Isostructural phase transition by point defect reorganization in the binary type-I clathrate Ba7.5Si45

Competition between microscopic point defect (vacancy and interstitial) configurations is inherent to crystalline phases of increased structural complexity. Phase transitions that preserve symmetry between them belong to a specific class of isostructural transitions. Type-I silicon clathrates are re...

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Bibliographic Details
Published in:Acta materialia 2021-05, Vol.210, p.116824, Article 116824
Main Authors: Debord, Régis, Euchner, Holger, Pischedda, Vittoria, Hanfland, Michael, San-Miguel, Alfonso, Mélinon, Patrice, Pailhès, Stéphane, Machon, Denis
Format: Article
Language:English
Subjects:
Condensed Matter
Isostructural phase transitions
Materials Science
Physics
Structural complexity
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Summary:Competition between microscopic point defect (vacancy and interstitial) configurations is inherent to crystalline phases of increased structural complexity. Phase transitions that preserve symmetry between them belong to a specific class of isostructural transitions. Type-I silicon clathrates are representatives of such structurally complex crystalline phases showing an intriguing structural transition at high pressure associated with an abrupt reduction of volume with no indication for any breakage of symmetry. Using isothermal high-pressure X-ray diffraction performed on a single crystal of the simplest representative type-I silicon clathrates, binary Ba8Si46, we confirm the isostructural character of the transition and identify the associated mechanism. A detailed analysis of the atomic structural parameters across the transition in combination with ab initio studies allow us to pinpoint a microscopic mechanism driven by a rearrangement of point defects initially present in the structure. An analysis based on the Landau theory gives a coherent description of the experimental observations. A discussion on the analogy between this transformation and liquid-liquid transitions is proposed. [Display omitted]
ISSN:1359-6454
1873-2453
DOI:10.1016/j.actamat.2021.116824