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Nuclear‐weighted X‐ray maximum entropy method – NXMEM

Nuclear‐weighted X‐ray maximum entropy method – NXMEM Subtle structural features such as disorder and anharmonic motion may be accurately characterized from nuclear density distributions (NDDs). As a viable alternative to neutron diffraction, this paper introduces a new approach named the nuclear‐weighted X‐ray maximum entropy method (NXMEM) for reconstructing pseudo NDDs. It calculates an electron‐weighted nuclear density distribution (eNDD), exploiting that X‐ray diffraction delivers data of superior quality, requires smaller sample volumes and has higher availability. NXMEM is tested on two widely different systems: PbTe and Ba8Ga16Sn30. The first compound, PbTe, possesses a deceptively simple crystal structure on the macroscopic level that is unable to account for its excellent thermoelectric properties. The key mechanism involves local distortions, and the capability of NXMEM to probe this intriguing feature is established with simulated powder diffraction data. In the second compound, Ba8Ga16Sn30, disorder among the Ba guest atoms is analysed with both experimental and simulated single‐crystal diffraction data. In all cases, NXMEM outperforms the maximum entropy method by substantially enhancing the nuclear resolution. The induced improvements correlate with the amount of available data, rendering NXMEM especially powerful for powder and low‐resolution single‐crystal diffraction. The NXMEM procedure can be implemented in existing software and facilitates widespread characterization of disorder in functional materials. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Acta Crystallographica Section A Foundations of Crystallography Wiley

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References (44)

Publisher
Wiley
Copyright
Copyright © 2015 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0108-7673
eISSN
1600-5724
DOI
10.1107/S2053273314024103
pmid
25537384
Publisher site
See Article on Publisher Site

Abstract

Subtle structural features such as disorder and anharmonic motion may be accurately characterized from nuclear density distributions (NDDs). As a viable alternative to neutron diffraction, this paper introduces a new approach named the nuclear‐weighted X‐ray maximum entropy method (NXMEM) for reconstructing pseudo NDDs. It calculates an electron‐weighted nuclear density distribution (eNDD), exploiting that X‐ray diffraction delivers data of superior quality, requires smaller sample volumes and has higher availability. NXMEM is tested on two widely different systems: PbTe and Ba8Ga16Sn30. The first compound, PbTe, possesses a deceptively simple crystal structure on the macroscopic level that is unable to account for its excellent thermoelectric properties. The key mechanism involves local distortions, and the capability of NXMEM to probe this intriguing feature is established with simulated powder diffraction data. In the second compound, Ba8Ga16Sn30, disorder among the Ba guest atoms is analysed with both experimental and simulated single‐crystal diffraction data. In all cases, NXMEM outperforms the maximum entropy method by substantially enhancing the nuclear resolution. The induced improvements correlate with the amount of available data, rendering NXMEM especially powerful for powder and low‐resolution single‐crystal diffraction. The NXMEM procedure can be implemented in existing software and facilitates widespread characterization of disorder in functional materials.

Journal

Acta Crystallographica Section A Foundations of CrystallographyWiley

Published: Jan 1, 2015

Keywords: ; ; ; ; ; ; ;

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