STUDIA UNIVERSITATIS BABEŞ-BOLYAI, PHYSICA, SPECIAL ISSUE, 2003
STUDY OF SOME CERAMIC SYSTEMS BASED ON SILICIUM OXIDE
I. Coroiu1, E. Culea1, Al. Darabont2, I. Bratu3, Gh. Borodi3
1
Technical University, 3400 Cluj-Napoca, Romania,
e-mail:coroiu@phys.utcluj.ro
2
Babes-Bolyai University, 3400 Cluj-Napoca, Romania
3
National Institute for Research and Development of
Isotopic and Molecular Technology, 3400 Cluj-Napoca,
P.O. Box 700, Romania
Increased interest in silicate systems containing different rare earth oxides
has resulted from their important applications. Glass-ceramics of
0.95SiO2-0.05Na2O composition containing 15% molar Gd2O3 were
obtained by sol-gel method, and heat-treated at 250oC, 500oC and 1000oC.
The samples were studied by means of X-ray diffraction, IR spectroscopy
and magnetic susceptibility measurements.
Introduction
Sol-gel processes have been intensively developed since they were found to be
suitable for preparing materials and designed devices with specific properties [1-3].
In comparison with ordinary ceramics, gel-derived ceramics offer the advantage of
good chemical homogeneity and purity and a better control of physical and
chemical properties.
Silicate systems containing different rare earth oxides, obtained by sol-gel
techniques, are important in various fields of technology [1-4] including laser,
optical fibre and optical waveguides in telecommunication applications,
microelectronics and catalysis.
The purpose of this paper was to study the structure of 0.95SiO2-0.05Na2O glassceramic containing 15% molar Gd2O3, heat-treated at 250oC, 500oC and 1000oC by
X-ray diffraction, IR spectroscopy and magnetic susceptibility measurements.
Experimental
Samples of xGd2O3(1-x)(0.95SiO2 0.05Na2O) composition, where x=0, and 0.15,
were prepared starting from tetraethoxysilane (99.9% purity, purchased from
Fluka Chemika) as source of silica, natrium peroxide and respectively,
gadolinium oxide. Gd2O3 (99.99% purity) and Na2O2 (99,95% purity) were
purchased from Aldrich and Merck, respectively.
The natrium peroxide and gadolinium oxide were converted to the corresponding
nitrates, NaNO3 and Gd(NO3)3. The water solutions of these nitrates were
evaporated on a water bath (100C). The tetraethoxysilane was mixed with
ethanol and water in molar ratio 1:3:1, and then stirred for 1 hour at room
temperature. After this hydrolysis, the natrium nitrate and the gadolinium nitrate
were added to give a H2O/tetraethoxysilane ratio of 20. Before this operation, the
I.COROIU, E. CULEA, AL. DARABONT, I. BRATU, GH. BORODI
nitrates were again dissolved in water. The obtained solution was stirred about 1
hour with magnetic agitator and then dried at 60C.
The achieved gel was heat-treated at 500C and 1000C in air under normal
pressure. For thermal treatment the samples were prepared in the following way:
the gel was dried at 250C, crumbled and pressed at 200kgf/cm2 as discs with a
diameter of =22mm and a thickness of approximately 1mm. The thermal
treatment both at 500C and 1000C was made for about 48 hours.
The X-ray diffraction measurements were carried out on a DRON 3 diffractometer
using CuK radiation. The diffraction patterns were compared to standard patterns
for phase’s identification.
Infrared absorption spectra were measured at room temperature (~20oC) in the 4004000 cm-1 range with a resolution of 4 cm-1 using a FT-IR Vector 25 Bruker type
infrared spectrophotometer and the KBr pellet technique.
Magnetic susceptibility measurements were performed operating a Weiss type
magnetic balance in the temperature range 80-300 K. The accuracy of the
temperature control was less than 0.1K over the whole range and the overall
accuracy of the measurements of magnetic moment was less than 0.5%.
Results and discussions
The X-ray diffraction patterns of the samples heat-treated at 250oC, 500oC and
1000oC, points out that the thermal treatment has a great importance for the
evolution of the crystallization process. The samples heat-treated at 250oC and
500oC present wholly amorphous phase.
The indexed X-ray powder diffraction patterns of the studied samples heat-treated
at 1000C are shown in Fig.1. It has been ascertained that an extensive crystalline
phase was developed for x=0. This crystalline phase decreases for x=0.15.
The presence of the gadolinium oxide in the 0.95SiO20.05Na2O matrix slows
down this process.
Fig. 1. X-ray diffraction patterns for the xGd2O3_(1-x)(0.95SiO2 0.05Na2O) samples, with
x=0 and x=0.15, heat-treated at 1000˚C.
STUDY OF SOME CERAMIC SYSTEMS BASED ON SILICIUM OXIDE
The increase of the amorphous phase in the presence of gadolinium oxide agrees
with the previously reported data [4], showing that the addition of the gadolinium
ions generates structural changes of the host glass ceramic matrix. Thus, the
gadolinium ions play a network modifier role of the glass ceramic structure.
The crystalline phase formed for x=0 is tridymite, crystallised in monoclinic
system with the a=18.49Å, b=4.99Å, c=25.83Å and β=177.55º lattice parameters.
For x=0.15 the crystalline phase diminishes and consists in a mixture of tridymite
(crystallised in orthorhombic system with a=5.046Å, b=8.236Å) and cristobalite
(crystallised in tetragonal system with a=4.971Å, b=6.918Å).
The IR absorption spectra of the xGd2O3(1-x)(0.95SiO20.05Na2O) samples, with
x=0 are displayed in Fig.2a and with x=0.15, heat-treated at 1000oC, in Fig.2b.
2a.
2b.
Fig.2. IR absorption spectra of the xGd2O3(1-x)(0.95SiO2 0.05Na2O) samples, with:
a. x=0, and b. x=0.15.
The IR data of the studied samples reveal the main features characteristic of the
silicate chains[5]: a sharp absorption band at 465-473cm-1 (bending vibrations of
Si-O-Si linkages), a slightly broadened absorption band at 550-581cm-1 (ring
I.COROIU, E. CULEA, AL. DARABONT, I. BRATU, GH. BORODI
vibrations of six or more than six-members rings composed of [SiO4]4- tetrahedral
units), a weak absorption band at 789-801cm-1 (symmetric stretching vibration of
[O-Si-O] bonds) and a strong and broad absorption band at 1083-1100cm-1
(antisymmetric stretching vibrations of bridging oxygen’s), which modify with
respect to the heat treatment temperatures.
The absorption band at 3420cm-1 is correlated with the molecular water.
The 40cm-1 shift of the symmetric stretching vibration of O-Si-O bonds for the
x=0.15 (see Fig. 2b) are denotative of the strengthening of the glass ceramic
network with increasing the gadolinium oxide content [6].
Figure 4 shows the temperature
dependence of the inverse
magnetic susceptibility for the
x=0.15 samples, heat-treated at
250oC, 500oC and 1000oC. The
data collapse to straight lines
indicating a Curie-Weiss type
magnetic behavior following the
 1  (T   p ) / C
law [7], where C is the Curie
constant
and
p
is
the
Fig.4. Temperature dependence of the inverse
paramagnetic Curie temperature.
magnetic susceptibility of the x=0.15 samples
Magnetic susceptibility data point
weak ferromagnetic interactions between the Gd3+ ions. Increasing the heat
treatment temperature decrease the intensity of these interactions.
Conclusions
Samples of xGd2O3(1-x)(0.95SiO2 0.05Na2O) composition, where x=0 and 0.15
were obtained and studied.
X-ray diffractograms show that addition of gadolinium oxide diminishes the
amount of crystalline phase in the samples.
IR data show that the heat treatment produce structural changes of the studied glass
ceramic.
Magnetic susceptibility measurements estimate weak ferromagnetic interactions
between the Gd3+ ions that decrease with the heat treatment temperature.
References
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