Zuo-Guang. Ye Advanced Dielectric Piezoelectric and Ferroelectric Materials: Synthesis, Characterisation and Applications

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Handbook of dielectric, piezoelectric and ferroelectric materials200

7.22

Domain structure of the (001)

cub

-oriented (1–

)Pb(Sc

1/2

−

PbTiO

crystals, which show the different dielectric maximums:

(a)

max

= 210 °C (estimated to be

≈ 0.26) and (b)

max

= 243 °C

(estimated to be

≈ 0.36), observed at room temperature under

cross polarized light microscopy.

(b)

(a)

100 µm

10 µm

80°

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Piezo- and ferroelectric (1–

)Pb(Sc

1/2

–

PbTiO

201

7.5 Concluding remarks and future trends

In this chapter we present the revised MPB phase diagram of the (1–x)Pb

(Sc

1/2

–xPbTiO

[(1–x)PSN–xPT] solid solution system, and describe

the optimized growth process and the characterization of the (1–x)PSN–xPT

single crystals with composition in the morphotropic phase boundary (MPB)

region.

The solid solution of (1–x)PSN–xPT with compositions within the MPB

region (0.35 ≤ x ≤ 0.50) has been synthesized in the pure perovskite phase by

an improved two-step wolframite precursor method. The MPB phase diagram

of the solid solution system has been established by means of dielectric

measurements, differential scanning calorimetry (DSC) and X-ray structural

analysis. It shows an MPB region, in which a complex phase mixture is

proposed with the presence of a monoclinic phase. The materials of MPB

compositions typically exhibit two phase transitions at T

and T

MPB

respectively, as revealed by the dielectric anomalies. The increasing substitution

of the Ti

ion for the complex (Sc

1/2

)

ions gives rise to an increase in

and a decrease in T

MPB

If we compare the MPB phase diagram of the (1–x)PSN–xPT solid solution

with those of the PZT, PZN–PT, and PMN–PT systems, we can see that the

phase diagrams of all these solid solutions show some common features,

such as the curvature of the MPB upper limit boundary and the presence of

an intermediate lower symmetry phase acting as a bridge connecting the

rhombohedral (R) and the tetragonal (T) phases. Interestingly, the dielectric

and piezoelectric properties are enhanced in the materials of the MPB

compositions. Therefore, the establishment of the phase diagram of the

(1–x)PSN–xPT solid solution with the monoclinic symmetry lying between

the R-phase and the T-phase gives another example of MPB system, useful

for understanding the MPB behaviour and the high electromechanical response

in these materials, and for developing new piezoelectric crystals for a wide

temperature range of applications.

Perovskite PSN and (1–x)PSN–xPT single crystals with composition near

the MPB have been grown by an improved flux method. The growth conditions

were optimized in terms of the chemical compositions and discussed in the

light of thermodynamics and kinetics of crystal growth. It is found that the

morphology, the quality, and the chemical and physical properties of the

grown crystals are affected by the growth conditions, such as the ratios of

PSNT/flux and PbO/B

. By adjusting the chemical and thermal parameters,

optimum growth conditions have been found, which lead to the growth of

(1–x)PSN–xPT single crystals of good quality and of medium size.

The characterization of the piezoelectric properties of the (1–x)PSN–xPT

crystals shows that the bipolar strain value and the longitudinal

electromechanical coupling factor k

are comparable with those of PZT

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Handbook of dielectric, piezoelectric and ferroelectric materials202

ceramics. Even though these properties are lower than those reported in the

PMN–PT and PZN–PT single crystals of the MPB composition, the T

, and

especially T

MPB

, of the (1–x)PSN–xPT crystals are much higher than those in

the PMN–PT and PZN–PT crystals, which represents an attractive feature of

this complex system. The rather mediocre piezoelectric performance of the

(1–x)PSN–xPT crystals could be attributed to the fact that the actual composition

of the grown crystals departed from the charged MPB one as a result of

phase segregation, and also the complexity of the phase mixture.

Future investigation of the (1–x)PSN–xPT crystals should focus on the

further improvement of crystal growth, the minimization of composition

segregation and the adjustment of the MPB composition, so as to improve

the piezoelectric properties. It is expected that upon optimization of the

MPB composition and properties, the (1–x)PSN–xPT single crystals can

constitute a new resource of high piezoelectric crystals with high T

and

high T

MPB

, potentially useful for a wide range of electromechanical transducer

applications.

7.6 Acknowledgements

This work was supported by the US Office of Naval Research (Grant No.

N00014-1-06-0166) and the Natural Science and Engineering Research Council

of Canada (NSERC).

7.7 References

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modified Bridgman technique’, Jpn. J. Appl. Phys., 39, 5581–5585.

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monoclinic ferroelectric phase in the Pb(Zr

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2/3

–xPbTiO

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study of field-cooling effects on the relaxor ferroelectric Pb[(Zn

1/3

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applications and issues’, Curr. Opin. Solid State & Mater. Sci. 6, 11–18.

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content/file_649.html

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Handbook of dielectric, piezoelectric and ferroelectric materials204

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material system’, Jpn. J. Appl. Phys., 33, 5328–5331.

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1/2

)

1–x

ceramics material near the morphotropic phase boundary’, Jpn. J. Appl. Phys. 33,

4652–4656.

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6042.

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–PbTiO

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–PbTiO

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8.1 Introduction

During the past 50 years barium titanate (BaTiO

BT) and lead zirconate

titanate (Pb(Zr,Ti)O

PZT) have become well established as the preferred

ferroelectric materials for a wide variety of ferroelectric devices such as

capacitors and piezoelectric actuators. However, in the past two decades,

relaxor materials with the general formula Pb(B′B″)O

where B′ is a low-

valence cation, e.g. Mg

, Ni

, Zn

, In

or Sc

, and B″ is a high-valence

cation, e.g. Nb

, Ta

, or W

, have been investigated for applications such

as multilayer ceramic capacitors and electrostrictive devices. In recent years,

a new approach to the development of piezoelectric materials based on PbZrO

free, relaxor–lead titanate (PT) systems has attracted particular attention

(Kuwata et al., 1982, Shrout et al., 1990, Harada et al., 1998). The advantage

of relaxor–PT piezoelectric materials compared with conventional PZT, as

shown in Table 8.1, is the ease with which piezoelectric single crystals

(PSCs) of MPB compositions can be grown.

In particular, Pb[(Zn

1/3

2/3

)

0.91

0.09

(PZNT 91/9) and Pb(Mg

1/3

)

0.68

0.32

)]O

(PMNT 68/32) binary PSCs are well known because they have

an extremely large electromechanical coupling factor in longitudinal mode

> 90%, and a large piezoelectric constants, d

> 2000 pC/N, along the

[001] axis.

Various applications, such as those in medical transducers, actuators,

and undersea sonars, have been proposed which would exploit these excellent

properties. The authors have already reported on the growth of large PZNT

91/9 PSC by the solution Bridgman method (Harada et al., 1998) and the

fabrication of a 3.7 MHz phased-array probe using PZNT 91/9 PSC has been

reported, as well as its pulse echo characteristics and the final imaging

quality (Saitoh et al., 1999).

However, these binary system PSCs have some disadvantages that must

be overcome. Although large PZNT and PMNT PSCs near the MPB are

grown by the solution-Bridgman method or the pure Bridgman method with

diameters of more than 80 mm, and good dielectric and piezoelectric properties

High Curie temperature piezoelectric single

crystals of the

Pb(In

1/2

–Pb(Mg

1/3

2/3

–PbTiO

ternary materials system

Y J YAMASHITA and Y HOSONO,

Toshiba R & D Center, Japan

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Handbook of dielectric, piezoelectric and ferroelectric materials206

Table 8.1

Relaxor materials, high

materials and their MPBs with lead titanate

Relaxor materials Abbrev.

K (°C) ε

max

Structure Ferro. Ti @ MPB

@MPB

(mol%) K (°C)

Pb(B

1/3

2/3

Pb(Cd

1/3

2/3

PCdN 273 (0) 8 000 PC F 28 653 (380)

Pb(Zn

1/3

2/3

PZN 413 (140) 22 000 R F 9–10 448 (175)

Pb(Mg

1/3

2/3

PMN 263 (–10) 18 000 PC F 30–33 428 (155)

Pb(Ni

1/3

2/3

PNN 153 (–120) 4 000 PC F 28–33 403 (130)

Pb(Mn

1/3

2/3

PMnN 153 (–120) 4 000 PC F 30–35 403 (130)

Pb(Co

1/3

2/3

PCoN 175 (–98) 6 000 M F 33 523 (250)

Pb(Mg

1/3

2/3

PMgT 175 (–98) 7 000 PC F 30? 373 (100)

Pb(B

1/2

Pb(Yb

1/2

PYbN 553 (280) 150 M AF 50 633 (360)

Pb(In

1/2

PIN 363 (90) 550 M F 37 593 (320)

Pb(Sc

1/2

PSN 363 (90) 38 000 R F 42 533 (260)

Pb(Fe

1/2

PFN 385 (112) 12 000 R F 7? 413 (140)

Pb(Sc

1/2

PST 299 (26) 28 000 R F 45 478 (205)

Others

*PbZrO

PZ 513 (240) 3 000 O AF 47 633 (360)

(Pb,La)(Zr,Ti)O

PLZT <623 (<350) 30 000 R, T F, AF 35–47 <623 (<350)

BiScO

BS >673 (>350) <1 000 R F 64 723 (450)

BiInO

BIn >973 (>700) <1 000 R F? 70 843 (570)

PbTiO

PT 763 (490) 9 000 T F

C: Cubic, M: Monoclinic, O: Orthorhombic, PC: Pseudocubic, PY: Pyrochlore, R: Rhombohedral, T: Tetragonal, AF: Antiferroelectrics, F:

Ferroelectrics.

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High Curie temperature piezoelectric single crystals 207

have been confirmed, they have a relatively low T

of approximately 140–

175 °C (Luo et al., 1999, 2000). In particular, the low T

prevents their use

in more general applications. Moreover, they have phase transition temperatures

from the rhombohedral to the tetragonal phase at around 50–80 °C, which is

referred to as T

(Hosono et al., 2002a). Figure 8.1 shows the schematic

phase diagrams of the PZNT and PMNT solid solution systems. The PZNT

91/9 and PMNT 70/30 PSC near the morphotropic phase boundary (MPB)

consist mainly of rhombohedral phases at room temperature and have excellent

dielectric and piezoelectric properties. The dielectric and piezoelectric

properties of PZNT and PMNT PSCs change at temperatures above T

because of the phase transformation (Feng et al., 2004, 2006; Yamashita et

al., 2004a). The coupling factor of the rectangular bar mode, k

, decreases

sharply at T

and then decreases gradually towards the T

. Therefore, it is

necessary to design the compositions of piezoelectric PSCs based on a

consideration of the requirements of the specific application so as to achieve

the optimum balance between piezoelectric properties and thermal stability.

However, it is difficult in either the PZNT or PMNT binary systems to raise

and T

simultaneously, as shown in Fig. 8.1. In general, when the T

increases, the T

decreases. Therefore, designing crystal compositions with

high T

and T

is difficult in these binary PSCs (Yamashita et al., 2004c).

On the other hand, the growth and electrical properties of some relaxor–

PT PSCs with high T

have been reported, such as (1–x)Pb(In

1/2

3–

xPbTiO

(PINT) (Yasuda et al., 1999, 2001) and (1–x)Pb(Yb

1/2

–

xPbTiO

(PYNT) PSCs (Zhang et al., 2002) with T

> 250 °C. Although the

crystals show high T

, the crystal qualities are poor, the PSC sizes are small

and the piezoelectric properties are inferior to those of PZNT and PMNT

PSCs. The present authors reported crystal growth and electrical properties

PbTiO

(mol%)

45 6001530

Temperature (°C)

–100

–50

100

150

200

250

Tetragonal

Cubic

Pseudocubic

PMNT 65/35

PMNT 70/30

PMNT 75/25

PbTiO

(mol%)

15 200510

Temperature (°C)

Cubic

Tetragonal

Rhombohedral

–100

–50

100

150

200

250

PZNT 88/12

PZNT 93/7

PZNT 95.5/4.5

8.1

Schematic PZNT and PMNT phase diagrams near the MPB.

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Handbook of dielectric, piezoelectric and ferroelectric materials208

of (1–x)Pb(Sc

1/2

–xPbTiO

(PSNT) PSCs (Yamashita and Shimanuki

1996).

PSNT has a relatively high T

(>200 °C); however, it has two major

limitations: a high melting point of 1420 °C and a high raw-material cost.

Thus, the authors focused on PINT 63/37, which has a high Curie temperature,

= 320 °C, and a relatively low melting point of 1294 °C,

as a candidate

substitute material for PMNT 68/32 (melting point of 1271 °C) (Hosono et

al., 2000).

Because the two melting points are similar, the crystal growth of

xPb(In

1/2

–yPb(Mg

1/3

2/3

)–zPbTiO

(PIMNT100x/100y/100z) should

be possible. Moreover, it was assumed that the line connecting the MPB

compositions of PMNT 68/32 and PINT 63/37 is the MPB composition of

the PIMNT ternary system. Therefore, the T

of the PIMNT ternary system

can be controlled from 150 to 320 °C at MPB compositions where it is

expected to exhibit good dielectric and piezoelectric properties.

In this chapter, the synthesis and evaluation of PIMNT ternary ceramics

are first described. An excellent electromechanical coupling factor, k

67%, a relatively high Curie temperature, T

= 197 °C, and a good perovskite

stability of the PIMNT 16/51/33 ceramics near the MPB have been confirmed

(Hosono, 2003a). Crystal growth in the PIMNT ternary system by the Bridgman

method will be discussed along with the compositional variation and the

dielectric and piezoelectric properties.

8.2 PIMNT ceramics

In this section, the physical and electrical properties of PIMNT 100x/100y/

100z ceramics near the morphotropic phase boundary (MPB) are presented.

We focus on the compositions of the PIMNT ternary system, which are on

the straight line connecting the MPBs of the PIMNT 0/68/32 (PMNT68/32)

and PIMNT 63/0/37 (PINT63/37) binary systems. The purpose of this work

was to study in detail the dielectric and piezoelectric properties of the PIMNT

ternary ceramic system in the vicinity of the MPB, and to determine a ceramic

material with good piezoelectric properties and a moderate T

of around

200 °C.

Figure 8.2 shows the compositions of the samples synthesized in the

PIMNT ternary system. Nine compositions along the MPB line and five

compositions across the MPB line were prepared. The details of the ceramic

sample preparation procedure have been reported in previous papers (Hosono

et al., 2002b, 2003a). Figure 8.3 shows X-ray diffraction (XRD) patterns for

PIMNT 100x/100y/100z ceramics. As shown in the figure, all ceramic samples

had a single phase perovskite structure without any trace of pyrochlore. The

result indicates that the perovskite structure is very stable in the PIMNT

system. Fired PIMNT 25/43/32 indicated a rhombohedral (R) phase, whereas

PIMNT 23/41/36 had a tetragonal (T) phase. However, compositions along

the MPB, PIMNT 8/59/33 to PIMNT 56/8/36, showed three different peaks

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High Curie temperature piezoelectric single crystals 209

at around 45 degrees, representing a mixture of the rhombohedral and tetragonal

phases. Hence, the MPB is an almost linear, narrow region between the

MPBs of the PIMNT 0/68/32 (PMNT 68/32) and PIMNT 63/0/37 (PINT 63/

37) binary systems.

Figure 8.4 shows the dielectric properties of PIMNT 100x/100y/100z

ceramics along the MPB measured at 100 kHz. The composition, PIMNT

0/68/32, showed a large dielectric constant maximum of 47 480. The dielectric

constant maximum decreased as the PIN content increased. This is due to the

low dielectric constant maximum of PIMNT 63/0/37. The dependence of T

as a function of PIN (x) is shown in Fig. 8.5. The T

varied from 160 to

320 °C almost lineally as the PIN content increased. This result suggests that

the T

of the MPB composition in the PIMNT system can be controlled,

leading to the realization of excellent piezoelectric properties.

Figure 8.6 shows the electromechanical coupling factor planar mode, k

for PIMNT ceramics along the MPB. The largest value of the electromechanical

coupling factor planar mode k

= 67.6% was observed for PIMNT 24/42/34.

The k

values of the PIMNT ternary ceramics were slightly higher than those

of the end member MPB compositions at PIMNT 0/68/32 and PIMNT

63/0/37. The compositions with high k

showed low

εε

. A high

piezoelectric constant, d

= 510 pC/N, was found at PIMNT 0/68/32 and

PIMNT 16/51/33. The high d

values are due to their high dielectric constants

and large coupling factors. Two compositions with moderate T

of around

200 °C were PIMNT 16/51/33 and PIMNT 24/42/34. The former composition,

with T

= 197 °C, showed

εε

= 2400, k

= 67.1% and d

= 510 pC/N

and the latter one with T

= 219 °C showed

εε

= 2120, k

= 67.6% and

PbTiO

(PT)

= 490°C

PMNT 68/32

= 150°C

PINT 63/37

= 320°C

Tetragonal

Rhombohedral

Pb(In

1/2

(PIN)

= 90°C

Pb(Mg

1/3

2/3

(PMN)

= 10°C

8.2

PIN–PMN–PT ternary system phase diagram.

WPNL2204