The Structure and the Electrical Properties of PbLa [Zr Ti (Mo ,In )]O Ferroelectric Ceramics
1200 0.95 0.05x(0.95–x)1/32/3 0.050.98753
and the phase coexistence with a composition is very
important because, first, they produce a great influence
on the characteristics of the PZT ceramics; and, second,
they stabilize the temperature and the time in the region
of the phase transition between the tetragonal and the
rhombohedral phases.
In this study,
Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3 piezoelec-
tric ceramics were investigated near the MPB by varying
the ratio of Zr/Ti. The purpose of this work was to study
the phase structure, the dielectric, and the piezoelectric
properties of these ceramics near the MPB in detail.
2. Experimental Procedure
The polycrystalline samples with a general composi-
tional formula Pb1–zLaz[ZrxTiy(Mo1/3,In2/3)1–(x+y)]1–z/4O3
with z = 0.05, (x + y)= 0.95 and 0.46 x 0.55 were
being prepared by a conventional dry ceramic method to
form the solid solution of a composition that follows:
Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3. The re-
agent grade oxide of PbO, ZrO2, TiO2, La2O3, MoO3 and
In2O3 were used as starting materials in a stoichiometric
ratio. The powders were, first, ball-milled for twelve
hours; and, then, calcined at 800˚C for two hours at the
following heating and cooling rates: 2˚C/min. After cal-
cination, the mixture was, first, ball-milled for twenty-
four hours; and then, dried and granulated with PVA as a
binder. After drying, the powders were pressed into discs
of a diameter of thirteen millimeters and of a thickness of
about one millimeter. The compacted discs were being
sintered at a temperature ranging from 1000˚C - 1180˚C
for two hours in air. To prevent PbO volatilization from
the pellets, a PbO atmosphere was controlled with a bed
of PbZrO3 powder placed in the vicinity of the pellets.
The X-ray diffraction (XRD, Simens D500) was used
to determine the crystalline phases present in the powder.
The compositions of PZT phases were identified by the
analysis of the peaks [(002)T, (200)R, (200)T] in the
twenty range 43˚ - 46˚. The Cu Kα radiation with a step
of 0.01˚ was used. The bulk densities of the sintered ce-
ramics were being measured by the Archimedes method.
The micrographs of the fractured samples were taken on
a JEOL scanning electron microscope. The average grain
size of the samples was determined from the micrographs
by the linear intercept technique. To investigate the elec-
trical properties, the electrodes were made by applying a
silver paste on the two major faces of the sintered disks
followed by a heat treatment at 750˚C for thirty minutes.
The dielectric constant was calculated from the capaci-
tance at a frequency of one kHz. It was measured at tem-
peratures ranging from 25˚C to 400˚C with a heating rate
of one ˚C/minute by using an impedance analyzer (HP
4192A, Hewlett-Packard). The piezoelectric samples were,
first, being poled in a silicone oil bath at 120˚C by apply-
ing a d.c. field of thirty kV/cm for thirty minutes; and,
then, were being cooled under the same electric field.
They were aged for twenty-four hours before testing.
The electromechanical coupling factor Kp, along with the
mechanical quality factor Qm were determined by the
resonance and anti-resonance technique from the equa-
tions [13]:
12
22
2
2.51
2
ar
p
a
ff
Kf
1
4
mar
QffRC
where:
fa: anti-resonant frequency (Hz)
fr: resonant frequency (Hz)
R: resonant resistance (ohms)
C: capacity (faraday)
3. Results and Discussion
The analysis of the phase was performed from the XRD
(at a room temperature) patterns over a range of 2θ = 43˚
to 46˚, where the tetragonal phase displays two peaks,
(002)T and (200)T, and the rhombohedral phase displays
one peak, (200)R. There was a broad region where the
two phases, the rhombohedral and the tetragonal, coex-
isted. This indicated a typical morpho-tropic phase be-
havior (MPB). The typical patterns of the X-ray diffrac-
tion of Pb0.95La0.05[ZrxTi(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3
compositions is shown in Figure 1. The samples ob-
tained in this study are summarized in Table 1. At
1150˚C, a typical tetragonal phase was observed at a
room temperature when xT 0.50. The (002)T and (200)T
peaks split into the (200)R peak as the ratio of Zr/Ti was
increased. The rhombohedral phase can be obtained
when xR 0.51. A transition from the tetragonal to the
rhombohedral phase was observed as the ratio of Zr/Ti
was increased. The Rhombohedral and the tetragonal
phases coexisted at x = 0.50 – 0.51, and demonstrated
that the ceramic resided at the morpho-tropic phase
boundary (MPB) [14]. The parameters of the lattice were,
then, determined from the triplets (200) by using a
non-linear least squares method [15]. The aR-parameter
of the rhombohedral phase and the aT-parameter, cT-pa-
rameter, and the tetragonality (cT/aT) of the tetragonal
phase of Pb0.95 La0.05[Zrx,Ti(0.95–x)(Mo1/3,In2/3)0.05]0.9875O3
ceramics are plotted as a function of the ratio of Zr/Ti in
Figure 2. The results showed that the parameters of the
lattice of the tetragonal phase changed when the ratio of
Zr/Ti was modified. While the value of the aT parameter
increased, the one of cT parameter decreased, and the aR
parameter of the rhombohedral phase increased along
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