Electronic structure and bonding of {beta}-SiAlON

Journal Article · Sat Apr 01 04:00:00 EST 2000 · Journal of the American Ceramic Society

OSTI ID:20050512

Ching, W Y; Huang, M Z; Mo, S D

The {alpha}- and {beta}-SiAlONs are ceramic solid solutions with charge-neutral substitutions in {alpha}- and {beta}-Si{sub 3}N{sub 4}. They have high potential for applications as structural materials. The authors have calculated the electronic structure and bonding of {beta}-Si{sub 6{minus}z}Al{sub z}O{sub z}N{sub 8{minus}z} decreases as z increases, in general agreement with experimental trends. Simultaneous substitution of the (Si,N) pair by (Al,O) results in impurity-like states in the upper portion of the bandgap of {beta}-Si{sub 3}N{sub 4}. As z increases, more and more states are introduced into the gap, forming a new conduction band (CB) edge for SiAlON. At z = 4, the calculated bandgap is {approximately}1.3 eV. Density of states (DOS) calculations show the top of the valence band remains steep for all z, and the bottom of the CB is formed predominantly by Si-O antibonding states. Orbitally resolved partial DOS calculations in the CG region are used to predict the trends of the electron-energy-loss near-edge spectra (ELNES) of Si-L{sub 2,3}, Al-L{sub 2,3}, Si-K, Al-K, O-K, and N-K edges in {beta}-SiAlON. The impurity-like states near the CB edge result in pre-edge structures in all ELNES spectra. Effective charge and bond order calculations show that the overall bond strength in {beta}-SiAlON decreases only slightly as z increases. Although the stronger Si-N bonds are replaced by weaker Al-O bonds, the remaining Si-N and Al-O bonds actually strengthen as z increases because of the effective charge redistribution after substitution. This is a very interesting finding that may partly explain the superior mechanical properties of the SiAlON system that render them suitable for structural applications.

• Research Organization: Univ. of Missouri, Kansas City, MO (US)
• Sponsoring Organization: US Department of Energy
• DOE Contract Number: FG02-84ER45170
• OSTI ID: 20050512
• Journal Information: Journal of the American Ceramic Society, Journal Name: Journal of the American Ceramic Society Journal Issue: 4 Vol. 83; ISSN 0002-7820; ISSN JACTAW
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM OXIDES
CHEMICAL BONDS
ELECTRONIC STRUCTURE
ENERGY LEVELS
QUANTUM MECHANICS
SILICON NITRIDES
SOLID SOLUTIONS