Fabrication of NiO nanoparticle-coated lead zirconate titanate powders by the heterogeneous precipitation method

Article abstract of DOI:10.1111/j.1151-2916.2003.tb03531.x

NiO nanoparticle-coated lead zirconate titanate (PZT) powders are successfully fabricated by the heterogeneous precipitation method using PZT, Ni(NO₃)₂·6H₂O, and NH₄HCO₃ as the starting materials. The

Full text of DOI:10.1111/j.1151-2916.2003.tb03531.x

J. Am. Ceram. Soc., 86 [9] 1631–34 (2003)
journal
Fabrication of NiO Nanoparticle-Coated Lead Zirconate Titanate
Powders by the Heterogeneous Precipitation Method
Ping-Hua Xiang, Xian-Lin Dong, Chu-De Feng, and Yong-Ling Wang
Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, P.R. China
NiO nanoparticle-coated lead zirconate titanate (PZT) pow-
ders are successfully fabricated by the heterogeneous precipi-
tation method using PZT, Ni(NO3)2⅐6H2O, and NH4HCO3 as
the starting materials. The amorphous NiCO3⅐2Ni(OH)2⅐2H2O
are uniformly coated on the surface of PZT particles. XRD
analysis and the selected-area diffraction (SAD) pattern indi-
cate that the amorphous coating layer is crystallized to NiO
after being calcined at 400°C for 2 h. TEM images show that
the NiO particles of ϳ8 nm are spherical and weakly agglom-
erated. The thickness of the nanocrystalline NiO coating layer
on the surface of PZT particle is ϳ30 nm.
the relatively low cost of the reactants and easily controlled
fabrication process. However, there is no report on the fabrication
of nanoparticle-coated PZT powders using this method.
In the present study, PZT powders coated with NiO nanopar-
ticles are fabricated by the heterogeneous precipitation method.
The microstructure of the coated powders is investigated in detail.
The purpose of this study is to obtain much better microstructure
and high-performance PZT/NiO nanocomposites.
II. Experimental Procedures
The coated PZT powders were prepared using PZT powders
with the diameter of 0.36 ␮m (self-made), Ni(NO3)2⅐6H2O (ana-
lytically) and NH4HCO3 (analytically) as starting materials. PZT
powders, Ni(NO3)2⅐6H2O solution of 1.0M (corresponding to
0.9–7.4 vol% NiO in the final coated powders) and polyacrylic
acid (1.0 wt% of PZT weight) as dispersant were mixed in a
polyethylene pot for 24 h using distilled water and ZrO2 balls as
the grinding medium. Then, NH4HCO3 solution of 1.0M was added
dropwise to the homogeneous slurry obtained above under vigorous
stirring. The reaction is shown in the following equation:14
I. Introduction
EAD zirconate titanate, Pb(ZrxTi1Ϫx)O3 (PZT), and related
ceramics are widely used in applications such as pressure
L
sensors, ultrasonic motors, and stack-type actuators because of
their excellent piezoelectric properties. However, their poor me-
chanical and electrical reliability are critical limitations on the
high-powered applications of these devices.1,2 Therefore, improv-
ing the mechanical properties and electrical reliability of PZT-
based materials has been intensely investigated in recent years.
Incorporating submicrometer- and nanosized second-phase (plati-
num, silver, MgO, and Al2O3) in the brittle PZT ceramic matrix
has been found to be a promising way to improve their mechanical
properties and electrical reliability.3–6 Because of the grain-size
reduction and the matrix grain boundaries reinforcement from
adding MgO nanoparticles, the fracture strength of a PZT/MgO
composite is 1.7 times higher than that of commercially available
PZT. The PZT/Al2O3 composite showed excellent electrical dura-
bility and fatigue resistance, owing to the microcrack pinned by
Al2O3 particles at the boundaries in the composites. For PZT
materials, NiO-like MgO and Al2O3 are known to belong to
acceptor additives and thus the PZT nanocomposite incorporating
NiO nanoparticles may obtain high mechanical properties and
excellent durability. The reinforcement mechanisms show the
importance of homogeneity and fine size of the second inclu-
sion.7,8 However, it is difficult to control the microstructure of a
PZT nanocomposite by conventional techniques involving the
mechanical mixing of ceramic powders and nanoparticles.
3Ni2ϩ ϩ 6HCO3Ϫ ϩ H2O ϭ
NiCO3⅐2Ni(OH)2⅐2H2O2ϩ 5CO21 (1)
To ensure completion of the reaction, an excess of NH4HCO3 was
added to the slurry and the pH value of the mixture was ϳ7–8.
Finally, the obtained precipitates were thoroughly washed with
distilled water and ethanol and dried at 60°C in an oven. The dried
precipitates were calcined at 400°C for 2 h in air. To investigate
the characteristic microstructure of the NiO nanoparticle-coated
PZT powders in more detail, the 7.4 vol% NiO-coated PZT
powders were selected to study.
The NiO content of coated powders was determined by induc-
tively coupled plasma atomic emission spectrometry (ICP-AES;
Varian Vista AX, Palo Alto, CA). The thermal decomposition
behavior of as-precipitated powders was analyzed by thermo-
gravimetry (TG) and differential scanning calorimetry (DSC) on
an automated thermal analyzer (Model STA 449C, Netzsch, Exton,
PA). DSC-TG analysis was conducted in air at a heating rate of
10°C/min from room temperature to 600°C. Transmission electron
microscopy (TEM) with energy dispersive spectroscope (EDS;
Model JEM-200CX, JEOL, Tokyo, Japan) was applied to inves-
tigate the microstructure of the coated powders. SAD pattern was
used to identify the crystalinity of the coated powders. For
powder-phase characterization, an XRD pattern was obtained
using automated diffractometry (Model RAX-10, Rigaku, Tokyo,
Japan) with CuK␣1 radiation.
In recent years, the coating process with nanoparticles has been
investigated for fabricating homogeneous ceramics. The process
improves not only the sintering activity and densification,9 but also
the different phase uniformity and mechanical properties of the
sintered body.10 Several methods are introduced to prepare the
coated powders, such as coprecipitation,11 sol–gel,12 and electro-
less plating.13 Coprecipitation is the most promising way, owing to
W.A. Schulze—contributing editor
III. Results and Discussion
DSC and TG curves of as-precipitated powders are shown in
Fig. 1. There are two major weight losses indicated in the TG
curve. The first major weight loss from room temperature to
Manuscript No. 186656. Received December 20, 2002; approved March 5, 2003.
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Vol. 86, No. 9
than that in the center field (Fig. 3(b)). The presence of carbon
is attributed primarily to the precipitates adhering to the surface
of PZT particles. This is a typical coated structure. The core is
a PZT particle and the coating layer is NiCO3⅐2Ni(OH)2⅐2H2O.
These
observations
suggest
that
the
nuclei
of
NiCO3⅐2Ni(OH)2⅐2H2O in the slurry grow on the surface of a
PZT core particle instead of forming discrete precipitates in the
presence of ultrafine PZT powders. The surface of PZT particle
serves as the heterogeneous nucleation site. The TEM image
and SAD pattern of the coated PZT powders calcined at 400°C
for 2 h are shown in Fig. 4. It is evident that the precipitates
decompose to nanoparticles in the coating layer with a thickness
of ϳ30 nm on the surface of PZT particle. The TEM image
(Fig. 4(b)) shows that the nanoparticles with an average size of
ϳ8 nm are spherical and weakly agglomerated.
The phase characterization of the coating layers on the
surface of PZT cannot be identified from the XRD analysis
patterns of the coated PZT powders before (Fig. 5(b)) and after
calcination (Fig. 5(c)). To verify the phase coating layers,
another sample was prepared using Ni(NO3)2⅐6H2O and
NH4HCO3 as starting materials by the same process without the
presence of PZT powders. The XRD analysis results (Figs. 5(d)
and 5(e)) indicate that the precipitate NiCO3⅐2Ni(OH)2⅐2H2O is
an amorphous phase that decomposes to NiO with cubic phase
after calcining at 400°C for 2 h. No new diffraction peaks
appear except for PZT in Fig. 5(b) because the coating layer is
amorphous phase. No obvious new diffraction peaks appear on
the XRD patterns of the calcined powders because the two
relatively strong peaks (111) and (200) of cubic NiO are
overlapped by the peaks (111) and (002) of tetragonal PZT,
respectively. Based on the XRD analysis, it can be concluded
that the amorphous coating layer on the surface of PZT particle
is crystallized to NiO with cubic phase after calcination. The
SAD pattern of the coated powders after calcination (Fig. 4(c))
further confirms this conclusion. There are two sets of diffrac-
tion patterns in NiO-coated PZT powders, the spots and the ring
patterns corresponding to PZT crystal and NiO polycrystal,
respectively. The diffraction ring patterns also reveal that the
nano-sized particles are NiO with cubic phase.
Fig. 1. DSC and TG curves of the as-precipitated PZT powders.
115°C is attributed to the desorption of physically absorbed
water and ethanol and the removal of crystalline water. This is
supported by an endothermic peak at 65°C on the DSC curve.
The temperature of endothermic peak is lower than the boiling
point of water, indicating that the elimination of crystalline
water of precipitate (NiCO3⅐2Ni(OH)2⅐2H2O) contributes more
to the weight loss. The other major weight loss from 240°–
320°C on the TG curve is due to decomposition of the
precipitate together with the removal of the organic compounds,
which coincides with the endothermic peak at 285°C. Accord-
ing to DSC-TG analysis, the calcination of as-precipitated
powder is conducted at 400°C for 2 h to ensure the complete
decomposition of the precipitate (NiCO3⅐2Ni(OH)2⅐2H2O).
Figure 2(a) shows the TEM image of uncoated PZT powders.
It can be seen that the PZT particles have relatively smooth and
dense surfaces. There are no other particle adhering to the
surface of PZT particles. A TEM image of coated PZT powders
obtained by precipitation is shown in Fig. 2(b). There is a
uniform coating on the surface of PZT particles in Fig. 2(b).
The EDS of the coated particles shows that the peak intensity
ratio of nickel to lead at the edge field (Fig. 3(a)) is much higher
Fig. 2. TEM images of (a) the uncoated PZT powders and (b) the coated (as-precipitated) PZT powders.

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Fig. 5. XRD patterns of (a) uncoated PZT powders, (b) coated (as-
precipitated) PZT powders, (c) coated PZT powders calcined at 400°C for
2 h, (d) precipitates without the presence of PZT, and (e) precipitates
without the presence of PZT calcined at 400°C for 2 h.
method. The surface of the PZT particle serves as the heteroge-
neous nucleation site and the nuclei of NiCO3⅐2Ni(OH)2⅐2H2O in
the slurry grow on the surface of particles instead of forming
discrete precipitates. The spherical NiO particles with the size of
ϳ8 nm are obtained by calcining the coated powders at 400°C for
2 h. The thickness of the coating layer of nanocrystalline NiO is
ϳ30 nm.
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