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Ferroelectric Lead Titanate (PbTiO 3 or PT) - PowerPoint PPT Presentation


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Ferroelectric Lead Titanate (PbTiO 3 or PT). Ferroelectric with similar structure to BaTiO 3 Phase transition from Paraelectric Cubic to Ferroelectric Tetragonal phases High Curie Point (~ 490 C)

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slide1

Ferroelectric Lead Titanate (PbTiO3 or PT)

  • 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 (er ~ 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

Lattice constants versus temperature for PbTiO3

slide2

(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 

slide4

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”

slide5

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)
  • and
  • PbTiO3 (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
slide6

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

PZT Solid Solution Phase Diagram

Zr/Ti ratio 52/48 MPB

slide7

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

PZT Solid Solution Phase Diagram

Zr/Ti ratio 52/48 MPB showing structure changes

slide8

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

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 er and d

slide9

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

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

slide10

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

Electromechanical coupling coefficients

Piezoelectric d constants

Variation of room temperature piezoelectric properties with PZT compositions

Note: highest values on tetragonal side of the composition

slide11

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

Piezoelectric g strain coefficients

Dielectric constants

Variation of room temperature piezoelectric properties with PZT compositions

Note: highest dielectric constants on tetragonal side of the composition

BUT high piezoelectric g strain coefficients into rhombohedral side

slide12

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

Possible domain states

Value of the mixed phase region at the MPB in poling of PZT

vs other perovskite ferroelectrics

slide13

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

  • 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
slide14

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 er are desired

 Near MPB compositions

OR

High Qm and low er are desired

 Compositions away from MPB

Grain Size

(composition and processing)

Fine-Grain ~ 1 mm or less

Coase-Grain ~ 6-7 mm

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

slide15

Compositions and Modifications of PZT System

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

slide16

Compositions and Modifications of PZT System

2. Modification by element substitution

  • Element 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, e33 , 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 e33 

slide17

Compositions and Modifications of PZT System

  • 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”
  • 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”
slide18

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

Dielectric constant vs temperature of various types PZT materials

slide19

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 ORTwo 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”

Rugged Applications

(High Temperature and High Driving Loads)

slide20

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 easily

Increased domain wall mobility

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

“Soft PZT”

Applications required higher piezoelectric activities

(Sensors, Actuators, and Transducers)

slide21

Modified PZT System

  • “Hard 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” 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
slide22

Modified PZT System

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

Ce-doped PZT  high r, Qm, Qe, e, Ec, kp 

 Cr-doped PZT  high Qm, tan d, with lower kp 

 U-doped PZT  high Qm, r , and tan d 

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

 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

slide23

Examples of Practical Modified PZT System

  • 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
  • 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
slide24

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

Examples of Commercially Available PZT from APC

slide25

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

Examples 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

slide26

La-Doped Lead Zirconate Titanate (PLZT) System

  • (Pb1-xLax)(Zr1-yTiy)1-x/4VB0.25xO3 and(Pb1-xLax)1-x/2(Zr1-yTiy)VAx/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
slide27

La-Doped Lead Zirconate Titanate (PLZT) System

(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 Research

PLZT 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

slide28

La-Doped Lead Zirconate Titanate (PLZT) System

MPB

Ferroelectric tetragonal and rhombohedral phases

Pyroelectric Applications

Orthorhombic

Anti-ferroelectric phases

Cubic

paraelectric phases

MPB Compositions for transducer applications

Diffused metastable relaxor (electrically inducible to ferroelectric)

for quadratic strain and electro-optics

Phase Diagram of the PZT and PLZT Solid-Solution Systems

slide29

La-Doped Lead Zirconate Titanate (PLZT) System

Room Temperature Phase Diagram of PLZT

with representative hysteresis loops at various compositions

slide30

PbZrO3

Mole% PbZrO3

PbTiO3

La-Doped Lead Zirconate Titanate (PLZT) System

Complex relationship between n and E

n ~ E

n ~ E2

Room Temperature Phase Diagram of PLZT

showing different electro-optic characteristics at various compositions

slide31

8/40/60 linear region

8/65/35 memory region

9/65/35 quadratic region

La-Doped Lead Zirconate Titanate (PLZT) System

Electro-optic applications of PLZT ceramics depends on the composition

In the tetragonal ferroelectric (FT) region  high EChysteresis loops  Linear electro-optic behavior for E < EC (linear electro-optic modulators, and optical switches)

In the rhombohedral ferroelectric (FR)  Low EChysteresis 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

slide32

La-Doped Lead Zirconate Titanate (PLZT) System

Examples of Applications of PLZT Ceramics

Flash Goggles : nuclear and arc radiations

Color Filter : optical shutter

Display : reflective display similar to LCD

Image Storage : strain-induced birefringence

Thin-Film Optical Switch

Photostriction