Ferroelectric Lead Titanate (PbTiO 3 or PT) Lattice constants versus temperature for PbTiO 3 Ferroelectric with similar structure to BaTiO 3 Phase transition

Ferroelectric Lead Titanate (PbTiO3 or PT)

Lattice constants versus temperature for PbTiO3

• Ferroelectric with similar structure to BaTiO3

• Phase transition from Paraelectric Cubic to Ferroelectric Tetragonal phases

• High Curie Point (~ 490 C)• Suitable for high-frequency and high-

temperature applications, as a result of high Curie Point, low dielectric constant (r ~ 200), and large

electromechanical anisotropy (kt/kp > 10)• An important end member of widely used PZT

(xPbTiO3-(1-x)PbZrO3)• Difficult to obtain a dense sintered body due to large volume change upon cooling ( as a

result of large c/a = 1.063 (strain > 6%))• Modified compositions with various dopant

( alkaline or rare earth elements, such as Ca, Sr, and Ba, and other dopants such as Sn, W, Bi, and Y to

obtain a crack free ceramic and to improve properties

(Ferroelectric?) Lead Zirconate (PbZrO3 or PZ)

Lattice constants versus temperature (in pseudo-tetragonal) for PbZrO3

Dielectric constant versus temperature for PbZrO3 ceramic

Above 230 C, the structure is cubic-perovskite (similar to BaTiO3) Dielectric constant shows “anomaly” at 230 C (reaches high peak)

Above 230 C, dielectric constant follows Curie-Weiss relation Ferroelectric Material ?

No ferroelectric hysteresis below “transition temperature” 230 C Volume contraction upon cooling (c/a < 1)

Orthorhombic Structure Anti-Ferroelectric Material

Antiferroelectricity

Antiferroelectricity

Anti-ferroelectric materials Non-polar, Non-ferroelectric materials that revert to a ferroelectric state

when subjected to sufficiently high electric field, causing a “double-loop hysteresis”

Lead Zirconate Titanate (Pb (Zrx Ti1-x)O3 or PZT) System

PZT (xPbZrO3 – (1-x)PbTiO3)

Binary Solid Solution PbZrO3 (antiferroelectric matrial with orthorhombic structure)

andPbTiO3 (ferroelectric material with tetragonal perovskite structure)

Perovskite Structure (ABO3) with Ti4+ and Zr4+ ions “randomly”

occupying the B-sites

Important Transducer Material (Replacing BaTiO3)

• Higher electromechanical coupling coefficient than BaTiO3

• Higher Tc results in higher operating and fabricating temperatures• Easily poled

• Wider range of dielectric constants• relatively easy to sinter at lower temperature than BaTiO3

• form solid-solution compositions with several additives which results in a wide range of tailored properties


PZT Solid Solution Phase DiagramZr/Ti ratio 52/48 MPB


PZT Solid Solution Phase DiagramZr/Ti ratio 52/48 MPB showing structure changes


Abrupt changes in lattice constants at room temperature for

PZT system lead to anomalous behaviors in dielectric and

piezoelectric properties

Variation of polarization with PZ contents indicates that the highest

polarization is in the rhombohedral structure that does

not have highest r and d


Composition dependence of dielectric constant (K) and

electromechanical planar coupling coefficient (kp) in PZT system

This shows enhanced dielectric and electromechanical properties at the

MPB

Increased interest in PZT materials with MPB-compositions for

applications


Variation of room temperature piezoelectric properties with PZT compositions

Electromechanical coupling coefficients Piezoelectric d constants

Note: highest values on tetragonal side of the composition


Variation of room temperature piezoelectric properties with PZT compositions

Piezoelectric g strain coefficients Dielectric constants

Note: highest dielectric constants on tetragonal side of the composition BUT high piezoelectric g strain coefficients into rhombohedral side


Value of the mixed phase region at the MPB in poling of PZT vs other perovskite ferroelectrics

Possible domain states


Advantages of PZT Solid-Solution System

• Above Curie Point (or Curie Temperature), the symmetry is cubic with perovskite structure

• High Tc across the diagram leads to more stable ferroelectric states over wide temperature ranges

• There is a two-phase region near the Morphotropic Phase Boundary (MPB) (52/48 Zr/Ti composition) separating

rhombohedral (with 8 domain states) and tetragonal (with 6 domain states) phases

• In the two-phase region, the poling may draw upon 14 orientation states leading to exceptional polability

• Near vertical MPB results in property enhancement over wider temperature range for chosen compositions near the MPB

Compositions and Modifications of PZT System

1. Effects of composition and grain size on properties

MPB compositions (Zr/Ti = 52/48)

Maximum dielectric and piezoelectric properties

Selection of Zr/Ti can be used

to tailor specific properties

High kp and r are desired Near MPB compositions

ORHigh Qm and low r are desired

Compositions away from MPB

Grain Size (composition and processing)

Fine-Grain ~ 1 m or less

Coase-Grain ~ 6-7 m

Some oxides are grain growth inhibitor (i.e. Fe2O3)

Some oxides are grain growth

promoter (i.e. CeO2)

Dielectric and piezoelectric properties are grain-size

dependent


Dependence of dielectric and piezoelectric properties on average grain size in the ceramic Pb(Zr0.51Ti0.49)O3 + 0.1 wt% MnO2 at a

constant density of 7.70-7.85 g/cm3

Piezoelectric properties increase linearly with increasing grain size


2. Modification by element substitutionElement substitution cations in perovskite lattice (Pb2+, Ti4+, and Zr4+) are replaced partially by other cations with the same chemical valence

and similar ionic radii and solid solution is formed

Pb2+ substituted by alkali-earth metals, Mg2+, Ca2+, Sr2+, and Ba2+

PZT replaced partially by Ca2+or Sr2+

Tc BUT kp, 33 , and d31 Shift of MPB towards the Zr-rich side

Density due to fluxing effect of Ca or Sr ions

Ti4+ and Zr4+ substituted by Sn4+ and Hf4+ , respectively

Ti4+ replaced partially by Sn4+ c/a ratio decreases with increasing Sn4+ content

Tc and stability of kp and 33


3. Influences of low level “off-valent” additives (0-5 mol%) on dielectric and piezoelectric properties

Two main groups of additives:1. electron acceptors (charge on the replacing cation is smaller)

(A-Site:K+, Rb+ ; B-Site: Co3+, Fe3+, Sc3+, Ga3+, Cr3+, Mn3+, Mn2+, Mg2+, Cu2+)(Oxygen Vacancies)

Reduce both dielectric and piezoelectric responses Increase highly asymmetric hysteresis and larger coercivity

Much larger mechanical Q

““Hard PZT”Hard PZT”

2. electron donors (charge on the replacing cation is larger)(A-Site: La3+, Bi3+, Nd3+; B-Site: Nb5+, Ta5+, Sb5+)

(A-Site Vacancies) Enhance both dielectric and piezoelectric responses at room temp

Under high field, symmetric unbiased square hysteresis loops low electrical coercivity

““Soft PZT”Soft PZT”


Dielectric constant vs temperature of various types PZT materials

Modified PZT System

3.1 Hard Doping: Hard PZT

(A-Site:K+, Rb+ ; B-Site: Co3+, Fe3+, Sc3+, Ga3+, Cr3+, Mn3+, Mn2+, Mg2+, Cu2+)

Oxygen Vacancies in either A-sites or B-sites or Both (Electroneutrality)

Two Pb2+ replaced by two K+ ions OR Two Zr4+ (or Ti4+) replaced by two Fe3+ ions

Space charges inhibit domain motion and Insoluble doped ions inhibit grain growth

Increased Qm and Ec, Decreased loss tangent, and Lowered dielectric and

piezoelectric activities

““Hard PZT”Hard PZT”

Rugged Applications(High Temperature and High Driving Loads)

Modified PZT System

3.2 Soft Doping: Soft PZT

(A-Site: La3+, Bi3+, Nd3+; B-Site: Nb5+, Ta5+, Sb5+)

A-Site Vacancies (Electroneutrality)

Two Pb2+ replaced by two La3+ ions OR Two Zr4+ (or Ti4+) replaced by two Nb5+ ions

Easier transfer of atoms leads to increased domain motion at lower electric filed ( Ec)Internal stress relieve more easilyIncreased domain wall mobility

Lowered Qm and Ec, Increased loss tangent, and Increased dielectric and

piezoelectric activities

““Soft PZT”Soft PZT”

Applications required higher piezoelectric activities(Sensors, Actuators, and Transducers)

““Hard PZT” MaterialsHard PZT” Materials

Curie temperature above 300 C NOT easily poled or depoled except at high temperature

Small piezoelectric d constants Good linearity and low hysteresis

High mechanical Q values Withstand high loads and voltages

““Soft PZT” MaterialsSoft PZT” Materials

Lower Curie temperature Readily poled or depoled at room temperature with high field

Large piezoelectric d constants Poor linearity and highly hysteretic

Large dielectric constants and dissipation factors Limited uses at high field and high frequency

Modified PZT System

Modified PZT System

3.3 Other Doping Ions (Ce, Cr, U, Ag, Ir, Rh, Ni, Mn, Nb, Al)

Ce-doped PZT high , Qm, Qe, , Ec, kp

Cr-doped PZT high Qm, tan , with lower kp

U-doped PZT high Qm, , and tan

Ag, Ir, or Rh-doped PZT high Qm, kp , and lower

Complexed doping (with two or more metal elements)

Better than single ion doping (enhances both Qm and kp)

Compound Dopings (BiFeO3, AgSbO3 or Ca2Fe2O5)

Reducing dielectric loss at high field

Examples of Practical Modified PZT System

1. Materials for ceramic filters: 1.1 Range 30-150 MHz (modified PT)

0.99[0.96PbTiO3 + 0.04 La2/3TiO3] + 0.01MnO2

1.2 Range 10-20 MHz Pb1.03[(Nb2O6)0.07(CrO2)0.03(Zr0.52Ti0.48O3)0.90] + 0.5 wt%MnO2 + 1 wt% La2O3

1.3 Range 1-10 MHz Pb0.95Sr0.05Mg0.03(Zr0.52Ti0.48)O3 + 0.5 wt%CeO2 + 0.225 wt% MnO2

2. Materials for underwater ultrasonic transducers:

Pb0.95Sr0.05 (Zr0.54Ti0.46)O3 + 0.9 wt%La2O3 + 0.9 wt% Nb2O5

3. Materials for high-voltage generator:

[Pb(Nb1/2Sb1/2)O3]0.05 [PbTiO3]0.41 [PbZrO3]0.54 + 0.2 mol%Nb2O5 + 0.2 mol%Y2O3 + 0.1 wt% MnO2

4. Materials for electro-acoustic applications:

[Pb(Ni1/3Nb2/3)O3]0.50 [PbTiO3]0.355 [PbZrO3]0.145


Examples of Commercially Available PZT from APCExamples of Commercially Available PZT from APC


Examples of Commercially Available PZT from PKIExamples of Commercially Available PZT from PKI

Navy Type I (PKI-402 and PKI-406)High power and low losses for driver applications (ultrosonic cleaners, fish finders,

medical applications, and sonars)

Navy Type II (PKI-502)High electromechanical activity and high dielectric constant for receiver applications (hydrophones, phono pickups, sound detectors, accelerometers,

delay lines, flow detectors, and flow meters)

Navy Type III (PKI-802 and PKI-804)High Q and low losses under extreme driving conditions for medical applications

Navy Type V (PKI-532)High sensitivity, high dielectric constant and low impedance for sensor applications

Navy Type VI (PKI-552 and PKI-556)High dielectric constant and large displacement for sensor applications PKI-556 is modified to give higher g33, higher k33, and lower loss factor

La-Doped Lead Zirconate Titanate (PLZT) System

(Pb1-xLax)(Zr1-yTiy)1-x/4VB0.25xO3 and (Pb1-xLax)1-x/2(Zr1-yTiy)VA

x/2O3

La3+ into A-sites with B-site-vacancies created and Vacancies created on A-sites(Charge Balance with combination of both A and B-sites vacancies)

Perovskite Structure (ABO3) similar to BaTiO3 and PZT

Important (First) Transparent Ceramic (Replacing Single Crystals)

(Prepared by Chemical Co-Precipitation and Hot-Press Sintering in Oxygen Atmosphere)

• Increased squareness of the hysteresis loop• Decreased coercive field and increased dielectric constant

• Maximum coupling coefficients and increased mechanical compliance• Enhanced optical transparency

As a result of high solubility of La3+ in the oxygen octahedral structure

Series of single-phase solid-solution compositions

Less unit-cell distortion and reduced optical anisotropy

Uniform grain-growth and densification leads to single-phase, pore-free microstructure

Phase Diagram of the PZT and PLZT Solid-Solution Systems


(Pb1-xLax)(Zr1-yTiy)1-x/4VB0.25xO3

( x ~ 2-30 at%)

Notation x / y / (1-y)

8/65/35 Pb0.92La0.08(Zr0.65Ti0.35)0.98O3

Majority of ResearchPLZT 6-9/65/35

In the phase diagram

1) La solubility depends on PZ/PT 2) Excess La results in reduced

transparency due to mixed phases of PLZT, La2Zr2O7, and La2Ti2O7 3) La reduces Tc 4) MPB compositions have

enhanced properties

Phase Diagram of the PZT and PLZT Solid-Solution Systems


Ferroelectric tetragonal and

rhombohedral phases

Orthorhombic Anti-ferroelectric

phasesCubic

paraelectric phases

MPB

Pyroelectric Applications

MPB Compositions for transducer

applications

Diffused metastable relaxor (electrically inducible to

ferroelectric)for quadratic strain and

electro-optics

Room Temperature Phase Diagram of PLZTwith representative hysteresis loops at various compositions


Room Temperature Phase Diagram of PLZTshowing different electro-optic characteristics at various compositions


PbZrO3 PbTiO3Mole% PbZrO3

n ~ E

n ~ E2

Complex relationship between n

and E

In the tetragonal ferroelectric (FT)

region high EC hysteresis loops

Linear electro-optic behavior for E < EC

(linear electro-optic modulators, and optical switches)

In the rhombohedral ferroelectric (FR)

Low EC hysteresis loops Optical

memory applications (light valves, optical-storage-display devices)

PLZT ceramic compositions with the relaxor ferroelectric behavior are

characterized by a slim hysteresis loop Large quadratic electro-optic effects for

making flash protection goggles


Electro-optic applications of PLZT ceramics depends on the composition

8/40/60 linear region

8/65/35 memory region

9/65/35 quadratic region

Examples of Applications of PLZT CeramicsExamples of Applications of PLZT Ceramics


Flash Goggles : nuclear and arc radiationsColor Filter : optical shutter

Display : reflective display similar to LCDImage Storage : strain-induced birefringence

Thin-Film Optical SwitchPhotostriction

Documents

Ferroelectric Lead Titanate (PbTiO 3 or PT) Lattice constants versus temperature for PbTiO 3 Ferroelectric with similar structure to BaTiO 3 Phase transition