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Electron density distribution and crystal structure of 21R-AlON, Al7O3N5

Published online by Cambridge University Press:  31 May 2013

Toru Asaka
Affiliation:
Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
Tatsunari Kudo
Affiliation:
Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
Hiroki Banno
Affiliation:
Department of Materials Science and Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
Shiro Funahashi
Affiliation:
Nano Ceramics Center, National Institute for Materials Science (NIMS), Ibaraki 305-0044, Japan
Naoto Hirosaki
Affiliation:
Nano Ceramics Center, National Institute for Materials Science (NIMS), Ibaraki 305-0044, 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: fukuda.koichiro@nitech.ac.jp

Abstract

The crystal structure of Al7O3N5 was characterized by laboratory X-ray powder diffraction (Cu1). The title compound is trigonal with a space group R3m (centrosymmetric). The hexagonal unit-cell dimensions (Z = 3) are a = 0.305 06(1) nm, c = 5.7216(1) nm, and V = 0.461 11(2) nm3. The initial structural model was derived by the charge-flipping method and refined by the Rietveld method. The final structural model showed the positional disordering of two of the four Al sites. The maximum-entropy method-based pattern fitting 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 disordered crystal structure was successfully described by overlapping five types of domains with ordered atom arrangements. The distribution of atomic positions in one of the five types of domains can be achieved in the space group R3m. The atom arrangements in the four other domains are non-centrosymmetric with the space group R3m. Two of the four types of domains are related by a pseudo-symmetrical inversion, and the two remaining domains also have each other in the inversion pseudo-symmetry.

Type
Technical Articles
Copyright
Copyright © International Centre for Diffraction Data 2013 

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