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

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Handbook of dielectric, piezoelectric and ferroelectric materials220

Temperature dependence of the dielectric properties of the PIMNT PSCs

(Wafer Nos. 1, 8 and 18) selected from the initial, middle and end parts of the

crystal were measured. The Curie temperature, T

, varied from 181 to 196 °C

with increasing wafer number. The T

of the end part is approximately 15 °C

higher than that of the initial part of the crystal. The results of the EPMA

indicate that the Ti content increases from the initial part to the end of the

crystal. Therefore, this variation of T

must be due to the increase of PbTiO

= 490 °C) in the crystal. Peaks in the dielectric constant are observed

below 100 °C in Nos. 1 and 8, probably due to the phase transition from the

rhombohedral to tetragonal phases. This result indicates that the crystals

show the rhombohedral phase at room temperature. On the other hand, a

small peak is observed in No. 18 at approximately 30 °C. Therefore, the

crystal must be near the MPB composition. In order to raise the T

, the

composition needs to be shifted slightly into the rhombohedral phase field

by decreasing the Ti content in the crystal.

Table 8.5 lists the dielectric and piezoelectric properties of the PIMNT

PSCs at the initial, middle and end parts. The dielectric constants of the plate

transducers,

εε

, were ranged from 1480 to 4400 at room temperature.

The end part, No. 18, showed low

εε

because it belongs to the MPB

composition near the tetragonal region at room temperature. Generally, the

εε

of the piezoelectric material belonging to the tetragonal phase is

small along the [001] direction. A maximum piezoelectric constant, d

1950 pC/N, was observed in the middle part, No. 8, which is almost the same

as that of the crystal obtained by the flux method. The maximum coercive

field, E

= 8.9 kV/mm, which is approximately twice that of PMNT 70/30,

was observed in the end part, on wafer No. 18. E

increases with increasing

. The remanent polarizations, P

, of the three wafers show almost the same

Table 8.5

Electrical properties of three wafers cut from the PIMNT 24/42/

34 PSC

Wafer Wafer Wafer

No. 1 No. 8 No. 18

Crystal part Initial Middle End

Dielectric constant

εε

4400 3630 1480

Phase-transition temp.

(°C) 91 55 –

Curie temp.

(°C) 181 191 196

Coupling factor

(%) 54.7 61.2 62.9

Piezoelectric const.

(pC/N) 1350 1950 1550

Remanent polarization

(µC/cm

) 39.3 38.2 39.4

Coercive field

(kV/cm) 4.4 7.0 8.9

Coupling factor

′

(%) 64.7 80.3 83.6

Frequency const.

′

(Hz m) 1610 1110 1000

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High Curie temperature piezoelectric single crystals 221

values. The end part, No. 18, also exhibits a large value because it belongs

to the MPB composition very near the tetragonal region. The coupling factors

sliver mode,

′

, which are important for phased array probes, were measured

using sliver transducers obtained by dicing, as mentioned above. Observation

by microscope revealed no serious cracking and chipping on the sides of the

sliver transducers diced from Nos. 8 and 18, but some cracks on the sides of

the transducers diced from No. 1. The reason for the cracking and chipping

is thought to be that the crystal quality of No. 1 was inferior to the others.

Therefore, very clear impedance behaviors and high

′

values were observed

in the sliver transducers of Nos. 8 and 18. Moreover, they had high-frequency

constants,

′

r = 1000–1100 Hz m. On the other hand, the

′

values of the

sliver transducers cut from No. 1 were lower than the other ones. The low

′

may be attributable to the poor crystal quality.

After the first crystal growth of the PIMNT 16/42/34, second crystal

growth was carried out with PIMNT 24/42/34 (Hosono et al., 2004) to

increase T

. Figure 8.11 shows the PIMNT 24/42/34 PSC produced by the

solution Bridgman process. A large size, 20 × 20 × 0.5 mm

, and a good

quality of the wafer were obtained. The chemical composition of the pulverized

powder of some PSCs is slightly different from that of the charged composition.

The PbO ratio was a little higher than that of the charged composition because

the PbO flux or PbO inclusion might be included in the crystal samples. The

PIMNT ternary system consists of four elements for the B-site (In, Mg, Nb

and Ti) in the perovskite structure. Those B-site elements show three

10 mm

Bottom

Top

8.11

The PIMNT 24/42/34 PSC near the MPB composition prepared by

the solution Bridgman method.

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Handbook of dielectric, piezoelectric and ferroelectric materials222

combinations, namely (In

1/2

)

, (Mg

1/3

2/3

)

and Ti

, in the crystal

in order to compensate electrons. Therefore, the Pb(In

1/2

and

Pb(Mg

1/3

2/3

show rhombohedral phase but the PbTiO

shows tetragonal

phase. The PIMNT ternary system changes the phase as a function of its

composition and the charged composition of the PIMNT 24/42/34 is around

the morphotropic phase boundary (MPB). A ratio, defined as (In

+ MgO)/

TiO

, between (In

+ MgO) content regarded as the rhombohedral phase

and TiO

content regarded as the tetragonal phase is 0.37 for the crystal

composition and 0.35 for the charged composition, respectively. This means

that the PIMNT PSC obtained this time consists of a composition which

shows the rhombohedral phase.

Figure 8.12 shows the temperature dependence of the dielectric constants

of poled plate transducers of PIMNT 24/42/34 and PIMNT 16/51/33 PSC

measured at 1 kHz. Small peaks of the dielectric constant are observed at 50–

90 °C, corresponding to the phase-transition temperature, T

. The T

and

of PIMNT 24/42/34 and PIMNT 16/51/33 PSC were 89 and 184 °C and

52 and 181 °C, respectively. The T

of PIMNT 24/42/34 PSC was about

40 °C higher than that of the PIMNT 16/51/33 PSC, whereas the T

of the

PIMNT 24/42/34 PSC was almost the same as that of the PIMNT16/51/33

PSC. The T

of the PIMNT 24/42/34 PSC was slightly lower than we expected

because the (In

+ MgO)/TiO

ratio was lower than that of charged

composition for the crystal growth. This means that the PIMNT PSC has low

PT content, which shows high T

of 490 °C. The T

(= 219 °C) of the PIMNT

24/42/34 ceramic has been confirmed in a previous report (Hosono et al.,

2003).

Table 8.6 lists the dielectric and piezoelectric properties of the PZNT 93/

7, PMNT 70/30, PIMNT 24/42/34 and the ideal PSC for medical transducers.

Temperature (°C)

0 50 100 150 200 250

PIMNT 16/51/33

PIMNT 24/42/34

Dielectric constants ε

T/ε

40000

30000

20000

10000

8.12

Dielectric properties of the PIMNT 24/42/34 and PIMNT 16/51/33

PSC.

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High Curie temperature piezoelectric single crystals 223

The dielectric constant after poling,

εε

, of the PIMNT 24/42/34 was

4900 at room temperature, which is almost the same value as that of PMNT

70/30. High dielectric constant of the piezoelectric material is very important

for the ultrasonic medical array transducer application. Recently, the capacitance

of the array transducer is becoming smaller, because the element size of the

array transducer is becoming smaller as the number of channels increases. In

order to match electrical impedance between a tiny piezoelectric element

and a coaxial cable, higher dielectric constant, which means larger capacitance,

is required. A large piezoelectric constant, d

= 2200 pC/N, was observed in

the PIMNT 24/42/34 PSC, which is almost the same as that of the PZNT 93/

7 and the PMNT 70/30 PSC. In ultrasonic applications, few waveforms of

pulse voltage are applied to the transducer. Therefore, the stability of the

piezoelectric properties when the inverse pulse voltage is applied to the

transducer is important for the relaxor–PSC with relatively low T

. The E

of the PIMNT PSC was 6.9 kV/mm, which is around 1.5 times larger than

that of the PMNT 67/33 PSC.

The coupling factors,

′

, which are important for the phased array probe,

were measured using sliver transducers obtained by dicing. Observation by

microscopy revealed no serious cracking and chipping on the sides of the

sliver transducers diced from the plane transducer. The transducer showed

very clear impedance behavior and high

′

value of around 80%, which is

almost the same as those of the PZNT 91/9 and PMNT 70/30 PSCs. Moreover,

it had high-frequency constant,

′

= 1200

Hz m, which is as high as that

of PMNT 70/30 PSC. The frequency constant,

′

, is expressed by the

following equation:

′

××Nr f d

= 2

8.2

where f

is series resonance frequency and d is thickness of the transducer.

Table 8.6

Electrical properties of the obtained and the ideal PSCs for medical array

transducers

PZNT PMNT PIMNT Ideal

93/07 70/30 24/42/34 PSC

Free dielectric constant

εε

4000 5500 4900 >4000

Clamped dielectric constant

600 1200 1000 >1000

Phase-transition temp.

(°C) 92 89 89 >100

Curie temp.

(°C) 165 145 184 >180

Coupling factor

(%) 58 50 70 <60

Coupling factor length mode

(%) 95 93 (90) >88

Piezoelectric const.

(pC/N) 2400 2200 2200 >1500

Coercive field

(kV/cm) 5 3.0 6.8 >6

Coupling factor sliver mode

′

(%) 82 82 80 >80

Frequency const.

′

(Hz m) 900 1180 1200 >1180

PSC size (mm) 50 70 25 >50

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Handbook of dielectric, piezoelectric and ferroelectric materials224

As indicated by the equation, high-frequency constant means a thicker

transducer can be used in order to vibrate the transducer at the same frequency.

Therefore, piezoelectric material with high-frequency constant is promising

for the high-frequency applications.

Next, the temperature dependence of

′

was measured using the sliver

transducers of the PIMNT 24/42/34 and PIMNT 16/51/33 PSCs. The phase-

transition temperatures, T

, the Curie temperatures, T

, and the coupling

factors,

′

, at room temperature of the PIMNT 24/42/34 and PIMNT

16/51/33 PSCs used for the measurement were 89 °C, 184 °C and 80%, and

52 °C, 181 °C, 82%, respectively. The T

and T

values were measured

using poled plate transducers before dicing to the sliver transducers. The

′

values are almost the same as each other. Figure 8.13 shows the temperature

dependence of the

′

of the PIMNT 24/42/34 and PIMNT 16/51/33 PSCs.

The

′

decreased in a step-like manner from 50 to 80 °C, which is similar

to the behavior of PZNT PSCs we reported in the past (Hosono et al.,

2002a). The authors think that the

′

exhibits a step-like decrease near the

because PIMNT PSC starts to transform from the rhombohedral to

tetragonal phase at those temperatures, and the directions of spontaneous

polarizations also change. Therefore, the degradation temperature of

′

was in agreement with the T

measured using the poled PIMNT PSC, as in

the case of the PZNT PSCs. Because the transducer may be heated to around

70 °C, thermal stability of piezoelectric properties is very important in the

medical transducer application. Although the

′

of the PIMNT 16/51/33

PSC decreased at about 50 °C, the

′

of the PIMNT 24/42/34 PSC hardly

changed until 70 °C. This result indicates that the PIMNT 24/42/34 PSC had

not only excellent piezoelectric properties but also that those properties had

good thermal stability due to its high T

. Moreover, it had good voltage-

proof nature due to its high T

. Therefore, the PIMNT 24/42/34 PSC may be

Temperature (°C)

120100806040200

100

Coupling factors

(%)

′

PIMNT 24/42/34

= 89°C

PIMNT 16/51/33

= 52°C

8.13

Temperature dependence of the

′

of the PIMNT 24/42/34 and

PIMNT 16/51/33 PSC.

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High Curie temperature piezoelectric single crystals 225

the best composition of the piezoelectric material for the medical array

transducer application. In particular, the large coercive fields and high-frequency

constants make the PIMNT 24/42/34 PSC useful for high-frequency transducer

and multi-layer transducer applications.

In summary, crystal growth of PIMNT and PSMNT ternary systems was

investigated by the solution Bridgman method using a PbO–B

flux. The

results obtained are as follows:

• A large PIMNT PSC of 25 mm in diameter and 30 mm in length was

obtained by driving the crucible at a speed of 0.4 mm/h from 1250 to

900 °C. On the other hand, PSMNT PSCs were multinucleated under the

same growth conditions.

• The results of EPMA revealed that the Ti content gradually increased

during the growth in PIMNT and PSMNT PSCs. However, the In/Mg

ratio was constant in the PIMNT PSC, whereas the Sc/Mg ratio varied

considerably in the PSMNT PSC.

• The Curie temperature, T

, of the PIMNT crystal ranged from 181 to

196 °C from the initial part to the end part, which is in agreement with

the EPMA results.

• Excellent dielectric and piezoelectric properties were confirmed in the

crystal with T

= 89 °C and T

= 184 °C: dielectric constant,

εε

4900, piezoelectric constant, d

= 2200 pC/N, coercive field of E

= 6.8

kV/cm, coupling factor,

′

= 80%

and frequency constant,

′

= 1200

Hz m.

It was confirmed that crystal growth in the PIMNT system was easier than in

the PSMNT system. Moreover, the compositional variation of the PIMNT

PSC was smaller than that in PSMNT PSC. Finally, the obtained PIMNT

PSC exhibited good dielectric and piezoelectric properties as well as a high

and T

Figure 8.14 shows the relationship between the Curie temperature, T

and piezoelectric constants, d

of relaxor–PT PSCs and PZT ceramics. The

values of relaxor–PT PSCs are larger than those of PZT ceramics,

particularly PMNT 70/30, PZNT 91/9 and PIMNT 24/42/34. PINT 72/28,

which has a high T

of 260 °C, shows lower d

than those of other PSCs.

The low d

may be due to the poor crystal quality and the high T

. Because

little d

data on relaxor–PT PSCs with T

over 200 °C has been reported, the

relationship between T

and d

is unclear.

In this study, the starting material selected was the PIMNT 16/51/33 and

PIMNT 24/42/34, which falls on the compositional line connecting the MPB

compositions of the PMNT 68/32 (T

= 150 °C) and PINT 63/37 (T

320 °C). The T

of the PIMNT ternary system with MPB compositions can

be controlled from 150 to 320 °C. Therefore, if the composition of PIMNT

PSCs is designed carefully with an optimum balance between the piezoelectric

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Handbook of dielectric, piezoelectric and ferroelectric materials226

properties, high T

and high T

, PIMNT PSCs may become excellent

candidates for applications such as medical imaging, non-destructive testing

and actuators. Figure 8.15 shows recent progress of the PSC growth of the

PIN–PMN–PT produced by JFE Mineral Co., Chiba, Japan, by the Bridgman

process. The crystal diameter is 80mm, the length is 80 mm and the weight

is 2.2 kg (http://www.jfe-mineral.co.jp/e_mineral/seihin/eseihin034.html).

Curie temperature (°C)

4003002001000

3000

2500

2000

1500

1000

500

Piezoelectric constant

(pC/N)

PZT ceramics

PINT 72/28

PIMNT 24/42/34

PZNT 91/9

PMNT 70/30

8.14

Piezoelectric constants as a function of Curie temperature of

several relaxor-PT single crystals and PZT ceramics.

8.15

Large, 80 mm in diameter PMN–PIN–PT PSC produced by the

Bridgman process. (Courtesy of JFE Minerals Co. of Japan.)

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High Curie temperature piezoelectric single crystals 227

8.5 Future trends

Ultrasonic array transducers are applied in medical echo diagnostic ultrasound

systems. Frequencies used for these applications are 2–20 MHz. The typical

cardiac transducer operates at a center frequency of 2–4 MHz and makes use

of a piezoelectric material plate with a size of 15 × 25 mm

. The key to

achieve this is the performance of the piezoelectric material, which transmits

and receives the echo ultrasound. High dielectric constant

( / > 3500)

εε

PZT5H ceramics have been mostly used for this application in decades.

However, recent research has focused on obtaining greater sensitivity and

broader bandwidth, and new transducers such as piezoelectric composites

have been studied.

PSCs of PZNT 91/9 and PMNT 70/30 have a large d

(>2000 pC/N) and

(>92%),

′

(>80%) and g

(>60 × 10

–3

V m/N), values far larger than

those obtained for any PZT ceramic specimens. This is one reason that

intensive research on medical transducers has been conducted in various

parts of the world during the last 10 years. After the initial reports and

presentations by Toshiba in the early 1990s several organizations in the

USA, South Korea and China, entered the field. Saitoh et al. (1999b) reported

the first images of B-mode and Doppler-mode obtained by using PZNT91/

09 PSC for cardiac transducers operating at 3.5 MHz with 96 channels. The

echo amplitude of the PZNT probe is about 6 dB higher than that of the PZT

probe, and the frictional bandwidth is 30% wider. This means that both the

penetration and the resolution of the PZNT probe are superior to those of

conventional PZT probes. Large coupling factor

′

(>82%), dielectric constant

after poling

( / > 3000)

εε

and low acoustic impedance Z

< 24 (×10

kg/m

s) make the PZNT 91/9 PSC an excellent transducer material for

medical diagnostic applications. At present, the size of PZNT, PMNT and

PIMNT PSC is sufficient for various applications. However, the quality and

uniformity of these crystals within and between the wafers larger than 50

mm in diameter, as well as among lots and among manufacturers, are still

insufficient (Yamashita et al., 2004c). Although it is usually easy to grow

PSCs in [111] or [110] directions, it is very difficult to grow them in the

[001] direction, but [001] wafers are used for medical transducers. There is

always some inhomogeneous TiO

distribution within wafers. This is one of

the causes of large scattering of k

, d

and dielectric constant within wafer.

In addition, the manufacture of high-frequency, i.e. more than 7 MHz, PSC

transducers that requires thin thickness plate (less than 150 µm), is very

difficult because of the low-frequency constant and low mechanical strength

of PSC. The present cost of PSC wafers is more than 10 times that of PZT

ceramics. Other drawbacks are temperature instability, mechanical properties,

chipping by dicing, matching layers/electrode/PSC bonding strengths, low

clamped dielectric constant, low E

, de-poling, low production yield, etc.

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Handbook of dielectric, piezoelectric and ferroelectric materials228

However, the PIMNT PSC introduced in this chapter can solve most of these

shortcomings.

The Bridgman and solution Bridgman processes and the TSSG process

are well-established PSC growth processes. However, these processes have

several shortcomings, such as Pt crucible cost and composition inhomogeneity.

In order to resolve these shortcomings, a new approach has been studied.

Solid-state crystal growth (SSCG) (Lee et al., 2000; Lee, 2004) and templated

crystal growth (TCG) processes have many advantages over conventional

PSC processes and they are expected to reduce the cost of homogeneous

relaxor PSCs for mass production in the near future. In addition, utilizing the

domain engineering (Wada et al., 2005) which revealed through PSC research,

the ceramic BaTiO

piezoelectric properties are also drastically improved by

Takahashi et al. (2006a,b). Therefore, it is plausible that PIMNT materials

may become the predominant materials for sophisticated, performance-oriented

piezoelectric products in the near future. To that end, research on methods of

evaluating PSC wafer quality and uniformity using non-destructive processes

is an urgent task. Improvement in the uniformity of capacitance,

electromechanical coupling factor k

and piezoelectric constant d

within

and between wafers is also a major task for crystal growers. Detailed basic

research to determine the mechanism accounting for the scattering of electrical

properties should be conducted from the viewpoints of composition, domain

structure and defect chemistry.

Finally, research on new PSC, ceramic materials and technology to solve

all the present problems is essential. From the application aspect, a new

dicing process that prevents cracking and deteriorating of PSC is also necessary

in order to make fine pitch, high-frequency array transducers. A conformation

of scalability which indicates the size dependency of physical, dielectric and

piezoelectric properties of small size less than 1.0 mm

is required to design

fine size piezoelectric medical array transducers.

8.6 Conclusions

Piezoelectric ceramics and PSCs in the xPb(In

1/2

–yPb(Mg

1/3

2/3

–zPbTiO

(PIMNT100x/100y/100z) ternary system have been

investigated in order to develop new piezoelectric materials with high Curie

temperature, T

The PIMNT PSCs have been grown using a PbO–B

flux both by the

conventional flux method and by the solution Bridgman method. The largest

crystal size obtained is 25 mm in diameter and 30 mm in length. Although

the Ti content gradually increased along the length of the grown crystal, the

In/Mg ratio was almost constant.

The obtained PIMNT 24/42/34 crystal shows excellent electrical properties

in the (001) plane, e.g. a dielectric constant

( / = 4900)

εε

, piezoelectric

WPNL2204

High Curie temperature piezoelectric single crystals 229

constant d

= 2200 pC/N, coupling factor sliver mode

′

= 80%

, which are

almost the same as those of the PZNT 91/9 and PMNT 68/32 PSCs. However,

PIMNT has a high phase transition temperature T

= 89 °C and Curie

temperature T

= 184 ° C. Moreover, it has a large coercive field E

6.8 kV/cm due to the high T

, T

, and a high frequency constant

′

=1200 Hz m. The high T

, large coercive field and high frequency

constant of the PIMNT PSCs make them promising candidates for medical

transducers and actuators which require a stable temperature performance.

In order to utilize the piezoelectric crystals for medical array transducers

application, a conformation of scalability of physical, dielectric and

piezoelectric properties is necessary.

8.7 References

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configuration and dielectric constant tenability in poled Pb(Mg

1/3

2/3

–PbTiO

crystals, J. Phys. Condens. Matter, 16, 6771–6778.

Feng Z, Zao X and Luo H (2006), Composition and orientation dependence of dielectric

and piezoelectric properties in poled Pb(Mg

1/3

2/3

–PbTiO

crystals, J. Appl. Phys.,

100, 024104, 1–5.

Harada K, Shimanuki S, Kobayashi T, Saitoh S and Yamashita Y (1998), Crystal growth

and electrical properties of Pb[(Zn

1/3

2/3

)

0.91

0.09

single crystals produced by

solution Bridgman method, J. Am. Ceram. Soc., 81, 2785–2788.

Hosono Y, Harada K, Yamashita Y, Dong M and Ye Z G (2000), Growth, electric and

thermal properties of lead scandium niobate–lead magnesium niobate–lead titanate

ternary single crystals, Jpn. J. Appl. Phys., 39, 5589–5592.

Hosono Y, Harada K, Kobayashi T, Itsumi K, Izumi M, Yamashita Y and Ichinose N

(2002a), Dielectric and piezoelectric properties of 0.93Pb(Zn

1/3

2/3

–0.07PbTiO

piezoelectric single crystals for medical array transducers, Jpn. J. Appl. Phys., 41,

7084–7088.

Hosono Y, Yamashita Y, Sakamoto H and Ichinose N (2002b), Large piezoelectric

constant of high-Curie-temperature Pb(In

1/2

–Pb(Mg

1/3

2/3

)–PbTiO

ternary

single crystal near morphotropic phase boundary, Jpn. J. Appl. Phys., 41, L1240–

L1242.

Hosono Y, Yamashita Y, Sakamoto H and Ichinose N (2003b), Dielectric and piezoelectric

properties of Pb(In

1/2

–Pb(Mg

1/3

2/3

–PbTiO

ternary ceramic materials

near the morphotropic phase boundary, Jpn. J. Appl. Phys., 42, 535–538.

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of high-Curie-temperature ‘Pb(In

1/2

–Pb(Mg

1/3

2/3

–PbTiO

ternary systems

near morphotropic phase boundary, Jpn. J. Appl. Phys., 42, 5681–5686.

Hosono Y, Yamashita Y, Sakamoto H and Ichinose N (2003c), Crystal growth of

Pb(In

1/2

–Pb(Mg

1/3

2/3

–PbTiO

and Pb(Sc

1/2

–Pb(Mg

1/3

2/3

)

–PbTiO

piezoelectric single crystals using the solution Bridgman method, Jpn. J.

Appl. Phys., 42, 6062–6067.

Hosono Y, Yamashita Y, Hirayama K and Ichinose N (2004), Dielectric and piezoelectric

properties of Pb[(In

1/2

)0.24(Mg

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2/3

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Phys., 44, 7037–7041.

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