Summary of doctoral in materials science: Fabrications of ferroelectric materials do not contain Pb on BaTiO3 substrate and study their electricity and piezoelectricity properties

The goads of this thesis: Successfully fabricated ceramic piezoelectric samples (Ba1-xCax) TiO3 (BCT) and BZT-BCT by solid phase synthesis method. BZTBCT 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.

MINISTRY OF EDUCATION AND

NGUYEN VAN KHIEN

Fabrications of ferroelectric materials do not contain Pb on BaTiO 3 substrate and study their electricity and piezoelectricity properties

Specialized: Electronic materials

Numerical code: 62.44.01.23

SCIENCE

Ha noi, 2018

The work is completed at:

INSTITUTE OF MATERIALS SCIENCE - VIET NAM ACADEMY OF SCIENCE AND TECHNOLOGY

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, “Ba

1-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,

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

La 0.7 Sr 0.3 MnO 3 /BaTiO 3 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 BaTiO 3 lên tính chất điện từ của vật liệu La 0.7 Sr 0.3 MnO 3, Tạp chí Khoa học và Công nghệ Đại học Thái Nguyên, tập 118 số 4, 2014, trang 197-

202

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

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

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)

2  (o)

BCT0 BCT10 BCT12

BCT14 BCT14.4

BCT14.6

BCT14.8 BCT15 BCT15.2 BCT16

BCT20 BCT30

BCT12

BCT14 BCT14.4

BCT14.6

BCT14.8 BCT15 BCT15.2

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)

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 Ca2+ (0.134 nm) compared with Ba2+ (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

BZT-BCT15 BZT-BCT20

BZT-BCT25 BZT-BCT28 BZT-BCT28.8

BZT-BCT29.6

BZT-BCT30

BZT-BCT30.4

BZT-BCT29.2 BZT-BCT35

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 (002)T, (200)T at 45,11o and 45,36o) and irhombohedral phase (peak (200)R at 45,21 o) According to W Wersing, W Heywang et al., The proportion of tetragonal components is determined by:

3.2 Effected of Ca substitution for Ba on AC conductivity of BCT and

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%

BCT-BZT28 BCT-BZT28.8 BCT-BZT29.6 BCT-BZT30 BCT-BZT30.4

Figure 3.5 AC conductivity depends on the frequency of the BCTx

BCT14.8 BCT15 BCT15.2

BZT-BCT28 BZT-BCT28.8 BZT-BCT29.2 BZT-BCT29.6 BZT-BCT30

BZT-BCT30.4

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 different frequency ranges can be attributed to different contributions of migration of charges (charges jump and/or ion migration) and polarization (ion or atomic) in low and high frequency region, respectively Basically δac in whole frequency range can be analyzed by using UDR model as presented in Eq 3

and the relation between the frequency exponent s and the potential barrier can be expressed by the relation:

s = 4kBT/Ws (4)

where Ws is the maximum barrier height

According to equation (4) the barrier height of all the BZT-BCTx samples were estimated and presented in table 4

It is clear that the barrier height changed abnormally, has a minimal value at the sample BZT-BCT28 that has maximal piezoelectric parameter d31and d33 corresponding the Ca concentration in the Morphology Phase boundary (MPB) region In the high frequency range the localized polarization dominated with the frequency exponent larger than 1.5 This is suggested to be related with the polarization of dipole and/or atomic polarization in material samples

3.3 Effected of Ca concentration on dieclectric properties of materials

3.3.1 Effected of Ca concentration on dieclectric properties of BCT materials

Figure 3.7 is the dependence of the dielectric constant on the temperature at 1 kHz of the BCT model We see that the dielectric constant increases with temperature and increases rapidly in the vicinity of the

Curie TC phase - transition temperature Dielectric constant increases with

temperature proving that surface polarization increases in the BCT

material

Figure 3.7 Real part of dielectric constant depends on temperature of BCT

samples

It is clear that at x = 0 or concentration of Ca2+ substitution for Ba2+

is low, the peak of transition phase ferroelectric – paraelectricity is sharp

Then the Tc phase transition temperature follows Curie-Weiss's law:

' = C/(T - TC) (5)

When the concentration of Ca increases, the phase shift peak is no

longer sharp, they gradually blur and the peak expands Then the phase

transition is spread over a temperature range and the dielectric constant

reaches the maximum at Tm In this case, when matching the Curie-Weiss

law above is not appropriate, we must use the Curie-Weiss law of

extension

'

11

is the coefficient representing the level blur of the phase transition (1 

2) The change in temperature Tm and the maximum permittivity constant

‟max by component in the sample groups arelist in table 3.2.The relatively

large dielectric constant values of the samples initially met some of the

requirements of the power material in practical applications