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 Tungsten-Bronze-Type Compounds
(such as PbNb2O6)
1.3 Bismuth Oxide Layer Structured Compounds
(such as Bi4Ti3O12 and PbBi2Nb2O9)
1.4 Lithium Niobate and Tantalate
(such as LiNbO3 and LiTaO3)
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)
Corner Sharing Octahedra
Mixed Oxide Ferroelectrics with
Corner Sharing Octahedra of O2- Ions
Inside each Octahedron  Cation Bb+ (3 < b < 6)
Space between the Octahedra  Aa+ Ions (1 <a < 3)
Corner Sharing Octahedra
In prototypic forms, Aa+, Bb+, and O2- ions geometrically coincide
 Non-Polar Lattice 
Phase Transitions Changes in Lattice Structure 
Aa+and Bb+ ions displaced w.r.t. O2- ions
 Polarized Lattice 
Perovskite-Type Compounds
Perovskite  Mineral Name of Calcium Titanate (CaTiO3)
B
A
O
General Chemical Formula ABO3
A  Cation with Larger Ionic Radii
B Cation with Smaller Ionic Radii
O  Oxygen
Perovskite-Type Compounds
Perovskite  Three-Dimensional Network of BO6- Octahedra
Perovskite  Cubic-Close-Packed of A and O ions with B in interstitial positions
Most Ferroelectric Perovskites
A2+B4+O3 or A1+B5+O3
Non-Ferroelectric Perovskites
A3+B3+O3
Perovskite-Type Compounds
Structural Classifications of A2+B4+O3 compounds
by A2+ and B4+ ionic radii
Perovskite-Type Compounds
Barium Titanate (BaTiO3)
Ti
Ba
O
Ti  6 coordinated to Oxygen (Octahedron)
Ba  12 coordinated to O (Cubic-Close-Packed)
O  4 coordinated to Ba AND 2 coordinated to Ti (Distorted Octahedron)
Perovskite-Type Compounds
Barium Titanate (BaTiO3)
Cubic-Close-Packed (CCP)
OR
Face-Centered-Cubic (FCC)
(abc-abc-abc arrangement)
Barium Titanate (BaTiO3)
Ti
Ba
O
Ti  6 coordinated to Oxygen (Octahedron)
Ba  12 coordinated to O (Cubic-Close-Packed)
O  4 coordinated to Ba and 2 coordinated to Ti (Distorted Octahedron)
Crystal Chemistry of BaTiO3
Phase Equilibria of BaTiO3 (BaO-TiO2)System
Very First Phase Equilibria
Effects of BaO/TiO2 Ratio
• Very little solubility of excesses BaO or TiO2
• Excess TiO2 results in Ba6Ti17O40 separated phase (melt at 1320 C) 
liquid phase sintering below 1350 C  wide grain sizes (5 –50 mm)
• Excess BaO results in Ba2TiO4 separated phase (melt at 1563 C) 
solid insoluble phase acts as grain growth inhibitor below 1450 C 
smaller grain sizes (1 –5 mm)
Phase Transitions in BaTiO3
Cubic (m3m)  Tetragonal (4mm)  Orthorhombic (mm2)  Rhombohedral (3m)
120 C
0C
-90 C
Paraelectric Phase
Ferroelectric Phase
Phase Transitions in BaTiO3
Lattice Parameters Variation
with Temperature during the
Phase Transitions
Through X-Ray and Neutron Diffractions,
during the Cubic-to-Tetragonal Phase
(Structural) Transition, Ba2+, Ti4+, and O2(w.r.t. center O2-) displaced along the c-axis
+0.06 Å, +0.12 Å, and –0.03 Å, respectively
Phase Transitions in BaTiO3
Spontaneous Polarization (Ps)
versus Temperature
I. No Spontaneous Polarization (Ps = 0)
II. Ps along [001] directions of the original cubic
III. Ps along [110] directions of the original cubic
IV. Ps along [111] directions of the original cubic
(Ps ~ 26 mC/cm2 at room temperature)
Phase Transitions in BaTiO3
Relative Permittivity of Single Crystal BaTiO3
Measured in the a and c Directions versus
Temperature
BaTiO3 Ceramics and Modifications
BaTiO3 ceramic was the first piezoelectric transducer developed,
BUT now use mainly for high-dielectric constant capacitors because
of TWO main reasons:
• Relatively low Tc (~120 C) limits its use as high-power transducers
• Low piezoelectric activities as compared to PZT
BaTiO3 for capacitor applications require special modifications to
suppress its ferroelectric/piezoelectric properties, and simultaneously
to obtain better dielectric features. This is done through additives
and compositional modifications, which can produce the following
effects:
• Shift of Curie Point and other transition temperatures
• Restrict domain wall motions
• Introduce second phases and compositional heterogeneity
• Control crystallite size
• Control oxygen content and the valency of the Ti ion
Effects of A and B Sites Substitutions in BaTiO3
Curie Point and Phase Transitions Shifters
This would enable the peak permittivity to be used in the temperature range
of interest. For example, Sr2+ in the A site would reduce the Curie Point
towards room temperature, while Pb2+ would raise the Curie Point. This
leads to tailoring dielectric properties with A and B sites substitutions.
Modified BaTiO3 Ceramics (Tc Suppressors)
Ba(Ti1-x Zrx )O3 Solid-Solution
Controlling the Permittivity
 Low
level
addition
the
dielectric peak rises sharply
 Higher level addition results in
peak
broadening
(probably
causes
by
“macroscopic
heterogeneity” in the composition
 Control of K in fine grained BT
 Control of “dirty” grain
boundary impedance to suppress
the Curie Peak at Tc (as compared
to
Curie
point
adjusted
compositions above)
Effects of Grain Sizes
At Curie Point
large grain  multiple domains 
more domain wall motions  higher K
At Room Temp
large grain  larger domains  less
internal stress  lower K
small grain  single domain  less
domain wall motions due to grain
boundary  lower K
small grain  smaller domains  less
internal stress relieved  larger
internal stress  higher K