scholarly journals Effect of the Free Volume on the Electronic Structure of Cu70Zr30 Metallic Glasses

Materials ◽  
2020 ◽  
Vol 13 (21) ◽  
pp. 4911
Author(s):  
Simon Evertz ◽  
Jochen M. Schneider
Keyword(s):  
Electronic Structure ◽  
Bond Strength ◽  
Coordination Number ◽  
Free Volume ◽  
Metallic Glasses ◽  
Volume Content ◽  
Short Distance ◽  
Volume Fraction ◽  
Plastic Behavior ◽  
Local Bonding

While it is accepted that the plastic behavior of metallic glasses is affected by their free volume content, the effect on chemical bonding has not been investigated systematically. According to electronic structure analysis, the overall bond strength is not significantly affected by the free volume content. However, with an increasing free volume content, the average coordination number decreases. Furthermore, the volume fraction of regions containing atoms with a lower coordination number increases. As the local bonding character changes from bonding to anti-bonding with a decreasing coordination number, bonding is weakened in the volume fraction of a lower coordination number. During deformation, the number of strong, short-distance bonds decreases more for free volume-containing samples than for samples without free volume, resulting in additional bond weakening. Therefore, we show that the introduction of free volume causes the formation of volume fractions of a lower coordination number, resulting in weaker bonding, and propose that this is the electronic structure origin of the enhanced plastic behavior reported for glasses containing free volume.

FREE VOLUME CHANGE OF METALLIC GLASSES STUDIED BY THERMAL EXPANSION MEASUREMENTS

1980 ◽  
Vol 41 (C8) ◽  
pp. C8-875-C8-877
Author(s):  
E. Girt ◽  
P. Tomić ◽  
A. Kuršumović ◽  
T. Mihać-Kosanović
Keyword(s):  
Thermal Expansion ◽  
Free Volume ◽  
Volume Change ◽  
Metallic Glasses

Elasticity of colloidal gels: structural heterogeneity, floppy modes, and rigidity

Soft Matter ◽  
2021 ◽  
Author(s):  
D. Zeb Rocklin ◽  
Lilian C Hsiao ◽  
Megan E Szakasits ◽  
Michael J Solomon ◽  
Xiaoming Mao
Keyword(s):  
Coordination Number ◽  
Volume Fraction ◽  
Structural Parameters ◽  
Structural Heterogeneity ◽  
Colloidal Gels ◽  
Shear Moduli ◽  
Rheological Measurements

Rheological measurements of model colloidal gels reveal that large variations in the shear moduli as colloidal volume-fraction changes are not reflected by simple structural parameters such as the coordination number,...

scholarly journals Boron Concentration Induced Co-Ta-B Composite Formation Observed in the Transition from Metallic to Covalent Glasses

2020 ◽  
Vol 5 (1) ◽  
pp. 18
Author(s):  
Simon Evertz ◽  
Stephan Prünte ◽  
Lena Patterer ◽  
Amalraj Marshal ◽  
Damian M. Holzapfel ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Metallic Glasses ◽  
Boron Concentration ◽  
High Strength ◽  
Point Of View ◽  
Composite Formation ◽  
Structural Applications ◽  
Glassy Materials ◽  
Metallic Bonding ◽  
Composite Region

Due to their unique property combination of high strength and toughness, metallic glasses are promising materials for structural applications. As the behaviour of metallic glasses depends on the electronic structure which in turn is defined by chemical composition, we systematically investigate the influence of B concentration on glass transition, topology, magnetism, and bonding for B concentrations x = 2 to 92 at.% in the (Co6.8±3.9Ta)100−xBx system. From an electronic structure and coordination point of view, the B concentration range is divided into three regions: Below 39 ± 5 at.% B, the material is a metallic glass due to the dominance of metallic bonds. Above 69 ± 6 at.%, the presence of an icosahedra-like B network is observed. As the B concentration is increased above 39 ± 5 at.%, the B network evolves while the metallic coordination of the material decreases until the B concentration of 67 ± 5 at.% is reached. Hence, a composite is formed. It is evident that, based on the B concentration, the ratio of metallic bonding to icosahedral bonding in the composite can be controlled. It is proposed that, by tuning the coordination in the composite region, glassy materials with defined plasticity and processability can be designed.

scholarly journals Shape and Temperature Expansion of Free Volume Holes in Some Cured Polybutadiene-Polyisoprene Rubber Blends

2021 ◽  
Vol 22 (3) ◽  
pp. 1436
Author(s):  
Giovanni Consolati ◽  
Eros Mossini ◽  
Dario Nichetti ◽  
Fiorenza Quasso ◽  
Giuseppe Maria Viola ◽  
...  
Keyword(s):  
Free Volume ◽  
Radial Direction ◽  
Volume Fraction ◽  
Spherical Shape ◽  
Suitable Model ◽  
Positron Annihilation Lifetime ◽  
Rubber Blends ◽  
Free Volume Fraction ◽  
Hole Model ◽  
Best Fit

The free volume fraction of a macromolecular structure can be assessed theoretically by using a suitable model; however, it can also be evaluated from experimental data obtained from dilatometry and positron annihilation lifetime spectra. In this second case, a regular geometry of the sub-nanometric cavities forming the free volume has to be assumed, although in fact they are irregularly shaped. The most popular approach is to guess spherical holes, which implies an isotropic growth of these last with temperature. In this work, we compared the free volume fraction, as obtained from experiments in a set of polybutadiene and polyisoprene cured rubbers and their blends, with the analogous quantity expected by using the lattice-hole model. The results allowed us to obtain insights on the approximate shape of the holes. Indeed, a cylindrical flattened geometry of the cavities produced a better agreement with the theory than the spherical shape. Furthermore, the best fit was obtained for holes that expanded preferentially in the radial direction, with a consequent decrease of the aspect ratio with temperature.

THE STRUCTURE OF AGGREGATES AND THE MOLECULAR KINEMATICS OF THE VISCOSITY OF A BERNAL LIQUID

1964 ◽  
Vol 42 (2) ◽  
pp. 304-320 ◽  
Author(s):  
F. W. Smith
Keyword(s):  
Coordination Number ◽  
Free Volume ◽  
Activation Volume ◽  
Molecular Volume ◽  
3 Dimensional ◽  
Theory Of Liquids ◽  
Kinetic Pressure ◽  
Steel Balls ◽  
Set Of Points ◽  
Structure Of Aggregates

The structure of 3-dimensional aggregates is discussed as a set of points on which graphs are constructed. By constructing the Voronoi honeycomb (Dirichlet regions) for the points and applying a small "irregularizing transformation", a "simplicial graph" and a "primitive coordination number" (whose value is close to 14 for all aggregates) can be defined universally for both regular and irregular aggregates. Recent studies of the geometry of irregular aggregates (of steel balls, crystal grains, etc.) are reviewed. The theory of liquids of J. D. Bernal is discussed and the simplicial graph is used to show that the "activation volume" of a Bernal liquid is about one-tenth of the molecular volume. The kinematics of flow of aggregates is discussed in terms of their graphs and in terms of a process of "volume exchange"—the production and destruction of free volume. Using these concepts, an equation is derived for the viscosity of a Bernal liquid as a product of five terms expressing respectively the kinematic, stoichiometric, kinetic, pressure-dependent, and shear-dependent factors.

Electronic structure of (Ni33Zr67)85X15 (XTi, V, Cr, Mn, Fe, Co and Cu) Metallic glasses studied by photoelectron spectroscopy

1988 ◽  
Vol 99 (1-2) ◽  
pp. 317-320 ◽  
Author(s):  
R. Zehringer ◽  
P. Oelhafen ◽  
H.-J. Güntherodt ◽  
Y. Yamada ◽  
U. Mizutani
Keyword(s):  
Electronic Structure ◽  
Metallic Glasses ◽  
Photoelectron Spectroscopy
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