Abstract
Anomalous structural characteristics of the so-called first sharp diffraction peak (FSDP) that arises in the total static structure functions of network-forming glasses and liquids at around 1-2 A-1 have been reviewed and discussed in details. Unlike other peaks in the static structure functions, the FSDP has anomalous dependencies on temperature, pressure and composition. Despite the fact that the FSDP is considered as a signature of intermediate range order (IRO) in network-forming glasses and liquids, its structural origin remains unclear and till now, it forms a subject of debate. A brief account for some anomalous characteristics of the FSDP followed by the different controversial interpretations about its structural origin has been reviewed and discussed. Some of the interpretations that seem to be inconsistent with recent experimental results have been ruled out. The most likely structural origins for the occurrence of the FSDP have been highlighted and discussed in details.
Highlights
One of the most characteristic features in the diffraction patterns of network-forming glasses and liquids is the so-called first sharp diffraction peak (FSDP) or sometimes called the pre-peak [1] [2]
The FSDP is observed in many different types of non-metallic, non-crystalline materials such as oxy-chalcogenide glasses [4] [5], AX2 or B2X3 (A = Si, Ge; B = P, As; X = O, S, Se), P4, VCl4 [6] and in zinc halides [7]
The FSDP is an unmistakable signature of intermediate-range order (IRO) in a glass, and it can potentially offer an insight into the glassy molecular connectivity: whether, e.g., the glassy intermediate-range structure is characterized by the layering of planes of atoms, the bundling of chains of atoms, or a random packing of basic molecular structural units
Summary
One of the most characteristic features in the diffraction patterns of network-forming glasses and liquids is the so-called first sharp diffraction peak (FSDP) or sometimes called the pre-peak [1] [2]. That is delocalized over the observed Q-range results in relatively sharp features in the real space, giving rise to the first and second neighbor shells of atoms in the structure, more difficultly, when S (Q) has features that are localized in a limited Q-range (such as the FSDP) In this case, Fourier transformation results in rather delocalized features in the real space, conveying little information about the involved interatomic correlations. Fourier transformation results in rather delocalized features in the real space, conveying little information about the involved interatomic correlations This difficulty makes it hard to elucidate the precise structural origin of the FSDP, despite the fact that the FSDP gives a clue to the extent of intermediate range order in the amorphous material. We rule out those interpretations that were proved to be inconsistent with the recent experimental findings, and we highlight the most likely interpretations that are-up to date-agreed with the experimental findings
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