystal structure of MgCl2·7H2O. This technique simultaneously meets the requirement of hydrostaticity for high-pressure experiments and has feasibility for further in-situ measurements.

scholarly journals Crystal structure of K[Hg(SCN)3] – a redetermination

2014 ◽  
Vol 70 (9) ◽  
pp. i46-i46 ◽  
Author(s):  
Matthias Weil ◽  
Thomas Häusler
Keyword(s):  
Crystal Structure ◽  
Room Temperature ◽  
Three Dimensional ◽  
Lattice Parameters ◽  
Bond Lengths ◽  
Dimensional Network ◽  
Anisotropic Displacement Parameters ◽  
Precision And Accuracy ◽  
Standard Deviations ◽  
Atomic Coordinates

The crystal structure of the room-temperature modification of K[Hg(SCN)3], potassium trithiocyanatomercurate(II), was redetermined based on modern CCD data. In comparison with the previous report [Zhdanov & Sanadze (1952).Zh. Fiz. Khim.26, 469–478], reliability factors, standard deviations of lattice parameters and atomic coordinates, as well as anisotropic displacement parameters, were revealed for all atoms. The higher precision and accuracy of the model is, for example, reflected by the Hg—S bond lengths of 2.3954 (11), 2.4481 (8) and 2.7653 (6) Å in comparison with values of 2.24, 2.43 and 2.77 Å. All atoms in the crystal structure are located on mirror planes. The Hg2+cation is surrounded by four S atoms in a seesaw shape [S—Hg—S angles range from 94.65 (2) to 154.06 (3)°]. The HgS4polyhedra share a common S atom, building up chains extending parallel to [010]. All S atoms of the resulting1∞[HgS2/1S2/2] chains are also part of SCN−anions that link these chains with the K+cations into a three-dimensional network. The K—N bond lengths of the distorted KN7polyhedra lie between 2.926 (2) and 3.051 (3) Å.

Effect of solution acidity on the crystallization of polychromates in uranyl-bearing systems: synthesis and crystal structures of Rb2[(UO2)(Cr2O7)(NO3)2] and two new polymorphs of Rb2Cr3O10

2021 ◽  
Vol 236 (1-2) ◽  
pp. 11-21
Author(s):  
Evgeny V. Nazarchuk ◽  
Oleg I. Siidra ◽  
Dmitry O. Charkin ◽  
Stepan N. Kalmykov ◽  
Elena L. Kotova
Keyword(s):  
Crystal Structure ◽  
Aqueous Solutions ◽  
Crystal Structures ◽  
Hydrothermal Treatment ◽  
Ambient Conditions ◽  
Screw Axis ◽  
3D Framework ◽  
Solution Acidity

Abstract Three new rubidium polychromates, Rb2[(UO2)(Cr2O7)(NO3)2] (1), γ-Rb2Cr3O10 (2) and δ-Rb2Cr3O10 (3) were prepared by combination of hydrothermal treatment at 220 °C and evaporation of aqueous solutions under ambient conditions. Compound 1 is monoclinic, P 2 1 / c $P{2}_{1}/c$ , a = 13.6542(19), b = 19.698(3), c = 11.6984(17) Å, β = 114.326(2)°, V = 2867.0(7) Å3, R 1 = 0.040; 2 is hexagonal, P 6 3 / m $P{6}_{3}/m$ , a = 11.991(2), c = 12.828(3) Å, γ = 120°, V = 1597.3(5) Å3, R 1 = 0.031; 3 is monoclinic, P 2 1 / n $P{2}_{1}/n$ , a = 7.446(3), b = 18.194(6), c = 7.848(3) Å, β = 99.953(9)°, V = 1047.3(7) Å3, R 1 = 0.037. In the crystal structure of 1, UO8 bipyramids and NO3 groups share edges to form [(UO2)(NO3)2] species which share common corners with dichromate Cr2O7 groups producing novel type of uranyl dichromate chains [(UO2)(Cr2O7)(NO3)2]2−. In the structures of new Rb2Cr3O10 polymorphs, CrO4 tetrahedra share vertices to form Cr3O10 2− species. The trichromate groups are aligned along the 63 screw axis forming channels running in the ab plane in the structure of 2. The Rb cations reside between the channels and in their centers completing the structure. The trichromate anions are linked by the Rb+ cations into a 3D framework in the structure of 3. Effect of solution acidity on the crystallization of polychromates in uranyl-bearing systems is discussed.

Visible-light-initiated Catalyst-free Oxidative Cleavage of Triaryl-Substituted Alkenes C=C Bonds under Ambient Conditions

2021 ◽  
Author(s):  
Wenjing Li ◽  
Shun Li ◽  
Lihua Luo ◽  
Yichen Ge ◽  
Jiaqi Xu ◽  
...  
Keyword(s):  
Visible Light ◽  
Room Temperature ◽  
Ambient Air ◽  
Oxidative Cleavage ◽  
Ambient Conditions ◽  
Blue Led ◽  
Catalyst Free

The catalyst-free oxidative cleavage of (Z)-triaryl-substituted alkenes bearing pyridyl motif with ambient air under irradiation of blue LED at room temperature has been developed. The reaction was facile and scalable,...

A comparative study of plastic deformation mechanisms in room-temperature and cryogenically deformed magnesium alloy AZ31

2021 ◽  
Vol 807 ◽  
pp. 140821
Author(s):  
Kai Zhang ◽  
Zhutao Shao ◽  
Christopher S. Daniel ◽  
Mark Turski ◽  
Catalin Pruncu ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Magnesium Alloy ◽  
Comparative Study ◽  
Room Temperature ◽  
Deformation Mechanisms ◽  
Alloy Az31 ◽  
Magnesium Alloy Az31
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