Fabrications of ferroelectric materials do not contain Pb on BaTiO3 substrate and study their electricity and piezoelectricity properties

MINISTRY OF EDUCATION AND TRAINING VIET NAM ACADEMY OF SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY ..*****. NGUYEN VAN KHIEN Fabrications of ferroelectric materials do not contain Pb on BaTiO3 substrate and study their electricity and piezoelectricity properties Specialized: Electronic materials Numerical code: 62.44.01.23 SUMMARY OF DOCTORAL IN MATERIALS SCIENCE Ha noi, 2018 The work is completed at: INSTITUTE OF MATERIALS SCIENCE - VIET NAM ACADEMY OF SCIENCE AND TECHNOLOGY Science supervisor: 1. PGS.TS Le Van Hong 2. PGS. TS. Nguyen Van Dang PhD dissertation reviewer 1: PhD dissertation reviewer 2: PhD dissertation reviewer 3: The thesis will be protected under supervisory board academy level at: Academy at .. hours.. day ..month .. 2018 People can find this thesis at: - National library - Graduate university of Science and Technology library LIST OF PROJECTS PUBLISHED Articles in the ISI directory 1. Le Van Hong, Nguyen Van Khien and Truong Van Chuong, “Dielectric Relaxation of Ba1¹xCaxTiO3 (x = 0.00.3)”, Materials Transactions, Vol. 56, No. 9 (2015) pp. 1374 to 1377. 2. Van Khien Nguyen, Thi Hong Phong Le, Thi Kim Chi Tran, Van Chuong Truong and Van Hong Le, “Influence of Ca Substitution on Piezoelectric Properties of Ba1xCaxTiO3” Journal of electronic materials, DOI: 10.1007/s11664-017-5332-0 (2017). 3. Nguyen Van Khien, Than Trong Huy, Le VanHong, “AC conduction of Ba1-xCaxTiO3 and BZT-BCTx”, Physica B, S0921-4526(17)30193-X (2017). Articles published in domestic magazines 4. Nguyễn Văn Khiển, Vũ Đình Lãm và Lê Văn Hồng, “Ba1- xCaxTiO3 và tính chất điện môi của chúng”, Tạp chí Khoa học và Công nghệ 52(3C) (2014) 725-730 5. Nguyen Van Khien, Vu Dinh Lam and Le Van Hong, “Ba1- xCaxTiO3 AND THE DIELECTRIC PROPERTIES”, Communications in Physics, Vol. 24, No. 2 (2014), pp. 170-176. 6. Nguyễn Văn Khiển, Trương Văn Chương, Đặng Anh Tuấn, và Lê Văn Hồng, “Ảnh hưởng sự thay thế Ca cho Ba lên tính sắt điện của hệ Ba1-xCaxTiO3”, Hội nghị Vật lý chất rắn và Khoa học vật liệu toàn quốc lần thứ 9 - SPMS2015 7. Nguyen Van Khien and Le Van Hong, “ Effect of Ca concentration substituting for Ba on structure and ferroelectric properties of BZT- BCT material”, Vietnam Journal of Science and Technology 56 (1A) (2018) 86-92 Related articles. 8. T. D. Thanh, P. T. Phong, D. H. Mạnh, N. V. Khien, L. V. Hong, T. L. Phan, S. C. Yu, Low-field magnetoresistance in La0.7Sr0.3MnO3/BaTiO3 composites, J mater SCI (2013) 24: 1389- 1394. 9. Nguyễn Văn Khiển, Trịnh Phi Hiệp, Nguyễn Thị Dung và Nguyễn Văn Đăng, Nghiên cứu ảnh hưởng của biên pha nano BaTiO3 lên tính chất điện từ của vật liệu La0.7Sr0.3MnO3, Tạp chí Khoa học và Công nghệ Đại học Thái Nguyên, tập 118 số 4, 2014, trang 197- 202 Introduction Piezoelectric materials is a material that can can generate a Voltage corresponding to mechanical stess change. Although it was discovered in 1880, it was not widely used until the 1950s. Over the past half decade, PZT ceramics materials (PbZr1-xTixO3) have been studied and demostrated by researchers and It has a relatively large piezoelectric coefficient (d33 = 220 ÷ 590 pC / N). That‟s why most piezoelectric applications, both telephone batteries and high-tech scanning-tunneling microscopes use PZT piezoelectric materials.However, Pb is a radioactive element. It not only is very dangerous to humans but also it is one of the causes of global environmental pollution if used extensively. Therefore, it is imperative for scientists to find out that piezoelectric materials not contain Pb with a high piezoelectric coefficient which can be use instead of traditional PZT materials. Some piezoelectric materials not contain Pb have recently been publish and have shown good results. Special, material systems not contain Pb on (K,Na)NbO3 and BaTiO3 substated. However, in our understanding, piezoelectric material systems not contain Pb have not been adequately researched. There are some publications published in international journals, but a few and sporadically. The physical mechanism to explain the cause of the high piezoelectric coefficient and the properties of the material is still a lot of unsoud, need to focus more research, deeper. In the country, piezoelectric material systems are studied by many scientists in centers, scientific institutes and universities such as Ha Noi unviersity of Science and Technology, University of Science-Hue University .... In order to promote the research activities on the family of piezoelectric materials not contain Pb and based on the actual situation as well as research conditions such as experimental equipment, references, research collaboration capabilities with domestic research team ... We think that studying and solving the problems mentioned above is useful and will give many positive results. Especially finding the relationship between the big piezoelectric coefficient and the dielectric recovery time of the object piezoelectric. This is why we choose this thesis “Fabrication of ferroelectric materials do not contain Pb on BaTiO3 substrate and study their electricity and piezoelectricity properties”. we believe that our work will be sussces and will be useful for the understand about the interaction electric mechanism in the ferroelectric material systems, piezoelectric not contain Pb, also open application capacibility of these material systems in fabrication of pin, senso contributory on the environment reduction. The main contents of my thesis is present in 4 chapters: Chapter 1. Theoritical overview Chapter 2. Experiment Chapter 3. Effected of Ca substitution for Ba on the structure and magnetic properties of BCT and BZT-BCT Chapter 4.The relationship between time of restore dielectric and piezoelectric properties of BCT and BZT-BCT The goads of this thesis:  Successfully fabricated ceramic piezoelectric samples (Ba1-xCax) TiO3 (BCT) and BZT-BCT by solid phase synthesis method. BZT- BCT materials must be good quality, high piezoelectric coefficient (500-600 pC / N).  Studying the relationship between morphological competition and dielectric ferroelectric properties, especially with the high piezoelectric properties of materials.  In addition, based on the results of the synchronized studies about the material phase structure, the electric polarization of the material depends on temperature, electric field and frequency which will provide the analysis and general discussion contribute. Demonstrate the physical mechanism of the phenomenon of high piezoelectri coefficient in ferroelectric material systems. Research object of my thesis  Research object: Piezoelectric materials.  Area of research: Piezoelectric materials do not contain Pb on BaTiO3 substrate  Research methods: The ceramic bulk is fabricated by solid phase reaction. Structure of materials, morphological phase, particle size, The morphologic form of the material was investigated and analyzed on the basis of X-ray diffraction pattern, Raman spectra and Scanning Electron Microscope SEM. After obtaining the necessary information on the phase structure, phase material cleanliness, morphology and supporting information as mentioned above we perform electrical measurements such as resistant R (T), capacity C (T), D (E). Measurement of C (T) will be made under the effect of high electric field to evaluate the maximum polarization of the material. In addition, C (f) frequency-dependent measurements of polarization are also performed to evaluate the dielectric recovery characteristics and to indirectly evaluate the piezoelectric coefficient of the material. Colecting all the results of the study will help us to evaluate the dielectric polarization mechanism in the material, the correlation between the morphological phase and the piezoelectricity ferroelectric properties of the materials. In the process of working and writing this thesis, although the author has tried hard but still can not avoid the errors. I wishes to receive the comments, the reviewer of the scientists as well as the people interested in the topic. It can help me complete the thesis with good result. Chapter 1. Overview. Chapter 2.Experiment. Chapter 3. Effected of Ca substitution for Ba on the structure and elctrical properties of BCT and BZT-BCT BZT-BCT is a material which is the largest piezoelectric property in the announced in piezoelectric material systems do not contain Pb. Before analyzing and investigating the cause of the piezoelectricity effect in the BZT-BCT systems. Firstly we studied the BCT system (BZT system, there were many publications of the authors in the world). The structure and physical properties of the BCT system will change when Ba are substituted by Ca. Does the morphological phase exist in the BCT material? And when the Ca substitution for Ba, the piezoelectric properties of the material is improved? We are going to disscus about this in the next chapters. 3.1. Effected of Ca substitution for Ba on the structure of BCT and BZT-BCT For convenience in the sample analysis, we call Ba1-xCaxTiO3 is BCTx ( x = 0, 10, 12, 14, 16, 18, 20 and 30:Atomic percentage of Ca concentration) and Ba(Ti0.8Zr0.2)O3 – Ba1-yCayTiO3 system is BZT-BCTy (y = 15, 20, 25, 28, 28.8, 29.2, 29.6, 30, 30.4 and 35, Atomic percentage of Ca concentration in this system is y/2). 20 30 40 50 60 70 80 90 2 ( o ) BCT0 BCT10 BCT12 BCT14 BCT14.4 BCT14.6 BCT14.8 BCT15 BCT15.2 BCT16 BCT20 BCT30 82 84 86 BCT12 BCT14 BCT14.4 BCT14.6 BCT14.8 BCT15 BCT15.2 BCT16 (0 0 1 ) (0 1 0 ) (0 1 1 ) (1 1 1 ) * ( 0 0 2 ) (0 2 0 ) (0 1 2 ) (0 2 1 ) ( 1 1 2 ) (1 2 1 ) (0 2 2 ) (2 2 0 ) (1 1 2 ) (0 1 3 ) (0 3 1 ) (1 1 3 ) (3 1 1 ) (2 2 2 ) Figure 3.1. X- ray diffraction pattern of BCTx samples The XRD patterns of all the samples are presented in Fig.3.1. It is easy to recognize that all the samples had the same tetragonal structure with c/a ratio close to unity but depending on the Ca concentration, changing from 1.0079 to 1.0083 as x was increased from zero to 0.16 (Table 3.1). Table 3.1. lattice spacing of samples BCT. sample a b C α β γ c/a V BCT0 3,9866 3,9866 3,9866 90 90 90 1 63,36 BCT10 3,9877 3,9877 4,0178 90 90 90 1,00754 63,89 BCT12 3,9905 3,9905 4,0223 90 90 90 1,00796 64,05 BCT14 3,9910 3,9910 4,0239 90 90 90 1,00824 64,09 BCT14.4 3,9914 3,9914 4,0244 90 90 90 1,00826 64,11 BCT14.6 3,9917 3,9917 4,0248 90 90 90 1,00829 64,12 BCT14.8 3,9919 3,9919 4,0252 90 90 90 1,00834 64,14 BCT15 3,9915 3,9915 4,0248 99 90 90 1,00834 64,12 BCT15.2 3,9897 3,9897 4,0232 99 90 90 1,00839 64,04 BCT16 3,9869 3,9869 4,0226 90 90 90 1,00859 63,91 BCT18 3,9860 3,9860 4,0212 90 90 90 1,00883 63,79 BCT20 3,9852 3,9852 4,0211 90 90 90 1,00901 63,66 BCT30 3,9651 3,9651 4,0021 90 90 90 1,00932 62,92 Tetragonal symmetry was also identified from HRTEM images for the BCT14 sample, as presented in Fig. 3.2a, which clearly shows parallel lattice faces with tetragonal structure having c/a ratio close to unity (supercubic structure). This result is consistent with the XRD analysis. As shown in our previous report, Ca successfully substituted for Ba and induced a shift of the (222) diffraction peak toward higher angle (as shown inthe inset). This shift is due to the smaller ionic radius of Ca 2+ (0.134 nm) compared with Ba 2+ (0.161 nm). It is known that, at room temperature, BTO crystallizes in tetragonal structure and its (222) diffraction peak should be single. In our case, the (222) diffraction line of the sample doped With x= 0.14 of Ca started to split into two peaks, indicating that this sample contained material with two structural symmetries. Probably, both tetragonal and orthorhombic structures coexist due to the grain-size effect, as also reported by other authors for BTO materials with average grain size in theregion of 0.1µm to 1.0µm. Karaki et al. also observed the orthorhombic–tetragonal transition at a temperature TOT of around 24C for BTO with grain size of micrometers. This may be evidence of the existence of a MPB in this ceramic compound. Using the commercial Rietveld program X‟PertHighScore Plus, we fit the XRD data and estimated the contribution of tetragonal and orthorhombic phases in the samples. The fitting results showed that tetragonal and orthorhombic phases coexisted at ratio of 93/7 in sample BCT14. On increasing x to 0.14, the (222) peak splitting increased, becoming triple with three small peaks for x= 0.148. For the samples doped with x higher than 0.148 (samples BCT15, BCT15.2, and BCT16) the (222) peak broadened, forming a wide single peak when x reached 0.16. This could be due to overlapping of the (222) peaks of BaTiO3 and CaTiO3 that started to coexist in these samples, as seen in their XRD patterns. Such coexistence can also be seen in the HRTEM image with clear parallel lattice faces for BCT16 (Fig 3.2b). The fast Fourier transform (FFT) for this material region exhibits three diffraction points arranged in a linear line. This suggests that, in this sample, there exists a region where the material phases are nested similar to a superlattice. These lected-area diffraction (SAED) image (Fig 3.2c) shows ordered repetition of the diffraction points of the (220) face of the tetragonal crystal lattice with a= 3.9975 A˚ and c= 4.0094 A˚. The diffraction points appeared to be repeated periodically as for a superlattice. The separation between lattice faces as estimated directly from the HRTEM images was about 2.6 A˚ to 2.7 A˚, in good agreement with the XRD analysis. Figure 3.2. HRTEM images Figure 3.3. X- ray diffraction of sample systems BZT-BCT. From X- ray diffraction of sample systems: It is found that when Ca concentration is less than 14,8 % atoms (the Ba: Ca ratio is 85.2: 14.8 corresponding to the y = 29,6). The sample systems are single phase. When the y concentration is more than 30, the new spectral peak of the CaTiO3 component appears on the Xray diffraction (this result is quite siutable with the BCTx material systems). Figure 3.3. Xray diffration pattern of sample systems of BZT-BCT It is clear that diffraction peaks tend to shift toward 2θ when the concentration of Ca increases and some diffraction peaks tend to split vertices. Particularly, we see that the diffraction peaks at 2θ= 44,70 .It separates the peak when the concentration of Ca increases and when the concentration of 14.8% of the atoms (y = 29.6), it was split into three distinct vertices (These vertices can correspond to two different types of structures: the tetragonal and the irhombohedral). However, when the concentration of y is more than 30, it tends to incorporate into two vertices corresponding to the tetragonal structure. The particularity in this structure may be the reason for the highest piezoelectric coefficient, at y = 29.6 which will be explored in detail later. When the y component is still small (less than 29.2), the material has a irhombohedral structure characteristic of BZT, whereas when the y component is higher, the material has a tetragonal structure characteristic of BCT. At y=29.6, two types of tetragonal and irhombohedral are exist. This assertion is confirmed by the separation of the special diffraction peaks corresponding to at 2θ= 44,70 and the Gaussian fitting of the components around y = 29.6. 20 30 40 50 60 70 80 90 100 BZT-BCT15 BZT-BCT20 BZT-BCT25 BZT-BCT28 BZT-BCT28.8 BZT-BCT29.6 BZT-BCT30 BZT-BCT30.4 BZT-BCT29.2 BZT-BCT35 2 o ) (1 0 0 ) (1 1 0 ) (1 1 1 ) (0 0 2 ) (2 0 0 ) (2 1 0 ) (2 1 1 ) (2 1 2 ) (2 2 0 ) (2 2 1 ) (3 1 0 ) (3 1 1 ) (3 2 2 ) 44.4 45.6 Figure 3.4. XRD in the 44 o -46 o area of the samples is fitted to the Gaussian function From the result shown in Figure 3.4: at y = 29.6, the material exits two phase: tetragonal (corresponding to T(002) , T(200) at 45,11 o and 45,36 o ) and irhombohedral phase (peak R(200) at o45,21 ). According to W. Wersing, W. Heywang et al., The proportion of tetragonal components is determined by: (1) where: 200 TI , 002 TI , 200 RI are the intensity of the diffraction peaks at (200), (002) corresponding to the tetragonal and irhombohedral respectively. In the case of BZT-BCT material system for y = 29.6, we calculated the tetragonal and irhombohedral ratio to be around 69%. This result also shows that the formation of the morphological boundary with the surrounding components y = 29.6%. 3.2. Effected of Ca substitution for Ba on AC conductivity of BCT and BZT-BCT As known BTO is an isolate ferroelectric material as oxygen deficiency in material is small. In this case the localized reorientation is a main contribution in AC conduction of BTO. For analysis the mechanism of AC conduction we applied the power law equation (Eq. 3.2) to fit the conduction data of the BCTx samples.The experimental data of conductivity of the BCT samples and fitting curves are presented in Fig 3.5. This fit provides a very good description of the data in the whole measured frequency and the obtained parameters are presented in table 2. As displayed in Fig. 3.6 the AC conductivity of the samples decreases with increasing the Ca concentration. It may be related with a pinning effect of electrical dipoles in material that induced a depression of dielectric relaxation time as Ca concentration lower than 16 at%. 44 44.5 45 45.5 46 BCT-BZT28 BCT-BZT28.8 BCT-BZT29.6 BCT-BZT30 BCT-BZT30.4 2 0 ) 200 002 T T T 200 200 002 T R T , I I I I I + = + + F Figure 3.5. AC conductivity depends on the frequency of the BCTx systems Figure 3.6. AC conductivity depends on the frequency of the BZT-BCT systems Increasing Ca concentration the AC conductivity continuously decreased. It is assigned for existing of the CaTiO3 phase formed in the samples with Ca concentration higher than 16 at %. From the fitting parameters one can see the BCT sample material is an isolating ceramic with very low ζdc. It suggests that no oxygen deficiency appears in the samples material. This suggestion is confirmed again from values of frequency exponent n reported in table 2. All the obtained value of n is about 1.4. It means the localized reorientation is a main contribution in AC conductivity of all the BCT samples. The term of the polaron hopping in inhomogeneous electronic microstructure was not seen. It has supposed that the BCT lattice with less of the structure deformation and oxygen vacancy was manufactured. By the same 0 5 10 -6 1 10 -5 1.5 10 -5 2 10 -5 2.5 10 -5 0 5 10 5 1 10 6 1.5 10 6 2 10 6 2.5 10 6 BCT0 BCT10 BCT12 BCT14 BCT16 BCT20 BCT30 ( S /m ) f (kHz) 0 2 10 -6 4 10 -6 6 10 -6 8 10 -6 1 10 -5 1.2 10 -5 1.4 10 -5 1.6 10 -5 0 5 10 5 1 10 6 1.5 10 6 2 10 6 2.5 10 6 BCT14 BCT14.4 BCT14.6 BCT14.8 BCT15 BCT15.2  ( S /m ) f (Hz) 0 0.002 0.004 0.006 0.008 0.01 0.012 0 200 400 600 800 100012001400 BZT-BCT15 BZT-BCT20 BZT-BCT25 BZT-BCT28 BZT-BCT30 BZT-BCT35   S /m ) f (kHz) 0 0.0005 0.001 0.0015 0.002 0.0025 0 200 400 600 800 100012001400 BZT-BCT28 BZT-BCT28.8 BZT-BCT29.2 BZT-BCT29.6 BZT-BCT30 BZT-BCT30.4   S /m ) f (kHz) way we have analyzed the frequency dependence of AC conductivity of the BZT-BCTy samples. As wellknown the change of AC conductivity in diffe