Acoustic properties of lead- based relaxor ferroelectric single - - PowerPoint PPT Presentation

Acoustic properties of lead- based relaxor ferroelectric single crystals studied by micro- Brillouin scattering

Jae-Hyeon Ko1*, Do Han Kim1, Seiji Kojima1, S. G. Lushnikov2 and Guo-Zuang Ye3

1Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki, Japan 2Ioffe Physicotechnical Institute, Russian Academy of Sciences, St. Petersburg,

194021, Russia

3Department of Chemistry, Simon Fraser University, Burnaby, British Columbia,

Canada V5A 1S6

Outline

Introduction to relaxor ferroelectrics Experimental Details

• tandem Fabry-Perot interferometer(FPI)

combined with a microscope

Experimental results and discussion

• complex dielectric constant of PMT
• Brillouin data of PZN-4.5% and 9%PT
• Brillouin data of PMT

Conclusions

• 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

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

Complex perovskite relaxors

Relaxor-based complex perovskite ferroelectrics:

• Pb[(Zn1/3Nb2/3)1-xTix]O3 (PZN-x%PT) PZN-4.5%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

• 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

• f

very small samples whose sizes are only a few microns.

• III. Results (1) – complex dielectric constant
• f PMT and BMT

20 21 2000 4000 6000 50 100 150 200 250 300 150 300 450 600 750

(a)

(10 kHz ~ 1 MHz)

BMT PMT

10 Hz 1 MHz

ε"

Temperature (K)

ε'

(10 kHz ~ 1 MHz)

BMT (b) PMT

10 Hz 1 MHz

1 1 max

exp[ / ( )]

• B

f

E k T T ν ν

− −

= −

• Typical dielectric dispersion in both real

and imaginary part of the dielectric constant

• Vogel-Fulcher relation from the maximum
• f ε’(ν)

with Tf = 124 K E/kB = 1250 K ν0 =1.6 x 1012 Hz

Does the existence of Tf indicate real freezing in the relaxation dynamics of relaxor ferroelectrics?

* A.K. Tagantsev, PRL 72, 1100 (1994)

*

( ) ( ) (ln ) 1 g d i τ ε ε ε ε τ ϖτ

∞ ∞

− = − +

∫

It is necessary to check the temperature dependence of the maximum relaxation time in the spectrum g(τ) in order to find whether there is a real freezing or not.

• III. Results (2) – Brillouin data of 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-

• rder 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

100 200 300 400 500 600 700 800 900 1000 41 42 43 44 45 46

TB

B M T P M T

Brillouin Shift (GHz) Temperature (K)

• III. Results (3) – Brillouin and dielectric data
• f PMT for extracting τmax(T)

50 100 150 200 250 300 20 21 2000 4000 6000

(a)

(10 kHz ~ 1 MHz)

BMT PMT

10 Hz 1 MHz

Temperature (K)

ε'

τmax(T=205K) ~ 1/2π(100kHz) ~ 1.6 x 10-6 s τmax(T=650K) ~ 1/2π(45GHz) ~ 3.5 x 10-12 s

• The onset of the dielectric and

acoustic dispersion gives us the temperature dependence of τmax.

Two assumptions for the analysis of τmax

(1) A single relaxation time distribution g(τ) contributes to both dielectric and acoustic dispersions. (2) The softening of Brillouin shift starts when the leading edge τmax of g(τ) becomes comparable to the time scale of the acoustic frequency of the longitudinal acoustic mode on cooling. g(τ,Τ) ln τmax (T2) ln τmin T1 T2 < T1 Tf~T3 < T1 ln τ

Temperature dependences of characteristic relaxation frequency ν(Tmax) and maximum relaxation time τmax

4.8 5.2 5.6 6.0 2 4 6 1 2 3 4 5 6 2 4 6 8 10 12

(a)

log ((2πτmax)

• 1) (Hz)

log (ν(Tmax)) (Hz) 1000/T (K

• 1)

1000/T (K

• 1)

(b)

1 1 max

exp[ / ( )]

• B

f

E k T T ν ν

− −

= −

with Tf = 124 2 K E/kB = 1250 K ν0 =1.6 x 1012 Hz ±

1 max

(2 ) exp[ / ( )]

B f

E k T T τ πν

−

= −

with Tf = 119 6 K E/kB = 1310 K ν0 =5.5 x 1011 Hz ±

Comparison of PMT with other relaxor ferroelectrics

PMT: this work PMN, PST: A.E.Glazounov, APL 73, 856 (1998) PLZT: S. Kamba, J. Phys.: Condens. Matter 12, 497 (2000)

• In four kinds of relaxor ferroelectric single crystal, the temperature

dependence of τmax followed the Vogel-Fulcher law with the same freezing temperature as that obtained from the frequency dependence of the temperature of dielectric maximum.

• It may serve as a direct evidence for the real freezing of the relaxation

time spectrum of PMT and other relaxor ferroelectrics.

Conclusions

1.

The temperature dependence of the maximum relaxation time,

τmax, in the spectrum g(τ) showed that there is a real freezing of

the relaxation time distribution at a finite temperature ~120 K in PMT relaxor single crystal.

2.

The freezing process is described by the Vogel-Fulcher law for

τmax with the same freezing temperature obtained from the

maximum dielectric constant.

3.

Brillouin scattering can be used to extend the frequency range for

• btaining

information

• f

relaxation dynamics

• f

relaxor ferroelectrics up to GHz range.

* Please refer to “E-08-P” presented by Mr. Do Han Kim regarding Brillouin study on PZN-9%PT.