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Ordered vacancy distribution in 2/1 mullite: a superspace model.
Paul B Klar1, Noelia de la Pinta1, Gabriel A Lopez2
1Dpto de Física de la Materia Condensada, Facultad de Ciencia y Tecnología, Universidad del País Vasco UPV/EHU, Apdo 644, Bilbao 48080, Spain.
Summary
This study reveals mullite
Area of Science:
- Materials Science
- Crystallography
- Solid-State Chemistry
Background:
- Mullite (3Al2O3·2SiO2 to 2Al2O3·SiO2) exhibits complex structural variations.
- Previous studies often treated mullite as either fully ordered or disordered, leading to conflicting conclusions.
Purpose of the Study:
- To investigate the ordered structure of a mullite single crystal using X-ray diffraction.
- To develop a superspace model that accounts for both ordered and disordered phases within mullite.
Main Methods:
- Single-crystal X-ray diffraction analysis.
- Refinement of a superspace model using different scale factors for main and satellite reflections.
- Analysis of displacive modulation related to vacancy distribution.
Main Results:
- A superspace model successfully describes an ordered mullite structure embedded within a disordered matrix.
- The ordered fraction features alternating vacancy blocks (VBs) and vacancy-free blocks (VFBs).
- The incommensurate nature arises from block size modulation dependent on composition.
Conclusions:
- The superspace model reconciles previous, often contradictory, findings on mullite structure.
- It highlights the coexistence of ordered and disordered states in mullite.
- An idealized commensurate approximation for 2/1 mullite is presented.
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