Influence Of Structural Relaxation Research Articles

Nature of anomalous electrical resistance in Co73-xFe4CrxSi12B11 amorphous microwires

Influence of structural relaxation and composition of microwires of metallic amorphous alloys Co73-xFe4CrxSi12B11 (x = 0, 2, 4, 6, 8) on the character and mechanisms of temperature dependence of electrical resistance r(T) has been studied in a wide temperature range (from 4.2 K to crystallization temperature). It is shown that alloys with more than 2 at.% Cr have a number of specific properties, which are significantly differentiate them from Fe- and Ni-rich alloys, as well as many Co-rich amorphous alloys. The features of Cr-doped Co-rich alloys are explained by two reasons: firstly, very strong quantum interference effects of the electron-electron interaction and weak localization of electrons caused by scattering of electrons by the potential created by randomly distributed chromium atoms, and secondly, partially reversible compositional structural relaxation leading to clustering of the amorphous phase at T > 300 °C. It is assumed that the resulting Cr-rich clusters, in which chromium atoms are bonded to metalloid atoms, can enhance these interference effects. The contributions from various mechanisms of interaction and scattering of electrons to the change in electrical resistance with temperature and composition of the alloy are analyzed. The fitting parameters for them are determined and compared with the known data.

Nanoindentation of Nanoglasses Tested by Molecular Dynamics Simulations: Influence of Structural Relaxation and Chemical Segregation on the Mechanical Response

We present molecular dynamics simulations of nanoindentation in order to investigate the effects of segregation and structural relaxation on the mechanical properties of Cu64Zr36 nanoglasses prepared by particle consolidation and long-time annealing. Our analysis of load-displacement curves shows that the effective elastic modulus of nanoglasses is lower than that of their homogeneous metallic glass counterpart. This is mainly because of the defective short-range order present in the glass-glass interface, but to a lesser extend due to chemical inhomogeneities. Structural relaxation obtained by long-time annealing (500 ns) at 0.8 Tg leads to a shift from a homogeneous deformation to a mix of homogeneous deformation and shear bands. The obtained hardness values of annealed nanoglass are comparable to those of homogenous glass samples, but significantly higher as compared to juvenile as-prepared nanoglass samples. The results are discussed in the context of recent nanonindentation experiments.

Effect of structural relaxation on crystal nucleation in a soda‐lime‐silica glass

AbstractThe influence of structural relaxation on crystal nucleation has been underexplored and remains elusive. This article discusses its possible effect on the nucleation process using a stoichiometric soda‐lime‐silica (2Na2O·CaO·3SiO2) glass as a model system. We show that the relaxation effect is powerful at low temperatures, close and below the glass transition, , and leads to a continuous increase in the nucleation rate. At any given temperature, the nucleation rate eventually reaches its ultimate steady‐state corresponding to the fully relaxed supercooled liquid (SCL). However, the time to reach the steady‐state is two to three orders of magnitude longer than the average relaxation time estimated by the Maxwell relation (shear viscosity / shear modulus). The proposed nucleation mechanism and model, which take relaxation into account, and related experimental results also explain the alleged “breakdown” of CNT at low temperatures reported for various glasses. It confirms a few recent papers that this apparent flaw is merely because most researchers did not prolong nucleation treatments enough to complete the relaxation process to achieve a steady state. Another remarkable result is that the actual maximum nucleation temperature, , is significantly lower than the previously reported values. Finally, a comparative analysis of the kinetic coefficient using viscosity versus growth velocity favors the last. These results for this soda‐lime‐silica glass extend and validate recent findings for lithium disilicate on the significant (but often neglected) effect of relaxation on crystal nucleation.

Thermal behavior, structural relaxation and magnetic study of a new Hf-microalloyed Co-based glassy alloy with high thermal stability

In the present work, the influence of a minor Hf addition on the atomic structure, crystallization behavior, thermal stability and magnetic properties of a Co-based metallic glass was studied. Thermal analysis indicates that the thermal stability of new glassy ribbons microalloyed with 2.5 at.% Hf is notably enhanced through increasing the incubation time prior to devitrification and enlarging the width of the supercooled liquid region from 72 K to 96 K. Magnetic studies reveal that the new glass exhibits an excellent soft magnetic behavior, i.e., a very low coercivity of 0.26 A/m in the relaxed state, and a comparable saturation magnetization as the Hf-free ribbon. Structural relaxation of the Hf-containing alloy upon isothermal annealing below the glass transition temperature, Tg, was investigated by differential scanning calorimetry (DSC) and high-energy synchrotron X-ray diffraction (XRD). The evolution of the recovered enthalpy with annealing time can be expressed by the Kohlrausch-Williams-Watts (KWW) exponential function with a Kohlrausch exponent of 0.88, indicating a broad spectrum of relaxation times. Analysis of the reduced pair correlation functions, G(r), reveals volume shrinkage upon annealing caused by elimination of liquid-like sites including free-volume and anti-free-volume according to the shift in the positions of the G(r) maxima in the medium-range scale. The influence of structural relaxation on the variation of the Curie temperature and the coercivity of the new Hf-microalloyed glassy ribbon is discussed. A faster evolution of the Curie temperature with annealing time compared to the coercivity indicates a preferential dependence of the former on the chemical short-range order (SRO).

Influence of structural relaxation on thermomechanical and shape memory performances of amorphous polymers

AbstractShape memory polymers (SMPs) have been intensively studied for a wide range of potential applications, including biomedical devices, morphing structures, and 4D printing. For amorphous polymers, the glass transition temperature measured by dynamic mechanical analysis (DMA) is an important consideration in designing SMPs. However, typical DMA curves are cooling- and heating-rate dependent and the cooling and heating traces for storage modulus form a (sometimes large) hysteresis loop. This paper first experimentally studies temperature-rate effects on DMA results. A constitutive relation is then developed based on the assumption that the stress relaxation behavior depends on both temperature and structural relaxation state. Good agreement is obtained between the experimental and the modeling results. This model is then applied to study the shape memory behaviors, showing that structural relaxation plays an important role in the free recovery; the model without considering structural relaxation tends to predict a fast recovery.

Influence of Structural Relaxation on Compressive Plasticity of Zr<sub>64.13</sub>Cu<sub>15.75</sub>Ni<sub>10.12</sub>Al<sub>10 </sub>Bulk Metallic Glass

Structural relaxation through isothermal annealing below the glass transition temperature was conducted on a Zr64.13Cu15.75Ni10.12Al10bulk metallic glass. Differential scanning calorimetry was used to quantify enthalpy differences between the as-cast and relaxed samples, which were then related to average free volume differences. The influence of structural relaxation on plasticity was examined. While the free volume decreasement can be clearly observed between the as-cast and relaxed samples, structural relaxation is not accompanied by severe embrittlement.

Influence of structural relaxation on wetting behavior of molten In–Sn alloy on Cu 40Zr 44Al 8Ag 8 bulk metallic glass

Influence of structural relaxation on wetting behavior of molten In–Sn alloy on Cu 40Zr 44Al 8Ag 8 bulk metallic glass (BMG) was studied using the sessile-drop method at isothermal condition in high vacuum. It was found that the equilibrium contact angle increased with the increase of the pre-annealing temperature of Cu 40Zr 44Al 8Ag 8 BMG substrate. Moreover, the high-temperature structural relaxation greatly affected wetting behavior of molten In–Sn alloy on Cu 40Zr 44Al 8Ag 8 BMG substrate. By analyses of interfacial microstructure, the interface between In–Sn alloy and pre-annealed Cu 40Zr 44Al 8Ag 8 BMG was continuous, while no interfacial reaction layer formed in the temperature range studied.

Influence of free volume on magnetoelastic coupling in iron-based amorphous alloys

In this paper, the influence of structural relaxation on magnetoelastic coupling in iron-based amorphous alloys is carefully examined. In order to change free volume content, the as-quenched samples were annealed for 1 h at temperatures corresponding to the structural relaxation. Magnetostriction measurements were carried out at room temperature using the infrared magnetodilatometer. It was shown that both the parallel magnetostriction coefficient λ∥ and the perpendicular magnetostriction coefficient λ⊥ decrease with decreasing free volume content, whereas the saturation magnetostriction λS (proportional to λ∥−λ⊥) remains constant. In contrast, the volume magnetostriction ω strongly depends on free volume content and follows the relation ω∝ m2 (where m is the reduced magnetization). Moreover, it was confirmed that λS can be attributed to one-ion spin correlations, short range in nature.

Influence of structural relaxation on the optical and electronic properties of embedded Ge nanocrystals

Structural relaxation is shown to be indispensable for the correct description of the electronic and optical properties of embedded group-IV nanocrystals. Ab initio calculations show that the energetic position of the localized gap states and, consequently, the optical spectra, are very sensitive with respect to the ionic relaxation. Comparison with the results obtained for the corresponding ideal structures allows to quantify the influence of the relaxation.

The influence of structural relaxation on the mechanical properties ofZr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass

Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG) was annealed at 573 Kunder a high pressure of 3 GPa. The effects of the structural relaxations of BMGon its mechanical and acoustic properties are investigated by using x-raydiffraction, ultrasonic study, density measurements, compression testing, as wellas microhardness. It is found that high-pressure relaxation results in amicrostructural transformation in the BMG. A sample relaxed under highpressure exhibits 3% plastic strain compared with the crystallized form, and thecompression strength achieved, 1800 MPa, is improved by nearly 20% over thatfor the as-prepared sample; moreover, a BMG with relaxed structure exhibitsmarkedly different acoustic properties.

Spectral analysis of creep recovery process in finemet type amorphous alloy

The creep recovery process in Finemet type amorphous alloy has been analyzed using the method for calculating the relaxation time spectra. The influence of structural relaxation and temperature on the spectra shape has been studied. The creep recovery spectrum of the anelastic deformation of the multicomponent Fe−Nb−Cu−Si−B amorphous alloy seems to be more complex in comparison with standard amorphous alloys.

Characteristic features of hysteresis in soft-magnetic amorphous alloys upon structural relaxation

The influence of structural relaxation on the hysteresis of soft-magnetic amorphous alloys in the case when structural relaxation proceeds above the Curie temperature is investigated. The results of the present study and previous works, in which similar studies were conducted for alloys with structural relaxation observed below the Curie temperature, have been generalized. The entire set of experimental data obtained makes it possible to formulate the recommendations regarding the choice of the annealing conditions for softmagnetic amorphous alloys.

Influence of structural relaxation and partial devitrification on the corrosion resistance of Fe 78B 13Si 9 amorphous alloy

Influence of structural relaxation and partial devitrification on the corrosion resistance of Fe 78B 13Si 9 amorphous alloy

Influence of structural relaxation on the low-temperature thermal conductivity of ancient natural glasses

The thermal conductivities κ of two natural glasses, amber and obsidian, were measured over the temperature range 0.06–10 K both in the as-received condition and following heat-treatments near and above the glass-transition temperature. The κ of amber decreased 6% with heat treatment revealing that this glass had undergone configurational relaxation during the 107 years prior to measurement, but with a relaxation time greater than seven years. The κ of the obsidian did not change with heat treatment, a null result possibly produced by the ratio of oxides comprising the glass.

Mössbauer study of long time annealed Fe30Ni44Cr4Mo2Si5B15 metallic glasses

The influence of structural relaxation caused by long time annealing on magnetic properties of Fe30Ni44Cr4Mo2B15Si5 metallic glasses is investigated by Mossbauer spectroscopy and by magnetization measurements. Remarkable hyperfine field distribution shift to the high field region and increase of the value of exchange constant and Curie temperature are observed after annealing. The observed findings are discussed in terms of the possible annealing induced effects on the local short-range order around the magnetic atoms in investigated samples.

The influence of structural relaxation on the fluorescent properties of N-naphthyl-substituted pyridinium cations

N-naphthyl-substituted pyridinium cations fluoresce in liquids at 293 and 77 K and have an unusually large Stokes shift ((9−15)×10 3 cm -1). The Stokes shift is a result of the torsional relaxation of different aromatic groups. Characteristic fluorescence spectra demostrate dependence of the Stokes shift on the solvent viscosity.

The Electronic Configuration of 121Sb in Semiconductors

AbstractIsomer shifts of the 37 ke V Mössbauer transition in 121Sb are determined for 121Sb constituents and impurities in III‐V and II‐VI compound semiconductors. Radioactive 121Xe isotopes decaying to 121Te, the 121Sb‐parent isotope, were implanted at the ISOLDE facility at CERN. The nature of the electronic configuration of Sb‐isoelectronic and Sb‐donor and ‐acceptor impurities in semiconductors is discussed in terms of bond hybridization and ionicity. The influence of structural relaxation is pointed out.

Influence of structural relaxation on the atomic dynamics of the metallic glass Mg 70Zn 30

Etude de la dynamique atomique de trois echantillons de verres metalliques Mg 70 Zn 30 avant et apres traitement thermique

Influence of structural relaxation on the low-temperature properties of glassy metals

The thermal conductivity $\ensuremath{\kappa}$ of glassy metals is shown to change reversibly with heat treatment at temperatures ${T}_{A}$ near the glass transition. If the change in $\ensuremath{\kappa}$ is interpreted as resulting from a change in the density $n(E)$ of the two-level states found in amorphous solids, the observed dependence of $n(E)$ on ${T}_{A}$ is in qualitative agreement with a prediction of a free-volume model for the glass transition.

Influence of structural relaxation on the magnetic permeability aftereffect of amorphous ferromagnetic alloys

Room temperature measurements of the aftereffect of the magnetic permeability have been performed on amorphous Fe-(Cu--Cr)-B ribbons annealed at various temperatures. The results, in good agreement with the predictions of a new theory, give information on the effect of structural relaxation on the shear stress defects responsible for the magnetic aftereffect.