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The Role of Hydrogen In The Structure of γ-Alumina

Published online by Cambridge University Press:  15 February 2011

Karl Sohlberg ,
Stephen J. Pennycook  and
Sokrates T. Pantelides
Karl Sohlberg
Affiliation:
Solid State Division, P.O. Box 2008, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6031
Stephen J. Pennycook
Affiliation:
Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235
Sokrates T. Pantelides
Affiliation:
Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235
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Abstract

The structure of a-alumina (α-A12O3) is well known to be hexagonal close packed. In contrast, the structures of the so-called transition aluminas (-γ-alumina, η-alumina,…) are the subject of controversy. We report theoretical calculations which show that -γ-alumina is actually a sequence of compounds with the general formula H3mAl2−mO3. (0 ≤ m ≤ ⅓). m = ⅛ is a unique form, HAl5O8, with a perfect spinel structure. For m > 8, there are interstitial H atoms whereas for m < ⅛. there are vacancies. This picture is supported m > ⅛ by calculations of material density and proton vibrational frequencies. The results are in excellent agreement with measured values. The present new systematic approach accounts for a wide range of seemingly contradictory data and leads to the conclusion that γ-alumina behaves as a “reactive sponge” by storing and releasing water in a novel reactive way.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 549: Symposium FF – Advanced Catalytic Materials - 1998 , 1998 , 165
Copyright
Copyright © Materials Research Society 1999

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