NDLI: The local crystal structure and electronic band gap of β-sialons

Content Provider	Springer Nature Link
Author	Boyko, Teak D. Gross, Toni Schwarz, Marcus Fuess, Hartmut Moewes, Alexander
Copyright Year	2014
Abstract	The electronic properties of β-Si$_{3}$N$_{4}$ and β-sialons (β-Si$_{6−z }$Al$_{ z }$O$_{ z }$N$_{8−z }$) solid solutions were characterized using a combination of X-ray emission spectroscopy (XES), X-ray absorption spectroscopy (XAS), and density functional theory (DFT). The electronic structure measurements reveal a single bonding environment for both the Si and Al atoms, which corresponds to a specific nonrandom structural arrangement of the Al–O solute atoms into nanotube-like clusters or channels, running parallel to the c-axis of the β-Si$_{3}$N$_{4}$ host structure. Compared to an arrangement of alternating Si–N and Al–O slabs (“Dupree model”), lower total energy and overall better agreement to the experimentally observed electronic features confirm this “Al–O nanotube” model for β-sialon originally proposed by Okatov to be closer to the true chemical topology of the β-Si$_{6−z }$Al$_{ z }$O$_{ z }$N$_{8−z }$ solid solution series. The β-sialons are shown to be wide band gap semiconductors with the band gap reduction arising from the O p-states moving toward the Fermi level. This band gap reduction provides the ability for direct band gap transitions, which is very important for practical applications. In contrast to the previous observations, both measurement and theory indicate a linear dependence of band gap energy with composition z. The experimental (theoretical) electronic band gaps of β-Si$_{6−z }$Al$_{ z }$O$_{ z }$N$_{8−z }$ with z = 0.0, 2.0, and 4.0 as determined by XAS/XES (DFT) are 7.2 ± 0.2 (5.88), 6.2 ± 0.2 (3.45), and 5.0 ± 0.2 (2.39) eV, respectively. The considerable discrepancy between experimental and theoretical values is attributable to the shortcomings of DFT, which often underestimates the electronic band gap energy.
Starting Page	3242
Ending Page	3252
Page Count	11
File Format	PDF
ISSN	00222461
Journal	Journal of Materials Science
Volume Number	49
Issue Number	8
e-ISSN	15734803
Language	English
Publisher	Springer US
Publisher Date	2014-01-23
Publisher Place	Boston
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Materials Science Characterization and Evaluation of Materials Polymer Sciences Continuum Mechanics and Mechanics of Materials Crystallography Mechanics
Content Type	Text
Resource Type	Article
Subject	Ceramics and Composites Mechanics of Materials Mechanical Engineering Polymers and Plastics

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