Properties Of Amorphous Materials Research Articles

Evidence of low-energy tunneling excitations in the high-Tc superconductor YBa2Cu3O7-x.

We have measured the internal friction Q/sup -1/ and the Young's-modulus sound velocity v/sub E/ at 1 kHz for YBa/sub 2/Cu/sub 3/O/sub 7-//sub x/. Below 20 K the relatiave change in the sound velocity and the temperature dependence of the internal friction perfectly resemble the behavior obtained for Suprasil W. Below 1 K we observe a logarithmic temperature dependence for the sound velocity and between 1 and 5 K a well-defined plateau in the internal friction is obtained. We find quantitative agreement with the predictions of the standard tunneling model which is widely used to explain the low-temperature properties of amorphous materials. The implications of the existence of tunneling systems in these materials are discussed.

Domain walls and a wall-pinning effect in amorphous magnetic materials

The wall thickness and the initial susceptibility as well as the coercivity of amorphous magnetic material were calculated on a simple theory concerned with the micro-structure-magnetic anisotropies in it. It is indicated that for amorphous materials the domain patterns observed by Bitter method can be incomplete. It is pointed out that the complication and irregularity of domain configurations and the inhomogeneity of anisotropies in as-prepared amorphous materials are two important reasons for their initial susceptibility to be rather low. It is expected that some of amorphous magnetic materials do not have a clear Hopkinson phenomenon. It is shown that the wall-pinning effect by the gradient of microstructure-magnetic anisotropies is a main mechanism forming the coercivity of amorphous soft-magnetic material, the effects of thermal treatments on the technical magnetic properties of amorphous material are distinct. All the results presented show agreement with experimental data.

A Model for the Variations in the Field‐Dependent Behaviour of the Poole‐Frenkel Effect

AbstractThe Poole‐Frenkel effect is often observed in the field‐dependent properties of amorphous materials. Experimentally, it is frequently found that the slopes of log σ versus E1/2 plots differ from that predicted by the Poole‐Frenkel equation and several theorems have been postulated to explain this discrepancy. Recently, Török used the concept of multiple ionisation to account for such discrepancies. In this paper some of the arguments presented by Török and others is examined in more detail, and the Poole‐Frenkel effect is discussed for two limiting cases. The situation when the free carrier density (n) in the case of an n‐type material containing both donor (Nd) and acceptor (Na) impurities, is of the same order of magnitude as Na where the two approximations are invalid, is more closely examined. It is shown that by assuming a field dependent value of n, a transition region situated between the two approximations is evident. It is also shown that by considering basic parameters such as temperature, and acceptor densities, a Poole‐Frenkel plot is obtained which is very sensitive to variations in temperature and acceptor density.

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.

Review on recent advances in the field of amorphous-metal sensors and transducers

Recent researches and developments of applications of amorphous ribbons and wires to sensors and transducers are reviewed. Various sensitive and quick response magnetic sensors with very small amorphous cores have been developed corresponding to strong demands in the fields of information devices, automobiles, power motor drives, industrial robots, and industrial measurement instruments. Relationship between amorphous material properties and the suitable applications to sensors and transducers, the basic principle of amorphous sensor constitutions, and the advantageous points of amorphous sensors are represented.

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.

Symposium on modelling of the structure and properties of amorphous materials

Symposium on modelling of the structure and properties of amorphous materials

Symposium on modelling of the structure and properties of amorphous materials

Symposium on modelling of the structure and properties of amorphous materials

A tunnelling-state model for the specific heat capacity and thermal conductivity of amorphous materials at low temperatures

Abstract This brief review of the tunnelling-state model explains the observed low-temperature thermal properties of amorphous materials. Below 1.0 K, the amorphous materials have, over and above contribution by phonons, a specific heat capacity c that varies almost linearly with temperature; and the thermal conductivity k is approximately proportional to T2 , becoming almost independent of T above 1.0 K. This behaviour is very different from that of crystalline materials, for which c α T 3 and k α T 3 in this range. A broad band of localized excitations is apparently an intrinsic characteristic of the amorphous state. The tunnelling-state model for these localized excitations can explain qualitatively the various unusual low-temperature properties found in amorphous materials, even though no physical description of the tunnelling entity for any material is available.

Magnetic properties of amorphous materials

AbstractThe magnetic properties of the amorphous alloys containing 75–85 at.-% transition metals and 15–25 at.-%.metalloids (P, C, B, Si) are reviewed. Attention is centred on the strongly ferromagnetic alloys, and on magnetic properties that are influenced by changes in structure brought about by annealing treatments that do not cause crystallization. A conceptual distinction is made between compositional short-range ordering and topological short-range ordering in the amorphous state: compositional ordering involves primarily changes in the chemical identity of nearest-neighbour atoms, while topological ordering involves a long-range cooperative motion of atoms over small distances, without significant changes in nearest-neighbour identity. Probable directions for the engineering applications of these materials are also discussed, especially their use in power transformers because of their very low magnetic losses andpotentially low production cost.

Low temperature specific heat of glasses and amorphous solids

IN a previous paper1 we attributed the anomalous low temperature thermal properties of amorphous materials to the inherent nature of the amorphous state, conceived of as the crystalline state saturated with the most favoured dislocations2. Using Granato's vibrating string model3 of a dislocation, an estimate of the excess specific heat of Pd0.775 Cu0.06 Si0.165 was provided. The purpose of the present note is to clarify several points in our earlier paper.

Study op electrical conductivity op some chalkogenide glasses under hydrostatic pressure up to 1000 MPa

The study of electrical properties of amorphous materials under high pressure can contribute to understanding of processes in these materials and helps to build the theory of amorphous materials. Properties of these materials under high pressure are studied for instance in papers /1–6/. The change of electrical conductivity is usually ascribed to the change of activation energy due to hydrostatic pressure.

Effect of anharmonicity on the properties of amorphous materials

Effect of anharmonicity on the properties of amorphous materials

Semiconducting properties of amorphous materials

Semiconducting properties of amorphous materials