[PPT] - Micro-Brilouin scattering study of field cooling effects on PowerPoint Presentation

SLIDE 1

Micro-Brilouin scattering study

f field cooling effects on

ferroelectric relaxor PZN-9%PT single crystals

Jae-Hyeon Ko1*, Do Han Kim2, Seiji Kojima2, D. C. Feng3

1Department of Physics, Hallym University, Chuncheon, Gangwondo, Korea 2Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki, Japan 3Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai,

200050, China * Corresponding author: hwangko@hallym.ac.kr

SLIDE 2

I. What is relaxor ferroelectrics?

Diffused,

rounded and frequency-dependent dielectric constant (high dielectric constant near room temperature)

Existence

f

nanopolar clusters at high temperatures

No macroscopic change of

the symmetry in many compounds

Dipolar

glass model / random field model

PbMg1/3Nb2/3O3

SLIDE 3

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

SLIDE 4

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

SLIDE 5

Phase Diagram of PZN-x%PT

What changes can we expect from

field cooling studies on PZN-9%PT rather than 8% composition?

Comparison

between PZN-8%PT and PZN-9%PT is necessary for our better understanding

f

the morphotropic phase boundary(MPB).

SLIDE 6

II. Experimental Details:

Tandem multi-pass Fabry-Perot interferometer

1. The conventional scanning-type

tandem multipass Fabry-Perot Interferometer is characterized by high contrast and resolution.

2. The combination of tandem FPI

and a microscope made it possible to examine elastic properties of very small samples whose sizes are only a few microns. 3. The phonon propagating direction was along [001] of PZN- 9%PT at a backward scattering geometry, which was the same direction of the applied DC bias

field. Incident polarization was

[010], and no analyzer was used for the scattered light.

SLIDE 7

III. Results (1) – temperature dependence of

Brillouin spectra of PZN-9%PT under ZFC

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

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

60
40
20

20 40 60

90

C

Frequency (GHz)

85

C

ZFH process

Intensity (arb. unit)

21

C

SLIDE 8

III. Results (2) – Comparison of Brillouin data

between PZN-4.5% and 9%PT

Clear hysteresis can be seen from the Brillouin shift measured during

heating and cooling in both components.

It may indicate complex dynamics related to the formation of

microdomains and glassy dynamics at low temperatures in case of PZN-4.5%PT and first-order character of the successive phase transitions in case of PZN-9%PT .

300 350 400 450 500 550

40 41 42 43 Temperature (K)

Cooling Heating

Frequency (GHz)

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

PZN-4.5%PT PZN-9%PT

SLIDE 9

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'

III. Results (3) –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.

SLIDE 10

III. Results (4) – Field cooling effects on the

Brillouin spectra of PZN-9%PT

50 100 150 200 250 1.0 1.5 2.0 2.5 3.0 3.5 38 39 40 41 42 43 E//[001], q//[001]

Phonon damping (GHz) ZFC 1.1 kV/cm 2.2 kV/cm 4.4 kV/cm 6.7 kV/cm

Temperature (

C)

LA mode Frequency (GHz)

(1) 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. (2) The discontinuity at TC−T under ZFC process is smeared out during the FC process as the amplitude of the biasing electric field increases. (3) The phonon damping has been greatly suppressed by the application

f the poling field probably due to the

marked decrease of scattering at domain walls.

SLIDE 11

III. Results (5) – Bias-field dependence of the

Brillouin data at constant temperatures

0 1 2 3 4 5 6 7 8 91011121314 38.5 39.0 39.5 40.0 40.5 41.0 41.5 42.0 42.5

E//[100], q//[100] LA mode Frequency Shift (GHz) ∆ν Electric Field (kV/cm)

230

C

210

C

205

C

190

C

180

C

170

C

110

C

70

C

50

C

30

C
At temperatures far above TC−T ~162 oC,

LA induced by the biasing field gradually approaches the value of the tetragonal phase. However, as the temperature approaches closer to TC−T , the change of the frequency shift becomes more drastic.

At temperatures of 180 and 170 oC above

TC−T , the smallest applied fields of 1.1 kV/cm was enough for making the frequency shift equal to the value of a tetragonal phase.

On the other hand, a tetragonal phase is

induced from a rhombohedral a phase at 50

C by applying an electric field of 6.7 kV/cm.

Only at 30

C

a low-temperature rhombohedral phase can be stable under the biasing field up to 6.7 kV/cm.

SLIDE 12

50 100 150 200 250 2 4 6 8

R

r X

T C

Temperature (

C)

Electric Field (kV/cm)

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

III. Results (6) – Tentative E-T phase diagram
f PZN-9%PT
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.

SLIDE 13

Conclusions

Variation of phase transition have been examined in PZN-9%PT under

the electric field along the [001] direction by the high-resolution micro- Brillouin scattering. Very sharp step-like changes in both LA mode frequency and damping factor have been observed in ZFH and ZFC processes. The significant thermal hysteresis was observed in cubic-to-tetragonal and tetragonal-to-rhombohedral phase transitions. The absolute values of frequency shift and damping factor depend on the thermal history, which may reflect the microheterogeneity of relaxor ferroelectrics.

The first-order nature of the cubic-to-tetragonal phase transition seems

to disappear at the poling field of 6.7 kV/cm along the [001] direction, while the sharp step-like transition from tetragonal to low-temperature phase still remained. The temperature range of a tetragonal phase of PZN-9%PT has been significantly widened under the electric field along [001] into both low-temperature and high-temperature sides, which is in contrast to the situation of PZN-8%PT. A new electric field-temperature phase diagram of PZN-9%PT has been determined based on the changes of the phase transition temperatures.

SLIDE 14

References

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