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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