Citrate sol-gel method to prepare nanoparticles of a piezoelectric crystal material: La3Nb0.5Ga5.5O14 at low temperature

Article abstract of DOI:10.1016/j.jallcom.2007.04.216

The nanoparticles of a piezoelectric crystal material: La₃Nb_0.5Ga_5.5O₁₄ (LGN) have been prepared via a citrate sol-gel method, the process of which was simple and the crystallization temperature of LGN nanoparticles was low. The sintered samples were characterized by means of thermogravimetry/differential thermal analysis (TG/DTA), X-ray powder diffraction (XRPD), Fourier transform infrared (FT-IR) spectra, transmission electron microscope (TEM) and high-resolution transmission electron micrography (HRTEM). All the results illustrate that the trigonal crystallographic phase LGN nanoparticles were well crystallized. It is significant to the LGN crystal growth, as in which, the problem of decompensate and evaporate of Ga₂O₃ at high temperatures may be resolved.

Full text of DOI:10.1016/j.jallcom.2007.04.216

Journal of Alloys and Compounds 459 (2008) L1–L4
Letter
Citrate sol–gel method to prepare nanoparticles of a piezoelectric crystal
material: La Nb Ga O at low temperature
3
0.5
5.5 14
a
a,∗
a
b
a
a
F.P. Yu , D.R. Yuan , X.L. Duan , L.M. Kong , X.Z. Shi , S.Y. Guo ,
a
a
a
L.H. Wang , X.F. Cheng , X.Q. Wang
a
State Key Laboratory of Crystal Materials and Institute of Crystal Materials, Shandong University, Jinan 250100, PR China
b
Institute 53 of China’s Ordnance Industry, P.O. Box 108, Jinan 250031, PR China
Received 19 December 2006; accepted 14 April 2007
Available online 19 April 2007
Abstract
The nanoparticles of a piezoelectric crystal material: La
3
Nb0.5Ga5.5O14 (LGN) have been prepared via a citrate sol–gel method, the process
of which was simple and the crystallization temperature of LGN nanoparticles was low. The sintered samples were characterized by means
of thermogravimetry/differential thermal analysis (TG/DTA), X-ray powder diffraction (XRPD), Fourier transform infrared (FT-IR) spectra,
transmission electron microscope (TEM) and high-resolution transmission electron micrography (HRTEM). All the results illustrate that the
trigonal crystallographic phase LGN nanoparticles were well crystallized. It is significant to the LGN crystal growth, as in which, the problem of
decompensate and evaporate of Ga
2 3
O at high temperatures may be resolved.
©
2007 Elsevier B.V. All rights reserved.
Keywords: Sol–gel synthesis; X-ray diffraction; Thermal analysis
1
. Introduction
tive way to get rid of these disadvantages is to use. Therefore,
pure phase polycrystalline becomes important to the growth of
high-quality single crystals. To our knowledge, there is no report
about the preparation of LGN polycrystalline raw materials by
sol–gel method. In the present work, we focus on the preparation
and characterization of the LGN nanoparticles by citric sol–gel
method using citric acid as a chelating agent.
Recently, progress of electric and communication technology
requires new piezoelectric crystals with high thermal stability
of the frequency and large electromechanical coupling factors
and leads to the development of new piezoelectric crystal. Com-
poundswithCa3Ga2Ge4O14 (CGG)-type[1]structurehavebeen
reported to be new promising piezoelectric materials for fabri-
cation of filters with large pass bandwidths and oscillators with
large shift or high frequency stability. Gallate crystals such as
2
. Experimental procedure
La3Ga SiO14 (LGS), La3Ga Nb0.5O14 (LGN) and La3Ga5.5
5
5.5
After Nb2O5 (99.99%) was dissolved by HF acid fully, ammonia was added
Ta0.5O14 (LGT) have been actively investigated for application
in the above-mentioned devices [2–5]. However, because one of
the starting materials Ga2O3 is apt to decompensate and evap-
orate at high temperatures, extra Ga2O3 of 1–2 wt.% must be
added to the starting materials in order to compensate for the
volatilization of Ga2O3 during the crystal growth process [6] or
control the growth atmosphere in order to avoid the evaporation
of gallium suboxide from melt during growth [3,7]. An alterna-
to form the white Nb(OH) deposition, which was washed, filtrated and then dis-
solved into citric acid, after the Nb–citric acid transparent solution was formed,
5
La(NO3)3, Ga(NO3)3 solutions were added, the final solutions were mixed with
3
+
3+
La :Ga :citric acid molar ratio of 3:5:16. After further mixing, the obtained
◦
solution was hearted and concentrated by slow evaporation at 80 C under con-
tinuous stirring using a magnetic agitator for several hours until the yellowish
◦
transparent gels were obtained. Finally, the gels were dried at 110 C for 24 h till
the colour turned into brown. The dried mass, which was the so-called precursor,
was then moved into a furnace and heated to different temperatures, pure phase
◦
LGN nanocrystals were obtained after sintered the precursor at 800 C for 6 h.
◦
The heating rate was controlled by FP21 at a speed of 100 C/h. The optimized
procedures by citric sol–gel method are illustrated in Fig. 1.
Thermogravimetric analysis/differential thermal analysis (TGA/DTA) of
the original precursor was carried out on a SETA-RAM Labsys TGA-DTA16
∗
Corresponding author. Tel.: +86 531 88362822; fax: +86 531 88564337.
E-mail address: dryuan@icm.sdu.edu.cn (D.R. Yuan).
0
925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2007.04.216

L2
F.P. Yu et al. / Journal of Alloys and Compounds 459 (2008) L1–L4
Fig. 1. Procedure diagram of synthesis of LGN nanocrystal by sol–gel method.
◦
◦
Fig. 3. XRPD patterns of the samples sintered at (a) 600 C, (b) 750 C, (c)
8
◦ ◦
00 C and (d) 900 C for 6 h.
Thermal Analyser in flowing air atmosphere (50 ml/min) with a heating rate of
◦
1
0 C/min. The crystallization process and phase identification of the powders
◦
calcined at different temperatures were identified by X-ray powder diffraction
XRPD) on a Bruker AXS (Advanced X-ray solutions) Inc. (D8 Advance) using
Cu K␣ radiation (λ = 0.1540598 nm), and a Fourier transform infrared (FT-IR)
Nicolet 20 SX FTIR) spectrometer. The grain size and morphology of the
strates that almost all of the weight loss occurred below 700 C
and the ratio of which is about 84.83%, it is fairly consistent
to the calculation in theory (85.02%). The obvious endothermic
peaks around 168.1 C may be caused by the decomposition of
nitrate and the loss of the crystalline water. One strong exother-
(
(
◦
heat-treated powders without being ground were characterized by an H-800
transmission electron microscope (TEM) and also, the microstructure of the
nanocrystal was analyzed by Philips Tecnai 20U-TWIN high-resolution trans-
mission electron microscopy (HRTEM) observation, which was performed with
JEOL-2010 transmission electron microscope using an accelerating voltage of
◦
mic peak at the range of 400–700 C attributes to the combustion
of citric acid, the other one around 700 C corresponds to the
◦
2
00 kV.
3
. Results and discussion
3
.1. Thermal analyses
The TGA/DTA curves of the original precursor are presented
in Fig. 2. The DTA curve shows only one endothermic peak and
◦
two exothermic peaks up to 900 C. The TGA curve demon-
Fig. 4. Fourier transform infrared spectrometry of the precursors sintered at (a)
◦ ◦ ◦
600 C, (b) 750 C, (c) 800 C for 6 h and LGN crystal (d).
Fig. 2. TGA/DTA curves of the original precursor.

F.P. Yu et al. / Journal of Alloys and Compounds 459 (2008) L1–L4
L3
crystallization of LGN phase. No significant weight loss was
◦
observed and the exothermic peak from 710 to 900 C can be
◦
presumed as the phase transformation started at about 710 C,
which is consistent with the XRPD result.
3
.2. X-ray powder diffraction
The XRPD patterns of the LGN powders calcined at various
temperatures are shown in Fig. 3. As the temperature increased,
the diffraction peaks became intense, which indicates the crys-
◦
tallization of the powders. At 750 C, though the LGN phase has
formed, Nb2O phase exits too (see Fig. 3b), so the product is not
5
◦
pure. At 800 C, the precursor completely transformed to LGN
and the diffraction peaks agreed well with those of pure LGN
(
JCPDS No. 840775). Trigonal La3Nb0.5Ga5.5O14 was the only
◦
Fig. 5. TEM micrograph of the sample sintered at 800 C for 6 h; inset, corre-
sponding SAEM pattern.
◦
phasedetectedinthesamplescalcinedabove800 C. Thesemain
peaks can be indexed as (2 0 0), (1 1 1), (0 2 1), (2 1 0), (0 0 2),
(
1 2 1)and(1 2 2)diffractionlines. AccordingtoScherrer’sequa-
◦
between 1000 and 1600 cm 1 are related to NO3 ions (see
−
−
tion, the grain size of the samples calcined 800 C is about
3
nanoscaled LGN powders are synthesized at fairly lower calcin-
ing temperature. The possible reasons for these cases may be the
molecular level mixing of La , Ga and Nb ions, the high
degree of homogeneity shortened the ion diffusion distance [9].
−1
0 nm. Compared with solid-stated synthesis method [6,8], these
Fig. 4a–c) [9]. The bands at 2168 and 2923 cm in Fig. 4a
represent the stretching vibrations of the remnant organic com-
pound of citrate ions. With the increasing of temperature, the
above-mentioned bands became weaker or disappeared. When
the samples were heated to 800 C, new absorption peaks at 668,
83 and 499 cm (see Fig. 4c) appeared, which indicates that
3+
3+
5+
◦
−
1
5
the formation of La3Nb0.5Ga5.5O14 nanocrystals. Fig. 4d shows
the FT-IR spectrum of LGN single crystal, from which, one can
see that the main absorbing peaks of Fig. 4c. This hypothesis was
also confirmed by XRPD analysis. The bands at about 1550 and
1490 cm were present in the powder calcined at 800 C and
theyshowtheexistenceofalittleresiduesoforganiccompounds.
3
.3. Fourier transform infrared spectrometry analysis
FT-IR spectra of the raw materials sintered at various tem-
peratures are shown in Fig. 4. The broad band centered at
−
1
◦
−1
3
403 cm is assigned to the O–H bond vibration of H2O, indi-
cating the existence of water absorbed in the samples. The bands
◦
Fig. 6. HRTEM image of the sample sintered at 900 C for 6 h; inset, corresponding SAEM pattern (region b in part a).

L4
F.P. Yu et al. / Journal of Alloys and Compounds 459 (2008) L1–L4
3
.4. Morphology and microstructure characterization
crystal growth process. Single crystal growth of LGN with such
kind of raw materials is presently under way.
Fig. 5 presents the morphologies and microstructure of the
◦
as-synthesized nanoscaled LGN powders calcined at 800 C.
From the TEM photograph, it can be observed that all
the particles are dispersed uniformly, and their sizes are
between 20 and 30 nm. The selected area electron diffrac-
tion (SAED) in Fig. 5 clearly indicated that the sample
Acknowledgment
This work is supported by the National Nature Science Foun-
dation of China (NNSFC No. 50372034).
◦
was well crystallized at 800 C. Also, the crystalline struc-
References
◦
ture of the sample sintered at 900 C is demonstrated in the
[
[
1] E.L. Beloknoeva, N.V. Belov, Sov. Phys. Dokl. 26 (1981) 931.
2] Yu.V. Pusarevsky, P.A. Senushencov, P.A. Popov, B.B. Mill, IEEE Trans.
Ultrason. Ferroelectr. Freq. Control 42 (1995) 653.
HRTEM image (Fig. 6a), from which, one can see that the
grains grew up significantly. In Fig. 6b, only one-dimension
crystalline image was observed and the crystalline face of
[
3] H. Takeda, K. Shimamura, T. Kohna, T. Fukuda, J. Cryst. Growth 169 (1996)
(
0 0 2) was confirmed by the parallel fringes with spacing of
503.
0
.2564 nm.
[4] Yu.V. Pusarevsky, P.A. Senushencov, B.V. Mill, N.A. Moiseeva, Proceedings
of the IEEE International Frequency Control Symposium, 1998, p. 742.
[
5] H. Kavanaka, H. Takeda, K. Shimamura, T. Fukuda, J. Cryst. Growth 183
1998) 274.
4
. Conclusions
(
[
[
6] H.K. Kong, J.Y. Wang, H.J. Zhang, X. Yin, J. Cryst. Growth 292 (2006) 408.
7] Z.M. Wang, D.R. Yuan, A.J. Wei, H.F. Qi, X.Z. Shi, D. Xu, M.K. Lv, J.
Cryst. Growth 263 (2004) 389.
8] J.Y. Wang, X. Yin, R.J. Han, S.J. Zhang, H.K. Kong, H.J. Zhang, X.B. Hu,
M.H. Jiang, Opt. Mater. 23 (2003) 393.
Single-phase nanoscaled LGN polycrystalline powders have
been prepared by citrate sol–gel method. The pure phase
powders were obtained by calcining the gel at fairly lower tem-
[
[
◦
perature (800 C) and shorter holding time (6 h) compared with
9] F.P. Yu, D.R. Yuan, X.F. Cheng, X.L. Duan, X.Q. Wang, L.M. Kong, L.H.
Wang, Z.F. Li, Mater. Lett. 61 (2007) 2322.
solid-stated synthesis, which may resolve the problem of decom-
pensate and evaporate of Ga2O3 at high temperatures in the