Atomic-level structure and structure–property relationship in metallic glasses

REVIEW ARTICLE: Glassy metals

Thermodynamic considerations on the formation and stability of metallic glasses

Extended X-ray absorption fine structure is used to study local order in silicate glasses around sodium and silicon atoms. It is demonstrated that modifying cations like sodium have well-defined short range order that is complementary rather than incidental to the glass forming silicate network.

Local structure of silicate glasses

The application of random packing models to amorphous metals and metal–metalloid alloys is discussed, with particular reference to the effects of soft potentials, boundary conditions, and density. The local atomic organisations found leads to structural speculation concerning the glass transition, and the existence of ‘amorphous polymorphs’.

Modelling the structures of amorphous metals and alloys

A model describing the structure of amorphous metallic alloys is proposed using a packing of non-equal-sized hard spheres. Models containing up to 1000 spheres were generated by computation. Hypotheses guiding the calculation are chosen in order to obtain a model as compact as possible and to take into account affinity between metal and metalloids: therefore two small spheres are not allowed to be in hard contact. This method of calculation is first tested by building up heaps of equal-sized spheres. Both the radial distribution function and the interference function are calculated for each model and the variations of these curves with the number of spheres are studied. In the case of two sizes of spheres heaps calculations are devoted to the study of the so-called ‘shoulder interference function’ which characterizes many amorphous alloys such as NiP, PdSi, etc. It is shown that the existence of such a shoulder depends on two parameters: the ratio of sphere diameters and the relative concentration of small and large spheres. These results are in good agreement with some recent experimental observations. This shoulder is well-marked when the diameter ratio reaches 10% and when the concentration in small spheres lies in the range 10–15%. In such a structure (e.g. amorphous NiP and PdSi alloys) it is observed that small spheres are always surrounded by nine large spheres such as P or Si atoms in crystalline Ni3P or Pd3Si. Large spheres, i.e. metallic atoms, form distorted icosahedra, the distortion of which varies from one to the other. The short-range order has a five-fold symmetry which is not compatible with any long-range order.

Theoretical calculation of dense random packings of equal and non-equal sized hard spheres applications to amorphous metallic alloys☆

X-ray diffraction studies are made for GexSe1−x glasses with 0 < x < 0.4. Interference functions exhibit a peculiar peak at about 1 A−1. The areas of the first two peaks of the Radial Distributions Functions increase with x.

According to the experimental results a random network model is made of Ge atoms with coordination number four and Se atoms with coordination number two. A computer program sets atoms one by one by allowing free rotation about all bonds.

First results of this model are presented. Calculated interference functions are compared with the experimental curve for x = 0.2. We draw attention to the first peak at about 1 A−2. Results are in agreement with optical absorption edge measurements and Raman scattering experiments by P. Tronc and al.[1], i.e. there is no GeGe bond and furthermore, GeSeGe sequences remain scarce, as long as the germanium concentration of the mixture makes its possible.

X-ray diffraction and local order modelling of GexSe1−x amorphous alloys

X-ray diffractometry situ of evaporated thin films: application to amorphous tellurium

In situ X-ray diffractometry of evaporated thin films: Application to amorphous tellurium

Preliminary results of neutron diffraction experiments on Ni-P and CO-P amorphous alloys are discussed. Scattering data for Ni-P have been recorded up to Kmax = 30. It is shown that a new extension of the interference function should not provide significant contribution to the Ni-P R. D. F. First details on the P atom distribution are given by using the reversion of the scattering amplitude ratios for CO and P atoms in X-Rays and neutrons diffraction patterns. Introduction. Le premier calcul de la fonction de distribution radiale de l'alliage Ni-P a CtC effectut par Moiseev en 1962 [ l] a partir d'un diagramme de diffraction X. Depuis, de nombreuses Ctudes similaires ont apportC des renseignements de plus en plus prCcis sur l'ordre local subsistant dans ce matCriau. On peut attribuer les progrbs rCalisCs B 2 causes : I'amClioration de la qualitC des mesures d'intensitt du rayonnement diffract6 (augmentation du rapport signal sur bruit, maitrise des corrections des donnCes expCrimentales) et l'enregistrement de la courbe d'interfkrence B des distances de plus en plus CloignCes du centre de l'espace rCciproque (grandes valeurs de K = 4 n sin 811). Jusqu'en 1974, seules des expCriences de diffraction X avaient CtC faites sur Ni-P et CO-P. La diffraction par les neutrons a permis de complCter les renseignements obtenus par les R. X. gr2ce aux caractCristiques propres B ce rayonnement. Nous faisons ici Ctat des premiers rCsultats d'expb riences de diffraction Clastique des neutrons sur les alliages amorphes Ni-P et CO-P. On sYintCressera uniquement B la structure atomique, c'est-&-dire que seule la composante nuclCaire de l'intensit6 diffractke sera prise en compte. La composante magne'tique due B I'interaction entre neutrons et Clectrons a CtC soustraite dans le cas de l'alliage ferromagnktique CO-P. Intkr2t de la diffraction des neutrons duns l'e'tude de la structure des alliages me'talliques amorphes. On sait que les facteurs de diffusion des Cltments vis-B-vis des (*) Lab. de Physique des Solides, associC au C. N. R. S., UniversitC Paris-Sud, 91405, Centre #Orsay, France. (**) I. L. L., Cedex 156, 38042, Grenoble, France. R. X. et des neutrons prisentent 2 diffkrences essentielles. Le rayonnement X diffusC par les atomes dtcroit avec l'angle de diffusion alors que cette dCcroissance n'est pas observCe pour les neutrons. La valeur du facteur de diffusion varie de f a ~ o n continue avec le nombre d'Clectrons des ClCments pour les R. X., alors que la section efficace de diffusion des neutrons varie d'une f a ~ o n erratique avec 2. Nous allons montrer les avantages que l'on peut tirer de ces 2 differences dans le cas qui nous intC-

J. Dixmier

Papers

Theoretical calculation of dense random packings of equal and non-equal sized hard spheres applications to amorphous metallic alloys☆

X-ray diffraction and local order modelling of GexSe1−x amorphous alloys

X-ray diffractometry situ of evaporated thin films: application to amorphous tellurium

In situ X-ray diffractometry of evaporated thin films: Application to amorphous tellurium

Étude de la structure des alliages métalliques amorphes par diffraction des neutrons