Acoustic properties of PZN-x%PT single crystals probed by micro- - - PowerPoint PPT Presentation

한국물리학회 2005년 가을 학술발표회 전북대학교

Acoustic properties of PZN-x%PT single crystals probed by micro- Brillouin scattering

Jae-Hyeon Ko1*, Do Han Kim2, Seiji Kojima2

1Department of Physics, Hallym University, Chuncheon, Gangwondo, Korea 2Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki, Japan

* Corresponding author: hwangko@hallym.ac.kr

한국물리학회 2005년 가을 학술발표회 전북대학교

• I. What is relaxor ferroelectrics?

Existence

• f

nanopolar clusters at high temperatures below the Burn’s temperature

Diffused,

rounded and frequency-dependent dielectric constant

No

• verall

macroscopic change of the symmetry in many compounds

Dipolar glass model

random field model SRBRF model …

PbMg1/3Nb2/3O3

한국물리학회 2005년 가을 학술발표회 전북대학교

Examples of Ferroelectric Relaxors

Complex Perovskites

B-site complex

Lead magnesium/zinc niobate PbMg1/3Nb2/3O3, PbZn1/3Nb2/3O3 Lead scandium/magnesium tantalate PbSc1/2Ta1/2O3, PbMg1/2Ta1/2O3 (cf: BaMg1/2Ta1/2O3)

A-site complex Lead lanthanum zirconate titanate (Pb1-xLax)(ZryTi1-y)O3 (PLZT100(x/y/1-y))

Tungsten bronze structure compositions

Strontium barium niobate Sr1-XBaXNb2O6

한국물리학회 2005년 가을 학술발표회 전북대학교

Complex Perovskite Relaxors

Relaxor-based complex perovskite ferroelectrics:

• Pb[(Zn1/3Nb2/3)1-xTix]O3 (PZN-x%PT)
• Pb[(Mg1/3Nb2/3)1-xTix]O3 (PMN-x%PT)
• utstanding piezoelectric properties when the

electric field is along non-polar direction like [001]

• strain level ~ 1.7 %
• electromechanical coupling constant > 90%

promising materials for electromechanical

applications like actuators, transducers…

superior to PZT due to the single crystal form

한국물리학회 2005년 가을 학술발표회 전북대학교

* Park et al., J. Appl. Phys. 82 (1997) 1804.

한국물리학회 2005년 가을 학술발표회 전북대학교

Phase Diagram of PZN-x%PT

?

• K. Ohwada et al., PRB 67 094111 (2004)

한국물리학회 2005년 가을 학술발표회 전북대학교

• What is the E-T phase diagram of PZN-9%PT, and

what are the differences compared to that of PZN- 8%PT?

• What changes would be expected from the field

effects on the relaxor behaviors of PZN-4.5%PT?

한국물리학회 2005년 가을 학술발표회 전북대학교

• II. Experimental Details:

(1) Tandem multi-pass Fabry-Perot interferometer

( ) ( )

514.5 nm * 10 mm 4 4 10 m 1.0 mm

L

f d D λ µ π π = <

• Sandercock-type tandem 6-pass Fabry-

Perot Interferometer

• micro-Brillouin scattering system

한국물리학회 2005년 가을 학술발표회 전북대학교

Light scattering from condensed Matters

4 2 sin sin 2 2

i i

n q k θ π θ λ = =

Ki,ωi Kf,ωf Kf q R

4 2 2 2

1 ( , , ) ( ,0) ( , ) exp ( ) 16 2

• f

if f if if f i

I k I R dt q q t i t R ω δε δε ω ω π ε π

+∞ −∞

⎡ ⎤ = < > − ⎢ ⎥ ⎢ ⎥ ⎣ ⎦

∫

q

Ki Dielectric constant fluctuations of wave vector q and frequency ω determines the scattering event in the experiment. What causes the fluctuations in the dielectric constant?

한국물리학회 2005년 가을 학술발표회 전북대학교

Brillouin scattering in solids

Raman spectroscopy – optic phonons Brillouin spectroscopy – acoustic phonons

, 2

1 ( , ) ( , ) t p t

αβ αβ γλ γλ γλ

δε ε ε − = ∑ r r

v Sound velocity v Elastic stiffness coefficient cij=ρv2 Elasto-optic constants pαβ,γλ

한국물리학회 2005년 가을 학술발표회 전북대학교

• II. Experimental Details:

(2) PZN-x%PT single crystals

PZN-4.5%PT PZN-9%PT

• two compositions

x = 4.5%, 9% [100]/[010]/[001] ITO coating for DC field (E // [001])

• either ZFH(zero-field-

heating)/ZFC(zero-field cooling) or FC(field- cooling) scan during cooling

• backscattering

geometry

한국물리학회 2005년 가을 학술발표회 전북대학교

• III. Results (1) – temperature dependence of

Brillouin spectra of PZN-x%PT under ZFH/ZFC

• 60
• 40
• 20

20 40 60

90

• C

Frequency (GHz)

85

• C

Intensity (arb. unit)

21

• C

longitudinal acoustic mode

• Typical Brillouin spectra consisted of
• ne longitudinal acoustic (LA) mode, one

weak transverse acoustic (TA) mode and a central peak (CP), where the TA mode is noticeable only in the low-temperature rhombohedral phase below 73 oC.

• From a symmetrical point of view, the

TA mode is not allowed at the present scattering geometry in both cubic and tetragonal phases.

ZFH process

transverse acoustic mode

한국물리학회 2005년 가을 학술발표회 전북대학교

PZN-4.5%PT PZN-9%PT

200 400 600 800 41 42 43 44 45 46 Brillouin Shift (GHz) Temperature (K) cooling heating

300 350 400 450 500 550

40 41 42 43 Temperature (K)

Cooling Heating

Frequency (GHz)

• two phase transitions from cubic

to tetragonal, and then to rhombohedral phases on cooling

• Clear hysteresis in two phase

transition temperatures

• broad softening accompanied

by broad phonon damping, typical behaviors in relaxor ferroelectrics

한국물리학회 2005년 가을 학술발표회 전북대학교

• III. Results (2) – Field cooling effects on the

Brillouin spectra of PZN-9%PT

• The temperature range of the tetragonal

phase is significantly extended into both high- and low-temperature sides under the electric field along the [001] direction.

• The discontinuity at TC−T

under ZFC process is smeared out during the FC process as the amplitude of the biasing electric field increases.

• The phonon damping has been greatly

suppressed by the application of the poling field probably due to the marked decrease

• f scattering at domain walls.
• D. H. Kim et al., JAP 98, 044106 (2005)

한국물리학회 2005년 가을 학술발표회 전북대학교

50 100 150 200 250 2 4 6 8

R

• r X

T C

Temperature (

• C)

Electric Field (kV/cm)

E // [001], q // [001]

• A E-T phase diagram of PZN-9%PT can be constructed from the present

study by observing the changes of the frequency shift as a function of the temperature under the constant biasing field or of the biasing field at a constant temperature.

• The change of the Curie temperature (Tc) under the applied field gives the

values of dTc/dE ~ 7.8 × 10−3 K cm/V and -5.8×10−3 K cm/V for TC-T and TT-R phase boundaries, respectively. E-T phase diagram of PZN-9%PT

한국물리학회 2005년 가을 학술발표회 전북대학교

• III. Results (3) – Field cooling effects on the

Brillouin spectra of PZN-4.5%PT

E // [001]

• two field-induced anomalies at

143 and 106 oC under the electric field of ~ 10kV/cm along [001]

• consistent with dielectric data,

which reports two phase transitions from cubic to tetragonal, and then to rhombohedral on cooling

• may be explained by two-step

phase transitions from paraelectric phase to microdomain structure, and then from micro- to macrodomain structures upon cooling

• D. H. Kim et al., APL 87, 072908 (2005)

한국물리학회 2005년 가을 학술발표회 전북대학교

• M. Shen et al., APL 83, 731 (2003)

Medium-range ordered phase between the long- range and short-range ordered phases ?

한국물리학회 2005년 가을 학술발표회 전북대학교

• III. Results (4) – Micro-heterogeneity of

PZN-4.5%PT

• Clear positional dependence of acoustic

properties at low temperatures

• Existence of micro-heterogeneity over a

length scale of at least a few microns ?

• D. H. Kim et al., APL 87, 072908 (2005)

한국물리학회 2005년 가을 학술발표회 전북대학교

PZN-4.5%PT

Bdikin et al., APL 83, 4232 (2003)

(001)-oriented (111)-oriented

한국물리학회 2005년 가을 학술발표회 전북대학교

• IV. Conclusion
• Electric field-temperature phase diagram of PZN-9%PT has for the first time

been suggested based on the change of acoustic properties upon the application of dc bias field probed by Brillouin scattering experiment, which showed differences from that of PZN-8%PT.

• Clear microheterogeneity has been observed in PZN-4.5%PT, which might

be related to the complex domain structure of this composition.

• Two step anomalies in acoustic properties have appeared in PZN-4.5%PT

upon field-cooling, consistent with dielectric measurements. This may signify two-step transformations from paraelectric phase to microdomain structure, and then from micro- to macrodomain structures upon cooling.

한국물리학회 2005년 가을 학술발표회 전북대학교

Acknowledgments

• This research was supported by Hallym University Research

Fund, 2005 (HRF-2005-23).

• This work was supported in part by the 21st Century COE

(Center of Excellence) Program, ”Promotion of Creative Interdisciplinary Materials Science for Novel Function” under MEXT (the Ministry of Education, Culture, Sports, Science and Technology), Japan.

한국물리학회 2005년 가을 학술발표회 전북대학교

PMN-35%PT

30oC

• F. Jiang and S. Kojima, APL 77, 1271 (2000)

한국물리학회 2005년 가을 학술발표회 전북대학교

한국물리학회 2005년 가을 학술발표회 전북대학교

300 350 400 450 500 550 2 3 40 41 42 43 FWHM (GHz)

ε' (x 10

4)

Temperature (K)

ZFC ZFH

Frequency (GHz) 2 4 6

ε'

Brillouin frequency shift and hypersonic damping of 9%PT

• Two abrupt step-like changes in

frequency shift and FWHM are very significant at two phase transition temperatures from cubic-to-tetragonal and tetragonal-to-rhombohedral phases(TC-T and TT-R).

• The differences of frequency shift

and FWHM in both phases below TC-T,

• bserved at the same measured

point of PZN-9%PT during heating and cooling processes, may reflect the microheterogeneity which is inherent in ferroelectric relaxors near MPB.