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Chen, Chuin-Shan, Chou, Chia-Ching, Chang, Shu-Wei, Fischer, Reinhard X. and Schneider, Hartmut (2010). First-principles study on variation of lattice parameters of mullite Al4+2xSi2-2xO10-x (x=0.125, 0.250, 0.375). Am. Miner., 95 (11-12). S. 1617 - 1624. CHANTILLY: MINERALOGICAL SOC AMER. ISSN 0003-004X

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Abstract

Mullite (Al4+2xSi2-2xO10-x) is known to exhibit a very distinct compositional variation in which the lattice constant in the a direction expands linearly, while that in the b direction slightly contracts with an increase of the x-value. In this study, first-principles density functional theory (DFT) simulations were applied to examine the cause. The atomic structure and charge density were examined. We found that the local charge redistribution due to a newly formed vacancy leads to the onset and recurrence of localized atomic relaxation. The charge redistribution and atomic relaxation causes the clockwise and counterclockwise rotations of the neighboring octahedral units. These rotations contribute to expansion in the a-axis and contraction in the b-axis. The mechanism is supported by the previous experimental measurements of the Al-O2 bond lengths projecting in the (001) plane. We conclude that the rotations of the octahedral units are the fundamental mechanism responsible for compositionally induced variations of mullite. Results derived from simulations also provide evidence for a preferred occurrence of oxygen vacancies parallel to the crystallographic b axis. It thus supports earlier findings of a partial ordering in mullite.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Chen, Chuin-Shan UNSPECIFIED UNSPECIFIED UNSPECIFIED Chou, Chia-Ching UNSPECIFIED UNSPECIFIED UNSPECIFIED Chang, Shu-Wei UNSPECIFIED UNSPECIFIED UNSPECIFIED Fischer, Reinhard X. UNSPECIFIED UNSPECIFIED UNSPECIFIED Schneider, Hartmut UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-492778
DOI:	10.2138/am.2010.3454
Journal or Publication Title:	Am. Miner.
Volume:	95
Number:	11-12
Page Range:	S. 1617 - 1624
Date:	2010
Publisher:	MINERALOGICAL SOC AMER
Place of Publication:	CHANTILLY
ISSN:	0003-004X
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language STRUCTURE REFINEMENT; CRYSTAL-STRUCTURE; ALUMINA Multiple languages Geochemistry & Geophysics; Mineralogy Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/49277