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Types of Ferroelectric Materials
Ferroelectric Materials can be structurally categorized into 4 groups:
1.
Corner Sharing Octahedra:
1.1 Perovskite-Type Compounds
(such as BaTiO3, PT, PZT, PMN, and PLZT)
1.2 Lithium Niobate and Tantalate
(such as LiNbO3 and LiTaO3)
1.3 Bismuth Oxide Layer Structured Compounds
(such as Bi4Ti3O12 and PbBi2Nb2O9)
1.4 Tungsten-Bronze-Type Compounds
(such as PbNb2O6)
2.
Compounds Containing Hydrogen Bonded Radicals
(such as KDP, TGS, and Rochelle Salt)
3.
Organic Polymers (such as PVDF and co-polymers)
4.
Ceramic Polymer Composites (such as PZT-PE)
Done
LiNbO3 and LiTaO3 Single Crystals
! Important ferroelectric crystals !
(FE discovered in 1949)
 Large crystals grown by Czochralski’s technique
 Excellent piezoelectric, pyroelectric, optical and electro-optics
properties
 Very stable with very high Tc (1210 C for LiNbO3 and 620 C
for LiTaO3 )
 Chemically stable and insoluble in water and organic solvents
 Mostly used in crystal form (partly due to limited piezoelectric
activity in ceramic form)
 High mechanical Qm and low acoustic losses
 Good high frequency transducers and surface acoustic wave
devices
 Good high temperature transducers
 Infrared detectors (due to LiTaO3’s good pyroelectricity)
 Laser modulator, frequency multiplier, wave generator (as a
result of their good optic and electro-optic properties
LiNbO3 and LiTaO3 Single Crystals
O
Li
Nb
O
Nb Li
O
Nb Li
O
“Restricted Perovskite”
Structures of LiNbO3 and LiTaO3 are similar (but not
identical) to Ilminite (FeTiO3)  Connected Distorted
Oxygen Octahedra  Neighboring octahedra connected
through a “common tie-end” oxygen ion (corner-sharing of
MO6 (M = Nb or Ta))  Share “one” face with LiO6 
Share opposite face with empty O6 octahedral  Sequence
Nb (or Ta), vacancy, Li, Nb (or Ta), vacancy, Li, ......
LiNbO3 and LiTaO3 Single Crystals
Ferroelectric-Paraelectric Phase Transition
Second-order or “very close to” second-order phase transition

Ps along c-axis (ions displacement direction) and only 180° domains
(hard to get substantial piezoelectricity in ceramics)

Nb5+ moves to center of the oxygen octahedral
Li+ moves towards the nearest oxygen plane

Nb5+
at the median between the nearest oxygen planes (Ps = 0)

Trigonal (or Hexagonal) structure with 3m ferroelectric phase
LiNbO3 and LiTaO3 Single Crystals
Orientation Dependence of electromechanical coupling factor k31 of LiNbO3
Piezoelectric Applications
Anisotropic Properties : Directional Dependent Properties

High coupling (~0.50) and low-temperature dependence of resonant frequency
(higher than quartz)
ZYw (20°-50°)-cut
High Qm

Suitable high-frequency filter applications
LiNbO3 and LiTaO3 Single Crystals
Orientations for LiNbO3 crystal plates for ultrasonic transducers
High Frequency Ultrasonic Transducer Applications
Four cut-types for different applications (up to several hundred GHz)

Z-cut for thickness-extension vibrational mode (low kt ~ 0.17)
35° Y-cut for another thickness-extension vibrational mode
163° Y-cut for strong thickness-sheer mode
X-cut for strong thickness-sheer mode with high effective coupling factor of 0.68
Other Piezoelectric Applications
Ultrasonic Wave Propagator (due to low acoustic loss) 
 Microwave Acoustic Amplifier 
LiNbO3 and LiTaO3 Single Crystals
Pyroelectric Applications
High Curie temperature, substantial pyroelectric coefficient, chemical
and physical stability, and lower dielectric constant

Materials for Infrared Detectors
Electro-optic Applications
Most important applications
Good linear electro-optical effect
Photoelastic effect
Non-linear optical effect
Large-sized and optical quality crystals

Electro-Optical (EO) Modulation Devices
• linear EO modulator •
• traveling-wave modulator •
• wave-guide modulator •
• EO Q-switch •
Optical Frequency Doubler
Bismuth Oxide Layer Structure Ferroelectrics
Bi4Ti3O12 and Pb(Bi2Nb2O9)

Corner-linked perovskite-like sheets separated by (Bi2O2)2+ layers
with perovskite-like unit (1, 2, 3, or more units)

General Formula
(Bi2O2)2+(Am-1BmO3m+1)2A = Bi, Pb, Ba, Sr, Ca, Na, K
B = Ti, Nb, Ta, W, Mo, Fe, Co, Cr

Ferroelectric at room temperature
Melting point above 1100 C
Curie Temperature ~ 300-700 C
Bi4Ti3O12  Tc ~ 675 C
T < Tc : FE Monoclinic (Pseudo-Orthorhombic)
T > Tc : PE Tetragonal
Bismuth Oxide Layer Structure Ferroelectrics
Bi2PbNb2O9
Bi4Ti3O12
Bi4BaTi4O15
Alternating Layer Structures of Oxygen Octahedra
A  a layer composed of (Bi2Ti3O10)2B  a unit of an imaginary perovskite structure of BiTiO3
C  a layer of (Bi2O2)2+
Bismuth Oxide Layer Structure Ferroelectrics
Bi4Ti3O12 and Pb(Bi2Nb2O9)

Plate-like crystal structure

Highly anisotropic FE properties

Ceramics do not have very good piezoelectric properties
(as a result of low poling efficiency and high coercive field)

Improved by grain-orientation during processing
(tape-casting and hot-forged sintering
Important Piezoelectric Ceramics

Higher stability
Higher operating temperature (High Tc)
Higher operating frequency

Piezoelectric Resonator
Ferroelectric Optical Memory Devices
(Bi4Ti3O12 crystals)
Tungsten-Bronze-Type Ferroelectrics
Projection of the Tungsten-Bronze Structure on the (001) plane
(Orthorhombic and Tetragonal Cells are shown in solid and dotted lines)
Tetragonal Tungsten Bronze KxWO3 (x<1)

(A1)2(A2)4(C)4(B1)2(B2)8O30
A1, A2, C, B1, B2 are partially or fully occupied
Tungsten-Bronze-Type Ferroelectrics
Tetragonal Tungsten Bronze
(A1)2(A2)4(C)4(B1)2(B2)8O30
A1, A2, C, B1, B2 partially or fully occupied

IF one in six of A1 and A2 is vacant

AB2O6

5
ions in A1 and A2
5+
10 Nb ions in B1 and B2

Pb2+
Structure with Open Nature

Wide range of cation and anion substitutions
without loss of ferroelectricity

More than 85 Tungsten-Bronze-Type
ferroelectrics
PbNb2O6
Lead Niobate

First Non-Perovskite Oxide-Type
Ferroelectric Discovered
Tungsten-Bronze-Type Ferroelectrics
Lead Niobate (PbNb2O6)

High Tc ~ 560 C, Large d33/d31,
Large dh (dh = d33+2d31), and Low mechanical Q

Broad-band, high-temperature, transducer applications

Processing difficulties
• hard to obtain ceramics with < 7% porosity •
• a stable non-ferroelectric rhombohedral phase formed •
• large volume change from phase trnasformation during cooling leads to cracks •
Other Alkali/Alkali-Earth Niobate Materials
PbTa2O6, BaNb2O6, SrNb2O6, Pb½Ba½Nb2O6, Sr½Ba½Nb2O6

Potential Applications
laser modulation 
 pyroelectric detectors 
 hydrophones 
 ultrasonic applications 
Some Other Corner-Sharing Octahedra Ferroelectrics
CaZrO3, SrZrO3,
SrTiO3, CaTiO3,
PbHfO3, KNbO3,
NaNbO3, AgNbO3,
KTaO3, NaTaO3, AgTaO3, RbTaO3,
KTa1-xNbxO3 (KTN),
BiFeO3, WO3
and their solid-solutions
PbTa2O6, SrTa2O7, Cd2Nb2O7,
KSr2Nb5O15, Ba2NaNb5O15,
Sr4KLiNb10O30
(K,Na)(Sr,Ba)Nb2O6 (KNSBN)
and their solid solutions
NaVO3, AgVO3, BaAl2O4
!! This is jut a small portion of an endless list of ferroelectric materials!!
Types of Ferroelectric Materials
Ferroelectric Materials can be structurally categorized into 4 groups:
1.
Corner Sharing Octahedra:
1.1 Perovskite-Type Compounds
(such as BaTiO3, PT, PZT, PMN, and PLZT)
1.2 Lithium Niobate and Tantalate
(such as LiNbO3 and LiTaO3)
1.3 Bismuth Oxide Layer Structured Compounds
(such as Bi4Ti3O12 and PbBi2Nb2O9)
1.4 Tungsten-Bronze-Type Compounds
(such as PbNb2O6)
2.
Compounds Containing Hydrogen Bonded Radicals
(such as Rochelle Salt, KDP, and TGS)
3.
Organic Polymers (such as PVDF and co-polymers)
4.
Ceramic Polymer Composites (such as PZT-PE)
Done
Ferroelectrics with Hydrogen Bonded Radicals
KDP, TGS, and Rochelle Salt

Still being used in some applications

Superior in some features and properties

Large crystals with optical quality easily grown from aqueous solution
Rochelle salt has very good piezoelectric properties
KDP family has good electro-optic and non-linear optic properties
TGS family has very excellent pyroelectric properties

Disadvantages

Reasonably weak ferroelectricity, low Tc,
poor mechanical properties. and water soluble

Gradually being replaced by piezoelectric ceramics and crystals
Ferroelectrics with Hydrogen Bonded Radicals
Rochelle Salt NaKC4H4O6 • 4H2O
Sodium Potassium Tantalate Tetrahydrate

First Ferroelectric Material Discovered

2 Transition Temperatures (-18 C and +24 C)

-18 C  Monoclinic Ferroelectric with point group 2  +24 C

T > 24 C Paraelectric Orthorhombic with point group 222

Second-Order FE-to-PE Phase Transition

PE Phase with Piezoelectric Properties

Rochelle Salt
Excellent Piezoelectric Transducers
Sonar, Hydrophone, Microphone
Ferroelectrics with Hydrogen Bonded Radicals
Rochelle Salt
Projection of the structure on (001) plan
showing the hydrogen-bond system
Ferroelectrics with Hydrogen Bonded Radicals
Rochelle Salt
Temperature dependence of the dielectric constant
showing the dielectric anomalies
corresponding to two transition temperatures
Ferroelectrics with Hydrogen Bonded Radicals
KDP KH2PO4
Potassium Dihydrogen Phosphate

Non-Ferroelectric Phase at Room Temperature
(Tetragonal 42m)

Non-Ferroelectric with Piezoelectric at Room Temperature

Curie Temperature at ~ –150 C

FE Orthorhombic Phase with point group mm2

First-Order FE-to-PE Phase Transition

KDP
Good Electro-Optic and Non-Linear Optic Properties
Electro-optic devices, High-power pulse laser
Electro-optic modulator, and Light-valve devices
Ferroelectrics with Hydrogen Bonded Radicals
KDP
Structural Framework of KDP
(Hydrogen positions are shown
only schematically)
Ps along c-axis as a result of K+ and
P5+ ions displacement in c-directions
(Ps aligned in 180°)
Ferroelectrics with Hydrogen Bonded Radicals
TGS (NH2CH2COOH)3H2SO4
Triglycine Sulfate

FE Phase at Room Temperature
(Monoclinic point group 2)

Curie Temperature at ~ 49.7 C

PE Monoclinic Phase with point group 2/m
(Paraelectric with E-induced Piezoelectricity)

Second-Order FE-to-PE Phase Transition (order-disorder type)

TGS
Good Pyroelectric Properties for Infrared Detectors
Largest response sensitivity among known pyroelectric crystals
Disadvantages include easily depolarized (even at room temperature)
(as a result of low Tc)
Ferroelectrics with Hydrogen Bonded Radicals
TGS
Structure of TGS: I, II, and III represent different glycine groups
Hydrogen-bonds between Groups II and III
Ordering of N in Group I results in Ps in b-direction
Types of Ferroelectric Materials
Ferroelectric Materials can be structurally categorized into 4 groups:
1.
Corner Sharing Octahedra:
1.1 Perovskite-Type Compounds
(such as BaTiO3, PT, PZT, PMN, and PLZT)
1.2 Lithium Niobate and Tantalate
(such as LiNbO3 and LiTaO3)
1.3 Bismuth Oxide Layer Structured Compounds
(such as Bi4Ti3O12 and PbBi2Nb2O9)
1.4 Tungsten-Bronze-Type Compounds
(such as PbNb2O6)
2.
Compounds Containing Hydrogen Bonded Radicals
(such as Rochelle Salt, KDP, and TGS)
3.
Organic Polymers (such as PVDF and co-polymers)
4.
Ceramic Polymer Composites (such as PZT-PE)
Done
Organic Polymer Ferroelectrics
During 1940s

Piezoelectricity in biological materials, e.g. wood

In the Mid 1970s

Ferroelectricity and Pyroelectricity
in synthetic materials
PVDF or PVF2
(P(VDF-TrFE), e- irradiated P(VDF-TrFE), Polyurethane, Silicone, and Acrylic)

Applications utilized Electromechanical Properties
Underwater ultrasonic transducers
Electro-acoustic transducers
(microphones, earphones, loudspeakers)
Other applications
button-switches
coin-sensors
Organic Polymer Ferroelectrics
PVDF  PVF2  (CH2-CF2)n  Polyvinylidene Fluoride

P(VDF-TrFE) Co-Polymers  TrFE  Tri-Fluoroethylene

e-irradiated P(VDF-TrFE) Co-Polymers

Ferroelectric Materials
Piezoelectric/Pyroelectric/Electrostrcictive Applications
Better for uses in transducers and medical imaging applications
• Advantages •
low-density provides little acoustical mismatch with water and human tissues
flexible and conformable to any shape
• Problems •
large dielectric loss at high-frequency
low Tc and degradation t low-temperature (70-100 C)
low poling efficiency in samples thicker than 1 mm
Organic Polymer Ferroelectrics
PVDF and P(VDF-TrFE) Co-Polymers
PVDF is a polar material by nature
(due to H+ and F- positions with respect to C-atoms)
Polarization can be induced by stretching, high-temperature
annealing, or application of high electric field
Organic Polymer Ferroelectrics
PVDF and P(VDF-TrFE) Co-Polymers
P-E loop with different crystal forms
d31 at different poling field
Ep
Polarization is induced from orienting crystalline phase of polymer
under application of high electric field

Piezo/Pyro Properties depend on degree of crystallinity and FE polarization
in the crystalline phase, and also on the poling conditions
(both electric field and temperature)
Organic Polymer Ferroelectrics
e-irradiated P(VDF-TrFE) Co-Polymers
Dielectric constant and loss as
a function of temperature for
P(VDF-TrFE) 50/50 copolymer
after 100 Mrad e-irradiation
dose
P-E Loops for P(VDF-TrFE)
50/50 copolymer at room
temperature before and after
e-irradiation dose
Organic Polymer Ferroelectrics
e-irradiated P(VDF-TrFE) Co-Polymers
P-E Loops for P(VDF-TrFE)
50/50 copolymer at different
temperatures after 100 Mrad
e-irradiation dose
Variation
of
remanent
polarization with temperature
for
P(VDF-TrFE)
50/50
copolymer before and after eirradiation dose
Organic Polymer Ferroelectrics
e-irradiated P(VDF-TrFE) Co-Polymers
Electric field induced strain
versus electric field for P(VDFTrFE) 50/50 copolymer at
room temperature after 100
Mrad e-irradiation dose
Influence of irradiation on
induced strain for P(VDFTrFE) 50/50 copolymer at
room temperature
Types of Ferroelectric Materials
Ferroelectric Materials can be structurally categorized into 4 groups:
1.
Corner Sharing Octahedra:
1.1 Perovskite-Type Compounds
(such as BaTiO3, PT, PZT, PMN, and PLZT)
1.2 Lithium Niobate and Tantalate
(such as LiNbO3 and LiTaO3)
1.3 Bismuth Oxide Layer Structured Compounds
(such as Bi4Ti3O12 and PbBi2Nb2O9)
1.4 Tungsten-Bronze-Type Compounds
(such as PbNb2O6)
2.
Compounds Containing Hydrogen Bonded Radicals
(such as Rochelle Salt, KDP, and TGS)
3.
Organic Polymers (such as PVDF and co-polymers)
4.
Ceramic Polymer Composites (such as PZT-PE)
Done
Ceramic-Polymer Composites
Why composites?

Drive for desired properties NOT obtainable in single phase
(ceramics or polymers)

For instance, Electromechanical Transducers
Requirements 
Maximum piezoelectric sensitivity, minimum density for better matching
flexible for conformity to any curved surface

!! Single Phase Ceramics or Polymers DO NOT match all these requirements !!
PZT: high d33, low dh, low voltage coefficient g
PVDF: highly sensitivity, low strain coefficient

 Composites 
Optimize the most useful properties of the two phases
which do not ordinarily appear together
Ceramic-Polymer Composites

Made up of an active ceramic phase
embedded in a passive polymer phase

Properties depend on 
Connectivity, volume percentage of ceramic phase,
and spatial distribution of the active phase in the composite

Connectivity
(developed by Newnham, Skinner, and Cross)

Arrangement of component phases within a composite

A-B

A: number of direction in which the active phase is self connected
B: number of direction in which the passive phase is self connected

Diphasic Composies : 10 types : 0-0, 1-0, 2-0, 3-0, 1-1, 2-1, 3-1, 2-2, 3-2, 3-3
Ceramic-Polymer Composites
10 Connectivity Patterns for Diphasic Composites
Ceramic-Polymer Composites
Connectivity of Constituent Phases in Piezoelectric
Ceramic-Polymer Composites
Ceramic-Polymer Composites
The piezoelectric coefficient of the
composite for the series connection can
be expressed as follows
V 1d 33 2 33  2V 2d 33 1 33

1 2
V  33  2V 1 33
The piezoelectric coefficient of the
composite for the parallel connection
can be expressed as follows
V 1d 33 2 s33  2V 2d 33 1 s33

1 2
V s33  2V 1s33
1
1
c
d 33
And using g33 = d33/33 :
c
g 33 V 1g 33  2V 2g 33
Note that: a very thin low r will
lower d, but no effect on g
c
d 33
If 1d33 >> 2d33 and 1s33 << 2s33 , then
for small 1V:
cd
33
~ 1d33 and very high cg33
!! Enhanced Properties!!
Ceramic-Polymer Composites
Volume Fraction Dependence of r, d33,
g33 in 3-1 PZT:Polymer Composite
Ceramic-Polymer Composites
Main Applications for Transducers

Transducers for Sonar 
Hydrophone : an element(s) in a sonar system used to detect ultrasound
gh = hydrostatic voltage coefficient = voltage induced from applied stress
dh = hydrostatic charge coefficient = charge induced from applied stress
Figure of Merit (FOM) = gh•dh
Medical Transducers 
Non-ionizing, low-risk o reproductive organs and foetus
Major organs and malfunction

Ideal Transducer Materials
Requirements 
High electro-mechanical coupling coeffcient
High FOM, Low Q, Acoustic Impedance Matching with medium

 Piezoelectric Ceramic-Polymer Composites 
Ceramic-Polymer Composites
Comparison of Hydrophone Figure of Merit
of Several Piezoelectric Ceramics and Transducer Designs
Ceramic-Polymer Composites
Piezoelectric Composites to Use as
Sensors, Actuators, and Transducers
Types of Ferroelectric Materials
Ferroelectric Materials can be structurally categorized into 4 groups:
1.
Corner Sharing Octahedra:
1.1 Perovskite-Type Compounds
(such as BaTiO3, PT, PZT, PMN, and PLZT)
1.2 Lithium Niobate and Tantalate
(such as LiNbO3 and LiTaO3)
1.3 Bismuth Oxide Layer Structured Compounds
(such as Bi4Ti3O12 and PbBi2Nb2O9)
1.4 Tungsten-Bronze-Type Compounds
(such as PbNb2O6)
2.
Compounds Containing Hydrogen Bonded Radicals
(such as Rochelle Salt, KDP, and TGS)
3.
Organic Polymers (such as PVDF and co-polymers)
4.
Ceramic Polymer Composites (such as PZT-PE)
Done