Zuo-Guang. Ye Advanced Dielectric Piezoelectric and Ferroelectric Materials: Synthesis, Characterisation and Applications
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Handbook of dielectric, piezoelectric and ferroelectric materials140
as a function of temperature for the PYNT40 single crystals, which are
compared with PZNT and PMNT crystals, where k
ij
are the electromechanical
coupling factors and d
ij
are the piezoelectric coefficients, for longitudinal
mode (ij = 33), lateral mode (ij = 31) and shear mode (ij = 15) samples,
respectively. ∆k/k represents the variation of the electromechanical coupling
factor at high temperature when compared with room temperature value,
while ∆d/d gives the variation of the piezoelectric coefficients. It was observed
that the values remain nearly constant for all the single crystals until their
PYNT40
PZNT8
PZNT4.5
PMNT31
Temperture (°C)
(a)
Depoled
2402001601208040
–0.5
–0.4
–0.3
–0.2
–0.1
0.0
0.1
∆
k
33
/
k
33
PYNT40
PZNT8
PZNT4.5
PMNT31
Temperture (°C)
(b)
2402001601208040
–1
0
1
2
3
∆
d
33
/
d
33
5.10
Relative change of longitudinal electromechanical and
piezoelectric properties as a function of temperature for different
relaxor–PT systems.
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High-performance, high-T
C
piezoelectric crystals 141
T
R-T
temperature, which was around 160 °C for PYNT40, nearly double the
upper temperature usage limit compared to PMNT crystals. In addition, the
electromechanical and piezoelectric properties of PYNT crystals are comparable
to those of the PZNT and PMNT crystals.
5.5 High
T
C
bismuth-based perovskite single
crystals
Based on the above Sections 5.3 and 5.4, we can see that the A-site or B-site
modifications on the PMNT single crystals can only increase the T
C
and
PYNT40
PZNT8
PZNT4.5
PMNT31
Temperature (°C)
(a)
Depoled
1601208040
∆
k
31
/
k
31
–0.5
–0.4
–0.3
–0.2
–0.1
0.0
0.1
PYNT40
PZNT8
PZNT4.5
PMNT31
Temperature (°C)
(b)
Depoled
1601208040
∆
d
31
/
d
31
–1
0
1
2
3
4
5.11
Relative change of lateral electromechanical and piezoelectric
properties as a function of temperature for different relaxor–PT
systems.
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Handbook of dielectric, piezoelectric and ferroelectric materials142
T
R-T
modestly by 10–20 °C. Of significant potential are crystals near the
MPB composition in the PYNT system, with a T
C
> 330 °C, even though
T
R-T
was found to be only half that value at ~160 °C, the result of a strongly
curved MPB. The usage range of the lead based relaxor–PTs are still
significantly lower than that of PZT-based ceramics.
Recently, a new perovskite system (1–x)BiScO
3
–xPbTiO
3
(BSPT) with
MPB (x = 0.64) between the rhombohedral and tetragonal structures, was
found to possess a Curie temperature around ~450
°C (100 °C higher than the
PYNT40
PZNT8
PZNT4.5
PMNT31
Temperature (°C)
(b)
1601208040
–2
–1
0
1
2
3
4
5
∆
d
15
/
d
15
PYNT40
PZNT8
PZNT4.5
PMNT31
Temperature (°C)
(a)
1601208040
∆
k
15
/
k
15
–0.6
–0.5
–0.4
–0.3
–0.2
–0.1
0.0
0.1
5.12
Relative change of shear electromechanical and piezoelectric
properties as a function of temperature for different relaxor–PT
systems.
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High-performance, high-T
C
piezoelectric crystals 143
commercial PZT5A materials) with comparable piezoelectric properties
(~460 pC/N) in polycrystalline ceramics.
76,82,83
Single crystals of BSPT were
grown and the addition of BaTiO
3
was used to aid in stabilizing the perovskite
phase. The characterization of the BSPT single crystals with different PT
content has been reported.
40–47
Figure 5.13 shows the dielectric permittivity as a function of temperature
for rhombohedral BSPT57 and tetragonal BSPT66 crystals. Two dielectric
anomalies were observed in the curves of the BSPT57 crystals, revealing a
T
R-T
of 349 °C and a T
C
of 402 °C,
46
both much higher than the lead based
relaxor–PT systems. For tetragonal BSPT66 crystals, however, only one
peak at 436
°C was found and believed to be associated with the T
C
.
44
This
T
C
was found to be more than 20 °C lower when compared with the reported
values for the tetragonal crystals
43
and ceramics,
82
due to the BaTiO
3
additive.
It was observed from Fig. 5.13 that the BSPT crystals exhibit a very flat
dielectric constant curve in the temperature range from room temperature to
300
°C.
The temperature dependence of the piezoelectric and electromechanical
properties of the rhombohedral BSPT57 and tetragonal BSPT66 crystals for
longitudinal mode are shown in Fig. 5.14(a) and (b), respectively. It was
found that the k
33
value for the BSPT57 crystal was 90% at room temperature
and kept constant to 330
°C, close to its T
R-T
. The piezoelectric coefficient
Temperature (°C)
500400300200100
20000
10000
0
30000
20000
10000
0
Dielectric permittivity
BSPT rhombohedral crystal
T
c
= 402°C
T
R–T
= 349°C
BSPT tetragonal crystal
T
c
= 436°C
5.13
Dielectric properties as a function of temperature for BSPT57
rhombohedral crystals and BSPT66 tetragonal crystals, measured at
1, 10 and 100kHz frequencies, respectively.
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Handbook of dielectric, piezoelectric and ferroelectric materials144
was about 1150 pC/N at room temperature, gradually increasing to 2050 pC/
N at 330 °C before dropping to 1800 pC/N at 340 °C because of the T
R-T
phase transformation.
46
The k
33
value for the tetragonal BSPT66 crystals
was found to be 88% at room temperature, decreasing slightly to 84% at
400
°C, decreasing due to depoling when the temperature approached its
Curie temperature. The d
33
value increased from 450 pC/N at room temperature
to 1300
pC/N at 400 °C, showing a similar tendency as observed in the
rhombohedral BSPT crystals.
44
Temperature (°C)
(a)
350300250200150100500
2400
2200
2000
1800
1600
1400
1200
1000
Piezoelectric coefficient
d
33
(pC/N)
Electromechanical coupling factor
k
33
0.9
0.8
0.7
0.6
0.5
Temperature (°C)
(b)
4003002001000
Piezoelectric coefficient
d
33
(pC/N)
2000
1600
1200
800
400
Electrochemical coupling factor
k
33
0.9
0.8
0.7
0.6
0.5
5.14
Electromechanical and piezoelectric properties as a function of
temperature for rhombohedral (a, after ref. 46) and tetragonal (b,
after ref. 44) BSPT crystals.
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High-performance, high-T
C
piezoelectric crystals 145
Table 5.2 summarizes the detailed dielectric and piezoelectric properties
of different single crystal systems, in which one can see that the BSPT
system possesses both higher T
C
and T
R-T
temperatures when compared with
other relaxor–PT systems. Figure 5.15 presents the coercive fields as a function
of Curie temperature, in which it is found the coercive field increases linearly
with increasing T
C
, indicating systems with higher Curie temperature possess
the potential higher acoustic of power (higher coercive field). Figure 5.16
shows the overall temperature usage range for the various relaxor–PT systems,
including PZNT, PMNT, PSNT, PINT and PYNT, compared with BSPT
system. As shown, the strongly curved MPB limits the temperature usage
range of these systems far less than T
C
. Of particular promising are crystals
in the bismuth-based BSPT system, with T
C
in the order of 450 °C and
T
R-T
of 350 °C.
In order to carry on the theoretical and practical studies of the BSPT
system, it is necessary to know the full set of material constants of the
crystals. The material constants of the rhombohedral BSPT57
42
and tetragonal
BSPT66 crystals
44
are compared with PZNT
44,84
and PMNT33
85
systems
and given in Tables 5.3 and 5.4.
5.6 Non-perovskite piezoelectric single crystals
Quartz is one of the earliest piezoelectric materials used in electronic devices
and can be grown by hydrothermal technique. The dielectric constant and
piezoelectric coefficient were found to be 4.5 and 2 pC/N, respectively.
Although piezoelectric α-quartz has a transition temperature of 573 °C, its
usage temperature is normally limited to 350 ° C, above which the crystal
structure is subject to twinning, destroying its piezoelectric properties. Lithium
niobate (LiNbO
3
-LN) can be grown from the melt directly using the Czochralski
pulling method. It was reported to possess a Curie temperature of 1150 °C,
with a dielectric constant and a piezoelectric coefficient of about 25 and
6 pC/N, respectively.
86
One of the advantages of LN crystals compared with
the perovskite systems is the large piezoelectric voltage coefficient, due to
the inherently low dielectric constant (for example, g
15
= 91×10
–3
V m/N,
three or four times higher when compared with most with the perovskite
single crystals). The application temperature range for the LN crystals is
limited to 650 °C due to its low resistivity.
86
Langasite (La
3
Ga
5
SiO
14
, LGS) crystals and its isomorphs (such as langanite
and langatite, to name a few) can be grown using the Czochralski method
87,88
and have been actively investigated because of high-temperature bulk acoustic
wave (BAW) and surface acoustic wave (SAW) applications.
89
Langasite
family crystals do not undergo any phase transformations up to their melting
temperatures around 1470 °C, which makes the usage temperature range
much broader. The dielectric constants and piezoelectric coefficients are
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Handbook of dielectric, piezoelectric and ferroelectric materials146
Table 5.2
Detailed dielectric and piezoelectric properties of various single crystals
Crystal
T
C
(° C)
T
R-T
(°C)
E
c
(kV/cm)
ε
ε
33
T
0
d
33
(pC/N)
k
33
(%)
d
31
(pC/N)
k
31
(%) Ref.
PMNT31 143 90 2.5 5100 2000 90 –750 80 37
PMNT31-A 138 110 2.2 3600 1400 89 / / /
PMNT31-B 150 110 3.1 4800 1500 90 / / 10
PZNT4.5 155 120 3.2 4400 2100 90–91 –900 83 37
PZNT8 170 100 4 6000 2500 93 –1300 89 37
PZNT12 190 / 8.5 870 576 86 –217 52 44
PSNT33 206 / 6 960 / 72 / / 11
PINT28 260 100 18 1500 700 85 / / 17–19
PINT34 200 <100 / 5000 2000 94 / / 22
PIMNT 191 55 7 3630 1950 ~88 / / 24
PYNT40 270 168 10 2700 1200 88 –500 76 37
PYNT45 325 160 12.5 2000 2000 88–90 –550 78 38
BSPT57 402 349 13.7 3000 1200 90 –560 77 42,46
BSPT58 410 357 23.5 3200 1400 91 –670 80 41
BSPT66 436 / 28 820 440 88 –162 52 44
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High-performance, high-T
C
piezoelectric crystals 147
found to be in the range of 18~25 and 5~8 pC/N, respectively.
90–92
Gallium
orthophosphate (GaPO
4
) crystal was firstly studied in France,
93
after which,
the application of GaPO
4
as a piezoelectric crystal was investigated. The
crystals can be grown using hydrothermal technique and presently are produced
commercially in autoclaves. It was reported to possess a high d
11
value of
4.5 pC/N and a low dielectric constant of ~6. Compared with quartz crystals,
Curie temperature (°C)
450400350300250200150100
Coercive field (kV/cm)
30
24
18
12
6
0
T
Rhom-Tet
T
Cubic
Relaxor–PT MPB system
BSPTPYNTPINTPSNTPZNTPMNT
Temperature (°C)
400
300
200
100
0
5.16
Temperature usage range of various single crystal piezoelectrics
(after ref. 45).
5.15
Coercive field as a function of Curie temperature for various
relaxor–PT single crystals.
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Handbook of dielectric, piezoelectric and ferroelectric materials148
Table 5.3
Measured and derived elastic compliance constants
s
ij
(10–12 m
2
/N) and elastic stiffness constants
c
ij
(1010 N/m
2
) for the
rhombohedral BSPT57 and tetragonal BSPT66 crystals, compared with PZNT and PMNT33 single crystals
Crystal
s
11
E
s
12
E
s
13
E
s
33
E
s
66
E
s
11
D
s
12
D
s
13
D
s
33
D
s
66
D
BSPT57 38.0 –12.2 –25.4 60.0 24.4 27.9 –22.3 –2.9 10.2 24.4
BSPT66 13.5 –2.7 –11.3 34.0 21.0 9.8 –6.3 –1.5 7.3 21.0
PZNT4.5 82.0 –28.5 –51.0 108.0 15.9 61.5 –49.0 –9.0 20.6 15.9
PZNT8 87.0 –13.1 –70.0 141.0 15.4 55.8 –44.2 –8.2 18.5 15.4
PZNT12 22.4 –3.5 –21.0 58.0 27.9 16.3 –9.7 –4.8 14.9 27.9
PMNT33 69.0 –11.1 –55.7 119.6 15.2 44.0 –34.0 –4.1 11.1 15.2
Crystal
c
11
E
c
12
E
c
13
E
c
33
E
c
66
E
c
11
D
c
12
D
c
13
D
c
33
D
c
66
D
BSPT57 12.6 10.6 9.9 10.0 4.1 15.4 11.6 8.9 12.5 4.1
BSPT66 18.6 12.4 10.3 9.8 4.8 20.2 14.0 7.1 16.6 4.8
PZNT4.5 11.1 10.2 10.1 10.5 6.3 11.3 10.4 9.5 13.5 6.3
PZNT8 11.5 10.5 10.9 11.5 6.5 11.8 10.8 10.0 14.3 6.5
PZNT12 15.2 11.4 9.7 8.7 3.6 15.4 11.6 8.9 12.5 3.6
PMNT33 11.5 10.3 10.2 10.3 6.6 11.7 10.5 9.0 17.4 6.6
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High-performance, high-T
C
piezoelectric crystals 149
Table 5.4
Piezoelectric coefficients, d
ij
(pC/N), e
ij
(C/m
2
), g
ij
(10
–3
Vm/N) and
h
ij
(10
8
V/m), electromechanical coupling factors k and dielectric constants ε (ε
0
) for
the rhombohedral BSPT57 and tetragonal BSPT66 crystals, compared to PZNT and
PMNT33 crystals.
Crystal
T
C
(°C)
E
C
ε
33
T
ε
33
S
k
33
k
31
k
31
k
t
(kV/cm) (45°)
BSPT57 402 13 3000 460 0.91 0.52 0.73 0.56
BSPT66 436 28 820 160 0.88 0.52 0.60 0.64
PZNT4.5 155 3.2 5200 1000 0.91 0.50 0.83 0.50
PZNT8 170 4 7700 984 0.94 0.60 0.89 0.45
PZNT12 190 8.5 870 220 0.86 0.52 0.58 0.55
PMNT33 160 2 8200 680 0.94 0.59 / 0.50
Crystal
d
33
d
31
e
33
e
31
g
33
g
31
h
33
h
31
BSPT57 1150 –520 13.6 –6.6 43.3 –19.5 33.4 –16.2
BSPT66 440 –162 9.8 –4.7 60.6 –22.3 69.7 –33.3
PZNT4.5 2000 –970 15.0 –3.7 44.0 –21.0 17.0 –4.3
PZNT8 2890 –1455 15.4 –5.1 42.4 –21.3 17.7 –5.8
PZNT12 576 –217 8.6 –1.9 74.9 –28.2 44.1 –9.6
PMNT33 2820 –1330 20.3 –3.9 38.8 –18.4 33.7 –5.9
GaPO
4
possesses nearly all the advantages of quartz, but also possess higher
electromechanical coupling and has thermally stable physical properties up
to 950 °C, at which temperature an irreversible transformation into a cristobalite-
like phase occurs.
94–98
Oxyborate crystals ReCa
4
O(BO
3
)
3
(Re = rare earth elements), including
GdCOB, YCOB and LaCOB, can be grown from the melt by using the
Czochralski method. This family of crystals was extensively studied for non-
linear optical or laser applications due to its large transparency range, reasonable
non-linear optical coefficient and high damage threshold.
99
The dielectric
constants and piezoelectric coefficients were reported to be in the range of
10–15 and 2–9 pC/N, while the electromechanical coupling factor is in the
range of 10–17%.
100–105
As observed in the langasite family of crystals, no
phase transformation was found to occur prior to its melting temperature
~1500 °C, making the oxyborate crystals promising materials for ultra-high-
temperature applications.
5.7 Summary
The applications of commercially available PMNT piezoelectric single crystals
may be limited by their strongly curved MPB, so it is desirable to obtain
crystals with a broader temperature usage range. This chapter introduced
various types of high-temperature piezoelectric crystals, with an emphasis
on the perovskite ferroelectric systems.
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