Aluminum oxide (Al2O3)
From Tropf & Thomas (1998; HOC III, p.653):
The hexagonal (rhombohedral) form of aluminum oxide is variously
called alpha-Al2O3,
alumina (usually applied to the non-fully-dense polycrystalline
ceramic), corundum (mineral name), ruby (red [chromium containing]
corundum), or sapphire (blue corundum; also frequently used to denote
the pure, synthetic crystal). It is a hard, stable material melting at
2319 K. The space group is R3c (or D63d)
with six formula units per
unit cell. Room-temperature cell dimensions are 4.759 A (a-axis) and
12.989 A (c-axis), giving an x-ray density of 3.987 g/cm3.
Atomic coordinates are as follows: aluminum atoms occupy the 12(c) sites at
0, 0, 0.347 (with point symmetry 3 or C3) and
the oxygen atoms occupy 18(e) sites at 0.306, 0, 1/4
(with point symmetry 2 or C2).
Aluminum oxide is a negative, uniaxial crystal transparent from
0.145 to 5.0 micron (ordinary ray) and 0.147 to 5.2 micron (extraordinary ray).
Optical anisotropy is small from the extreme ultraviolet through the
infrared, becoming larger in the microwave region. Optical-quality
crystalline aluminum oxide (or "sapphire") is made by several techniques
including Czochralski growth, flame fusion (Verneuil method),
the heat-exchanger method (HEM), and the edge-defined, film-fed growth (EFG)
technique. The high mechenical and dielectric strength of aluminum oxide
make it a desirable laser host material. Chromium- and
titanium-doped aluminum oxide are common solid-state laser-gain media.
To the top
Back to previous page
Created by
V.I.
Last modified:
29/12/99, V.I.
