Lead-free Ceramics for High Temperature Actuator Applications

221 Pages·2017·14.59 MB·English

Lead-free Ceramics for High Temperature Actuator
Applications

Thesis by
Amir Khesro

Submitted in partial fulfilment for the degree of
Doctor of Philosophy

Thesis supervisors
Prof. Ian M Reaney
Prof. Derek C Sinclair

Department of Material Science and Engineering
University of Sheffield
October 2016
This thesis is
dedicated to the source of my existence
Mor and Lalda

On, On and Onwards
I am maddened with cares, and tired of searching
Is that not what I am here for? I don’t understand-
But on, on, and onwards I go, ever onwards,
Towards a destiny I will one day reach;
And whatever comes on the way, night or day,

I revel in light
But do not fear the dark.
Ghani Khan
(Translation by Taimur Khan)

1
Outcome of the thesis so far…..
Published articles
 A. Khesro, R. Boston, I. Sterianou, D. C. Sinclair, and I. M. Reaney, “Phase
transitions , domain structure, and pseudosymmetry in La- and Ti-doped
BiFeO .,” J. Appl. Phys., vol. 119, no. 5, p. 054101, 2016.
3

 A. Khesro, D. Wang, F. Hussain, D. C. Sinclair, A. Feteira and I. M. Reaney,
“Temperature Stable and Fatigue Resistant Lead-free Ceramics for Actuators,”
Appl. Phys. Lett., vol. 109, no. 14, p. 142907, 2016.

Patent
 Ian M Reaney and Amir Khesro, "Temperature Stable Lead-Free
Piezoelectric/Electrostrictive Materials with Enhanced Fatigue Resistance" Patent
Application No. GB 1609368.4 (2016)
Conference Presentations
 Amir Khesro “PbO-free temperature-stable, fatigue resistant electrostrictive
ceramics" Sustainable Functional Materials April 2016, Scarborough, UK
 Amir Khesro, "Lead-Free Multi-layered Actuators for High Temperature
Actuator Applications", 2016 Joint IEEE International Symposium on the
Applications of Ferroelectrics, European Conference on Applications of Polar
Dielectrics & Workshop on Piezoresponse Force Microscopy, Darmstadt
Germany.

2
Abstract
In the quest of lead-free ceramics with stable electromechanical strains at higher
temperatures, the ternary system 1-x-yBiFeO -xREFeO -yRE TiO (RE = La, Nd)
3 3 2/3 3
B(RE)FT and pseudo-binary solid solutions (1-x)K Bi TiO -x(0.80BiFeO -
1/2 1/2 3 3
0.15LaFeO -0.05La TiO ), KBT-BLFT, (1-x)K Bi TiO -x(0.82BiFeO -0.15NdFeO -
3 2/3 3 1/2 1/2 3 3 3
0.03Nd TiO , KBT-BNFT and (1-x)K Na NbO x(BiFeO ) KNN-BF, were studied.
2/3 3 0.4 0.6 3- 3
Unlike undoped BiFeO B(RE)FT,ceramics in the ternary series can sustain large electric
3,
fields up to 8 kV/mm but no ferroelectric/antiferroelectric switching is observed indicating
that the coercive fields are very high and therefore these ceramics are not likely to be used
for actuator applications.
The pseudo-binary solid solutions KBT-BLFT and KBT-BNFT offer opportunities of
fabricating ceramics ranging from conventional ferroelectrics to pure electrostrictors.
With increase in BLFT/BNFT concentrations, ferroelectric order is disrupted and relaxor-
like behaviour is promoted. Promotion of relaxor-like behaviour is accompanied by an
increase in positive strain and decrease in hysteresis of these ceramics. Electromechanical
strain up to 0.16 % at 6 kV/mm can be achieved. The optimum strains are predominantly
electrostrictive and exhibit fatigue resistant behaviour. More importantly the optimised
electromechanical strains are stable up to a temperature of 300 °C making them superior
to PZT-based ceramics in terms of temperature stability. The ceramics can be fabricated
into a multilayer structure by tape casting technique as demonstrated by a prototype
multilayer actuator.
The binary solid solution KNN-BF is very limited and dense ceramics could not be
fabricated with x > 0.01. Within the limited range studied, ceramics yield a strain of 0.05
% (2kV/mm) but the operating window is strongly hampered by the ferroelectric to
ferroelectric phase transition which is close to ~100 °C. With Li doping the strain values
could be enhanced to 0.12 % (3 kV/mm), however the room temperature phase is strongly
polymorphic in nature and a monotonic decay in properties is observed with increase in
temperature making these ceramics unsuitable for high temperature applications.
3
Acknowledgements
First of all, I would like to acknowledge my supervisor Prof. Ian M Reaney, whose
continuous support and academic guidance realised this project. There were times in my
PhD, when I was hopeless, you motivated me, encouraged me and appreciated every bit
of little efforts that I did. You will always remain an inspiration to me. I am also thankful
to my co-supervisor Prof. Derek Sinclair for all the insightful discussions and guidance
throughout the project. I am really grateful to Dr. Antonio Feteria for giving me access to
his brand new ferroelectric testing system. The experiments were crucial to the project
and your kind support and guidance in this regard is highly appreciated. Further I would
like to thank Prof. Andrew Bell (University of Leeds) and Prof. Mike Reece (Queen Mary
University of London) for giving me access to their respective labs for strain
measurements and am thankful to Dr. Aurang Zeb (University of Leeds) and Dr. Ye Tian
(Queen Mary University of London) for their help with carrying out these experiments.
I would like to mention, that I benefitted from all the postdocs, who worked in the group,
but I want to especially thank Dr. Iasmi Sterianou, Dr. Rebecca Boston and Dr. Dawei
Wang, who directly contributed to my work. All the PhD students in electroceramics
group were great people to work with and I thank you all for the valuable suggestions and
discussions. Thanks to Mr Fayaz Hussain for his help with fabrication of multilayer
actuators. Thanks to Andrew Mould for quick repairs and fixes of processing and
characterisation equipments. Thanks to Nik Maclaren and Sorby Centre staff for
facilitating with X-ray diffraction and electron microscopy.
Special thanks to Abdul Wali Khan University Mardan (AWKUM), for generous funding,
without which pursuing a PhD was not possible.
I never travelled abroad before coming to England and living away from home in a
different world was not easy. With passage of time, amazing friends like Fayaz, Kashif,
Ansar, Andy, Kasim and Sarban came into my life and now Sheffield feels like home.
Thank you guys. I am also thankful to chums back home for their countless phone calls
and encouragements.
4
I would like to show deepest appreciations to my parents and siblings, who were always
there when I needed a shoulder. Thanks for your unconditional love and support. I will be
indebted forever to my wife Naz, who sacrificed her happiness for my career. You were
not supposed to live away from me for two long years but you happily accepted it for the
sake of my studies. Thanks for standing beside me in through thick and thin. Last but not
the least, thanks to my kids (Ayza and Zari), who are a source of unending joy, happiness
and smiles.
Amir Khesro

5
Contents
Chapter 1: Introduction ............................................................................................................... 11
1.1 Introduction ..................................................................................................................... 11
1.2 References ....................................................................................................................... 14
Chapter 2: Basic Theory and Literature Review ........................................................................... 15
2 Introduction ......................................................................................................................... 15
2.1 Basic theory ...................................................................................................................... 15
2.1.1 Piezoelectricity ......................................................................................................... 15
2.1.2 Dielectrics ................................................................................................................. 16
2.1.3 Classification of dielectrics ....................................................................................... 19
2.1.4 Ferroelectrics ........................................................................................................... 20
2.1.4.1 Ferroelectric domains and hysteresis .................................................................. 24
2.1.4.2 Relaxor ferroelectrics ........................................................................................... 27
2.1.5 Basic tensor properties of piezoelectric materials .................................................. 29
2.1.6 Electrostrictors ......................................................................................................... 31
2.2 Strategies to enhance electromechanical coupling ......................................................... 33
2.3 Literature review .............................................................................................................. 35
2.3.1 Piezoelectric materials ............................................................................................. 35
2.3.2 Lead-free piezoelectric materials ............................................................................. 35
2.3.3 Bismuth ferrite (BF) .................................................................................................. 36
2.3.3.1 Structure of BF ..................................................................................................... 36
2.3.3.2 Processing of BF ................................................................................................... 38
2.3.3.3 Properties of BF .................................................................................................... 39
2.3.3.3.1 Doped BF .......................................................................................................... 41
2.3.3.3.1.1 A-site doping in BF ....................................................................................... 41
2.3.3.3.1.2 B-site doping in BF ....................................................................................... 42
2.3.4 K Bi TiO (KBT)$ .................................................................................................... 44
1/2 1/2 3
2.3.4.1 Structure of KBT ................................................................................................... 44
2.3.4.2 Processing of KBT ................................................................................................. 45
2.3.4.3 Properties of KBT ................................................................................................. 45
2.3.5 (K Na)NbO (KNN) .................................................................................................... 48
, 3
6
2.3.5.1 Structure of KNN .................................................................................................. 48
2.3.5.2 Processing of KNN ................................................................................................ 49
2.3.5.3 Properties of KNN ................................................................................................ 50
2.4 References ................................................................................................................... 52
Chapter 3: Characterisation Techniques ...................................................................................... 66
3.1 Introduction ..................................................................................................................... 66
3.2 Particle size analysis ......................................................................................................... 66
3.3 Density measurements .................................................................................................... 66
3.3.1 Archimedes’ density ................................................................................................. 66
3.3.2 Geometric density .................................................................................................... 67
3.3.3 Theoretical density ................................................................................................... 67
3.4 Structural and microstructural analysis ........................................................................... 68
3.4.1 X-ray diffraction (XRD) ............................................................................................. 68
3.4.2 Raman spectroscopy ................................................................................................ 70
3.4.3 Differential scanning calorimetry (DSC) ................................................................... 72
3.4.4 Dilatometry .............................................................................................................. 72
3.4.5 Scanning electron microscopy (SEM) ....................................................................... 73
3.4.6 Transmission electron microscopy (TEM) ................................................................ 74
3.5 Electrical measurements .................................................................................................. 75
3.5.1 Capacitance and dielectric loss measurements ....................................................... 75
3.5.2 Impedance spectroscopy ......................................................................................... 76
3.5.3 Piezoelectric measurements .................................................................................... 80
3.5.3.1 Small signal dynamic measurements (Resonance method) ................................ 80
3.5.3.2 Small signal quasi-static measurements (Berlincourt method) ........................... 85
3.5.3.3 Large signal quasi-static measurements .............................................................. 85
3.6 References ....................................................................................................................... 88
Chapter 4: Processing of Materials .............................................................................................. 90
4.1 Introduction ..................................................................................................................... 90
4.2 Raw materials ................................................................................................................... 91
4.2.1 Drying of raw materials ............................................................................................ 92
4.2.2 Phase analysis of raw Materials ............................................................................... 94
4.2.3 Particle size analysis of raw materials ...................................................................... 96
7
4.3 Processing of ceramics ..................................................................................................... 97
4.3.1 Weighing of powders ............................................................................................... 97
4.3.2 Mixing and milling of powders ................................................................................. 97
4.3.3 Calcination................................................................................................................ 99
4.3.4 Compaction into green bodies ............................................................................... 103
4.3.5 Sintering ................................................................................................................. 103
4.6 References ..................................................................................................................... 106
Chapter 5: RE (La/Nd)- and Ti- co-doped BiFeO ....................................................................... 107
3
5.1 Introduction ................................................................................................................... 107
5.2 The (1-x)BiFeO -xRE TiO (RE = Nd, La) system ............................................................ 108
3 2/3 3
5.3 The (0.97-x)BiFeO -xNdFeO -0.03Nd TiO (BNFT) system .......................................... 111
3 3 2/3 3
5.3.1 Phase analysis and microstructure ........................................................................ 111
5.3.2 Structural phase transitions in BNFT ceramics ...................................................... 112
5.3.3 Electrical properties of BNFT ceramics .................................................................. 114
5.4 The (0.95-x)BiFeO -xLaFeO -0.03La TiO (BLFT) system .............................................. 119
3 3 2/3 3
5.4.1 Phase analysis and microstructure ........................................................................ 119
5.4.2 Structural phase transitions and domain structure in BLFT ceramics ................... 121
5.4.3 Electrical microstructure and P-E loops ................................................................. 129
5.4.4 General discussion on BLFT ceramics .................................................................... 131
5.5 Conclusions .................................................................................................................... 132
5.6 References ..................................................................................................................... 134
Chapter 6: (1-x)K Bi TiO -xBLFT/BNFT Ceramics ................................................................... 137
1/2 1/2 3
6.1 Introduction ................................................................................................................... 137
6.2 Structural analysis .......................................................................................................... 138
6.2.1 XRD results ............................................................................................................. 138
6.2.2 Raman spectroscopy .............................................................................................. 140
6.3 Microstructure ............................................................................................................... 142
6.4 Dielectric properties ...................................................................................................... 144
6.5 Electromechanical Properties ........................................................................................ 148
6.5.1 Small signal response ............................................................................................. 148
6.5.2 Large signal response ............................................................................................. 149
6.6 Impedance spectroscopy ............................................................................................... 153
8
6.7 Temperature stability of electromechanical strains ...................................................... 155
6.8 Electrical Fatigue ............................................................................................................ 159
6.9 Conclusions .................................................................................................................... 161
6.10 References ..................................................................................................................... 163
Chapter 7: Multilayer Actuator based on composition N9 ........................................................ 167
7.1 Introduction ................................................................................................................... 167
7.2 Processing of MLA .......................................................................................................... 168
7.2.1 Slurry formation ..................................................................................................... 169
7.2.2 Tape Casting ........................................................................................................... 170
7.2.3 Printing electrodes ................................................................................................. 171
7.2.4 Cutting and lamination .......................................................................................... 171
7.2.5 Binder burnout and sintering ................................................................................. 173
7.2.6 Cleaning and termination electrodes..................................................................... 174
7.3 Characterisation of MLA ................................................................................................ 175
7.3.1 Phase analysis and microstructure ........................................................................ 175
7.3.2 Multilayer cross section and active electrode area ............................................... 175
7.3.3 Dielectric properties............................................................................................... 176
7.3.4 Polarisation and displacement vs. voltage at room temperature ......................... 177
7.3.5 Temperature stability of displacement .................................................................. 180
7.3.6 Fatigue .................................................................................................................... 182
7.4 Conclusions .................................................................................................................... 184
7.5 References ..................................................................................................................... 185
Chapter 8: Further Compositional Development of PbO-free piezoelectrics based on KNN. ... 187
8.1 Introduction ................................................................................................................... 187
8.2 The (1-x) K Na NbO -xBiFeO (KNN-BF) system ......................................................... 188
0.4 0.6 3 3
8.2.1 Phase analysis ........................................................................................................ 188
8.2.2 Microstructure ....................................................................................................... 189
8.2.3 Dielectric Properties ............................................................................................... 191
8.2.4 Small signal response ............................................................................................. 193
8.2.5 Large signal response ............................................................................................. 194
8.2.6 Temperature dependence of piezoelectric coefficients ........................................ 197
8.3 Li doped KNN1 (0.99K Na NbO -0.01BiFeO ) ............................................................ 200
0.4 0.6 3 3
9