Preparation of zirconia nanoparticles by pulsed laser ablation in liquid

Article abstract of DOI:10.1246/cl.2009.1102

We report on the synthesis of zirconia nanoparticles by nanosecond pulsed laser ablation in water or ammonia at room temperature. Mixtures of tetragonal and monoclinic zirconia nanoparticles were obtained in water, while tetragonal zirconia nanoparticles

Full text of DOI:10.1246/cl.2009.1102

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Chemistry Letters Vol.38, No.11 (2009)
Preparation of Zirconia Nanoparticles by Pulsed Laser Ablation in Liquid
ꢀ
Dezhi Tan, Yu Teng, Yin Liu, Yixi Zhuang, and Jianrong Qiu
State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, P. R. China
(Received July 30, 2009; CL-090710; E-mail: qjr@zju.edu.cn)
We report on the synthesis of zirconia nanoparticles by
nanosecond pulsed laser ablation in water or ammonia at room
temperature. Mixtures of tetragonal and monoclinic zirconia
nanoparticles were obtained in water, while tetragonal zirconia
nanoparticles were synthesized in ammonia. The mechanism
of the formation of zirconia nanoparticles was discussed.
Zirconia has three crystallographic phases: monoclinic
(m-ZrO2), tetragonal (t-ZrO2), and cubic (c-ZrO2) phases. The
monoclinic zirconia is stable at room temperature and transforms
ꢁ
ꢁ
to tetragonal zirconia at 1170 C and cubic zirconia at 2370 C.
The martensitic phase transformation from tetragonal to mono-
clinic zirconia is accompanied by 5% volume expansion which
is important in the application of structural ceramics. In addition,
tetragonal zirconia is extensively used as catalysts, catalyst sup-
Figure 1. XRD patterns of ZrO2 produced by pulsed laser abla-
tion in water (a) and ammonia (b). The standard JCPDS card data
for monoclinic (c) and tetragonal (d) ZrO2 are provided as refer-
ences.
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ports, oxygen sensors, and fuel cells. Therefore, synthesis of
tetragonal zirconia at room temperature attracts the ongoing in-
terest. Adding impurities, such as Y2O3, is one way to synthesize
tetragonal zirconia. Due to effect of a critical particle size on the
stability of tetragonal zirconia, reducing particle size is another
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way to stabilize tetragonal zirconia. Additionally, the aggrega-
tion of zirconia nanocrystallites can improve the stability of
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tetragonal zirconia significantly. Many methods were used to
synthesize tetragonal zirconia, while all these methods need cal-
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cination at high temperature.
Recently, pulsed laser ablation in liquid (PLAL) has attract-
ed great attention in the synthesis of metastable nanomateri-
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als.
High temperature and high pressure can be created in a
local region in the liquid by pulsed laser ablation which leads
to the formation of metastable nanomaterials. Moreover, the
products are quenched quickly and can be frozen and preserved.
In this letter, we report the synthesis of zirconia nanoparticles us-
ing a simple method of pulsed laser ablation in water or ammo-
nia at room temperature.
Figure 2. Raman spectra of ZrO2 produced by pulsed laser
ablation in water (a) and ammonia (b).
A zirconium metal plate submerged in deionized water or
ammonia was irradiated by a third harmonic (355 nm) of a
Nd:YAG pulse laser for 60 min. Other parameters of the laser
were: pulse width ꢀ ¼ 7 ns, repetition rate ꢁ ¼ 10 Hz, and pulse
energy = 100 mJ. The target was fixed on the bottom of a glass
vessel, and then water or ammonia was poured into the vessel.
The depth from the liquid surface to the target was 5 mm. The
ammonia was chemically pure, and the concentration was
water is a mixture of tetragonal and monoclinic zirconia, while
the sample obtained in ammonia is mainly tetragonal zirconia.
The differences in component with different starting solu-
tions can be further proved by Raman spectra. As shown in
Figure 2, the Raman peaks at 173, 186, 216, 328, 376, and
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610 cm are the characteristic bands of monoclinic zirconia,
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1,12
and the Raman peaks at 145, 262, 471, and 633 cm can be as-
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25 wt %. The laser beam was focused onto the target surface us-
ing a lens with a focal length of 100 mm. The samples were col-
signed to tetragonal zirconia.
Therefore, both of tetragonal
and monoclinic zirconia were produced in water, while the sam-
ple obtained in ammonia is mainly tetragonal zirconia. No appa-
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lected after evaporating the solutions at 80 C. X-ray diffraction
analysis (XRD) and Raman spectra were used to study the crys-
tal phases of the samples. Transmission electron microscopy
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rent peak at 610 cm assigned to characteristic band of cubic
zirconia is observed in the Figure 2b, which indicates the ab-
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(
TEM) was used to study the shape and size distribution of the
sence of cubic zirconia. The Raman spectra were consistent
with the XRD results.
Figure 3 shows the TEM and HRTEM images of ZrO pro-
synthesized nanoparticles. High-resolution TEM (HRTEM)
was used to analyze the crystal phases.
XRD patterns in Figure 1 show that the sample produced in
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duced by pulsed laser ablation in water (a), (b) and ammonia (c),
Copyright Ó 2009 The Chemical Society of Japan

Chemistry Letters Vol.38, No.11 (2009)
1103
as shown in Figures 3b and 3c, which contradicted the prediction
about the critical size.
Many factors, such as particle size, hydrostatic strain ener-
gy, hard aggregation tendencies, and surface energy could affect
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the stability of tetragonal zirconia. The phase transformation
from tetragonal to monoclinic is accompanied by 5% volume ex-
pansion. Shukla et al. suggested that this transformation would
induce hydrostatic stresses and improve the stability of tetrago-
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nal zirconia. Then the critical size can be larger than 30 nm.
Meanwhile, small nanocrystallites aggregated to form larger
hard aggregated particles, as shown in Figure 3c. The aggrega-
tion of zirconia nanocrystallites could improve the stability of
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tetragonal zirconia. All these factors could explain the presence
of tetragonal nanoparticles larger than 30 nm.
We now discuss the difference between the products pre-
pared in water and ammonia. Mitsuhashi et al. reported that
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OH played an important role in stabilizing tetragonal zirco-
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nia. According to the study by Shukla, OH could be present
on the particle surface which enhanced the interfacial difference
between tetragonal and monoclinic phases. OH could also be
Figure 3. TEM and HRTEM images of ZrO2 produced by
pulsed laser ablation in water (a), (b) and ammonia (c), (d).
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inside tetragonal lattice and then induced hydrostatic stresses.13
These factors could improve the stability of tetragonal zirconia.
In our case, the pH measurements revealed that the solution
changed from the initial neutral to an acidic state (pH 3.8) after
laser ablation in water, while in ammonia, the pH value (12.8)
almost remained unchanged. These results suggested that there
(
d). The TEM image of ZrO2 synthesized in water shows that the
particles are almost spherical. Tetragonal zirconia lattices (with
interplanar spacing of 0.294 nm) are observed in the products in
water, as shown Figures 3a and 3b, which confirm the presence
of tetragonal zirconia. Figure 3c is a TEM image of ZrO2 nano-
particles synthesized in ammonia which shows the size of parti-
cles distributed mainly in two regions: 10–15 and 100–150 nm.
The lattice (with interplanar spacing of 0.294 nm), as shown in
Figure 3d, confirms the presence of tetragonal zirconia nanopar-
ticles.
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could be more OH adsorbed on tetragonal zirconia surface
and inside tetragonal lattice in ammonia than water. These
may result in better stability of tetragonal zirconia in ammonia
than water.
In conclusion, mixtures of monoclinic and tetragonal zirco-
nia were prepared in water by pulsed laser ablation, while tetrag-
onal zirconia was synthesized in ammonia. The stability resulted
from the inherent advantages of pulsed laser ablation in liquid,
To understand the formation and stability mechanisms of
tetragonal zirconia nanoparticles, it is necessary to examine
the mechanism of pulsed laser ablation in liquid and to consider
factors affecting the stability of tetragonal zirconia. Pulsed laser
ablation in liquid is a highly nonequilibrium process. When the
laser pulse irradiates the interface between the solid target and
liquid through the liquid, species will be ejected out with large
kinetic energy. Then a plasma plume will be generated on the in-
terface. The plasma plume expands quickly while the liquid con-
fines it. The confinement of liquid could drive the plasma plume
into an extreme thermodynamic state in which the temperature
can reach several thousand K and the pressure goes into the order
ꢂ
hydrostatic stresses, and hard aggregation. Additionally, OH
may play an important role in the stabilization of tetragonal zir-
conia in ammonia.
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According to the surface energy theory, the critical size for
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stabilized tetragonal zirconia is 30 nm. In our case, many single
spherical tetragonal zirconia particles smaller than 30 nm were
produced in water and ammonia, as shown in Figures 3a and
3d. Tetragonal particles larger than 30 nm were also present,
Published on the web (Advance View) October 24, 2009; doi:10.1246/cl.2009.1102