April 28, 2015
16:5
147-mplb
S0217984915500463
Mod. Phys. Lett. B 2015.29. Downloaded from www.worldscientific.com
by LOMONOSOV MOSCOW STATE UNIVERSITY on 04/02/25. Re-use and distribution is strictly not permitted, except for Open Access articles.
Modern Physics Letters B
Vol. 29, No. 11 (2015) 1550046 (7 pages)
c World Scientific Publishing Company
DOI: 10.1142/S0217984915500463
Preparation and effect of thermal treatment
on Gd2 O3 :SiO2 nanocomposite
Rachna Ahlawat
Materials Science Lab., Department of Physics,
Chaudhary Devi Lal University, Sirsa 125055, Haryana, India
rachnaahlawat2003@yahoo.com
Received 9 August 2014
Revised 3 January 2015
Accepted 11 January 2015
Published 30 April 2015
Rare earth oxides have been extensively investigated due to their fascinating properties such as enhanced luminescence efficiency, lower lasing threshold, high-performance
luminescent devices, drug-carrying vehicle, contrast agent in magnetic resonance imaging (MRI), up-conversion materials, catalysts and time-resolved fluorescence (TRF)
labels for biological detection etc. Nanocomposites of silica gadolinium oxide have
been successfully synthesized by sol–gel process using hydrochloric acid as a catalyst.
Gd(NO3 )3 · 6H2 O and tetraethyl orthosilicate (TEOS) were used as precursors to obtain powdered form of gadolinum oxide:silica (Gd2 O3 :SiO2 ) composite. The powdered
samples having 2.8 mol% Gd2 O3 were annealed at 500◦ C and 900◦ C temperature for 6 h
and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy
(FTIR), scanning electron microscope (SEM) and transmission electron microscope
(TEM). The effect of annealing on the phase evolution of the composite system has
been discussed in detail. It was found that the sintering of gadolinium precursor plays a
pivotal role to obtain crystalline phase of Gd2 O3 . Cubic phase of gadolinium oxide was
developed for annealed sample at 900◦ C (6 h) with an average grain size ∼12 nm.
Keywords: Nanocomposite; XRD; FTIR; SEM; TEM.
1. Introduction
Among rare earth oxides, gadolinium oxide (Gd2 O3 ) is an Ln2 O3 -type oxide that
has been extensively studied due to its optoelectronic, data storage, sensors, scintillator, solid electrolytes and display applications.1,2 These electrical and optical
characteristics of very small particles are caused by quantum effects due to their
high surface to volume ratio, which increases the band gap by reducing the number of allowable quantum states in the small particles and improves surface and
interfacial effects.
1550046-1
page 1
April 28, 2015
16:5
147-mplb
S0217984915500463
Mod. Phys. Lett. B 2015.29. Downloaded from www.worldscientific.com
by LOMONOSOV MOSCOW STATE UNIVERSITY on 04/02/25. Re-use and distribution is strictly not permitted, except for Open Access articles.
R. Ahlawat
The rare earth oxides are very expensive, which has limited their use in a
number of technical applications. Combining the promising properties of Gd2 O3
with nanoparticles in the form of powder of inert host is important for the fabrication of the cost-efficient nanocomposites. Silicon oxide prepared by the acid
catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) form an interesting class
of matrices for the deposition of metals, oxides and functional polymers. Various groups have employed some wet chemical methods to coat silica spheres with
nanoparticles of noble metals, rare earth oxides and transition metal oxides.3–5
Sol–gel technology appears a possible tool in order to produce composite materials constituting of rare earth oxide embedded into an inert host. Our goal is to
investigate the incorporation of Gd2 O3 in silica matrix and to study the effect of
sintering temperature on the prepared composites. The size of nanocrystallites thus
obtained is ascertained from X-ray diffraction (XRD), Fourier transform infrared
spectroscopy (FTIR), scanning electron microscope (SEM) and transmission electron microscope (TEM) experimental techniques.
2. Experimental
2.1. Sample preparation
To prepare the samples, molar ratio of starting solution was taken as
2.30:0.72:0.29:0.027 for H2 O:C2 H5 OH:HCl:TEOS. About 2.8 mol% Gd2 O3 was introduced in the pre-hydrolyzed solution under heating. Using sol–gel technique,
hydrous gadolinium nitrate and hydrous silicon oxide were mixed at room temperature. For this purpose, high purity reagents, namely, TEOS (Aldrich 99.99%),
ethanol (Merck 99.9%) and double distilled water were mixed in the presence of
hydrochloric acid as catalyst. The prepared gel was kept at room temperature for
21 days for aging of the samples. In this process, initially networking of bonds
took place and subsequently with time shrinkage, stiffening of the gel occurred.
After aging, the samples were further dried at 100◦ C for 24 h and dried samples
were powdered by pestle mortar. Furthermore, the dried samples were sintered in
a programmable furnace at different temperatures to study the effect of sintering
on phase evolution of powdered samples of Gd2 O3 :SiO2 composite.
2.2. Characterizations
As-prepared and sintered samples were characterized by an X’pert Pro X-Ray
Diffractometer with Cu Kα1 radiation in the range of 5◦ –80◦ , in steps of 0.017◦
(40 mA, 45 kV) for the determination of crystalline structure of nanocomposite
which were further conformed by Hitachi 4500 TEM. The surface morphology of
the prepared samples has been studied by the help of JEOL-JSM-6100 SEM. FTIR
of as-prepared and sintered samples were collected by PerkinElmer Spectrum 400
spectrophotometer in 4000–450 cm−1 range to obtain the information about phase
composition and bonding in the samples.
1550046-2
page 2
April 28, 2015
16:5
147-mplb
S0217984915500463
Preparation and effect of thermal treatment on Gd2 O3 :SiO2 nanocomposite
Mod. Phys. Lett. B 2015.29. Downloaded from www.worldscientific.com
by LOMONOSOV MOSCOW STATE UNIVERSITY on 04/02/25. Re-use and distribution is strictly not permitted, except for Open Access articles.
3. Results and Discussion
3.1. XRD
XRD patterns of 2.8 mol% Gd2 O3 :SiO2 samples are shown in Fig. 1. The XRD
pattern of as-prepared sample (see Fig. 1(a)) has a sharp and intense diffraction line
at 2θ ∼ 14.55◦ along with some weaker peaks at 2θ ∼ 22.48◦ and 34.08◦ which may
be attributed due to gadolinium nitrate hydride and compared with JCPDS card no.
84-2385. The XRD pattern of the sample annealed at 500◦ C (see Fig. 1(b)), clearly
shows that the typical diffraction peak of Gd(OH)3 disappeared. It indicates that
Gd(OH)3 is completely decomposed, while a hump around 2θ ∼ 28.78◦ appeared.
Furthermore, the temperature was raised up to 900◦ C, which could be responsible
for the initial development of cubic phase of crystalline Gd2 O3 . At this sintering
temperature, a single diffraction peak appeared which could be assigned to cubic
Gd2 O3 having lattice constant a = 10.80 Å and space group Ia-3 (206) [JCPDS
card no. 43-1014].6 The possible reason for the single peak observed in Fig. 1(c)
could be the low concentration of Gd2 O3 in the composite powder.
The nanocrystallite size was calculated by the well-known Debye–Scherer’s equation: D = Kλ/β cos(θ). The average crystalline size (D) of the nanocomposite
having 2.8 mol% Gd2 O3 was calculated using the above equation and found to be
12 nm for the sample sintered at 900◦ C. From the above results, we may conclude
that proper sintering is responsible for the development of initial crystalline phase
of cubic Gd2 O3 in Gd2 O3 :SiO2 nanocomposite.
Fig. 1. XRD patterns of Gd2 O3 :SiO2 samples: (a) as-prepared; (b) annealed at 500◦ C and
(c) at 900◦ C.
1550046-3
page 3
April 28, 2015
16:5
147-mplb
S0217984915500463
R. Ahlawat
Mod. Phys. Lett. B 2015.29. Downloaded from www.worldscientific.com
by LOMONOSOV MOSCOW STATE UNIVERSITY on 04/02/25. Re-use and distribution is strictly not permitted, except for Open Access articles.
3.2. FTIR
FTIR spectrum of the as-prepared Gd2 O3 :SiO2 sample shows very broad and strong
bands at 3440 cm−1 and 1638 cm−1 . In FTIR spectroscopy, generally, the bands at
3600–3200 cm−1 are assigned to the presence of H2 O or hydrogen bonded silanol
(Si–OH) bond.7 The broadening of bands at 3390 cm−1 is due to the overlapping
of the water band and silanol hydroxyl group vibrations.8
The absorption band at 1100 cm−1 and 815 cm−1 are attributed to asymmetric
and symmetric stretching modes of Si–O–Si respectively.9,10 The sharp peak at
973 cm−1 appeared due to stretching vibrations of Si–OH group which disappeared
at higher temperatures. The strong peaks around 1384, 1512 and 1362 cm−1 have
been found to originate from the characteristic vibrations of impurities like NO3 ,
CO2−
and C=O respectively.11,12 It may be seen from Fig. 2, that major change
3
is observed in the FTIR spectrum of the sample (see Fig. 2(c)) whereas a small
absorption peak assigned to Gd–O bond appeared at 540 cm−1 . This result supports
the XRD results and is in good agreement with the literature.13
3.3. SEM analysis
Figure 3 shows micrographs of the as-prepared and annealed samples containing
2.8 mol% Gd2 O3 samples. The SEM image of the as-prepared (see Fig. 3(a)) sample
shows morphology of amorphous Gd2 O3 :SiO2 samples. At 500◦ C, water molecules
content, Si–OH and volatile matter content were found to decrease in the sample
Fig. 2. FTIR patterns of Gd2 O3 :SiO2 samples: (a) as-prepared; (b) annealed at 500◦ C and
(c) at 900◦ C.
1550046-4
page 4
April 28, 2015
16:5
147-mplb
S0217984915500463
Mod. Phys. Lett. B 2015.29. Downloaded from www.worldscientific.com
by LOMONOSOV MOSCOW STATE UNIVERSITY on 04/02/25. Re-use and distribution is strictly not permitted, except for Open Access articles.
Preparation and effect of thermal treatment on Gd2 O3 :SiO2 nanocomposite
(a)
(b)
(c)
Fig. 3. SEM micrographs of Gd2 O3 :SiO2 samples: (a) as-prepared; (b) annealed at 500◦ C and
(c) at 900◦ C.
(see Fig. 3(b)) annealed at 500◦ C for six hours. This results in the increase of
densification of the sample. Further increase of the annealing temperature up to
900◦ C, the sample (see Fig. 3(c)) indicates the development of initial phase of
crystallinity of Gd2 O3 with silica and these results support the XRD and FTIR
data of the corresponding sample. The microstructure of the rare earth powder
obtained by sol–gel method can be favorably controlled by selecting the correct
heat treatment.
3.4. TEM analysis
Figure 4(a) represents the TEM image of the Gd2 O3 :SiO2 nanocomposite annealed
at 900◦ C. The prepared Gd2 O3 :SiO2 nanocomposite having 2.8 mol% Gd2 O3 exhibits almost spherical morphology of the nanocrystallites and homogeneous distribution within SiO2 matrix. At this annealing temperature, both densification and
density are significantly increased which are clearly illustrated in the TEM image
1550046-5
page 5
April 28, 2015
16:5
147-mplb
S0217984915500463
R. Ahlawat
50
(b) 900°C
40
Count (in %)
Mod. Phys. Lett. B 2015.29. Downloaded from www.worldscientific.com
by LOMONOSOV MOSCOW STATE UNIVERSITY on 04/02/25. Re-use and distribution is strictly not permitted, except for Open Access articles.
(a) 900°C
30
20
10
0
5
10
15
20
25
30
Particle Size (nm)
Fig. 4.
(a) TEM micrograph of Gd2 O3 :SiO2 sample and (b) particle size distribution.
of the sample. Important information from the micrograph is that the most of the
nanocrystallites were found in the range of their size 15–50 nm, but there were also
some smaller (∼5 nm) and bigger non-agglomerated nanocrystallites (up to 25 nm)
as indicated by the particle size distribution shown in Fig. 4(b).
4. Conclusion
Using sol–gel process, Gd2 O3 :SiO2 nanocomposites were successfully obtained upon
heat treatment in air. Sintering temperature results in aggregation in the nanocomposites is due to solid-state bonds formed between nanoparticles and the gel. The
nanocrystalline size for Gd2 O3 :SiO2 composite was calculated as ∼12 nm by the
help of Debye–Scherer’s equation and further confirmed with TEM micrographs.
References
1. S. K. Singh, K. Kumar and S. B. Rai, Sens. Actuators A 149 (2009) 16.
2. X. Y. Sun, D. G. Jiang, S. W. Chen, G. T. Zheng, S. M. Huang, M. Gu, Z. J. Zhang
and J. T. Zhao, J. Am. Ceram. Soc. 96 (2013) 1483.
3. Y. Iwaka, Y. Akimoto, M. Omiya, T. Ueda and T. Yokomori, J. Lumin. 130 (2010)
1470.
4. V. G. Il’ves, S. Yu. Sokovnin, S. A. Uporov and M. G. Zuev, Phys. Solid State 55
(2013) 1262.
5. V. G. Pol, A. Gedanken and J. C. Moreno, Chem. Mater. 15 (2003) 1111.
6. C. Steiner, B. Bolliger and M. Erbudak, Phys. Rev. B 62 (2000) 10614.
7. R. Ramamoorthy, S. Ramasamy and D. Sundaraman, J. Mater. Res. 14 (1999) 90.
8. S. T. Tan, B. J. Chen, X. W. Sun, W. J. Fan, H. S. Kwok, X. H. Zhang and S. J.
Chua, J. Appl. Phys. 98 (2005) 013505.
9. L. G. Jacobsohn, M. W. Blair, S. C. Tornga, L. O. Brown, B. L. Bennett and R. E.
Muenchausen, J. Appl. Phys. 104 (2008) 124303.
1550046-6
page 6
April 28, 2015
16:5
147-mplb
S0217984915500463
Mod. Phys. Lett. B 2015.29. Downloaded from www.worldscientific.com
by LOMONOSOV MOSCOW STATE UNIVERSITY on 04/02/25. Re-use and distribution is strictly not permitted, except for Open Access articles.
Preparation and effect of thermal treatment on Gd2 O3 :SiO2 nanocomposite
10. Z. H. Liu, Y. M. Tian, F. Sun, F. Y. Meng, Y. H. Zheng and F. M. Jiang, Colloids
Surf. A 122 (2008) 318.
11. A. M. Pires, O. A. Serra and M. R. Davolos, J. Lumin. 113 (2005) 174.
12. Y. K. Kim, H. K. Kim and D. K. Kim, J. Mater. Res. 19 (2004) 2.
13. Z. Xu, J. Yang, Z. Hou, C. Li, C. Zhang, S. Huang and J. Lin, Mater. Res. Bull. 44
(2009) 1850.
1550046-7
page 7