handbook of advanced dielectric, piezoelectric and ferroelectric materials (1420070851)(CRC, 2008)

Handbook ofdielectric, piezoelectric and ferroelectric materials Synthesis, properties and applications Edited by Zuo-Guang Ye Woodhead Publishing and Maney Publishing on behalf of The I

iHandbook of dielectric, piezoelectric

and ferroelectric materials

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Handbook of

dielectric, piezoelectric and

ferroelectric materials

Synthesis, properties and

applications

Edited by Zuo-Guang Ye

Woodhead Publishing and Maney Publishing

on behalf of The Institute of Materials, Minerals & Mining

CRC Press Boca Raton Boston New York Washington, DC

Cambridge England

iii

WPNL2204

Woodhead Publishing Limited and Maney Publishing Limited on behalf of

The Institute of Materials, Minerals & Mining

Woodhead Publishing Limited, Abington Hall, Abington

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Published in North America by CRC Press LLC, 6000 Broken Sound Parkway, NW, Suite 300, Boca Raton, FL 33487, USA

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Part I High-strain, high-performance piezo- and

ferroelectric single crystals

1 Bridgman growth and properties of PMN-PT based

2 Flux growth and characterization of PZN-PT and

L-C L IM , National University of Singapore, and Microfine Materials

Technologies Pte Ltd, Singapore

2.2 Flux growth of PZN-PT and PMN-PT single crystals 40

2.4 Growth of relaxor single crystals of low PT contents:

2.7 Properties of flux-grown PZN–PT and PMN–PT single

3 Recent developments and applications of

W S H ACKENBERGER , J L UO , X J IANG , K A S NOOK and P W R EHRIG

TRS Technologies, USA and S Z HANG and T R S HROUT ,

Pennsylvania State University, USA

3.2 Crystal growth and characterization of relaxor

3.3 Dynamic performance of piezoelectric crystals with

4 Piezoelectric single crystals for medical ultrasonic

S M R HIM , Humanscan Co Ltd, Korea and M C S HIN and S-G L EE ,

IBULe Photonics Co Ltd, Korea

5 High-performance, high-TC piezoelectric crystals 130

S J Z HANG , Pennsylvania State University, USA, J L UO , TRS

Technologies Inc., USA and D W S NYDER and T R S HROUT ,

Pennsylvania State University, USA

5.2 Background on the growth of relaxor–PT single crystals 135

5.5 High TC bismuth-based perovskite single crystals 141

5.6 Non-perovskite piezoelectric single crystals 145

6 Development of high-performance piezoelectric

single crystals by using solid-state single crystal

H-Y L EE , Sunmoon University and Ceracomp Co Ltd, Korea

6.3 Dielectric and piezoelectric properties of BZT, PMN–PT,

7 Piezo- and ferroelectric (1–x)Pb(Sc1/2Nb1/2)O3–xPbTiO3

Y-H B ING and Z-G Y E , Simon Fraser University, Canada

7.2 Synthesis, structure, morphotropic phase diagram, and

properties of the (1–x)Pb(Sc1/2Nb1/2)O3–xPbTiO3 solid

7.3 Growth of relaxor ferroelectric Pb(Sc1/2Nb1/2)O3 and

(1–x)Pb(Sc1/2Nb1/2)O3–xPbTiO3 single crystals 1857.4 Properties of Pb(Sc1/2Nb1/2)O3 and (1–x)

Pb(Sc1/2 Nb1/2)O3–x PbTiO3 single crystals 191

8 High Curie temperature piezoelectric single crystals

of the Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3

Y J Y AMASHITA and Y H OSONO , Toshiba R&D Center Japan

8.4 PIMNT and PSMNT single crystals grown by the Bridgman

8.5 Future trends 227

Part II Field-induced effects and domain engineering

9 Full-set material properties and domain engineering

W C AO , Pennsylvania State University, USA

9.2 Technical challenges and characterization methods 2379.3 Complete set material properties for a few compositions

9.4 Correlation between single domain and multi-domain

properties and the principle of property enhancement in

domain engineered ferroelectric single crystals 256

10 Domain wall engineering in piezoelectric crystals

S W ADA , University of Yamanashi, Japan

10.3 Effect of engineered domain configuration on

10.4 Crystal structure and crystallographic orientation

dependence of BaTiO3 crystals with various engineered

10.5 Domain size dependence of BaTiO3 crystals with

10.6 Role of non-180° domain wall region on piezoelectric

11 Enhancement of piezoelectric properties in

perovskite crystals by thermally, compositionally,

electric field and stress-induced instabilities 304

D D AMJANOVIC , M D AVIS and M B UDIMIR , Swiss Federal Institute of

Technology – EPFL, Switzerland

12 Electric field-induced domain structures and phase

V H S CHMIDT and R R C HIEN , Montana State University, USA and

C-S T U , Fu Jen Catholic University, Taiwan

13 Energy analysis of field-induced phase transitions in

relaxor-based piezo- and ferroelectric crystals 366

T L IU and C S L YNCH , The Georgia Institute of Technology, USA

Part III Morphotropic phase boundary and related

14.5 Stability of the MPB phases under external and internal

15 Size effects on the macroscopic properties of the

relaxor ferroelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 solid

M A LGUERÓ , J R ICOTE , P R AMOS and R J IMÉNEZ , Instituto de Ciencia

de Materiales de Madrid (CSIC), Spain, J C ARREAUD , J-M K IAT and

B D KHIL , Ecole Centrale Paris, France and J H OLC and M K OSEC ,

Institute Jozef Stefan, Slovenia

15.3 The relaxor ferroelectric Pb(Mg1/3Nb2/3)O3–PbTiO3 solid

Part IV High-power piezoelectric and microwave

dielectric materials

16 Loss mechanisms and high-power piezoelectric

K U CHINO , Pennsylvania State University and Micromechatronics

Inc., USA; J H Z HENG , Y G AO , S U RAL , S-H P ARK and

N B HATTACHARYA , Pennsylvania State University, USA and

S H IROSE , Yamagata University, Japan

16.2 General consideration of loss and hysteresis in

17.3 Phase equilibrium and phase relation of BZN pyrochlores 509

Part V Nanoscale piezo- and ferroelectrics

18 Ferroelectric nanostructures for device applications 541

J F S COTT , Cambridge University, UK

18.4 Magnetoelectrics and magnetoelectric devices 55118.5 Toroidal and circular ordering of ferroelectric domains in

I A K ORNEV , University of Arkansas, USA and Mads Clausen

Institute, University of Southern Denmark, Denmark and B-K L AI ,

I N AUMOV , I P ONOMAREVA , H F U and L B ELLAICHE , University of

Arkansas, USA

19.4 Domains in one-dimensional and zero-dimensional

I S ZAFRANIAK -W IZA , Poznan University of Technology, Poland and

M A LEXE and D H ESSE , Max Planck Institute of Microstructure

Physics, Germany

21 Nano- and micro-domain engineering in normal and

V Y S HUR, Ural State University, Russia

21.2 Main experimental stages of domain structure evolution

during polarization reversal in normal ferroelectrics 624

21.5 Domain growth: from quasi-equilibrium to highly

22 Interface control in 3D ferroelectric nano-composites 670

C E LISSALDE and M M AGLIONE , University of Bordeaux1, France

22.2 Interface defects and dielectric properties of bulk

22.3 Interdiffusion in bulk ceramics and composites 674

23 Single crystalline PZT films and the impact of extended

structural defects on the ferroelectric properties 695

I V REJOIU , D H ESSE , and M A LEXE , Max Planck Institute of

Microstructure Physics, Germany

23.2 Pulsed laser deposition of epitaxial ferroelectric oxide

23.3 Epitaxial ferroelectric oxide thin films and nanostructures

23.4 Single crystalline PbTiO3 and PZT 20/80 films free from

23.5 Comparison of ferroelectric properties of PZT 20/80 films

Contents xiii

23.6 Summary 717

Z W ANG , W Z HU and J M IAO , Nanyang Technological University,

Singapore

24.2 A composite coating process for preparing thick film on

24.4 Piezoelectric micromachined ultrasonic transducer

25 Symmetry engineering and size effects in

B N OHEDA , University of Groningen, The Netherlands and

G C ATALAN , University of Cambridge, UK

25.3 Heterogeneous thin films: superlattices and gradients 76425.4 Symmetry and ferroelectric properties: polarization

Part VII Novel processing and new materials

26 Processing of textured piezoelectric and dielectric

perovskite-structured ceramics by the

T K IMURA , Keio University, Japan

26.1 Enhancement of piezoelectric properties of

26.2 Reactive-templated grain growth method 801

27.2 Bismuth layer-structured ferroelectrics (BLSF) 819

27.4 Grain orientation effects on electrical properties 823

28 Novel solution routes to ferroelectrics and relaxors 852

K B ABOORAM and Z-G Y E , Simon Fraser University, Canada

28.2 Soft chemical methods for the synthesis of mixed metal

28.3 Polyethylene glycol-based new sol–gel route to relaxor

ferroelectric solid solution (1–x)Pb(Mg1/3Nb2/3)O3−xPbTiO3

29 Room temperature preparation of KNbO3

nanoparticles and thin film from a perovskite

K T ODA and M S ATO , Niigata University, Japan

29.2 Mechanisms of generation of KNbO3 nanoparticles 885

29.4 Conclusions and future trends 894

31.9 References and further reading

32 Dielectric and optical properties of perovskite

T T SURUMI and T H ARIGAI , Tokyo Institute of Technology, Japan

32.3 Lattice distortions in artificial superlattices 980

32.5 Dielectric properties of artificial superlattices 987

33 Crystal structure and defect control in

Bi4Ti3O12-based layered ferroelectric single

33.8 Effects of La and Nd substitutions on the electronic band

Contents xvii

Contributor contact details

National University of Singapore

9 Engineering DriveSingapore 117576and

Microfine Materials TechnologiesPte Ltd

10 Bukit Batok Crescent

#06-02 The SpireSingapore 658079

E-mail: mpelimlc@nus.edu.sg

Chapter 3

Wesley S Hackenberger*, Jun Luo,Xiaoning Jiang, Kevin A Snookand P W Rehrig

TRS Technologies Inc

2820 E College AvenueState College, PA 16801USA

(* = main contact)

xix

Shujun Zhang and Tom R Shrout

Materials Research Institute

Pennsylvania State University

Min Chul Shin and Sang-Goo Lee*

IBULe Photonics Co Ltd

Materials Research Institute

Pennsylvania State University

Sunmoon UniversityAsan 336-708Korea

andCeracomp Co Ltd3F-3309

Chungnam Techno ParkCheonan

Chungnam 330-816Korea

E-mail: hlee@sunmoon.ac.kr;hlee@ceracomp.com

Chapter 7

Yonghong BingDepartment of ChemistryUniversity of WashingtonBox 351700

SeattleWashington, 98195-1700USA

E-mail: bingy@u.washington.edu

Materials Research Institute

Pennsylvania State University

of Medical and EngineeringUniversity of Yamanashi4-4-37 Takeda

KofuYamanashi 400-8510Japan

E-mail: swada@yamanashi.ac.jp;swada@ceram.titech.ac.jp

Chapter 11

Dragan Damjanovic,* MatthewDavis and Marko BudimirEPFL STI IMX LCMXD 236

Station 12

1015 LausanneSwitzerland

Contributor contact details xxi

T Liu and C S Lynch*

The George W Woodruff School of

Laboratoire Structures Propriétés et

Modélisation des Solides

Ecole Centrale Paris

E-mail: kiat@spms.ecp.fr

Chapter 15

Miguel Algueró,* Jesús Ricote,Pablo Ramos and Ricardo JiménezInstituto de Ciencia de Materiales

de Madrid (CSIC)Cantoblanco

28049 MadridSpain

E-mail: malguero@icmm.csic.esJulie Carreaud, Jean-Michel Kiatand Brahim Dkhil

Laboratoire Structures Proprieté etModélisation des Solides

Ecole Centrale Paris

92295 Châtenay-Malabry CedexFrance

Jean Michel-KiatLaboratoire Léon Brillouin

CE Saclay

91191 Gif-Sur-Yvette CedexFrance

Janez Holc and Marija KosecInstitute Jozef Stefan

Jamova 39

1000 LjubjlanaSlovenia

Chapter 16

K Uchino,* J H Zheng, Y Gao, S

Ural, S-H Park, N Bhattacharya

International Center for Actuators

Hong Wang* and Xi Yao

Electronic Materials Research

Centre for Ferroics

Earth Sciences Department

Igor A KornevMads Clausen InstituteUniversity of Southern DenmarkDenmark

E-mail: ikornev@uark.edulaurent@uark.edu

Chapter 20

Izabela Szafraniak-Wiza*

Poznan University of TechnologyInstitute of Materials Science andEngineering

M Sklodowska-Curie Sq 560-965 Poznan

Poland

E-mail: izaszaf@sol.put.poznan.plMarin Alexe and Dietrich HesseMax Planck Institute of

Microstructure PhysicsWeinberg 2

06120 Halle (Saale)Germany

E-mail: hesse@mpi-halle.demalexe@mpi-halle.deContributor contact details xxiii

I Vrejoiu,* D Hesse and M Alexe

Max Planck Institute of

50 Nanyang AvenueSingapore 639798Zhihong WangMicromachines CentreSchool of Mechanical andAerospace EngineeringNanyang Technological University

50 Nanyang AvenueSingapore 639798

E-mail: ewzhu@ntu.edu.sg;

EZHWang@ntu.edu.sgJianmin Miao

Micromachines CentreSchool of Mechanical andAerospace EngineeringNanyang Technological University

50 Nanyang AvenueSingapore 639798

Chapter 25

B Noheda*Zernike Institute for AdvancedMaterials

University of GroningenNijenborgh 4

9747AG GroningenThe Netherlands

Department of Applied Chemistry

Faculty of Science and Technology

Faculty of Science and Technology

Tokyo University of Science

Laurentian UniversitySudbury

Ontario, P3E 2C6Canada

E-mail: kbabooram@laurentian.caZuo-Guang Ye*

Department of ChemistrySimon Fraser University

888 University DriveBurnaby

BC, V5A 156Canada

E-mail: zye@sfu.ca

Chapter 29

Kenji Toda* and Mineo SatoGraduate School of Science andTechnology

Center for TransdisciplinaryResearch

Niigata University

8050 Ikarashi 2-nochoNiigata 950-2181Japan

E-mail: ktoda@eng.niigata-u.ac.jp;inorg@gs.niigata-u.ac.jpContributor contact details xxv

Chapter 30

Annie Simon* and Jean Ravez

Institut de Chimie de la Matière

Condensée de Bordeaux

Y N Qin and S Q Zhu*

National Laboratory of Solid

Meguro-kuTokyo 153-8904Japan

Yuji NoguchiSORST, Japan Science andTechnology Corporation (JST)4-1-8 Honcho

Kawaguchi-shiSaitama 332-0012Japan

E-mail: tokyo.ac.jp

Research and development in dielectric, piezoelectric and ferroelectric materialshas advanced at an unimaginable rate in the past decade, driven mainly bythree factors:

1 new forms of materials have been prepared in a multitude of sizes (e.g.buck single crystals and ceramics, nano-structured films, tubes, wiresand particles) by a variety of techniques (e.g melt growth, physicaldeposition and to soft chemical synthesis),

2 novel and intricate structural and physical properties have been discovered

in these materials (e.g morphotropic phase boundary and relatedphenomena, domain engineering under fields, effects of nanostructuresand superlattices), and

3 the extraordinary potential offered by these materials to be used in thefabrication of a wide range of high-performance devices (such as sensors,actuators, medical ultrasonic transducers, micro electromechanical systems(MEMS), microwave tuners, ferroelectric non-volatile random accessmemories (FeRAM), electro-optical modulators, etc.)

It was based on these three themes that this book has been conceived, inorder to provide an up to date account of the state-of-the-art in this rapidlygrowing field

The book is organized under eight main topics Part I covers high strain,high performance piezo- and ferroelectric single crystals This area has thrivedwith the (re)discovery of the extremely large piezoelectric strains and veryhigh electromechanical coupling factors in the single crystals of the solidsolutions between a lead magnesium (zinc) niobate relaxor and lead titanateferroelectric The outstanding performance of these crystals makes them theprimary candidates for the next generation of electromechanical transducersfor a broad range of applications, e.g powerful undersea sonar systems,high-resolution ultrasonic imaging Materials synthesis and propertyspecification are discussed, along with their implications to devices Newmaterials systems with high Curie temperature and high piezoelectricperformance are presented as a beacon for future development On the other

xxvii

hand, the development of piezocrystals has generated many perplexing issues,whose resolution is important to our fundamental understanding and for thetechnological applications of the materials Of particular interest are themechanism of high piezoelectric response and the enhancement of materialsperformance by domain engineering, and the morphotropic phase boundaryand related phenomena Together, they naturally constitute the topics of thefollowing two sections.

Field-induced effects and domain engineering are described in Part II Afull set of materials properties and the domain engineering principles arepresented for ferroelectric single crystals Excellent piezoelectric propertiesare realized in conventional materials, such as barium titanate crystals, byappropriate domain-wall engineering The enhancement of piezoelectricperformance in perovskite crystals is demonstrated to arise from the variouskinds of instabilities induced thermally, chemically, electrically andmechanically Since the mechanism of high-piezoelectric response is associatedwith the rotation of the polarization directions by an appropriate electricfield, the examination of complex domain structures and the phase energies

of the relaxor ferroelectric single crystals provides a better understanding ofthe complex phenomenon

Part III deals with the morphotropic phase boundary and its relatedphenomena, in which the complex structural features of relaxors and therelated MPB systems are presented and analyzed in greater detail Furthermore,the size effects on the macroscopic properties are also discussed

Part IV is dedicated to high power piezoelectrics and microwave dielectricsand their applications Current and future applications often requirepiezoelectrics to be driven to highest amplitude Therefore, understanding ofthe loss mechanisms and heat generation is crucial for designing low-lossand high-power piezoelectric materials As excellent microwave dielectrics,bismuth-based pyrochlore ceramics appear to be promising for tunable deviceswith low loss

Part V explores nanoscale piezo- and ferroelectric materials Great potentialfor device applications has emerged recently, mostly because of the capability

to make nanostructured ferroelectrics These materials have in turn ushered

in new challenges both in the understanding of fundamental issues such asdomains and domain engineering, and in the fabrication of materials in theforms of nanocrystals or 3D nano-composites

Equally important is Part VI, which follows up along the lines of dimensional materials with piezo- and ferroelectric films The ability toproduce near-perfect, single-crystalline thin films and high-quality thick filmshas paved the road to device applications such as FeRAM and MEMS Thedomain structure and polarizations specific to ferroelectric thin films aretreated under symmetry engineering

low-Non-conventional processing techniques and new materials are presented

in Part VII The preparation of textured or grain orientation-controlled materialshas vastly improved the piezo- and ferroelectric properties of perovskite-based materials, making them more suitable for applications in electronicdevices New soft chemical routes have led to the formation of ferroelectricsand relaxors in the forms of nanoparticles, thin films and ceramics at lowtemperature (even room temperature), with enhanced properties

Lastly, in Part VIII, we focus on some novel physical properties of dielectricand ferroelectric superlattices and their applications, as well as the complexstructure-property relations of bismuth layer-structured single crystals.This book is aimed to serve as a comprehensive reference to a broadspectrum of graduate students, academic researchers, development scientists,materials producers, device designers and applications engineers who areworking in, or are interested in moving into, the fascinating field of advanceddielectric, piezoelectric and ferroelectric materials research and development.The publication of this book would not have been possible without thehelp and support from many people I thank all the authors for theirknowledgeable contributions which I am sure will be highly valued by thereaders Their enthusiasm, dedication, hard work and cooperation in themaking of this book were invaluable I thank several anonymous referees forhelping me review some of the chapters I thank Wallace Smith and Carl Wu

of the US Office of Naval Research for their constant support Many of mycolleagues here at Simon Fraser have lent me their encouragement that ismuch appreciated I also thank the members of my research group and myfamily for their understanding and support

It has also been a great pleasure to work with the competent and patienteditorial staff at Woodhead Publishing Limited in Cambridge In particular,

I thank Rob Sitton, the Commissioning Editor, who initiated the project andbrought it to fruition, and Ian Borthwick, the Publications Co-ordinator,who, as the main contact person throughout the project, effectively ensuredthe communication among the authors, the publisher and the editor, to allowthe timely completion of all the chapters Special thanks also go to LauraBunney, the Project Editor, Melanie Cotterell, the Product Delivery Manager,and Francis Dodds, the Editorial Director

Zuo-Guang YeDepartment of Chemistry and

4D LABSSimon Fraser UniversityBurnaby, British Columbia

CanadaIntroduction xxix

Part I

High-strain, high-performance piezo- and

ferroelectric single crystals

1

of acoustic transduction devices.

The recent shift in focus from blue water to littoral operations for the USNavy has placed additional requirements on sonar systems New materials ofhigh energy density and improved properties are needed for enhanced sonartransduction performance Material property improvements include:

• increased strain to enhance acoustic source level;

• increased electromechanical coupling to broaden bandwidth;

• increased energy density to reduce transducer weight and give higherefficiencies;

• reduced hysteresis to produce greater thermal stability;

• increased sensibility to improve signal/noise ratio

A breakthrough was announced at the Piezoelectric Crystal Planning Workshop1sponsored by the Office of Naval Research in May 1997 Single crystals ofPZN–PT (lead zinc niobate–lead titanate) and PMN–PT near MPB(morphotropic phase boundary) compositions exhibit extraordinarypiezoelectric properties, namely, electrical field-induced strains exceeding1%, and electromechanical coupling exceeding 90% (compared with 0.1%and 70–75%, respectively, in the state-of-the-art PZT piezoceramics)2,3 Theseperovskite relaxor ferroelectric crystals have opened up new opportunitiesnot only in current acoustic transduction devices, where traditional PZT

1

Bridgman growth and properties of

PMN–PT-based single crystals

P H A N, J T I A N and W Y A N

H C Materials Corporation, USA

ceramics are used, but also in exploration of new applications, such as medicalultrasonics, non-destructive detection, marine seismic exploration and energyharvesting These new crystals of giant-piezoelectric properties will enable

“revolutionary” developments for the next generation of acoustic transductiondevices Thus, there is an urgent need to develop crystal-growth techniquesfor the fabrication of large, high-quality piezoelectric crystals at industrial scale

1.1.2 Challenges in the growth of large PMN–PT crystals

It is a great challenge to develop a cost-effective method for the growth ofthe high-strain piezocrystals of large sizes (75–100 mm (3–4 inches) in diameter

by 150–200 mm (6–8 inches) in length, and high quality Generally speaking,the difficulties found when growing large-sized crystals of lead-containingmaterials are their complex thermodynamic behavior and special physicalproperties For example, common problems include incongruent melting andlow thermal conductivity The incongruent melting means that crystals cannot

be grown from stoichiometric melts The low thermal conductivity affectsthe transport of latent heat released during the crystallization process, therebycausing interface instability, defects, inclusions and phase segregation, etc.The difficulties here stemmed from a basic discrepancy between theoreticalpredictions and experimental data on the congruent behavior and the perovskiteprecipitation characteristics for the MPB solid solution systems associatedwith PT

In addition, solid-state phase transformations commonly occur on cooling

to room temperature that lead to twinning and possible cracking problems.Furthermore, the growth of lead-containing crystals at high temperaturesencounters more special technical barriers, including:

• corrosion of container materials – platinum crucibles are attacked bylead-containing melt at temperatures above 1300oC, leading to severeleakage;

• high volatility of toxic PbO from the melt at high temperatures;

• difficulties in controlling compositional homogeneity for multi-componentsystems due to the compositional segregation

The critical problems enumerated above make the growth of large PMN–PTcrystals for commercialization a challenging task

1.1.3 Growth of PMN–PT crystals from stoichiometric

melt using the Bridgman method

PMN–PT is a binary solid solution of lead magnesium niobate (PMN) and lead

titanate (PT) It can be represented by the formula (1–x)[Pb(Mg1/3Nb2/3)

O3]–x[PbTiO3] PMN–PT has the ABO3 perovskite structure and an MPB

Bridgman growth and properties 5

where the structure changes from rhombohedral to tetragonal at x ~0.34–

0.35 To obtain crystal samples, the high-temperature solution (flux) growth

as a ‘universal’ method has been widely used for a variety of complex oxidecompounds including the perovskite relaxor ferroelectric materials In the1990s millimeter-sized crystals of PMN–PT were grown from high-temperaturesolution with PbO/B2O3 as the flux4 Recently, inch-sized (~25 mm) PMN–

PT crystals with improved quality have been successfully grown using theflux growth method5–8 and a modified flux growth, the so-called ‘solution-Bridgman’ method9 However, the growth rate and crystal size of the abovecrystal growth methods were limited and not suitable for commercialproduction To suppress the evaporation of the volatile melt component PbO,crystal growth of PMN–PT under high pressure (80 atm Ar with 1% oxygen)10was demonstrated using a vertical Bridgman furnace It confirmed that leadevaporation was significantly reduced even for the unsealed crucible, but thecrystal quality was degraded due to inclusions such as voids and Mg–Si–O-rich impurities A possible reason is that high pressure also influenced theinterface dynamic process, leading to the occurrence of constitutionalsupercooling

It has been well known that the most straightforward and economical way

of growing high-quality large crystals is the Bridgman11-Stockbarger12 method,which normally freezes stoichiometric melt without flux: a molten ingot isgradually crystallized from one end to the other However, the stoichiometricmelt growth of the single crystals of ABO3 perovskite relaxor ferroelectricmaterials is suitable only for systems that satisfy the following essentialcriteria: (i) the system is congruent melting and/or (ii) in the compositionalphase diagram there must exist a window from which the perovskite as theprimary phase (instead of the pyrochlore phase of the same chemicalcomposition) can be directly crystallized from the melt Unfortunately, most

of the known MPB systems associated with PT (PbTiO3) are incongruentand thus no window exists in the phase diagrams for the perovskite phase tocrystallize first As a result, these perovskite crystals cannot be grown fromstoichiometric melts Fluxes or mineral agents must be used for the crystalgrowth to avoid interference from unexpected nuclei of the non-perovskitephases

Perovskite PMN melts congruently at 1320°C13 and perovskite PT meltscongruently at 1285°C Thus, both end compounds of the PMN–PT binarysystem are congruent-melting perovskite phases This implies that PMN–PT

is more likely to form the perovskite phase, instead of the parasitic pyrochlorephase, than the other MPB binary solid solutions such as PZN–PT (PZNmelts incongruently) Since the first experimental report in 199714,15 on themelt growth of high-quality PMN–PT crystals from stoichiometric melt(without flux) in sealed platinum crucibles using a modified Bridgman furnace,more efforts16–19 have been made to the melt growth of the PMN–PT-based

crystals; however, undesired compositional segregations were encountered13.

At the present time, <001>-seeded PMN–PT crystals of 75 mm (3 inch)diameter and 200 mm (8 inch) length (6 kg each boule) have been commerciallymanufactured using the multi-crucible vertical Bridgman method20

In the following sections, the details of the melt growth of based crystals using the Bridgman method developed at the H C MaterialsCorporation are described The physical properties are systematicallycharacterized and discussed in the context of domain engineering and elasto-piezo-dielectric tensor concepts, which are important for the appropriateselection of crystal cut directions and vibration modes

1.2.1 Phase equilibrium

A prerequisite for growing PMN–PT crystals is the detailed knowledge ofthe high-temperature phase equilibrium of the binary solid solution Thereare limited data about the PMN–PT phase diagram As mentioned above,only congruent melting at 1320°C for perovskite PMN and 1285°C for PTwas known In 1999, we reported the results of the compositional segregation(Fig 1.1) based on ICP (induction coupled plasma spectroscopy, accuracybetter than 0.5%) analysis of a PMN–31%PT single crystal16 The growthparameters are: seeding [210], growth rate 0.8 mm/h, temperature gradient

20°C/cm, and maximum temperature 1365°C The effective segregationcoefficient is estimated ~85% for PT The result of the crystal growth fromstoichiometric melt indicated that the phase equilibrium diagram may be atypical binary solid solution system In 2003,the first high-temperature phasediagram of the PMN–PT binary system was reported19 A combination of allavailable data, provides a phase equilibrium diagram, as proposed in Fig.1.2 This phase diagram is accurate enough as the guidance for the thermalprocess control during crystal growth and it has been successfully used in thePMN–PT crystal growth

1.2.2 Platinum crucible leakage and lead

is chemically stable, so does not contaminate the melt However, the operatingtemperature is over the safety temperature limit of 1300°C in air for Pt

Bridgman growth and properties 7

metal Thus, it is probable that the platinum crucible could be attacked bylead-containing melt, especially at temperatures above 1350°C The crucibleleakages due to PbO attack pose a serious threat to crystal growth Aftersystematic investigations, we have found that there are two main reasonsleading to the crucible leakage

First the purity and the quality of the platinum crucible are not highenough During crystal growth at high temperatures platinum grains grow to

up to sub-millimeter sizes and some of the large grains can penetrate the wall

of the crucible As the platinum grains grow, impurities in the platinum metal

Pb Mg Nb Ti

1.1 ICP analysis of a PMN–PT crystal boule.

can be segregated and expelled into the tri-junctions of platinum grains Thelead-containing melt, acting as a strong flux, would ‘eat’ (dissolve) theimpurities and thus form micro-holes in the platinum crucible wall (Fig.1.3).

Second, the chemical behavior of lead oxides before melting is complex21.The commercial lead oxide (PbO) generally contains some Pb3O4 Tounderstand the influence of the chemical reaction on the platinum corrosion,TGAs (thermal gravity analyses) on PbO and Pb3O4 powders were performed

in conjunction with X-ray diffraction for phase identifications Figure 1.4clearly indicates that PbO absorbed oxygen in the temperature range from

430 to 520°C to form Pb3O4 (or PbO1.1/3) Above 600°C, the PbO1.1/3 releasedone-third of the oxygen and returned to PbO So, one can imagine the followingscenario: if (i) some free PbO exists in the chemical batch loaded in aplatinum crucible and (ii) the temperature of the crucible in the furnace ishotter at the upper segment, i.e the heating rate of the upper crucible isfaster than the lower part, then oxygen deficiency inside the sealed cruciblewill occur when the temperature at the lower segment of the crucible ramps

up to around 520°C If the temperature of the upper segment increases overthe liquidus temperature of PbO 888°C, some PbO may be reduced to formmicrometer drops of lead metal The reduced lead immediately forms alloywith platinum, which has a much lower melting point than platinum or leadand thus causes crucible leakage To avoid the leakage of platinum crucible,the following measures are suggested: