Noncrystalline Solids Prepared by Compacting Nanometer - Sized Particles
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NONCRYSTALLINE SOLIDS PREPARED BY COMPACTING NANOMETER - SIZED PARTICLES U. GONSER AND A. KRAMER*, R. BIRRINGER*, J. JING**, J. WEISSMOLLER-, H.GLEITER* 3) Werkstoffwissenschaft, UniversitAt des Saarlandes, D-66 SaarbrOcken, FRG =) Australian Defence Force Academy, Dept. of Physics, Canberra, Australia ABSTRACT X-ray presented. A new method of preparing amorphous solids is diffraction, thermal stability and Mgssbauer spectroscopy give evidence for and an atomic structure with reduced short-range order in Si75Auz5 Pd72FeloSil8 alloys prepared by this method. INTRODUCTION Noncrystalline metals or semiconductors can be prepared in numerous ways, such as melt quenching, deposition from vapour or solution, mechanical alloying, to name only a few. In the present work, yet another way of preparing noncrystalline solids will be presented; it consists in producing nm-sized noncrystalline particles by inert-gas condensation and compacting them in situ under HV conditions to form a bulk amorphous solid. There are two, main reasons why this is of interest: First, by introducing a novel mode of preparation, we may generally hope to produce amorphous solids with different characteristics like e.g. glassforming range, sample mass, or purity. The second reason for investigating these "nanoamorphous" solids is of more fundamental interest and actually motivated the present study (fig.l): According to a simple hypothesis, each particle has the glass structure -still according characteristic of e.g. the meltspun volume glass. However to the hypothesis- since the particles solidify when isolated, and are they are where at a temperature in random orientations compacted configurationally frozen, the atomic spacing across the interface between two formerly isolated, now adjacent particles will be randomly distributed instead of reflecting the short-range order (SRO) of the volume glass. If the particles are extensively deformed on compaction, then shear bands are expected to give rise to a similar effect in the interior of the grains. The structure of glasses can generally be characterized as the structure of the undercooled melt frozen at the glass transition temperature; a recent study [1] indicates that amorphous solids prepared by methods as different as mechanical alloying and proton irradiation invariably liquid quenching, assume this structure. There are two classes of glass structures: dense random packing of hard sphere (DRPHS) - like structures characteristic of structures metallic systems and continuous random network system (CRNS) characteristic of amorphous semiconductors and oxide glasses. It is common to is missing, a considerable amount of both that while long-range order (LRO) SRO is present. If the hypothesis concerning the structure of "nanoamorphous"
SFig.l
Schematic representation of the hypothetical structure of a "nanoamorphous" material showing nmsized glassy spheres embedded in disordered interface component
Mat. Res. Soc. Symp. Proc. Vol. 195. ©1990 Materials Research Society
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