HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY MASTER’S THESIS Effect of Zr and La based co-doping on electrical properties of lead-free barium titanate BaTiO3 thin films TRAN THI DOAN Doan.vn Major: Materials Science Supervisor: Prof. Vu Ngoc Hung Department: Micro-Electro-Mechanical-System Laboratory Institute: International Training Institute for Materials Science HANOI, 05/2022 HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY MASTER’S THESIS Effect of Zr and La based co-doping on electrical properties of lead-free barium titanate BaTiO3 thin films TRAN THI DOAN Doan.vn Major: Material Science Supervisor (Sign and write full name) HANOI - 05/2022 Acknowledgment Firstly, I would like to express my deepest appreciation to my supervisor, Prof. Vu Ngoc Hung, who directly instructed me throughout this research project. I am also grateful to Dr.
Nguyen Duc Minh of MESA+ Institute for Nanotechnology at University of Twente, Netherlands. I am extremely thankful and indebted to him for sharing his expertise as well as the valuable guidance and encouragement extended to me. I would like to extend my sincere thanks to MSc. Dang Thi Ha, Dr.
Vu Thu Hien, Dr. Ngo Duc Quan, and all of members in MEMS laboratory for their enthusiasm to help me through the process of research. I take this opportunity to express gratitude to all professors, lecturers, and employees at ITIMS for their kindness to support me during a period I have already studied and worked there. Finally, I want to give special thanks to my family for providing me with their unfailing support and encouragement during my years of study and research.
Abstract BaTiO3-based materials with a perovskite structure have attracted interest because some of them are potentially valuable materials due to their environment-friendly properties. In this study, lead-free Ba(Zr0.75)O3 (BZT) and La-doped Ba(Zr0.75)O3 (BLZT) thin films were grown on Pt/Ti/SiO2/Si substrates via a sol-gel spin-coating method. The effects of various annealing temperatures (450–700 oC) for BZT thin films on microstructure, dielectric, and energy storage performances were systematically investigated. As XRD result, it was found that the degree of crystallization of the films increased with the increasing annealing temperature (Ta).
This result indicated a pure polycrystalline perovskite phase of BZT thin films achieved at 700 oC. At the same time, the dielectric constant of the BZT film also increases as the annealing temperature increases. In particular, the optimal energy-storage density of 30.9 J/cm3 and a large energy-storage efficiency of 67.8% could be obtained in the film annealed at 500 oC, which not only achieved a large breakdown strength (up to 7000 kV/cm) but also exhibited a great temperature-dependent energy storage performance stability in a wide temperature (from 30 oC to 200 oC) a good frequency-dependent energy storage performance stability in ranging from 100 to 10000 Hz and an excellent charge- discharge cycling life with fatigue-free performance up to 109 cycles. Moreover, the effects of La doping of BZT thin films (from 0 – 8 mol.%) on microstructure, dielectric, and energy storage performances were also investigated.
As XRD result, it was shown that La doping enhanced the ability of crystallization of the films with the perovskite BZT phase achieved at 650 oC. La-doped BZT thin films indicated prominently increasing relaxor behavior with increasing La-doping concentration. In particular, the films with 5 mol.% La- doping simultaneously exhibit a quite high recoverable energy-storage density (~7.0 J/cm3) and a large energy-storage efficiency (~ 60.7%) under an EBD of 1650 kV/cm. Moreover, dielectric constant of La-doped BZT thin films was found to be significantly improved, reaching the maximum value of 164 for 3 mol.% La-doped BZT thin film.
These results indicated that lead-free Ba(Zr0.75)O3 and La-doped Ba(Zr0.75)O3 thin films were expected to become a candidate materials for energy-storage capacitors. Master student (Sign and write full name) TABLES OF CONTENTS LIST OF ABBREVIATIONS. i LIST OF FIGURES. ii LIST OF TABLES .1 Overview of ferroelectric and relaxor ferroelectric properties .2 Principles for High Energy-Storage in Dielectric Capacitors .1 Basic knowledge on dielectric capacitor.2 Measuring methods of energy-storage density for dielectric capacitor….3 Potential dielectrics for high energy-storage application .3 Overview of barium titanate-based materials .1 Barium titanate (BaTiO3) structure .2 Effects of doping on BaTiO3 properties.
EXPERIMENTS AND METHODS .1 Fabrication of BZT and BLZT thin films by sol-gel spin coating method….1 Overview of sol-gel spin coating method .2 Fabrication of BZT and BLZT Sols .3 Fabrication of BZT and BLZT thin films .2 Methods to investigate the structure and properties of BZT and BLZT films…. RESULTS AND DISCUSSION .1 Effect of annealing temperature (Ta) on properties of BZT thin films .2 Ferroelectric properties and breakdown strength (EBD) .3 Energy - storage properties .2 Effects of La-doping on properties of BZT thin films .2 Ferroelectric properties and breakdown strength (EBD) .3 Energy-storage properties .3 Thermal stability, frequency stability and fatigue endurance. 52 LIST OF PUBLICATIONS. 55 LIST OF ABBREVIATIONS Acronyms Description AFE Anti-ferroelectrics CVD Chemical Vapor Deposition DSC Differential scanning calorimetry BTO Barium titanate, BaTiO3 BZT Barium zirconate titanate, Ba(Zr,Ti)O3 BLZT Barium lanthanum zirconate titanate, (Ba,La)(Zr,Ti)O3 FE Ferroelectrics HR-SEM High resolution scanning electron microscopy LD Linear dielectric MEMS Micro electro mechanical systems MPB Morphotropic phase boundary P-E Polarization hysteresis loop PLD Pulsed laser deposition PZO Lead zirconate, PbZrO3 PZT Lead zirconate titanate, Pb(Zr,Ti)O3 PLZT Lead lanthanum zirconate titanate, (Pb,La)(Zr,Ti)O3 PNRs Polar nanoregions PMN Lead magnesium niobate, Pb(Mg1/3Nb2/3)O3 PZT Lead zirconate titanate, Pb(Zr,Ti)O3 RFE Relaxor ferroelectric TGA Thermogravimetric analysis XRD X-Ray diffraction i LIST OF FIGURES Figure 1.
Polarization as a function of temperature in (a) first and (b) second order phase transition [18]. Frequency dependence of polarization [19]. Ferroelectric hysteresis loop [19]. Orientation of dipoles in the ferroelectric materials (a) absence of electric field (b) under electric field and (c) after removal of electric field [23].
Temperature evolution of dielectric constant showing the characteristic temperatures in RFE. Representative hysteresis loops for each temperature interval are showed below [24]. Hysteresis behavior in (a) ferroelectric and (b) relaxor materials [27]. Polarization and temperature in (a) ferroelectric and (b) relaxor materials [28].
The diagram of charge separation in parallel-plate capacitor under the function of electric field [30]. The diagram of measurement circuit for the energy-storage density [30]. Diagram of hysteresis and energy storage density for (a) linear dielectrics, (b) ferroelectrics, (c) relaxor ferroelectrics, and (d) anti-ferroelectrics. The green area in the first quadrant is the recoverable energy density Ureco, and the red area is the energy loss Uloss [32].
Schematic of the perovskite structure of BaTiO3 (a) Cubic lattice (above Curie temperature, 120oC), (b) Tetragonal lattice (below Curie temperature, 120oC) [34]. Reversal in the direction of spontaneous polarization in BaTiO3 by reversal of the direction of the applied field [35]. An overview of the various stages of the sol-gel process. Schematic representation of: (a) dip coating; (b) spin coating; and (c) spray coating [45].
Example of processing routes to obtain sol-gel spin coatings [46]. Flow diagram for producing BZT and BLZT sols. TGA-DSC plots of BZT material. Schematic of spin-coating and heat treatment process for producing BZT thin films.
Spin-coating machine at International Training Institute for Materials Science (ITIMS). Schematic representation of the Bragg‟s law for diffraction [48]. The working principle diagram of X-ray diffractometer and the PANalytical X‟Pert PRO system [48]. The schematic drawing of a Sawyer-Tower circuit used for hysteresis measurement of ferroelectric thin film [49].
Equipment for measuring ferroelectric properties of materials BLZT (aixACCT- TF2000). Cross-sectional SEM images of BZT thin films, grown on Pt/Ti/SiO2/Si, at various annealing temperatures (a) 450 oC, (b) 500 oC, (c) 600 o C, (d) 650 oC, (e) 675 oC, (f) 700 oC. (a) XRD patterns of BZT thin films, grown on Pt/Ti/SiO2/Si, at various annealing temperatures, Ta, (b) Schematic of the dependence of phase transition on annealing temperature, Ta for BZT thin films. Polarization-electric field (P-E) hysteresis loops and (b) values of Pmax, Pr and Pmax - Pr for BZT thin films at various annealing temperatures.
The measurements were performed at 1000 kV/cm and 1 kHz. Electric field dependence of Pmax and Pr values for BZT thin films at various annealing temperatures, measured until their corresponding electric breakdown strength (EBD). The data were calculated from the corresponding P-E loops. Dependence of volumetric energy-storage density Ustore, recoverable energy-storage density Ureco, and energy-storage efficiency (η) on applied electric field for BZT thin films at various annealing temperatures.
The data were calculated from the corresponding P-E loops. (a) Energy-storage densities, recoverable energy-storage and (b) energy-storage efficiency were measured at the corresponding EBD values, for BZT thin films at various annealing temperatures. (a) Dielectric constant – electric field (-E) curves and (b) dielectric loss curves of BZT thin films at various annealing temperatures, measurement at room temperature frequency 1 kHz. SEM images of (a) BZT and (b) BL5ZT thin films.
XRD patterns of BLZT thin films grown on Pt/Ti/SiO2/Si with various La-doping contents. Polarization-electric field (P-E) hysteresis loops and (b) values of Pmax, Pr and Pmax - Pr for BZT thin films with various La doping contents (0-8 mol. The measurements were performed at 1000 kV/cm and 1 kHz. Electric field dependence of Pmax and Pr, values for La-doped BZT thin films at various La doping contents, measured until their corresponding electric breakdown strength (EBD).
The data were calculated from the corresponding P-E loops. Dependence of volumetric energy-storage density (Ustore), recoverable energy-storage density (Ureco), and energy-storage efficiency (η) on applied electric field for BZT thin films with various La doping contents (a) 0%, (b) 3%, (c) 5%, (d) 8%. The data were calculated from the corresponding P-E loops. (a) Energy-storage densities, recoverable energy-storage and (b) energy-storage efficiency were measured at the corresponding EBD values, for BZT thin films with various La doping contents.
(a) Dielectric constant – electric field (-E) curves and (b) dielectric loss curves of BZT thin films with various doping content, measurement at room temperature frequency 1000 Hz. The operating-temperature dependence of (a) P-E loops, (b) Pmax, Pr and Pmax – Pr values for BZT thin film at an annealing temperature of 500 oC. The measurements were performed at 4000 kV/cm and 1000 Hz. The operating-temperature dependence of (a) energy storage density (U) and (b) energy-storage efficiency (η) for BZT thin film at annealing temperature of 500 oC.
The measurements were performed at 4000 kV/cm and 1000 Hz. The frequencies-temperature dependence of P-E loops for BZT thin film at annealing temperature of 500 oC. The measurements were performed at 4000 kV/cm and room temperature. The operating-frequencies dependence of (a) Pmax, Pr and Pmax - Pr values, (b) Ec values, (c) energy storage density (U) and (d) energy-storage efficiency (η) for BZT thin film BZT thin film at annealing temperature of 500 o C.
The measurements were performed at 4000 kV/cm and room temperature. a) Comparison of P-E hysteresis loops measured at different charge-discharge cycles, (b) Pmax and Pr values as a function of number charge- discharge cycles under an applied electric field of 4000 kV/cm and 1 kHz, for the BZT thin film at annealing temperature of 500 oC. The fatigue testing was performed by applying a bipolar electric field of pulse height 200 kV/cm and at pulse width 100 kHz (or 5 μs). Dependence of (a) energy storage density and (b) energy storage efficiency (η) on cycling for BZT thin film at an annealing temperature of 500 oC.
The data were calculated from the corresponding P-E hysteresis loops performed at 4000 kV/cm, 1 kHz and room temperature. 49 iv LIST OF TABLES Table 2. Parameters of chemical components used to synthesize BZT and BLZT materials. Breakdown strength EBD values of BZT thin films at various annealing temperatures.
The measured dielectric constant, dielectric loss for BZT thin films at various annealing temperatures. Electric breakdown strength (EBD) of BZT thin films with various La doping contents. The measured dielectric constant, dielectric loss for BZT thin films with various La doping contents (0 - 8%). 45 v INTRODUCTION Nowadays, energy storage is realized mainly based on traditional devices such as accumulators and electrochemical cells.
Electrochemical cells typically have a fairly high energy density but their power density takes on a relatively low value.