eLearning

vides the short-range order of the network, but the long-
range order is absent as in any other typical inorganic glass.
Although the importance of
-Al2O3 and its many appli-
cations have been well recognized by the research commu-
nity, there is little experimental data on pure samples of

-Al2O3. Work has been reported on structure determination
using x-ray diffraction
XRDRef. 6 and transmission elec-
tron microscopy
TEM.
18,37 Infrared
IR spectroscopy,
14,20
x-ray emission spectroscopy,
13
x-ray photoelectron
spectroscopy,
19 and Al NMR spectroscopy20,21,23 have been
used to study
-Al2O3 films or related materials. Electron
energy-loss spectroscopy
EELS has played a very impor-
tant role in the characterization of
-Al2O3.
15–17
However,
most of these measurements are either inclusive of surface
effects, on porous samples, or with intentionally doped
transition-metal elements as part of the sample preparing
process. Without a clear understanding of the properties of
pure bulk
-Al2O3, interpretation of these experimental data
will be difficult or even misleading. In this respect, careful
ab initio calculations on a well defined structural model of

-Al2O3 can provide much of the missing information that
can be used to properly interpret the data for more complex
and nonstoichiometric samples.
In this paper, we report a comprehensive study of many of
the physical properties of
-Al2O3 based on the structure
published in Ref. 26. The crystal structure reported by these
authors is far superior to other models proposed earlier and
could represent the smallest unit cell of the true bulk

-Al2O3 that contains all the essential ingredients of the
structure of
-Al2O3. We used their data as the initial struc-
ture and further relaxed the atomic positions with high accu-
racy using the VIENNA Ab initio SIMULATION PACKAGE

VASP.
42,43 A high energy cutoff of 600 eV and a 5    5
2 Monkhorst k-point sampling were used. The criteria for
electronic state updating and ionic step updating were set to
10−7
eV and 10−4
eV/Å, respectively. The structure we ob-tained does not change