Zuo-Guang. Ye Advanced Dielectric Piezoelectric and Ferroelectric Materials: Synthesis, Characterisation and Applications
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Handbook of dielectric, piezoelectric and ferroelectric materials210
d
33
= 505 pC/N. The obtained electrical properties are excellent for high T
C
piezoelectric materials. The high d
33
values and reasonable T
C
of PIMNT
ceramic materials make them good candidates to replace conventional PZT
ceramics in various piezoelectric applications. Tables 8.2 and 8.3 summarize
all the electrical properties of the PIMNT ceramics along and across the
MPB.
Intensity (arb. units)Intensity (arb. units)
2θ (degree)
20 40 60 80
2θ (degree)
20 40 60 80
PIMNT24/42/34
PIMNT23/41/36
PIMNT23.5/41.5/35
PIMNT24.5/42.5/33
PIMNT25/43/32
PIMNT0/68/32
PIMNT8/59/33
PIMNT16/51/33
PIMNT24/42/34
PIMNT32/33.5/34.5
PIMNT40/25/35
PIMNT48/16/36
PIMNT56/8/36
PIMNT63/0/37
8.3
X-ray diffraction of the PIN–PMN–PT ternary ceramics system
near the MPB.
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High Curie temperature piezoelectric single crystals 211
The ceramic samples across the MPB were used to confirm that the line
connecting the MPBs of PIMNT 0/68/32 and PIMNT 63/0/37 is the MPB of
the PIMNT ternary system. The peak post-poling dielectric constant at room
temperature reached 3890 at PIMNT 23/41/36. This compound had a low
coupling factor, k
p
= 60.5%, and was slightly tetragonal phase. On the other
hand, compositions on the rhombohedral side had high coupling factors, k
p
> 65%, but low dielectric constants,
εε
33
T
0
/
< 2000. PIMNT 24/42/34 (on
the line connecting the MPBs of PIMNT 0/68/32 and PIMNT 63/0/37) showed
the highest coupling factor and a moderate dielectric constant as mentioned
above. Therefore, the MPB of the PIMNT ternary system is an almost linear,
narrow region between the MPBs of PIMNT 0/68/32 and PIMNT 63/0/37.
Temperature (°C)
0 100 200 300 400
Dielectric constant, ε
r
50 000
40 000
30 000
20 000
10 000
PIMNT0/68/32
PIMNT8/59/33
PIMNT16/51/33
PIMNT24/42/34
PIMNT32/33.5/34.5
PIMNT40/25/35
PIMNT48/16/36
PIMNT56/8/36
PIMNT63/0/37
8.4
Dielectric constant as a function of temperature measured at
f
=
1.0 kHz of the PIN–PMN–PT ternary ceramics system near the MPB.
PIN (mol%)
6040200
300
250
200
150
Curie temperature (°C)
8.5
Curie temperature
T
c
of
the PIN–PMN–PT ceramics ternary system
near the MPB.
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Handbook of dielectric, piezoelectric and ferroelectric materials212
The PIMNT material system has a more stable perovskite structure than
PZNT or PMNT ceramics. The raw-material cost of In
2
O
3
is lower than that
of the Sc
2
O
3
which is used for PSNT. The PIMNT materials have reasonably
high k
p
and d
33
. A high T
C
ranging from 180 to 240 °C is also attractive
compared with that of PZNT 91/9 (T
C
= 175 °C) or PMNT 70/30 (T
C
=
145 °C). The material system may have a high coercive field E
c
, which is
closely related to T
C
. PIMNT materials are suitable for use in high-T
C
PSC
applications if crystals of high quality and reasonable size are obtained.
8.3 PIMNT single crystals grown by the flux
method
In this section, PIMNT piezoelectric single crystals (PSCs) grown by the
conventional flux method and their dielectric and piezoelectric properties
are presented. An excellent electromechanical coupling factor, k
p
= 67%, a
relatively high Curie temperature, T
C
= 197 °C, and good perovskite stability
of the PIMNT 16/51/33 and PIMNT 24/42/34 ceramics near the MPB have
been confirmed. Therefore, PIMNT ternary PSCs with MPB compositions
are expected to have excellent piezoelectric properties, as well as a high T
C
(> 200 °C). However, to date there have been no reports on the synthesis of
ternary PSCs that consist of six elements, Pb, In, Mg, Nb, Ti and O. The
purpose of this work is to investigate the possibility of growing PIMNT
ternary PSCswith good enough quality and size near the MPB and to
characterize their properties.
High-purity chemicals (higher than 99.9%), PbO, In
2
O
3
, MgO, Nb
2
O
5
and TiO
2
(Kojundo Chemical Lab. Co., Ltd, Saitama, Japan), were used as
PIN (mol%)
6040200
70
65
60
55
Electromechanical coupling factor
k
p
(%)
8.6
Electromechanical coupling factor planar mode
k
p
of the PIN–
PMN–PT ternary ceramics system near the MPB.
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High Curie temperature piezoelectric single crystals 213
Table 8.2
Dielectric and piezoelectric properties of PIMNT 100
x
/100
y
/100
z
ceramics along the MPB
Sample # Composition
T
C
(°C)
ε
r
/
ε
0
εε
33
T
0
/
ε
max
k
p
(%)
d
33
(pC/N)
1 PIMNT0/68/32 160 1830 2320 47 480 63.8 510
2 PIMNT8/59/33 181 1800 2230 37 880 63.4 500
3 PIMNT16/51/33 197 2080 2400 40 460 67.1 510
4 PIMNT24/42/34 219 2010 2120 34 430 67.6 505
5 PIMNT32/33.5/34.5 239 2140 2160 36 520 66.7 495
6 PIMNT40/25/35 258 1840 2130 21 000 61.4 430
7 PIMNT48/16/36 279 1840 2120 20 890 60.3 430
8 PIMNT56/8/36 300 1870 2440 23 110 60.5 440
9 PIMNT63/0/37 320 1800 2450 24 190 57.7 435
Table 8.3
Dielectric and piezoelectric properties of PIMNT ceramics across the MPB
Sample # Composition
T
C
(°C) ε
r
/
ε
0
εε
33
T
0
/
ε
max
k
p
(%)
d
33
(pC/N)
10 PIMNT 23/41/36 231 2630 3890 32 860 60.5 550
11 PIMNT 23.5/41.5/35 223 2670 2560 35 710 62.1 515
4 PIMNT 24/42/34 219 2010 2120 34 430 67.6 505
12 PIMNT 24.5/42.5/33 211 1740 1910 35 250 65.3 465
13 PIMNT 25/43/32 213 1660 1850 35 720 66.8 465
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Handbook of dielectric, piezoelectric and ferroelectric materials214
starting materials. A flux composition of 80 mol% PbO–20 mol% B
2
O
3
was
selected for PSC synthesis. The flux and the precalcined PIMNT powder
were lightly mixed in a plastic bag without any solvent. The selected ratio
was 50 PIMNT 16/51/33 : 40 PbO : 10 B
2
O
3
(mol%). The mixture (100 g)
was placed in a 20 cm
3
platinum crucible with a lid after twice premelting at
1000 °C for 1 h. The Pt crucible was placed in 100 cm
3
and 300 cm
3
Al
2
O
3
double crucibles with lids to prevent the evaporation of lead oxide and
possible damage to the furnace. The crucible was placed in a computer-
controlled electric furnace. The temperature was increased to 1230 °C and
maintained for 5 h before being slowly reduced to 850 °C at 1.2 °C/h. After
cooling to room temperature at a rate of 100 °C/h, the crucibles were weighed
to determine the weight loss of the contents during heat treatment. After the
crystal growth, the contents were rinsed in boiling 50% acetic acid for 24 h
to separate the PSCs from the residual flux. The PbO–B
2
O
3
flux caused
negligible damage to the Pt crucible and the weight losses due to PbO
evaporation were less than 1.4% for the temperature profile described above.
Crystals in the crucibles were visible to the naked eye.
Figure 8.7 shows the top view of the PIMNT crystal obtained by the flux
method. This large yellowish brown crystal was obtained at the top of the
contents. The crystal structure was studied by X-ray diffraction (XRD) after
pulverizing some of the crystals. The grown crystals showed a single phase
perovskite structure. PIMNT wafers with (001) faces were sliced from the
crystals. The wafers have no serious inclusions, but consist of transparent
and opaque areas. A rectangular plate (9 mm × 7 mm × 0.4 mm) was used for
electrical measurements. Au/Cr electrodes were sputtered on both sides of
the test specimen. The specimen was poled by applying an electrical field of
10 mm
8.7
The PIMNT 16/51/33 PSC near the MPB composition prepared by
the flux method.
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High Curie temperature piezoelectric single crystals 215
1 kV/mm for 10 min at room temperature. The electrical capacitance and
dielectric loss were measured at 1 kHz using a computer-controlled impedance
analyzer (HP4192A). The temperature dependence of dielectric properties
was measured at 1 kHz using the same measurement system in a temperature
range of 30 to 220 °C. The piezoelectric constant, d
33
, was measured using
a d
33
meter (Institute of Acoustics Academia Sinica, Model ZJ-3D).
Figure 8.8 shows the dielectric properties of one of the PIMNT PSCs with
a maximum dielectric constant at 187 °C, indicating a T
C
that is about 40 °C
higher than that of the PMNT 68/32 PSC. The broad peak of the dielectric
constant at around T
C
is due to the scatter of the T
C
resulting from the
compositional variation in the crystal. A small peak of the dielectric constant
is observed near 50 °C, which is considered to be the phase-transition
temperature, T
RT
, from the rhombohedral to the tetragonal phase. This indicates
that the PSC is in the rhombohedral phase at room temperature. This result
agrees with the XRD pattern without split peaks. The T
RT
of the obtained
crystal was slightly lower than expected from the same ceramics value. In
order to increase the T
RT
, the composition should be shifted slightly towards
that of the rhombohedral phase by reducing the Ti content or increasing the
Pb(In
1/2
Nb
1/2
)O
3
content. The room-temperature dielectric constant,
εε
33
T
0
/
,
and dielectric loss factor after poling were 3100 and 0.8%, respectively. The
piezoelectric constant, d
33
= 2200 pC/N, is extremely large and the value
is comparable to those of the PZNT 91/9 and PMNT 70/30 PSCs. The d
33
value of PINT 72/28 PSC with a high Curie temperature, T
C
> 250 °C, is
700 pC/N. Therefore, the d
33
value of the PIMNT crystal is one of the highest
values reported so far for any piezoelectric material with a T
C
> 185 °C.
In conclusion, PIMNT 16/51/33 PSCs of high quality were synthesized
by the flux method. The crystals show a large piezoelectric constant, d
33
=
2200 pC/N, with T
C
= 187 °C (Hosono et al., 2002b).
Temperature (°C)
250200150100500
10
8
6
4
2
0
Dissipation factor (%)
Dielectric constant ε
r
40000
35000
30000
25000
20000
15000
10000
5000
0
Dissipation factor
Dielectric constant
8.8
Dielectric constant and dissipation factor of the PIMNT 16/51/33
PSC near the MPB composition prepared by the flux method.
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Handbook of dielectric, piezoelectric and ferroelectric materials216
8.4 PIMNT and PSMNT single crystals grown by
the Bridgman method
In this section, PIMNT and Pb(In
1/2
Nb
1/2
)O
3
–Pb(Mg
1/3
Nb
2/3
)O
3
PbTiO
3
(PSMNT) piezoelectric single crystals (PSCs) grown by the Bridgman method,
and the dielectric and piezoelectric properties of these crystals are discussed.
As mentioned above, the present authors investigated the ceramics and PSCs
of the PIMNT ternary system and reported that the PIMNT PSCs showed the
highest piezoelectric constant among piezoelectric materials with a Curie
temperature of higher than 185 °C (Hosono et al., 2003a,b,c). Moreover,
we reported that PSMNT ceramics, a ternary system similar to PIMNT,
exhibited a large coupling factor, k
p
= 70%, and piezoelectric constant, d
33
=
680 pC/N, with a high Curie temperature, T
C
= 207 °C, which is slightly
superior to those of PIMNT ceramics (Yamashita and Shimanuki, 1996).
Therefore, PSMNT PSCs are also expected to show excellent piezoelectric
properties if high-quality crystals are obtained. However, the crystal growth
of PSMNT ternary system is very difficult because of the high melting point
of Pb(Sc
1/2
Nb
1/2
)O
3
(1420 °C) (Yamashita and Shimanuki, 1996).
The purpose of this work was to grow large and high-quality PIMNT and
PSMNT PSCs using the solution Bridgman method and to investigate the
compositional variation of the obtained crystals in order to select a promising
candidate piezoelectric material with high T
RT
and T
C
. Moreover, the electrical
properties of PIMNT PSCs grown by the Bridgman method are reported and
compared with those of PZNT and PMNT binary PSCs.
High-purity chemicals (better than 99.9%), PbO, In
2
O
3
, Sc
2
O
3
, MgO,
Nb
2
O
5
and TiO
2
(Kojundo Chemical Lab. Co., Ltd, Japan) were used as
starting materials. PIMNT 16/51/33 and PSMNT 16/49/35 were selected as
crystal compositions, which are on the MPB lines. In order to compare
crystal growth, similar compositions were used. After wet-mixing the raw
materials using a plastic ball mill with 5 mm diameter ZrO
2
balls for 24 h,
the slurry was dried in an oven. Calcining was performed at 850 °C for 2 h.
The precalcined PIMNT (PSMNT) powders and flux were lightly mixed in
a plastic bag without any solvent. The flux used for the crystal growth was
PbO–B
2
O
3
. The ratio selected was 50 PIMNT (PSMNT) : 40 PbO : 10 B
2
O
3
(mol%). A mixture weighing 245 g was placed in a 25 mm diameter, 150 mm
long, 0.35 mm thick Pt crucible after one premelt at 1000 °C. The Pt crucible
was driven down through the hot zone at a speed of 0.4 mm/h after maintaining
it at 1250 °C for 5 h. After the crystal growth, the crucibles were weighed to
determine the weight loss of the contents during the heat treatment. The Pt
crucibles were stripped off using a pair of nippers to observe the features of
the solidified contents.
The Pt crucible suffered negligible damage and the weight losses due to
PbO evaporation were less than 2% for the temperature profile described
WPNL2204
High Curie temperature piezoelectric single crystals 217
above. The PbO–B
2
O
3
flux is very effective for preventing evaporation of
PbO. A large PIMNT PSC was found on the bottom of the crucible and many
small crystals were observed on the sides of the crucible. The features of the
solidified content are very similar to those of the PZNT system. On the other
hand, the solidified content of PSMNT boule differed considerably from that
of PIMNT. It had an opaque yellow area of ceramic-like material at the
bottom side and many crystals of medium size over the opaque area. Although
the crucible was kept in the highest temperature zone for 5 h before starting
the cooling, the raw materials at the bottom of the crucible did not melt
sufficiently. The holding time should be longer in order to melt the raw
materials into the flux completely. The XRD patterns of two parts of the
solidified contents were investigated; the opaque area mainly consists of a
perovskite structure but with a small portion of pyrochlore. The crystalline
area consists of a single perovskite phase.
The solidified content of PIMNT was rinsed in boiling 80% acetic acid
for 12 h to separate the PSC from the residual flux. The crystal was 25 mm
in diameter and 30 mm in length, and its weight was 109.1 g, which is equal
to approximately 44.4% of the raw materials. The morphology of the crystal
indicates that a single nucleation event occurred on the bottom of the crucible
and the crystal grew in the [111] direction. The crystal obtained was sliced
along the (001) plane after its orientation was determined from Laue X-ray
diffraction patterns. Nineteen wafers 0.5 mm in thickness were obtained and
lapped to about 0.36 mm in thickness. The PIMNT wafers were numbered in
ascending order from the part of the crystal grown near the crucible bottom
(the initial part). Figure 8.9 shows one of the wafers obtained from PIMNT
PSC prepared by the Bridgman process. Some wafers cut from the bottom
10 mm
1
402
3
8.9
The PIMNT 16/51/33 PSC wafer near the MPB composition
prepared by the solution Bridgman method and EPMA measurement
points.
WPNL2204
Handbook of dielectric, piezoelectric and ferroelectric materials218
side contained some inclusions. The quality of the wafers improves from the
initial part to the end of the crystal. Six wafers were selected from the initial
(Nos. 1 and 2), middle (Nos. 8 and 9) and end parts (Nos. 18 and 19) for
evaluation of the compositional variations and electrical properties.
The compositional variation of the PIMNT wafers was evaluated using an
electron probe microanalyzer (EPMA, Shimadzu Corp., Model V6). Five
measurement points in the form of a cross were set as shown in Fig. 8.9. The
distance between neighboring points was 8 mm. Three wafers were selected
from the initial (No. 2), middle (No. 9) and end (No. 19) of the PIMNT PSC
for the compositional analysis. Table 8.4 lists the average of five points for
the EPMA results and the theoretical values of the starting material: PIMNT
16/51/33. Figure 8.10 shows the EPMA results among the three wafers. The
Ti content increased gradually from the initial part to the end part. Luo et al.
(2000) reported the same behavior for PMNT PSCs. On the other hand, the
In/Mg ratios of the three wafers were almost the same as the theoretical
value. The PIMNT ternary system consists of four elements for the B-site
(In, Mg, Nb and Ti) in the perovskite structure. Those elements have
combinations such as (In
1/2
Nb
1/2
)
4+
, (Mg
1/3
Nb
2/3
)
4+
and Ti
4+
in the crystal in
Table 8.4
EPMA results of three wafers cut from the PIMNT 16/51/33 PSC
Wafer number PbO In
2
O
3
MgO Nb
2
O
5
TiO
2
(wt%) (wt%) (wt%) (wt%) (wt%)
2 (initial) 70.21 3.17 1.93 17.42 7.51
9 (middle) 69.59 3.23 2.37 17.65 7.76
19 (end) 69.39 3.16 2.14 17.54 8.81
Theoretical value 69.03 3.43 2.12 17.26 8.15
of PIMNT 16/51/33
Wafer number
20151050
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
Element content (wt%)
Theoretical value
MgO
In
2
O
3
TiO
3
8.10
EPMA result of the PIMNT 16/51/33 PSC wafers near the MPB
composition prepared by the solution Bridgman method.
WPNL2204
High Curie temperature piezoelectric single crystals 219
order to compensate for the charges. If the In/Mg ratio differs considerably
in the crystal, obtaining a homogeneous crystal is very difficult. However,
the In/Mg ratio is relatively constant in the PIMNT crystal. This is the key
to obtaining a homogeneous PSC in the ternary system. Moreover, some
wafers had yellowish brown and black areas. In the black area, the Pb content
was slightly higher than that in the yellowish brown area.
The solidified content of PSMNT was cut lengthwise to evaluate the
compositional variation because the crystals were multinucleated. The crystal
structure was studied by X-ray diffraction after pulverizing some parts of the
solidified content. Compositional variation of the PSMNT crystals was
evaluated using an (EPMA, Shimadzu Corp., Model V6). The surface of the
solid was lapped to a mirror finish for the measurement. Nine measurement
points, which were designated by the irradiating spots, were set; five points
(Nos. 3 to 7) are on the crystal. The distance between neighboring points was
5 mm.
The measured Pb contents were slightly higher than the theoretical values.
The reason is an excess flux (PbO) inclusion within the crystal measurement
area. Although the Sc content gradually decreased from the top to the
bottom portion, the Mg content increased. Therefore, the Sc/Mg ratio changed
considerably in the same crystal. Moreover, similar to the case of the PMNT
and PIMNT PSCs, the Ti content increased from the bottom to the top of the
crystals in the solidified content. Because of the large compositional variations
for Sc, Mg and Ti, it is very difficult to obtain a homogeneous crystal by the
conventional Bridgman process. These results of crystal growth and
compositional analysis suggest that the PIMNT PSC system offers an advantage
in terms of crystal growth in that it is easier to grow than the PSMNT PSC.
Rectangular plates cut from three PIMNT wafers (Nos. 1, 8 and 18) were
used for electrical measurements. Au/Cr electrodes were sputtered on both
sides of the test specimen. The dielectric constants and dielectric losses
before and after poling were measured at 1 kHz using an impedance analyzer
(HP4192A). Sliver transducer for coupling factor,
′
k
33
, measurement was
obtained by dicing with a dicing saw (DISCO, Model DAD-2H/6T). The
dicing pitch and wheel thickness were 0.22 mm and 0.05 mm, respectively.
The sliver transducers were poled after dicing by applying an electric field
of 1 kV/mm at room temperature. The coupling factors
′
k
33
were calculated
using equation (8.1) after measuring the impedance curve using a network
spectrum analyzer (HP4195A):
kk
f
f
ff
f
t
33
s
p
ps
p
, =
2
tan
2
( + )
′
⋅⋅
ππ
(8.1)
where f
p
is the parallel resonance frequency and f
s
is the series resonance
frequency.
WPNL2204