Medium-range atomic correlation in simple liquids. I. Distinction from short-range order

Polyvalent metal melts (gallium, tin, bismuth, etc.) have microscopic structural features, which are detected by neutron and X-ray diffraction and which are absent in simple liquids.

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Structural Aspects of Metallic Glasses

MRS Bulletin ◽

10.1557/mrs2007.124 ◽

2007 ◽

Vol 32 (8) ◽

pp. 629-634 ◽

Cited By ~ 133

Author(s):

Daniel B. Miracle ◽

Takeshi Egami ◽

Katharine M. Flores ◽

Kenneth F. Kelton

Keyword(s):

Free Volume ◽

Metallic Glasses ◽

Short Range ◽

Short Range Order ◽

Structural Model ◽

Experimental Studies ◽

Range Order ◽

Medium Range Order ◽

Packing Model ◽

Medium Range

AbstractA recent structural model reconciles apparently conflicting features of randomness, short-range order, and medium-range order that coexist in metallic glasses. In this efficient cluster packing model, short-range order can be described by efficiently packed solute-centered clusters, producing more than a dozen established atomic clusters, including icosahedra. The observed preference for icosahedral short-range order in metallic glasses is consistent with the theme of efficient atomic packing and is further favored by solvent-centered clusters. Driven by solute—solute avoidance, medium-range order results from the organization in space of overlapping, percolating (via connected pathways), quasi-equivalent clusters. Cubic-like and icosahedral-like organization of these clusters are consistent with measured medium-range order. New techniques such as fluctuation electron microscopy now provide more detailed experimental studies of medium-range order for comparison with model predictions. Microscopic free volume in the efficient cluster packing model is able to represent experimental and computational results, showing free volume complexes ranging from subatomic to atomic-level sizes. Free volume connects static structural models to dynamic processes such as diffusion and deformation. New approaches dealing with “free” and “anti-free” microscopic volume and coordinated atomic motion show promise for modeling the complex dynamics of structural relaxations such as the glass transition. Future work unifying static and dynamic structural views is suggested.

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Fluctuation Microscopy: A New Class of Microscopy Techniques for Probing Medium Range Order in Amorphous Materials

Microscopy and Microanalysis ◽

10.1017/s1431927600023631 ◽

1998 ◽

Vol 4 (S2) ◽

pp. 702-703

Author(s):

J. M. Gibson ◽

M. M. J. Treacy ◽

P. M. Voyles

Keyword(s):

Long Range ◽

Short Range ◽

Amorphous Materials ◽

Short Range Order ◽

Nearest Neighbor ◽

Range Order ◽

Regular Tetrahedron ◽

Long Range Order ◽

Medium Range Order ◽

Medium Range

Amorphous materials are devoid of periodic long range order, but at the nearest-neighbor level they possess a high degree of short-range order. In amorphous tetrahedral semiconductors, such as Si and Ge, this short-range order arises because each atom attempts to satisfy four bonds arranged as a regular tetrahedron. It is the rotations about each bond, from the second-nearest-neighbor outwards, that result in the loss of long-range order. It is apparent from modeling of amorphous materials, that there is considerable flexibility as to how rapidly the medium-range-order diminishes. The continuous random network (CRN) is a hypothetical tetrahedral extended structure wherein the atoms possess full four-connected coordination, but have minimal medium-range order. However, real amorphous materials infrequently exhibit true CRN-like topologies. Traditionally, diffraction has been used to study short- and medium-range order in amorphous materials. Assuming kinematical scattering, and that every atom has a similar environment, a radial distribution function (RDF) can be extracted which is sensitive only to the averaged atom pair-correlations out to ∼1 nm.

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