Compositional Dependence of Compositional Dependence of Electromechanical Behavior of Ba,ZrElectromechanical Behavior of Ba,Zr--Codoped Codoped

Sodium Bismuth TitanateSodium Bismuth Titanate

Andrey N. SoukhojakAndrey N. SoukhojakLehigh UniversityLehigh University

YetYet -- Ming ChiangMing ChiangMITMIT

I CI M, June 2003I CI M, June 2003

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4. TITLE AND SUBTITLE Compositional Dependence of Electromechanical Behavior ofBa,Zr-Codoped Sodium Bismuth Titanate

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Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18

Collaborators

Greg Farrey

Sossity Sheets

Haifeng Wang

Hong Cai

Ben Nunes

Garry Maskaly

Out line

• I nt roduct ion: doped Na1/ 2Bi1/ 2TiO3 (NBT) as the best high-st rain lead- free com pet itor oflead- relaxors

• Studied com posit ions and experim ental setup

• Diverse elect rom echanical behavior

• Free energy expansion and phase diagram

• Nanost ructure im aged by TEM

Doped NBT as a lead- free a lternat ive

† Y.-M. Chiang group (MIT).* Park & Shrout, 1997.

–New Lead-Free actuator m aterials

–High st rain at high fields

–Polycrystals with actuat ion com parable to PZT-8, PMNT

–Single crystals 2x higher ult im ate st rain

Na1/2Bi1/2TiO3 polycrystals† vs. lead perovskites*

Z3B14

Z4B12

Z4B14

Single Crystal

0.56 0.58 0.6 0.62 0.64 0.66 0.68 0.7 0.72 0.74 0.76 0.781.2

1.25

1.3

1.35

1.4

1.45

1.5

1.55

1.6

RA,Å

RB, Å

PMN PZN PZPT

BT

NBT

BZ

Tilt

Shift Line of close

packing (t= 1)

Sh

i ft

& T

ilt

NBZ

)(2 OB

OA

RRRR

t+

+=

Goldschm idt tolerance factor:

Ti4+ Zr4+

Pb2+

Ba2+

Bi3+

Na+

Map of Distort ions in Perovskites ABO3*

* Kassan-Ogly & Naish, Acta Cryst. B42 297 (1986)

Intensities of octahedral tilt superlattice reflections vs. temperature – neutron diffraction data for single crystal NBT.

Vakhrushev et al. Ferroelectrics 63 [1-4] 153-60 (1985).

a0a0c+a−a−a−

Phases of NBT

R3c ↔ P4bm ↔ Pm3m

Jones & Thomas, Acta Cryst. B58, 168-178 (2002).

–

NBT- BT Solid Solut ions

BNT–Na1/2Bi1/2TiO3, F–ferroelectric phase, AF–antiferroelectric phase, P–paraelectric phase

Takenaka et al., Jap. J. Appl. Phys., 30 [9B], 2236 (1991)

Composit ions close to morphot ropic phase boundary (MPB) at 6% BT exhibit enhanced piezoelect r ic performance

(Bi1/2Na1/2)1-xBaxZryTi1-yO3 ( BNBZT)

Hypothet ic Phase Diagram

→ BaTiO3

→ N

a 1/2

Bi 1

/2Z

rO3

6 %

FETetrFERh

PE

NBT

• Zr on B-site suppressesferroelect r icity* , so at som e concent rat ion the phase should becom e paraelect r ic (PE)

• Term inat ion of the Rh-Tet r boundary is a t r icr it ical point at which elect rom echanical response should reach its m axim um

_______________* Rossetti, J. Solid State Chem. 144 (1) 188-194 (1999)

Electrom echanically Tested Polycrystalline

(Bi1/2Na1/2)1-xBaxZryTi1-yO3 ( BNBZT) Sam ples

0 5 10 15 200

1

2

3

4

5

x⋅100% (mol. % Ba)

%Zr

NBT

• Sam ples by solid state synthesis m ethod, sintered into ∅10 m m disks with > 95% density:

• Com posit ion was confirm ed by EPMA

• > 98% perovskite phase purity was confirm ed by XRD

mol.

y⋅100%

Voltage Source & Polarizat ion Meter

Au-electroded Sample

V-Cont rol and Data Acquisit ion System

Silicone oil bath

Elect rom echanical Test ing Setup

Precision Workstationby Radiant Technologies Inc.

Strain Sensor

Nano-DVRTby Microstrain Inc.

Electrom echanical Behavior of BNBZTw ith 1 % Zr and 7 % Ba ( z1 b7 )

� �

� �

-40

-30

-20

-10

0

10

20

30

40

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

Field, kV/cm

Pol

ariz

atio

n, µ

C/c

m²

0

0.1

0.2

0.3

0.4

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

Field, kV/cm

Stra

in, %

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60

Field, kV/cm

Pol

ariz

atio

n, µ

C/c

m²

0.2 Hz1 Hz10 Hz22 Hz47 Hz

0

0.1

0.2

0 10 20 30 40 50 60

Field, kV/cm

Stra

in, %

0.2 Hz1 Hz10 Hz22 Hz47 Hz

Bipolar actuat ion Unipolar actuat ion

Electrom echanical Behavior of BNBZTw ith 3 % Zr and 4 % Ba ( z3 b4 )

Bipolar actuat ion Unipolar actuat ion�

-40

-30

-20

-10

0

10

20

30

40

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

Field, kV/cm

Pol

ariz

atio

n, µ

C/c

m²

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60

Field, kV/cm

Pol

ariz

atio

n, µ

C/c

m²

0.2 Hz1 Hz10 Hz47 Hz

0

0.1

0.2

0 10 20 30 40 50 60

Field, kV/cm

Stra

in, %

0.2 Hz1 Hz10 Hz47 Hz

0

0.1

0.2

0.3

0.4

-60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60

Field, kV/cm

Stra

in, %

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 500 1000 1500 2000P²

S

0.2 Hz1 Hz10 Hz22 Hz47 Hz

Frequency I ndependent Elect rostr ict ive Relat ion

S = Q P2

Typical for all sam ples bipolar st rain vs. (polarizat ion) 2

Com posit ional m ap of Q·102 (m 4/ C2)�

�

��%D�

��=U�

Com posit ional m ap of large signal d33 (pC/ N)

�%D�=U�,� G���,��� ��

�% Zr

% Ba

Com posit ional m ap of large signal H33 · 1 0 - 3

�

%D�=U�,� ε���� ��−�⋅�,�(� )�

�% Zr

% Ba

Com posit ional m ap ofrelat ive unipolar polar izat ion hysteresis HP at 0 .2 Hz

HP = ∆Pmax / Pmax

0

2

4

6

8

10

12

14

0 10 20 30 40 50 60

Field, kV/cmP

olar

izat

ion,

µC

/cm

²

0.2 Hz1 Hz10 Hz22 Hz47 Hz

% Zr

% Ba

�

%D�=U�,� G3�,��� ��

���

Free Energy Expansion

U (P) = aP2 + bP4 + cP6

G(E) = U (P) – EP

∂G / ∂P = 0 ⇒ E = 2aP + 4bP3 + 6cP5

60 45 30 15 0 15 30 45 602000

0

2000

4000

6000

E = 0E = 30E = 60min G

P, µC/cm2

G,kJ/m3

60 50 40 30 20 10 0 10 20 30 40 50 6040

30

20

10

0

10

20

30

40

P

E

60 50 40 30 20 10 0 10 20 30 40 50 6040

30

20

10

0

10

20

30

40

Pi

Exx 1,

Emini Exx 0,,

60 50 40 30 20 10 0 10 20 30 40 50 600

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

Q Pi( )2⋅

Exx 2, 0.034+

Emini Exx 0,, �]�E��

j( )

60 50 40 30 20 10 0 10 20 30 40 50 6050

40

30

20

10

0

10

20

30

40

50

Pi

Exx 1,

Emini Exx 0,,

60 50 40 30 20 10 0 10 20 30 40 50 600

0.15

0.3

0.45

0.6

Q Pi( )2⋅

Exx 2,

Emini Exx 0,, �]�E���

Envelope curves from free energy expansion and experim ental data points

P

S

n% Zr

o % Ba

a b · 103

c · 107

Com posit ional Maps of Free Energy Expansion Coefficients

Free energy U [ kJ/ m 3] vs. polar izat ion P profiles

% NBZ

PE(Incipient FE)

FETetragonal

FERhombohedral

% BTNBT

Phase Diagram Based on Electrom echanical Behavior of Polycrystalline BNBZT Sam ples

Phases:PE—paraelect r icFE—ferroelect r ic

Nanostructure of High- Strain NBT- BT Crystal

Raw TEM image Fourier-filtered image

10 nm

Raw TEM image Fourier-filtered imageRaw TEM image Fourier-filtered image

10 nmNo larger scale features observed

[001]

Nanodom ains in z3 b6 Polycrystal

Raw [001] TEM image Fourier-filtered image

4 nm

No larger scale features observed

• BNBZT system offers r ich possibilit ies for lead- free ferroelect r ics with high elect romechanical propert ies

• The peak of elect romechanical response has been found at the composit ion z2b7

• Composit ional dependence of ferroelect r ic phase stabilit y in the BNBZT system has been mapped by means of a free energy expansion in terms of polarizat ion with coefficients obtained by fit t ing of the predicted to the observed hysteresis loops.

• Nanodomain relaxat ion as a mechanism of frequency dependent elect romechanical response of BNBZT has been supported by m icroscopic observat ions

Sum m ary