Preface - kmutt

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maximum of which was achieved at 20.00 GPa.
The presence of F-type defects in AlN films was
investigated by X-band (~9.44 GHz) ESR
spectrometer at 295 K. The ESR experiments
were carried out by applying magnetic field
perpendicular to AlN film, which showed the
ESR six-peak multiplet signal at ~290 mT
arising from superhyperfine interactions
between nuclear spin I = 5/2 of 27 Al and electron
spins trapped in nitrogen vacancies. The ESR
signals are simulated and the ESR parameters
are calculated. The vacancies are clearly
randomly distributed as the ESR signals are
independent of rotation angle (φ) about the
normal of the film. All these results were
analyzed and presented as a function of the
deposition parameters and composition, and
crystalline phases existed in the films.
IJ-061 EFFECTS OF HEAT TREATMENT ON
BLUE SAPPHIRES AS MONITORED BY ESR
SPECTROSCOPY
Nitinai Udomkan, Pichet Limsuwan,
Pongtip Winotai, Siwaporn Meejoo
International Journal of Modern Physics B,
Vol. 19, No. 20, 2005, pp. 3273-3284
We report effects of heat treatments on
physical properties and finding optimal heating
condition to add value to Thai blue sapphires.
The color of sapphire arises from the presence of
trace 3d-transition ions in its crystal lattice. For
blue sapphire, the color is due to a charge
transfer mechanism between Fe 2+ and Ti 4+ ions.
However, iron may adopt both Fe 3+ and Fe 2+ due
to oxygen vacancies. Fe 3+ and Fe 2+ yield
sapphire yellow and green colors, respectively.
Therefore, we have to convert as many as
possible of Fe 3+ to Fe 2+ by heating the blue
sapphire in N2 atmosphere for 12 h.
Experimental results reveal that the ratio of
lattice parameter c/a increases with the heating
temperature and reaches maximum at 1700°C,
which can be caused by displacement of Fe 3+
ions or more Fe 3+ ions being converted to Fe 2+ .
ESR signals show that the number of Fe 3+ ions
decreases roughly linearly with the heating
temperature. The intense sky blue color was
achieved after the 1500°C heat treatment, having
the Fe 3+ / Fe 3+ RT ratio ~0.78. The optimal heat
treatment should therefore be at 1500°C in
flowing N 2 atmosphere for Thai blue sapphires
which yield intense sky blue color and good
crystal clarity. The blue sapphires exhibited
KMUTT Annual Research Abstracts 2005
good clarity but light sky blue due to the
increase in lightness after the treatment at
1700°C. A monoclinic distortion of the
corundum structure has been found to start at the
1600°C treatment by ESR spectrometer. This is
also clearly evident from low angle shifts of
XRD peaks after heating at 1700°C. We can
therefore conclude that the color change of Thai
blue sapphires arises from the conversion of Fe 3+
to Fe 2+ and thus the change in crystal field. The
monoclinic distortion of the crystal structure
may also play an important role in coloring the
sapphires after the heat treatment at 1600-
1700°C.
IJ-062 ELECTRON SPIN RESONANCE
STUDIES OF MN 2+ IN FRESHWATER SNAIL
SHELLS : POMACEA CANALICULATA
LAMARCK AND FOSSILIZED SNAIL SHELL
Nitinai Udomkan, Siwaporn Meejoo,
Pichet Limsuwan, Pongtip Winotai,
Yaowalak Chaimanee
Chinese Physics Letters, Vol. 22, No. 7, July
2005, pp. 1780-1783
We study paramagnetic Mn 2+ ions
present in the nowadays shells of univalve
freshwater snails of Pomacea canaliculata
lamarck (PCL) and the fossilized freshwater
snail (FFS), Viviparus. All these shells are
abundant in Thailand. The PCL shells were
ground into fine powder. A set of seven samples
were then separately annealed for 2 h in air
atmosphere at different annealing temperatures
while the FFS powder was characterized asreceived.
The PCL shells mainly consist of
aragonite and a fraction of calcite. The heat
treatments of the PCL powder samples at
temperature higher than 450 o C resulted in an
irreversible phase transformation from aragonite
to calcite. However, it is found that the FFS
shell is mainly made of calcite, with a minor
fraction of aragonite. The crystal structure of the
high-temperature-annealed PCL samples are
quite similar to that of FFS, which indicates that
the metamorphosis (aragonite → calcite) in the
FFS shell had occurred but was not yet
completed, although it had remained under the
pressure and temperature of the Earth's crusts
over millions of years. Our detailed ESR
spectral analyses of PCL and FFS show that
Mn 2+ ions enter the Ca 2+ sites during a
biomineralization process. Simulated ESR
parameters of PCL-500 of Mn 2+ at a uniaxial site
International Journal