“ALEXANDRU IOAN CUZA” UNIVERSITY DEPARTAMENT OF PHYSICS Perovskite systems with ferroelectric/antiferroelectric character A thesis submitted by IOANA… [609953]

“ALEXANDRU IOAN CUZA” UNIVERSITY
DEPARTAMENT OF PHYSICS

Perovskite systems with ferroelectric/antiferroelectric
character

A thesis submitted by
IOANA VERONICA CIUCHI

in partial fulfilment of the requirements
for the title of Doctor of Science in Physics

SCIENTIFIC COORDINATOR :
PROF. UNIV. DR. LILIANA MITOȘERIU

Iași
2017

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Table of Contents

Abstract

Acknowledgements

Thesis organization

CHAPTER 1 Introduction and theoretical considerations

1.1 Introduction
1.2 Brief history
1.3 Definition of Ferroelectricity and Antiferroelectricity
1.4 Basic properties of ferroelectric and antiferroelectric materials
1.4.1 Perovskite Structure
1.4.2 Domain switching: Ferroelectric versus antiferroelectric behaviour
a) Domain switching in ferroelectric materials
b) Domain switching in antiferroelectric materials
1.4.3 Tunabili ty
a) Tunability in ferroelectrics
b) Tunability in antiferroelectrics
1.4.4 Energy storage properties
1.5 Landau -Ginzburg -Devonshire Theory of Ferroelectricity
1.6 Landau Theory of Antiferroelectrics

CHAPTER 2 Short literature review on PZT and La doped PZT
systems

2.1 Introdu ction
2.2 General properties of PZT solid solutions
2.2.1 PbZrO 3
2.2.2 PbTiO 3
2.2.3 Phase diagram of the PZT solid solution
2.3 Properties of PLZT solid solutions
2.4 The High Zr content side of PZT and PLZT systems
2.5 Systems investigated for this thesis and motivation for the proposed research
topic

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CHAPTER 3 Characterization: Principles and Techniques

3.1 Introduction
3.2 Preparation of PLZT ceramics
3.2.1 Preparation of dense PLZT Pellets
3.3 Characterization techniques
3.3.1 Microstructural characterization
a) Scanning Electron Microscopy (TEM )
b) Transmission Electron Microscopy (TEM)
3.3.2 Structural Characterisation
a) X-Ray Diffraction and High Resolution X -Ray diffraction
a) Raman Spectroscopy
3.3.3 Electrical characterization
a) Impedance spectroscopy
b) Polarization -Field Hysteresis loop measurements
c) Piezoelectric characterization

CHAPTER 4. Microstructural and Structural Characterization

4.1 Introduction
4.2 Phase purity
4.2.1 Phase purity of calcined PLZT powders
4.2.2 Phase purity of PLZT sintered ceramics
4.3 Microstructure
4.4 Structural characterization
4.1.1 Phase characterization by XRD
4.1.2 Crystalline structural characterization by HXRD
4.5 Domain structure and local characterization by TEM
4.6 RAMAN analysis
4.7 Conclusions

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CHAPTER 5 Room Temperature Electrical Properties

5.1 Introduction
5.2 Dielectric Properties
5.3 Piezoelectric properties
5.4 Conclusions

CHAPT ER 6. Study of antiferroelectric -to-ferroelectric switching

6.1 Introduction
6.2 Polarization vs. electric field study
6.2.1 Influence of the La3+ composition on ferroelectric/antiferroelectric
properties of PLZT x/90/10 ceramics
6.2.2 Frequency dependence of AFE -to-FE switc hing of PLZT ceramics
6.3 Study of AFE -to-FE switching by XRD
6.3.1 Dynamic in situ XRD study
6.3.2 Ex situ High Resolution X -ray Diffraction (HXRD) study
6.4 Energy storage properties
6.5 Conclusions

CHAPTER 7 Study of temperature -induced phase transitions in
PLZT x/90/10 ceram ics

7.1 Introduction
7.2 Dielectric study
7.2.1 Influence of La addition on the phase transitions of PLZT x/90/10
ceramics
7.2.2 Influence of frequency on the phase transition of PLZT x/90/10 ceramics
7.2.3 Analysis of FE/AFE -PE phase transition with Curie Weiss law
7.2.4 Analysis of FE /AFE -PE phase transition with modified Curie Weiss law
7.2.5 Influence of poling on the phase transitions sequence of PLZT x/90/10
ceramics

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7.3 In situ XRD temperature study
7.3.1 Phase transitions in virgin PLZT x/90/10 ceramics
7.3.2 Phase transitions in poled PLZ T 3/90/10 ceramic
7.4 Raman Spectroscopy Study
7.5 Revised phase diagram of the PLZT x/90/10 solid solution
7.6 Conclusions

General Conclusions

Appendix: Publication and conference participation Lists

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Abstract

The t hesis entitled “Perovskite systems with ferro electric/antiferroelectric character” is
focus ed on the study of antiferroelectric propert ies in perovskite ceramic materials . The large
majority of studies related to antiferroelectric phenomena have focus ed on systems with FE –
AFE boundaries owing to roo m temperature electric field AFE -to-FE induced transition and
their relevance to applications. Materials investigated in this study comprises solid solutions
for which the room -temperature state is known beforehand to be either FE or antiferroelectric
(AFE ). The compositions were chosen from the phase diagram of lanthanum doped lead –
zirconate titanate ( PLZT x/90/10 ) system , with Lanthanum composition across the border
between FE and AFE states, having the formula : Pb1-xLax(Zr 0.9Ti0.1)1-x/4
x/4O3 (with La3+
content x=0.020, 0.030, 0.031, 0.032, 0.033, 0.035, 0.038 and 0.040) . The local and
macroscopic structure and properties of PLZT x/90/10 ceramics with selected compositions
across the FE -AFE phase boundary were studied in en effort of understanding the eff ect of
compositional fluctuation on the stability of AFE and FE phases. The room temperature
structure and the stability region of FE and AFE phase s has been established from high
resolution synchrotron X-ray powder diffraction , Raman and transmission elec tron microscopy
measurements . According to the se studies, t he FE -to-AFE border is very sensitive to the La
addition and show s a broad compositional dependence structure and properties across it. From
the detailed structural analysis , it was found that the room temperature state of PLZT
compositions with x<0.02 0 is rhombohedral R3c, while ones with x>0.03 3 are AFE with
orthorhombic Pbam structure. In-between, the compositions with 0.025 ≤x≤0.033 show a
coexistence of the AFE/FE phase . However, the results of Raman investigation s suggest ed that
the ground state of th ese composition s at low er temperature has a lower symmetry and this
structure may be locally present even at room temperature in a small amount s and probably
located in nanoregions . The use of complementary dielectric, in situ temperature XRD and
Raman technique s to investigate the temperature phases stability of PLZT ceramics a llowed us
to establish more precisely the phase dia gram of PLZT x/90/10 in the compositional range
around the AFE/FE phase boundary (0<x<0.04). A tilt instability line which separate the R3c
and R3m low and high temperature phases, has been added. In addition, a new transition,
associated with the onset of disordered tilting preceding the long range order of the R3c phase,
previously found in Zr -rich Pb(Zr,Ti)O 3, is confirmed in rhombohedral PLZT x/90/10

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compositions . The phase stability were discussed in term s of Goldschmidt’s tolerance factor,
Curie Weiss thermodynamic and soft -mode theories.
One of the major original results of the present thesis represent the study of field –induced
antiferroelectric to ferroelectric (AFE -FE) phase transformations in PLZT x/90/10 . Polarization
measurements and in situ XRD analysis were employed to monitor the real -time evo lution of
the domain switching and crystal structure during the field -induced AFE -to-FE transition . This
analysis has show n that during the field -induced AFE -to-FE transition two phenomena occur
alongsid e: domain swi ching and a structural transition. A fter experiencing the field-induced
AFE -to-FE phase switching , the PLZT 4/90/10 and PLZT 3/90/10 compositions exhibit
irreversible preferential orientation. Depending on the La composition ( i.e. the relative amount
between the AFE and FE phases presented in the investigated samples) , the structure which
develops at the AFE–FE switching phase may be recovered or not during the field reversal.
This is the reason why PLZT 4/90/10 show s no remanent polarization while PLZT 3/90/10
presents a high remanent polarization after the AFE -to-FE switching during the field reversal .
However, the structural and dielectric response recorded under heating the poled sample
evidenced that the AFE phase may be recovered from the previously induced irreversible AFE –
to-FE transition at a temperature of 100oC. In addition, in situ X-ray diffraction studies
evidences apparently unlikely FE -to-AFE field induced transition from the previous field
induced AFE -to-FE structure. This field-induced FE-to-AFE transition is quite uncommon ,
since it is widely accepted that electric fields favour the FE state with parallel orientation of the
electric dipoles over the AFE state. This kind of transition require a broad field range and
demonstrate a rather slow kinetics, which may explain why usual macroscopic experiments
were unable to detect it. Furthermore, d uring the electrical cycling process with an electric field
of adequate amplitude and low frequency, polarisation vs. electric field dependen ce
demonstrated some new or even unexpected physical phenomena , like for example the fact that
samples cycled with ultralow frequency (below 1 Hz ) show an increasing extent of polarization
effects. Based on these experimental data , we assume d that the AFE PLZT materials undergo
multiple FE phase transitions , depending on the field frequencies under high field. This latter
behaviour nicely illustrate s that there polymorphic phases with close energy may exist and
suggests the feasibility of phase -change pheno mena by electric field and frequency , besides the
temperature . Therefore , the as called reversible or irreversible AFE -to-FE field assisted/induced
transition are highly questioned. To better understand the origin of th ese phenomena in the
AFE -FE-AFE trans formations, a more detailed crystallographic study is in progress.

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These result s provide i mportant insight into the close relationship between the structure and
the FE/AFE properties of P LZT 90/10 . In particular, investigations of the structure of poled
samples have shown that the field induced monoclinic distortion may be the origin of the
unusually high piezoelectric response of P LZT. According to the structural calculations ,
polarisation vs. electric field dependence at the frequency of 1 Hz demonstrate that these
compositions transit from FE to AFE phases, with a stabilisation of the AFE phase at higher
La3+ content.
The AFE materials show a high potential to be used in energy storage devices.
Therefore, the energy storage ability of PLZT x/90/10 composi tions has been also evaluated .
The obtained results demonstrate d that t he FE/AFE phase superposition plays an important role
for the storage energy enhancement , due to the interplay between the response of the FE phase
component itself and of the field -induced AFE -FE phase transition. By adjusting the La addition
in 90/10 PLZT ceramics across the FE -AFE compositional boundary, an optimum composition
which show both high energy storage and high efficiency, at reasonable available fields, was
found. The high energy density (0.85 ≤ Wre ≤ 1.85) and high energy efficiency (41 % ≤ η ≤ 65%)
at relatively low electric field (30 ≤ Emax ≤ 65 kV/cm), evidence that all the investigated PLZT
ceramics are quite promising for pulse power capacitors applications.

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Acknowledgements

I am deepl y grateful to my PhD supervisor, Prof . dr. Liliana Mitoseriu . She initiated me
into the world of science and she has been an exc ellent mentor, teaching me all she could with
lovely patience. I thank her also for her continuous encouragement, patience, supp ort and
valuable advice s. Her guidance during my academic studies have highly influenced my overall
scientific formation. I want to thank to all the members of the “Dielectrics, Ferroelectrics &
Multiferroics” Group from the “Alexandru Ioan Cuza” Universit y of Iasi for their help. I have
enjoyed working with all of you throughout the years .
I also express my gratitude to Dr. Carmen Galassi from the Institute of Science and
Technology for Ceramics, National Research Council (ISTE C – CNR), Faenza, Italy for
providing all the necessary support for an efficient research work and for insightful comments
during my stay in Faenza . I thank Claudio Capiani (from ISTEC -CNR) for his support in the
preparation of PLZT ceramics. I also thank ISTEC -CNR for allowing me to use experimental
facilities available in the institute needed for samples preparation, microstructural and electrical
characterization . It was a great opportunity to work in such a well specialized institution.
I equally would like to express my gratitud e to Prof J acob Jones and his research group
for their availability, fruitful discussions and for allowing me to use Analytical facilities
available in North Carolina S tate University (from Raleigh, North Carolina, USA) needed for
in situ field XRD and in situ temperature XRD as well as for kind support, availability and
warm hospitality during my stay in NCSU .
I want to thank Alexandra Neagu and the research group from Stockholm University,
Faculty of Science, Department of Materials and Environmental Chem istry (MMK) for
collaboration in TEM analysis for PLZT ceramics inveastigated in this thesis, along with
abundant insights on the research.
I would like to thank to dr. Catalin Harnagea from Centre Energie , Matériaux et
Télécommunications, Research Center (INRS ) and dr. Marco Deluca from Materials Center
Leoben Forschung from Austria for collaboration for P FM and RAMAN experiment s.
I would like to thank to my committee members, Asist. dr. Lavinia Curecheriu, dr.
Cristina Ciomaga, Conf. dr. Ioan Dumitru , and to the members of the thesis committee for

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kindly accept ing to participate to the public defence and for their insightful comments ,
constructive discussions and suggestions.
I would like to express my deepest appreciation to my parents who always susta ined me
to study , supporting me with endless love, concern, and lifelong sacrifices during my graduate
studies. Finally, my deepest love and gratitude go es to my husband, for his love, support, and
especially his patience during my PhD studies.
The JECS TR UST financial support for my research stage at NCSU is highly
acknowledged .

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Thesis Organization

The thesis begins with a state -of-the-art and the motivation of th is study pointing out the
importance of antiferroelectrics and the main issues on this fi eld. The first chapter deals with
the fundamental principles of ferroelectricity and antiferroelectricity, the applications and the
main characteristics of the se kind of advanced materials.
Chapter 2 give a brief review of the ferroelectric and a ntiferroe lectric ceramics, explains
the importance of PZT ceramics in technological applications, their crystallographic features,
and the modifications induced by doping with La.
Chapter 3 presents the principles of the ceramic processing and methods of analysis u sed in
the experiments.
In the following chapters, the original results obtained from the the oretical and experimental
studies carried out in the current research are discussed . Chapter 4 elucidates the evolution of
the structure of PLZT across the AFE -to-FE phase boundary as studied through various
scattering techniques. This chapter provides a scenario for the explanation of the phase
transition in PLZT, using the interactions between the AFE and FE instabilities in the system.
The effect of La additi on on the structure of PLZT ceramics was studied. Chapter 5 analyses
the dielectric and piezoelectric properties of the investigated ceramics. The observation of
typical antiferroelectric behaviour through the dielectric responses of the ceramics is discu ssed,
and the effect of the La addition and the structure on the dielectric responses is analysed. Phase
transitions between ferroelectric (FE) and antiferroelectric (AFE) states are of considerable
interest for solid state physics. A particular attention is paid, in Chapter 6, where the transition
from AFE -to-FE induced by an external electric field is analysed by polarization studies and in
situ applied field during the XRD structural analysis . The range of temperature for the stability
of the antiferroel ectric behaviour is limited for PLZT ceramics due to the structural transition
from AFE orthor hombic to paraelectric cubic state. In Chapter 7, a de tailed study of this
transition is presented , based on different experimental results as dielectric spectros copy,
RAMAN spectroscopy and in situ temperature dependent structural study .
A list and reprint s of our original publications in the topic of the present PhD study is
presented at t he end of the thesis.