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7/9/2014 Physics 403 Summer 2014 2
Ferroelectricity.
outline
•Ferroelectricity. Definition
•Discovery
•Main properties
•Phenomenological theory
• Some materials
•Relaxors
•Applications
7/9/2014 Physics 403 Summer 2014 3
Ferroelectricity. Definitions.
Ferroelectric Materials. A ferroelectric material is
a material that exhibits, over some range of
temperature, a spontaneous electric polarization
that can be reversed or reoriented by application
of an electric field.
An American National Standard
IEEE Standard Definitions of
Primary Ferroelectric Terms
7/9/2014 Physics 403 Summer 2014 5
Rochelle Salt KNaC4H4O6*4H2O
Joseph Valasek (1897-1993)
University of Minnesota
1. J. Valasek, Phys. Rev. 17, 475 (1921) 2. J. Valasek, Phys. Rev. 19, 478 (1922)
Fig.1. The first published
hysteresis loop [1] Fig3. Piezoelectric
response as a function
of temperature [2]
Ferroelectricity: Discovery
1920 1969
7/9/2014 Physics 403 Summer 2014 6
Ferroelectricity: Two classes of ferroelectrics
Displacement type
N
O
O
Order-Disorder
disorder
order
NaNO2
Ba
Ti O
P
P BaTiO3
-40 -30 -20 -10 0 10 20 30 40
-40
-30
-20
-10
0
10
20
30
40 Sn:Ti = 0.24:0.11
PLZST ceramics
P (
C
/cm
2)
EDC
(kV/cm)
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Ferroelectricity: Polarization reversible
(P-E hysteresis)
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Ferroelectricity: Domains
+
-
Pnet~0
Single domain state
Multi domain state
180o domain pattern
90o domains
Y Lu et al. Science 1997;276:2004-2006
Courtesy of Igor Lukyanchuk
http://www.lukyanc.net/stories/nano-worldofdomains
7/9/2014 Physics 403 Summer 2014 9
Ferroelectricity: Domains
Courtesy of Benjamin Vega-Westhoff
and Scott Scharfenberg, P403, Fall2009
BaTiO3
BaTiO3
Crystal from Forschungsinstitut für mineralische und metallische
Werkstoffe -Edelsteine/Edelmetalle
KH2PO4
Courtesy of Allison Pohl, P403,
Fall2009
KD2PO4 191K
PMN-PT40%
PMN-PT30%
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Ferroelectricity: Landau-Ginzburg
phenomenological theory
EPcPbPaPFP ...6
1
4
1
2
1 642
Free energy Order parameter (polarization) Electric field
To find the equilibrium solution we need to
find the minima of FP by solving the equation: 0
P
F
Ignoring higher terms we can get the linear solution:
0F
aP EP
aE
P 1
Assuming linear dependence of a on temperature we will have:
1( )
cT T
C and finally we will have Curie-Weiss law
( )c
C
T T
-7 0 7
0
10
20
30
40
50
60
70
80
F (
a.u
.)
P (a.u.)
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Ferroelectricity: Landau-Ginzburg
phenomenological theory
In case of b>) (C>0 also) We will
have the solution for second order
phase transition with two
equilibrium points –p0 and p0. Both
these states are equivalent
T>Tc
T=Tc
T<Tc
E=0
p0 -p0
-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12-20
-10
0
10
20
30
40
F (
a.u
.)
P (a.u.)
-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12-20
-10
0
10
20
30
40
F (
a.u
.)
P (a.u.)
-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12-20
-10
0
10
20
30
40
F (
a.u
.)
P (a.u.)
-40 -30 -20 -10 0 10 20 30 40
-40
-30
-20
-10
0
10
20
30
40 Sn:Ti = 0.24:0.11
PLZST ceramics
P (
C
/cm
2)
EDC
(kV/cm)
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Ferroelectricity: Landau-Ginzburg
phenomenological theory
EPcPbPaPFP ...6
1
4
1
2
1 642
Including EP term can illustrate
the P-E hysteretic behavior
-Ps Ps
Pr
Pr
Ps
400 450 5000
3
6
9
T (K)
'/1
000
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Ferroelectricity: Susceptibility
0P E
0 0 0 0 0(1 )D E P E E E E
For ferroelectrics >>1 and ≈
Curie-Weiss law:
00)(
CWTT
C
C=1.9*105;
TCW=385.2K
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Ferroelectricity: Typical ferroelectric materials
KH2PO4
Courtesy Max Candocia, P403 Spring 2011
EDC=1.2kV/cm
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Ferroelectricity: Typical ferroelectric materials
BaTiO3
cubic
tetragonal orthorhombic rhombohedral
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Ferroelectricity: Typical ferroelectric materials
Number of publications concerning ferroelectricity.
From Jan Fousek “Joseph Valasek and the Discovery of
Ferroelectricity”
Number of ferroelectric substances discovered in each year.
Springer Handbook of Condensed Matter and Materials Data
TC(K) Ps (C/cm2)
KDP
type KH2PO4 123 4.75
KD2PO4 213 4.83
RbH2PO4 147 5.6
Perovskites BaTiO3 408 26
KNbO3 708 30
PbTiO3 765 >50
LiTiO3 938 50
LiNbO3 1480 71
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Antiferroelectrics
<P> ~0
PNZST (film)
PLZST (ceramic)
Courtesy of E. Colla and
City University of Hong Kong
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Antiferroelectricity in BaTiO3
Courtesy of Alan Selewa and
Nathaniel Scheidler (2014,
unpublished)
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Ferroelectricity: Relaxors - PMN Pb(Mg1/3 Nb2/3)O3
Frequency dispersion of e’
at different temperatures
Temperature dependencies of the
real part of the dielectric constant
measured in a broad frequency
range: 3*10-3 -106 Hz [1,2]
1. E.V. Colla et all., J. Phys.: Cond. Matter, 4,3671, (1992)
2. E.V. Colla et all. J. Appl. Phys., 83, 3298, (1998)
150 200 250 300 350 400 4500
7
14
21
28
35
T (K)
'/1
03
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
10
00
/'
101
102
103
104
105
106
4
6
8
10
12
14
16
18
20
22
220K
230K
240K
250K
'/1
03
f (Hz)
0.0 0.1 0.2 0.3 0.4 0.5
300
400
500 Literature data
single crystals
ceramics
Tc
(K)
x
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(PMN)(1-x)(PT)(x)
phase diagram
“Relaxor”state
(pseudocubic)
Regular ferroelectric
(tetragonal)
Paraelectric
(cubic)
(PMN)0.9(PT)0.1 (PMN)0.7(PT)0.3
(PMN)0.6(PT)0.4
(PMN)0.7(PT)0.3 PT: PbTiO3, ferroelectric with
Curie temperature 763K
Ferroelectricity: Solid solution relaxor-regular
ferroelectric.
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Material Dielectric
constant
Piezoelectric
coefficient, (pC/n)
Electromechanical
coupling factorQuartz 4.5 2.3 0.1
Rochelle salt (30C) 9.2 27 0.3
Barium titanate
ceramic
1700 190 0.52
Lead zirconate
titanate PZT 45/55
450 140 060
PMN-PT (sc) 4200 2200 0.92-0.94
PZN-PT (sc) 2500 2400 0.91-0.93
Actuators
Transducers
Adaptive optics
Capacitors
Line motors for SFM
Transducer stack for
ultrasonic sonar application
(TRS Ceramics)
Piezoelectric
properties of different
materials
Ferroelectricity: Relaxors - some aplications