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

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Handbook of dielectric, piezoelectric and ferroelectric materials840

Log impedance, |

| (Ω)

-mode

= 13500

158 158.4 158.8

Frequency,

(kHz)

–30

–60

–90

–30

–60

–90

–30

–60

–90

Phase, θ(°)

389 390 391 392 393 394

Frequency,

(kHz)

1.5 1.505 1.51 1.515

Frequency,

(kHz)

33-mode

= 8800

15-mode

= 6000

27.15

Frequency dependence of impedance,

(magnitude |

|, and phase θ, of (p)-, (33)- and (15)-modes for the SBTT2

(1.25) ceramic.

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Grain orientation and electrical properties of bismuth 841

SBTT2 ceramics were very difficult because of the very high E

. On the other

hand, the Q

values of SBTT2 ceramics are larger than those of SBTT3 ceramics.

27.4.6 Pyroelectric properties

Temperature dependences of the pyroelectric coefficient, p, were measured

by the modified Byer–Roundy technique,

9,37,38

over the temperature range

from –20 to 200°C. The coefficient, p, was calculated from the relation

p = (i/A)/(dT/dt), as a function of temperature, where i is the pyroelectric

current, A the electroded area of the specimen and dT/dt the heating rate. The

measurements were made during the heating cycles with a typical heating

rate of 2–3°C/min. The room temperature value of the p was obtained from

the average value of 20–25°C.

The suitability of a pyroelectric material for infrared sensing is usually

judged by its figures of merit, F

and F

, which can be calculated using the

material constants and the expressions as follows: F

= [p/(C

ε)] and

FpC

= [ /( tan )]εδ

, where

εε ε = /

is free dielectric constant, C

the volume specific heat, C

specific heat and ρ

measured density.

Table 27.3 summarizes the pyroelectric properties of the NCBT ceramics,

along with the figures of merit, F

and F

, comparing HF values with OF

ones. In these calculations, the C

of the NCBT ceramics was assumed to be

the same value as that (C

= 0.41J/g°C) of the PT-based ceramics, because

no data on the C

values of NCBT ceramics exist. The F

and F

of HF

samples are two times larger than those of OF ones, having the same

enhancement

21,23

as that of the piezoelectric properties. The F

of HF NCBT

ceramics is comparable to the typical values obtained for the PT-based ceramics,

but the F

is smaller compared with the values for the PZ-based ceramics.

This is mainly due to the fact that the pyro-coefficient, p, in the case of

Table 27.2

Piezoelectric properties of HF and/or OF SBTT3(0) (BIT), SBTT3 (0.3) and

SBTT2 (1.25) ceramics

Composition (SBTT

(

)) BIT SBTT3 (0.3) SBTT2 (1.25)

HF OF HF OF

Curie temperature,

(°C) 675 540 540 770

Density, ρ

(g/cm

) 7.90 7.75 7.77 8.66

Orientation factor,

(%) 80 – 70 –

Dielectric constant,

εε

129 188 187 122

Coupling factor,

(%) 25.5 12.8 37.1 15.7

(%) 3.20 3.73 3.40 5.99

(%) – 4.61 – 8.99

Quality factor,

(

-mode) – 1243 – 2848

Piezoelectric anisotropy,

7.96 3.43 10.9 2.61

Fiezoelectric constant,

(pC/N) 25.3 14.6 45.3 15.7

Frequency constant,

(Hzm) 1990 2026 2046 1791

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Handbook of dielectric, piezoelectric and ferroelectric materials842

Table 27.3

Pyro-coefficient,

, dielectric constant, ε, loss tangent, tan δ, volume heat capacity,

, figure of merit,

and

, and Curie

temperature,

, of the OF and HF (Na

1/2

)

1–

(NCBT-100

) (

= 0: NBT) ceramics

Sample p ε tan δ

(×10

–8

) C/cm

°C (%) J/cm

°C(× 10

–11

) C cm/J (× 10

–9

) C cm/J °C

NBT (HF) 1.3 149 0.32 2.99 2.9 6.3 660

+ Mn(0.1) (OP) 0.56 140 0.29 2.87 1.4 3.1 658

NCBT-5 (HF) 1.1 149 0.38 2.95 2.5 5.0 670

(OF) 0.68 151 0.33 2.86 1.6 3.4 674

NCBT-5 (HF) 1.0 134 0.17 2.84 2.6 7.4 665

+Mn(0.1) (OF) 0.82 148 0.16 2.82 2.0 6.0 680

PT 1.8 190 3.2 3.0 460

PZ 3.5 250 0.5 2.6 5.4 12 200

= , =

tan

⋅

εδ

, where

and

· ρ

: measured density,

= 0.41 J/g °C (PbTiO

+Mn(0.1) : + MnCO

(0.1 wt%).

PT = PbTiO

-based ceramics, PZ = PbZrO

-based ceramics.

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Grain orientation and electrical properties of bismuth 843

NCBT ceramics is smaller than that obtained in PZ-based or PT-based

compositions.

Grain-oriented (HF) NCBT ceramics with a large pyroelectric coefficient,

low dielectric constant, low loss tangent, and high Curie temperature produce

a superior candidate for excellent pyroelectric sensor materials to be used as

highly stabilized infrared temperature detectors.

27.4.7 Recent progress on Bi

-based system

Bismuth titanate, Bi

(BIT) is a typical well-known BLSF

1,20,28,39

and

the BIT single crystal has a good piezoelectricity. However, it is difficult to

measure piezoelectric properties on the BIT single crystal because the shape

of the grown BIT single crystals is always platelet and usually very thin. On

the other hand, fully reliable piezoelectric properties of BIT ceramics have

not been reported because of some problems such as the low resistivity and

the large coercive field.

2,3,6,12,40–43

To solve these problems, Nb

and V

ions were doped into BIT ceramic to obtain higher resistivities.

44,45

Recently,

3–x

[BITN–x] and Bi

3–x

[BITV–x] ceramics are studied

regarding on their dielectric, ferroelectric, and piezoelectric properties.

Furthermore, the grain orientation effects of BITN and BITV ceramics on

their piezoelectric properties are discussed using the grain-oriented ceramics

prepared by the HF method.

X-ray diffraction patterns for BITN and BITV ceramics (OF) show a

single phase of bismuth layer-structured compounds with the layer number,

m = 3. No peaks of Nb

and V

were observed within x ≤ 0.12. Both

BITN and BITV ceramics have relative density ratios higher than 95% of the

theoretical density.

Figure 27.16 shows T

as a function of Nb and V concentration. The T

the BIT (x = 0) ceramic is 683°C and gradually decreases lower with increasing

Curie temperature,

(°C)

700

690

680

670

660

650

640

630

BITV

BITN

1MHz

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Nb and V concentration,

27.16

Curie temperature,

, of BITN and BITV ceramics as a function

of Nb and V concentrations.

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Handbook of dielectric, piezoelectric and ferroelectric materials844

Nb and V concentration. Therefore, it is thought that the Nb and V ions

occupy the B-site of the pseudo-perovskite cell in the bismuth layer-structure.

However, the T

of BITV has a tendency to saturate with the increasing V

concentration, compared with the BITN ceramics. Therefore, it is thought

that V ions to be in the place of Ti ions. Excess V ions seem to exist on the

grain boundary and/or the triple point when the V concentration increases.

This consideration is estimated by the ionic radii of Ti, Nb, and V ions. The

ionic radii of Ti

(IV coordination), Nb

(IV coordination), and V

(IV

coordination) are 0.605, 0.64, and 0.54 Å, respectively, according to Shannon.

It is thought that the ionic radius of the V ion is too small to substitute on the

B-site of the pseudo-perovskite cell in the bismuth layer-structure. The

resistivity, ρ, of BIT (x = 0) is about 10

–10

Ω cm, and, those of BITN and

BITV ceramics are about 10

–10

Ωcm. It is clear that ρ is enhanced by

some donor-dopings. The optimum charge neutrality was observed for each

composition of BITN-0.08 and BITV-0.01, respectively. Figure 27.17 shows

the compositional dependences of the electromechanical coupling factor k

on the dopant Nb and V concentration (x). The k

of BITN reaches the

saturated value (0.20) for the composition of x = 0.08, while the k

of BITV-

0.02 is 0.25, which is a relatively high value for BLSF ceramics with random

orientations.

Figure 27.18 shows X-ray diffraction patterns of BITN-0.08 and BITV-

0.04 ceramics for the perpendicular plane (polished) of the HF ceramics and

the OF ones. It is very clear that grains in the HF ceramics were oriented

along the c-axis because the intensities of the (00l) planes of the HF samples

are very high. The grain orientation factors, F, of BITN-0.08 and BITV-0.04

were 0.91 and 0.75, respectively.

Figure 27.19 shows the frequency dependence of the impedance, Z

(magnitude |Z| and phase θ), of HF BITN-0.08 and HF BITV-0.04 ceramics.

BITV-0.02→24.7%

BITV-

BITN-

0 0.02 0.04 0.06 0.08 0.1 0.12

Nb and V concentration (

)

Coupling factor,

(%)

27.17

Electromechanical coupling factor

of BITN (OF) and BITV

(OF) as a function of the dopant concentration (

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Grain orientation and electrical properties of bismuth 845

Good profiles were obtained and their k

values were enhanced to 0.39 and

0.38 for BITN-0.08 and BITV-0.04, respectively. These values are about

twice as large as those of non-oriented (OF) ones, and are larger than the

reported value (k

= 0.27)

of HF BIT ceramics. In this investigation, a

saturated k

value of the BIT ceramic was not observed because of an

electrical breakdown during the poling process. Figure 27.20 shows the k

of the HF BITN-0.08 and the BITV-0.04 as a function of the orientation

factor, F. Accurate F was obtained using the X-ray diffraction (XRD) patterns

for the k

specimen, that is, XRD was performed directly on the k

specimen

shown in Fig. 27.21. From this measurement, the relationship between k

and F is clear: k

increases linearly with the increasing orientation factor, F.

From this figure, the k

value for the specimen with a perfect orientation

(F = 1) could be extrapolated to be almost 0.42.

Figure 27.22 shows the temperature dependence of the k

and the ratio of

impedance peak/depth, P/D, obtained from the resonance and antiresonance

curve for the HF BITN-0.08 ceramic. The k

higher than 0.35 was maintained

from room temperature up to 650°C. However, the P/D decrease rapidly at

temperatures higher than 350°C. In other words, sharp resonance and anti-

resonance peaks with high P/D greater than 1000 was kept up to 350°C. It

is clear that the HF BITN-0.08 ceramic maintains high piezoelectric properties

from RT up to 350°C. The donor doped-BIT ceramics seem to be a superior

candidate for lead-free high-temperature piezoelectric materials.

Intensity [arb. units]

10 20 30 40 50 60 70

2θ [°]

HF-BITN-0.08

OF-BITN-0.08

HF-BITV-0.04

OF-BITV-0.04

117

326

111

117

020,200

208,028

220

317,137

326

117

326

111

117

020,200

208,028

220

317,137

326

27.18

X-ray diffraction patterns of BITN-0.08 and BITV-0.04 ceramics

for the perpendicular plane (polished) of the HF and the OF.

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Handbook of dielectric, piezoelectric and ferroelectric materials846

Log impedance,

(Ω)

= 0.39

450 500 550

Frequency,

(kHz)

–30

–60

–90

450 500 550

Frequency,

(kHz)

= 0.38

88.7°

–30

–60

–90

Phase, θ (°)

HF BITN-0.08

Poling field (

) 10.5 kV/mm

Poling temp. (

) 200°C

Poling time (

) 7min

88.8°

HF BITV-0.04

Poling field (

) 8kV/mm

Poling temp. (

) 200°C

Poling time (

) 7min

27.19

Frequency dependence of the impedance,

(magnitude |

|, and phase θ, of HF BITN-0.08 and HF BITV-0.04.

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Grain orientation and electrical properties of bismuth 847

27.5 Conclusions and future trends

The results of our investigations on hot-forged (HF) ceramics indicate that

the HF method produces strongly preferred grain orientation, which was

confirmed by X-ray diffraction patterns, SEM observation and electrical

measurements.

BITV–0.04

BITN–0.08

0 0.2 0.4 0.6 0.8 1

Orientation factor,

Coupling factor,

(%)

27.20

Coupling factor,

, of HF BITN-0.08 and BITV-0.04 as a

function of orientation factor,

4mm

Forging axis

X-ray

Electrode

27.21

Shape for measuring of the orientation factor,

, and the

coupling factor,

27.22

Temperature dependence of

and the ratio of impedance

peak/depth,

, of the HF BITN-0.08.

Coupling factor,

(%)

P/D

HF BITN-0.08

0 100 200 300 400 500 600 700

Temperature,

(°C)

Peak/depth,

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Handbook of dielectric, piezoelectric and ferroelectric materials848

The degree of grain orientation F calculated from X-ray diffraction patterns

increases as an area ratio γ (or a thickness contraction rate λ), and is found

to be as large as F = 0.95 when γ = 8 in Bi

(BIT). Considerable

anisotropy in the dielectric constant ε

of HF BIT ceramics was observed,

and the value of ε

[⊥]/ε

[//] was 5 at the Curie temperature of 680°C.

Moreover, we have noted that remanent polarizations P

[⊥] and P

[//] in the

HF BIT ceramics correspond to the components P

along the a

-axis and

along the c

-axis, respectively, of the spontaneous polarization P

of a

single crystal. It was made clear that the remanent polarization P

[⊥] in the

HF ceramics is much larger than that of the non-oriented (OF) ones, the ratio

[⊥]/P

[//] and P

[⊥]/P

[OF] being about 11 and 4 in BIT, respectively, for

F = 0.95 at room temperature. The value of the remanent polarization P

[⊥]

for F = 0.95 is estimated to be 82% of the calculated value.

Grain orientation of calcium modified (Na

1/2

)

1–x

(NCBT)

system enhanced their piezoelectric and pyroelectric properties by two or

more times. From the viewpoint of piezoelectric applications, 5 mol% Ca-

modified, Mn-doped and grain-oriented NCBT (HF NCBT-5 + Mn) ceramics

are superior, with a lower free permittivity,

εε

(≅ 130) and a higher

electromechanical coupling factor, k

(= 0.36–0.40), along with a higher

anisotropy, k

(= 13–17). Therefore, the HF NCBT-5 + Mn ceramics

seem to be potential candidate materials for hydrophone applications or for

high-frequency ultrasonic transducers at high temperatures. Pyroelectric

properties of the HF NCBT-5 + Mn are also very interesting and the figure

of merit (F

) is comparable to that of the PZ-based or PT-based materials.

One of the bismuth layer-structured ferroelectrics (BLSF) series,

m–3+x

4–x

m–x

3m+3

(1 ≤ x ≤ 2 for m = 2, 0 ≤ x ≤ 2 for m = 3) (SBTTm

(x)) has very interesting dielectric, ferroelectric, and piezoelectric properties.

It is clear that SBTT2 (1.25) (m = 2) ceramic has high Curie temperature

(=785°C) and is considered as a superior candidate for piezo- or pyroelectric

sensor materials with high T

. The SBTT3 (0.3) ceramic shows a relatively

large remanent polarization, P

(=12.3 µC/cm

), compared with SBT (m = 2,

x = 0) and BIT (m = 3, x = 0). The SBTT3 (0.3) ceramic shows strong

ferroelectricity and high piezoelectricity. The electromechanical coupling

factor, k

and piezoelectric constant, d

, of the grain-oriented SBTT3 (0.3)

ceramic were relatively high: k

= 0.37 and d

= 45.3pC/N, respectively.

The mechanical quality factor, Q

, of the SBTT2 (1.5) ceramic was higher

than 6000. The SBTT ceramics seem to be a superior candidate for lead-free

piezoelectric resonator materials with high mechanical quality factors, Q

or high-temperature piezoelectric sensor materials with high Curie

temperatures.

47,48

Future trends of the research in bismuth layer-structured ferroelectrics

(BLSFs) seem to be focused on environmentally gentle lead-free piezoelectric

materials for high-temperature sensors, high-frequency applications and

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Grain orientation and electrical properties of bismuth 849

temperature-stable ceramic resonators. Also textured grain orientations such

as the templated grain growth (TGG) and the seeded polycrystal conversion

(SPC) methods are other important keywords for the future trends of BLSF

research and developments. Trend toward the thick and thin films is important

for film bulk acoustic wave (FBAW) and micro-electro-mechanical systems

(MEMS) applications.

27.6 Acknowledgments

This work was partially supported by a Grant-in-Aid for Scientific Research

and 17360327) from the Japan Society for the Promotion of Science.

The author would like to express sincere thanks to the late Professor

Masakazu Marutake of University of Electro-Communications for valuable

discussion, particularly on the calculation of the remanent polarization. He

would also like to thank Professor Emeritus Koichiro Sakata of Tokyo

University of Science for encouraging this work for many years.

27.7 References

1. Subbarao E C (1962), ‘Crystal chemistry of mixed bismuth oxides with layer-type

structure’, J. Am. Ceram. Soc. 45 (4), 166–169.

2. Ikegami S and Ueda I (1974), ‘Piezoelectricity in ceramics of ferroelectric bismuth

compound with layer structure’, Jpn. J. Appl. Phys. 13 (10), 1572–1579.

3. Takenaka T and Sakata K (1982), ‘Dielectric and piezoelectric properties of some

bismuth layer-structured ferroelectric ceramics’, Jpn. J. IEEE (C), J65-C (7), 514–

521 [in Japanese].

4. Takenaka T, Shoji K, Takai H and Sakata K (1976), ‘Ferroelectric and dielectric

properties of press forged Bi

ceramics’, Proc. 19th Jap. Cong. Materials

Research, Tokyo, 1975 (The Society of Materials Science, Kyoto, 1976), 230–233.

5. Takenaka T, Shoji K and Sakata K (1977), ‘Grain orientation and microstructure of

hot-forged Bi

ceramics’, Proc. 20th Jap. Cong. Materials Research, Kyoto,

1976 (The Society of Materials Science, Kyoto, 1977), 212–214.

6. Takenaka T and Sakata K (1980), ‘Grain orientation and electrical properties of hot-

forged Bi

ceramics’, Jpn. J. Appl. Phys. 19 (1), 31–39.

7. Takenaka T and Sakata K (1984), ‘Grain orientation effects on electrical properties

of bismuth layer-structured ferroelectric Pb

(1–x)

(NaCe)

x/2

solid solution’, J.

Appl. Phys. 55 (4), 1092–1099.

8. Takenaka T and Sakata K (1989), ‘Piezoelectric and pyroelectric properties of calcium-

modified and grain-oriented (NaBi)

1/2

ceramics’, Ferroelectrics 94, 175–

181.

9. Takenaka T and Sakata K (1983), ‘Pyroelectric properties of grain-oriented bismuth

layer-structured ferroelectric ceramics’, Jpn. J. Appl. Phys. 22 (Suppl. 22-2), 53–56.

10. Takenaka T and Sakata K (1991), ‘Pyroelectric properties of bismuth layer-structured

ferroelectric ceramics’, Ferroelectrics 118, 123–133.

11. Cummins S E and Cross L E (1967), ‘Crystal symmetry, optical properties, and

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