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Electron-density distribution and disordered crystal structure of 12H-SiAlON, SiAl5O2N5

Published online by Cambridge University Press:  10 June 2014

Hiroki Banno
Affiliation:
Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
Takaaki Hanai
Affiliation:
Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
Toru Asaka
Affiliation:
Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
Koji Kimoto
Affiliation:
Advanced Key Technologies Division, National Institute for Materials Science, Tsukuba 305-0044, Japan
Hiromi Nakano
Affiliation:
Cooperative Research Facility Center, Toyohashi University of Technology, Toyohashi 441-8580, Japan
Koichiro Fukuda*
Affiliation:
Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
*
a) Author to whom correspondence should be addressed. Electronic mail: [email protected]

Abstract

The crystal structure of SiAl5O2N5 was characterized by laboratory X-ray powder diffraction (CuKα1). The title compound is hexagonal with space group P63/mmc (Z = 2). The unit-cell dimensions are a = 0.303153(3) nm, c = 3.28153(3) nm, and V = 0.261178(5)  nm3. The initial structural model was successfully derived by the direct methods and further refined by the Rietveld method. The final structural model showed the positional disordering of two of the four (Si,Al) sites. The maximum-entropy method-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from the MPF were R wp = 5.00%, S (=R wp/R e) = 1.25, R p = 3.76%, R B = 1.26%, and R F  = 0.90%. The disordered crystal structure was successfully described by overlapping four types of domains with ordered atom arrangements. The distribution of atomic positions in each of the domains can be achieved in the space group P63 mc. Two of the four types of domains are related by a pseudo-symmetry inversion, and the two remaining domains also have each other the inversion pseudo-symmetry.

Type
Technical Articles
Copyright
Copyright © International Centre for Diffraction Data 2014 

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