Physical Properties Of Amorphous Materials Research Articles

Elastic properties of Fe95-yNb2Mo2Cu1Siy-xBx (x=5-8, y=20-26) at % amorphous alloys

Amorphous materials exhibit complex atomic structures characterized by the absence of long-range order, in contrast to the well-defined periodicity of crystalline materials. This structural complexity is further pronounced in compositions such as FeMCuSiB (M = Nb, Mo, W and Ta), which incorporate elements with varying atomic radii and valencies. The Young's modulus of structures generated using traditional methods, such as melt-quenching and random packing, shows poor agreement with experimental data. In this study, we employ hybrid methods for generating the structures, which involve randomly packing elements without overlap, followed by thermalization at room temperature using Ab-initio Molecular Dynamics simulations. The Young's modulus evaluated from these structures aligns well with values measured using Dynamic Mechanical Analysis. Additionally, we utilize these structures to determine other elastic moduli including the bulk modulus and tetragonal shear modulus and find that the obtained values are consistent with the expected range for these compounds. We attribute the improved accuracy to a more representative approximation of the amorphous structure and the direct application of energy-strain relationships, rather than stress-strain relationships, for elastic moduli determination. Our methodology facilitates reliable predictions of the physical properties of amorphous materials and contributes to the design of FeMCuSiB (M = Nb, Mo, W and Ta) alloys with enhanced mechanical properties.

Persistent homology-based descriptor for machine-learning potential of amorphous structures.

High-accuracy prediction of the physical properties of amorphous materials is challenging in condensed-matter physics. A promising method to achieve this is machine-learning potentials, which is an alternative to computationally demanding abinitio calculations. When applying machine-learning potentials, the construction of descriptors to represent atomic configurations is crucial. These descriptors should be invariant to symmetry operations. Handcrafted representations using a smooth overlap of atomic positions and graph neural networks (GNN) are examples of methods used for constructing symmetry-invariant descriptors. In this study, we propose a novel descriptor based on a persistence diagram (PD), a two-dimensional representation of persistent homology (PH). First, we demonstrated that the normalized two-dimensional histogram obtained from PD could predict the average energy per atom of amorphous carbon at various densities, even when using a simple model. Second, an analysis of the dimensional reduction results of the descriptor spaces revealed that PH can be used to construct descriptors with characteristics similar to those of a latent space in a GNN. These results indicate that PH is a promising method for constructing descriptors suitable for machine-learning potentials without hyperparameter tuning and deep-learning techniques.

Merging of relaxations and step-like increase of accompanying supercooled liquid region in metallic glasses via ultrafast nanocalorimetry

Glassy materials under external stimuli usually display multiple and complex relaxations. The relaxations and the evolution paths of glassy materials significantly affect their properties and are closely related to many key issues in glass physics, such as glass transition and thermoplastic forming. However, until now, the relaxation dynamics in the presence of external stimuli and the microscopic atomic motion of glassy materials have been unclear due to the lack of structural information. By combining Flash and conventional differential scanning calorimetry (DSC), we applied a very large range of heating rate of six orders of magnitude and investigated the relaxation dynamics of three typical metallic glasses. We discovered the merging of distinct relaxation events with increasing rate of heating. Most interestingly, the experiments revealed new behaviors with step-like increases in the supercooled liquid region and excess heat capacity during the merging of multiple relaxations. A comprehensive scheme was proposed for the evolution of the thermal relaxation spectrum, the heterogeneity of the corresponding atomic motion and the potential energy landscape with rate of heating. These experimental results shed light on the mechanism of atomic rearrangement during heating and provided a new approach to regulate the physical properties of amorphous materials by controlling their intrinsic relaxation dynamics.

Amorphous materials based on perovskite ferroelectrics

The methods of preparation, as well as the structure and most relevant physical properties of amorphous materials based on ferroelectrics with perovskite structure are reviewed. The theoretical basis for the possibility of ferroelectricity in non-crystalline solids is discussed. The structural relaxation in a glassy state and the crystallization processes leading to the formation of a ferroelectric phase are considered. The structure and physical properties of thin-film amorphous ferroelectrics that demonstrate noticeable differences from the properties of the same materials in bulk state are discussed separately

Thickness dependence of the physical properties of atomic-layer deposited Al2O3

Inspired by nature, we investigate the short-range order effect on the physical properties of amorphous materials. Amorphous Al2O3 thin films exhibit a higher proportion of their 4-coordinated Al sites close to the surface, causing variations in the average short-range order of the film. Below some thickness, the density of these films changes with size. In this work, we address the short-range order effect, through the thickness, on the electronic and optical properties of atomic layer deposited Al2O3 thin films. Both the refractive index and the permittivity were found to vary with size. The refractive index increased with thickness, and for thick films (∼50 nm), it was comparable to that of bulk amorphous Al2O3. The permittivity values increased with thickness as well, but did not reach those of the bulk material. Our experimental design circumvents the unpredictable Al2O3–Si interface, allowing new insights into the permittivity–thickness relations. By combining this design with accurate thickness and density measurements, we systematically correlate the refractive index and permittivity with the density and short-range order. These results shed light on the size effects in thin amorphous oxides and may guide the design of electronic and optical components and devices.

Nuclear quadrupole resonance of 35Cl nuclei in glassy solution of chlorobenzene in pyridine.

Pulsed nuclear quadrupole resonance (NQR) measurements of $^{35}\mathrm{Cl}$ nuclei were performed on 43.5 mol % chlorobenzene solution in pyridine (a) in glassy state (${\mathit{T}}_{\mathit{g}}$=131 K) after quenching in liquid nitrogen and (b) in crystalline precipitate under slow cooling starting from liquid phase. In both cases the NQR line shape, obtained by the fast Fourier transform (FFT) method, consisted of a structure of two peaks, interpreted as contributions of two nonequivalent $^{35}\mathrm{nucleus}$ sites. A theoretical model is proposed for the line-shape analysis and the best-fit parameters yield excellent agreement with experimental spectra. It is suggested that the nonequivalent sites consist of nearly parallel and antiparallel alignment of chlorobenzene and pyridine molecules and that the line-broadening mechanism is due to a random distribution of angular displacements from these positions. Our data are in agreement with Goldstein studies of molecular-relaxation processes related to the changes observed on physical properties of amorphous materials at ${\mathit{T}}_{\mathit{g}}$.

Physical Properties of Amorphous Materials: Institute for Amorphous Studies Series

David Adler et al (eds) 1985 New York: Plenum xiii + 443 pp price $62.50 ISBN 0 306 41907 6 This book is a collection of 14 lectures given at the Institute of Amorphous Studies in Bloomfield Hills, Michigan, USA. This centre was founded by S R Ovshinsky and one is very much aware of his presence in the book.

Theory of the Power Spectrum and Scattering Properties of Three‐Dimensional Disordered Systems Having a Variable Degree of Short‐Range Order. II. Line Spectrum and Cross‐Relation Technique

AbstractA new approach to the power spectrum calculation of the three‐directional distribution of physical events characterized by a variable degree of order, ranging from a perfect long‐range order to a complete disorder, including short‐range order properties, is given in Part I of the paper. In this second part simple analytical expressions of the line component of the power spectrum are obtained. The scattering properties of disordered or partially ordered atomic or molecular structures (like for instance, liquid crystals) are considered, concerning both, the diffuse and the line component of the spectrum. The case when in the local order different types of sublattices can still be identified is also considered. Applications of the above results include X‐ray and neutron scattering properties of disordered or partially ordered atomic or molecular structures concerning both, the line and diffuse component of spectrum, excess energy and power loss calculation in ferromagnets and superconductors, and physical properties of amorphous materials. Some of these applications will be discussed in a forthcoming paper.

Laser Anneal and the Amorphous-Crystalline Transition in the Cu60-Zr40 Alloy System

ABSTRACTRecently, significant advances have been made in establishing a theoretical basis for explaining the many structural-sensitive physical properties of amorphous materials. Viewed from both the theoretical and experimental realms, reversible annealing dependency and the structural relaxation mechanism of the amorphous solids are conceptually deducible from the concept of localized structural fluctuations. In the case of annealing, however, the limiting temperature below which no permanent atomiclevel rearrangements occur is not known and may well be dependent on several intrinsic properties of the amorphous state. In an effort to establish this limiting temperature, amorphous Cu60-Zr 40 samples have been annealed using a 1kv pulsed laser. Samples annealed during 1200, 800, 600 400, and 200 μ sec. have been analyzed by using Differential Scanning Calorimetry (DSC), High Resolution Electron Microscopy (HREM), and microanalysis. Analysis of the DSC indicates variations in both height and the shape of the exotherms from the samples annealed above 600 μ sec. duration. The results from HREM of these samples indicate the onset of amorphous-crystalline transition evidenced during 200 μ sec. annealing.