Tài liệu Research on fabrication and the physical properties of the multi-component ceramics based on pzt and the relaxor ferroelectric materials

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HUE UNIVERSITY COLLEGE OF SCIENCES ------------------- LE DAI VUONG RESEARCH ON FABRICATION AND THE PHYSICAL PROPERTIES OF THE MULTI-COMPONENT CERAMICS BASED ON PZT AND THE RELAXOR FERROELECTRIC MATERIALS Major: Solid State Physics Code: 62.44.01.04 ABSTRACT OF THE THESIS Hue, 2014 The thesis had implemented at College of Sciences, Hue University Academic Supervisor: Assoc. Prof. Dr. Phan Dinh Gio Reviewer 1:..................................................................................................... Reviewer 2:..................................................................................................... Reviewer 3:..................................................................................................... This thesis will be reported at Hue University Date & Time …../ …./…./…. 1 INTRODUCTION For more than 50 years, the ferroelectric materials are one of the most the important materials and have been intensively investigated in both fundamental research and applications. The reason is that they exist in many important physical effects such as ferroelectric, piezoelectric, photovoltaic, non-linear optical, pyroelectric effects, etc. These materials have the ability for application in manufacturing of capacitors, high capacity memory, power ultrasonic transducers used in biology, chemistry, pharmacology, and piezoelectric transducers [3], [5], [35], [36], [81]. The important and main materials of applications often have the perovskite structures, ABO3. That is the Pb(Zr,Ti)O3 (PZT) ceramics, and PZT doped ‘‘soft’’and ‘‘hard’’ such as La, Ce, Nd, Nb, Ta, ... and Mn, Fe, Cr, Sb, In. In addition to these families, there is a wide variety of complex perovskite forms resulting from multiple ionic substitutions. Many of the materials in the complex perovskite family are known to be relaxor ferroelectrics. The general formula for the complex perovskite is: (A’A’’…An’)BO3 or A(B’B’’..Bn’)O3, and their dielectric, piezoelectric and ferroelectric properties of ceramics may be improved for high power applications [3], [5], [16], [18], [30], [31], [37], [56], [57], [76], [81]. The characteristics of relaxor ferroelectric materials are a high dielectric constant, a broad ferroelectric- paraelectric transition (the diffuse phase transition) and a strong frequency dependency of the dielectric properties. In addition, above the Curie temperature of several tens of degrees still have spontaneous polarization and hysteresis loops [5], [5], [58], [81]. Recently, the materials scientists have been intensively investigating the application of multi-component ceramic systems combining the normal ferroelectric PZT and relaxor ferroelectric materials such as: Pb(Zr,Ti)O3– Pb(Zn1/3Nb2/3)O3 (PZT–PZN) [23], [24], [30], [31], [35], [42], [90]; Pb(Zr,Ti)O3–(Mn1/3Nb2/3)O3 (PZT-PMnN) [4], [15], [52]; Pb(Zr,Ti)O3– Pb(Mn1/3Sb2/3)O3 (PZT-PMS) [5], [60], [80], [83]; Pb(Zr,Ti)O3– Pb(Zn1/3Nb2/3)O3–Pb(Mg1/3Nb2/3)O3 (PZT–PZN–PMN) [13]; Pb(Zr,Ti)O3 – Pb(Zn1/3Nb2/3)O3 – Pb(Mn1/3Nb2/3)O3 (PZT–PZN–PMnN) [29], [34], [64], 2 [84], [87]. These ceramics often have low dielectric loss (tanδ), large dielectric constant ε, high mechanical quality factor (Qm), high electromechanical coupling factor (kp) [3], [5], [29], [34], [64], [84], [87]. Recent research has demonstrated that the PZT–PZN–PMnN quaternary ceramics (by combining PZT-PZN and PZT-PMnN ceramics) have excellent piezoelectric properties: the high Qm, the low tanδ and the large kp, the high remanent polarization, and the large dielectric constant [29], [34], [64], [75], [84], [87] satisfy the requirements for practical application in piezoelectric transformers, ultrasonic motors. However, the sintering temperature of the ceramics is quite high (> 1150 oC) [29], [34], [64], which leads to evaporation of PbO during the sintering process, resulting in reduced properties of ceramic compositions and environmental pollution. Therefore, lowering sintering temperature of PZT based ceramics is very necessary. In order to reduce the sintering temperature at which satisfactory densification could be obtained, various material processing methods such as the 2-stage calcination method [5]; hot-pressed method [3], [5], [32]; high energy mill [5]; liquid phase sintering [13], [15], [26], [23], [33], [35], [41], [53]; using nano power [2], [17], [22] have been performed. Among these methods, liquid phase sintering is basically an effective method for aiding densification of specimens at low sintering temperature. Many researchers have successfully decreased the sintering temperature of PZT-based ceramics by using various additives such as Li2CO3 (735 °C), Bi2O3 (820 °C), B2O3 (450 °C), CuO-PbO (790 °C), etc. In some cases, these additives can facilitate a lower sintering temperature, but decrease simultaneously the piezoelectric properties of ceramics due to the formation of piezoelectrically inactive phases in the grain boundary regions. Therefore, the research and fabrication ceramics sintered at low temperature, while improving or not reducing the piezoelectric properties of ceramics system is very important [16], [23], [44], [75], [80]. Thus, the PZT - PZN - PMnN ceramics is very attractive for both fundamental research and applications. From the above fact, we have chosen dissertation topic is “Research on fabrication and the physical properties 3 of the multi-component ceramics based on PZT and the relaxor ferroelectric materials”. The objective of the thesis is: (i) Fabrication and research the effects of Pb(Zr0,47Ti0,53)O3 on the structure, microstructure and the physiscal properties of xPb(Zr0,47Ti0,53)O3 - (0,925-x)Pb(Zn1/3Nb2/3)O3 - 0,075Pb(Mn1/3Nb2/3)O3 ceramic systems. (ii) To study the effect of Zr/Ti ratio in PZT on the structure, and the properties of the PZT - PZN - PMnN ceramics, determine PZT content which ceramics have good electrical properties and the relaxor ferroelectric characteristics. (iii) To study the characteristic properties of the Fe2O3 doped PZT - PZN - PMnN ceramics. (iv) To study the effect of CuO on the sintering behavior and electrical properties of PZT–PZN–PMnN ceramics. Research objects: The main research objects of the dessertation were the PZT - PZN - PMnN multi-component ceramic systems and the PZT - PZN PMnN doped CuO, Fe2O3 ceramics. The ceramic samples have been prepared in our laboratory by ourself. Experimental methods: To obtain the above objectives, we have used the conventional ceramic technology and the B-site oxide mixing technique (BO) for preparing the ceramic samples. Scientific significance and practical: The thesis is a fundamental research have oriented applications. The systematic research of the dielectric, piezoelectric and ferroelectric properties contribute further understanding of the physical properties of the multi-component ceramics based on PZT and the relaxor ferroelectric materials, Pb(Zn1/3Nb2/3)O3 and Pb(Mn1/3Nb2/3)O3. The results of the thesis will open up prospects for the fabrication of electronic ceramic materials in our country, particularly the feasibility of application of ceramic materials for fabricating ultrasonic sensors, ultrasonic cleaners. The layout of the thesis: The thesis is presented in four chapters including 118 pages. Chapter 1. LITERATURE REVIEWS 4 Chapter 1 presents literature reviews in dissertation research, as a basis for research and explains the survey results of physical properties of materials such as: ferroelectric phase transition, hysteresis loops, domain ferroelectric. Some characteristics of the PZT based ferroelectric ceramics and the relaxor ferroelectric materials (PZN, PMnN). In addition, Raman spectroscopy has also been introduced to explain the experimental results for the next section. Chapter 2. FABRICATION, STRUCTURE AND MICROSTRUCTURE OF PZT –PZN – PMnN CERAMICS 2.1. Fabrication of PZT – PZN– PMnN ceramics The PZT – PZN – PMnN ceramcis has been fabricated by the conventional method and the B-site Oxide mixing technique (BO) includes the following the sample groups: Group 1: xPb(Zr0,47Ti0,53)O3 – (0,925-x)Pb(Zn1/3Nb2/3)O3 – 0,075Pb(Mn1/3Nb2/3)O3 + 0,7 % kl Li2CO3 (0,65 ≤ x ≤ 0,9); (MP: MP65, MP70, MP75, MP80, MP85 và MP90). (2.1) Group 2: 0,8Pb(ZryTi1-y)O3 – 0,125Pb(Zn1/3Nb2/3)O3 – 0,075Pb(Mn1/3Nb2/3)O3 + 0,7 % kl Li2CO3 (0,46 ≤ y ≤ 0,51); (MZ: MZ46, MZ47, MZ48, MZ49, MZ50 và MZ51). (2.2) Group 3: 0,8Pb(Zr0,48Ti0,52)O3 – 0,125Pb(Zn1/3Nb2/3)O3 – 0,075Pb(Mn1/3Nb2/3)O3 + 0,7 % kl Li2CO3 + z % kl Fe2O3 (0,0 ≤ z ≤ 0,35); (MF: MF0, MF1, MF2, MF3, MF4, MF5 và MF6). (2.3) Group 4: 0,8Pb(Zr0,48Ti0,52)O3 – 0,125Pb(Zn1/3Nb2/3)O3 – 0,075Pb(Mn1/3Nb2/3)O3 + w % kl CuO (0,0 ≤ w ≤ 0,175); (MC: MC0, MC1, MC2, MC3, MC4, MC5 và MC6). (2.4) Firstly, the mixture of (Zn,Mn)Nb2(Zr,Ti)O6 (BO) [33], [51] was prepared by reactions of ZnO, MnO2, Nb2O5, ZrO2 and TiO2 at temperature of 1100oC for 2h. According to the results thermal analysis (DTA) and thermogravimetric analysis (TGA) of (Zn,Mn)Nb2(Zr,Ti)O6 power (Figure 2.1) can see that the formation reaction occurs when the temperature exceeds 978oC. However, experimental results showed that (Zn,Mn)Nb2(Zr,Ti)O6 power was calcined at temperature 5 of 1100oC, the PZT-PZN-PMnN ceramics had the good electrical properties, similarly to reports of methods [33]. Secondly, (Zn,Mn)Nb2(Zr,Ti)O6 and PbO were weighed and milled for 20 h. The powders were calcined at temperature 850 oC for 2 h, producing the PZT–PZN–PMnN compound. Then, 0,7wt% Li2CO3 was mixed with the calcined PZT–PZN–PMnN powder and then, powders milled for 20h. The ground materials were pressed into disk 12mm in diameter and 1.5mm in thick under 2 ton/cm2. The samples were sintered in a sealed alumina crucible with PbZrO3 + 10 % kl ZrO2 coated powder at temperature 950 oC for 2 h. Where, the purity of reagent grade oxide powders are above 99 %. Δm (mg) -2.552 Δm (%) -6.208 TG |c (mg) 1 0 -1 -2 0.05 0 -0.05 HeatFlow (mW) T: 239.63 (°C) 0 -10 T: 341.73 (°C) T: 544.04 (°C) -0.1 dTG |c (mg/min) -3 T: 978.83 (°C) Exo T: 964.15 (°C) -20 T: 240.19 (°C) -30 -40 0 200 T: 342.15 (°C) 400 600 Sample Temperature (°C) 800 1000 Figure 2.1. TG and DTA curve of (Zn,Mn)Nb2(Zr,Ti)O6 2.2. Structure and microstructure of PZT – PZN – PMnN ceramics 2.2.1. Structure and microstructure of MP sample group The X-ray diffraction analysis results (Figure 2.6) showed that all samples have pure perovskite phase with tetragonal structure. When increasing PZT content, the tetragonality c/a ratio increases (insert picture in Figure 2.6). According to the PbZrO3–PbTiO3 phase diagram, at room temperature Pb(Zr0.47Ti0.53)O3 is of the tetragonal phase (space group P4mm) [24], [25], while Pb(Mn1/3Nb2/3)O3 is cubic structure [34], [60] and the PZN composition was determined to be the rhombohedral (space group R3m) [3], [24]. Therefore, with increasing molar fraction of PZT, the crystal symmetry of ceramics should change due to the tetragonal distortions of PZT. 6 SEM image analysis results show that the sample group of the MP have particle density of ceramic is quite dense and are closely-packed (Figure 2.8). The average grain size and the density of samples are increased with an increasing amount of PZT and reach maximum (∼ 1,04 µm, 7.81 g/cm3, respectivety) at the PZT content of 0.8 mol and then rapidly decrease. The grain size and the density of ceramics have a strong effect on dielectric, piezoelectric and ferroelectric properties of ceramic materials. The relationships between the grain size and the density of ceramics and electrical properties are discussed in the next section. 1 .0 3 0 500 1 .0 2 5 T h e c/a ratio 600 Intensity (a.u) 400 1 .0 2 0 300 1 .0 1 5 200 1 .0 1 0 0 .6 0 .7 0 .8 P Z T c o n te n t (m o l) 0 .9 100 0 M P90 M P85 M P80 M P75 M P70 M P65 20 25 30 35 40 45 50 55 60 65 70 2 θ (D e g re e ) Figure 2.6. X-ray diffraction patterns of MP sample group Figure 2.8. SEM image of MP80 sample 20 30 40 50 (2 0 0 ) T (0 0 2 ) T 112 211 44 45 2 θ (D e g re e ) 102 201 002 200 111 110 43 60 46 300 1 2 3 4 5 6 202 220 - Intensity (a.u) M Z46 M Z47 M Z48 M Z49 M Z50 M Z51 001 100 Intensity (a.u) 101 2.2.2. Structure and microstructure of MZ sample group 6 5 4 3 2 1 70 2 θ (D e g re e ) Figure 2.10. X-ray diffraction patterns of MZ sample group Figure 2.12. Microstructures of MZ48 sample Figure 2.10 shows X-ray diffraction patterns (XRD) of the PZT–PZN– PMnN ceramics with the variation of Zr/Ti ratio content. All the samples showed a tetragonal perovskite phase. The tetragonal structures can be determined from the double (002)T and (200)T peaks at 2θ ≈ 44.5o (insert 7 picture in Figure 2.10). The c/a ratio decreases with increasing Zr/Ti ratio, indicating that the tetragonality of PZT-PZN-PMnN ceramics decreased when Zr increased. With increasing Zr content (decreasing of Ti content), the average grain size and the density of samples increases and reaches the maximum value at Zr/Ti ratio of 48/52, then decreases. In order to determine chemical composition of the PZT-PZN-PMnN ceramics, the EDS spectrum is analyzed and shown in Figure 4.14. As shown in Figure 2.14, the EDS spectrum clearly identifies that the Pb, Zr, Ti, Nb, Zn and Mn elements are composed in PZT-PZN-PMnN ceramics. Based on the EDS analysis, it can be confirmed that the qualitative and quantitative chemical composition of the PZT-PZN-PMnN ceramic are quite good. Nb Pb O Ti Zr Nb Ti Mn Zn Pb Pb Figure 2.14. EDS spectrum of PZT-PZN-PMnN ceramics Chapter 3. STUDY DIELECTRIC, FERROELECTRIC AND PIEZOELECTRIC PROPERTIES OF PZT–PZN–PMnN CERAMICS 3.1. Dielectric properties of PZT–PZN–PMnN ceramics 3.1.1. The dielectric constant of MP, MZ sample groups at room temperature In order to study the dielectric properties of PZT–PZN–PMnN ceramics, the dielectric constant (ε) and dielectric loss (tanδ) of the ceramics at room temperature was calculated from the capacitance (Cs) of the MP, MZ sample groups measured at frequency of 1kHz shown in Table 3.1. When the content of PZT increases from 0.65 to 0.8 mol, values of dielectric constant ε increase and reach maximum (ε = 1230) at 0.8 mol PZT, 8 and then rapidly decreased. At this contant, the dielectric loss tanδ of 0.007 (Table 3.1). Table 3.1 shows the dielectric constant ε of MZ samples in the range from 758 to 1319 and dependence of Zr/Ti ratio. When the ratio of Zr/Ti increases the values of ε increase and reaches a maximum (ε = 1319) at Zr/Ti = 48/52, and then decreases. While the dielectric loss tanδ desreases with increasing Zr/Ti ratio. The minimum values of tanδ of 0.005 was obtained at Zr/Ti = 48/52 and then increased. The increasing of dielectric constant can be explained by increasing grain size effect [81]. Table 3.1. The average values of dielectric constant  and dielectric loss tan of the sample groups MP, MZ at room temperature and at 1kHz Samples  tanδ Samples  tanδ MP65 1130 ± 3 0,007 MZ46 1109 ± 4 0,007 MP70 1134 ± 2 0,008 MZ47 1227 ± 2 0,007 MP75 1152 ± 2 0,008 MZ48 1319 ± 2 0,005 MP80 1226 ± 2 0,007 MZ49 1162 ± 2 0,006 MP85 1154 ± 2 0,09 MZ50 1146 ± 3 0,006 MP90 1143 ± 3 0,01 MZ51 758 ± 4 0,007 0.32 0.28 0.24 0.20 8000 0.16 4000 0.12 0.08 0 0.04 0 50 100 150 200 250 0 Temperature ( C) 300 0.00 350 Dielectric constant, ε 12000 20000 0.36 16000 12000 1 2 3 4 5 6 0.20 3 M Z46 M Z47 M Z48 M Z49 M Z50 M Z51 4 5 6 (b) 2 1 0.16 0.12 8000 0.08 4000 0.04 Dielectric loss, tanδ 0.40 (a) M P65 M P70 M P75 M P80 M P85 M P90 16000 Dielectric loss, tanδ Dielectric constant, ε 20000 0 0.00 50 100 150 200 250 300 350 0 Temperature ( C) Figure 3.1 Temperature dependence of the dielectric constant and dielectric loss at 1 kHz of MP (a), MZ (b) sample groups Figure 3.1 shows the dependence of the dielectric constant ε and dielectric loss tanδ on the temperature of MP (Figure 3.1 (a)), MZ (Figure 3.1 (b)) the sample groups measured at frequency of 1kHz. As seen in Figure 3.1, the dielectric properties exhibited characteristics of the relaxor ferroelectric material in which the phase transition temperature occurs within a broad temperature range. This is one of the characteristics of ferroelectrics with 9 disordered perovskite structure. It is different compare with the PbTiO3 ferroelectric materials [1], [3], [81]. The plot of ln(1/ε – 1/εmax) versus ln(T – Tm) of PZT-PZN-PMnN ceramics at 1 kHz is shown in figure 3.2. The slopes of the fitting curves are used to determine the γ value. For MP sample groups, the values of γ decrease from 1.88 to 1.70 (Figure 3.2(a)) and the MZ sample groups, the values of γ increase from 1.74 to 1.94 (Figure 3.2(b)). The temperature Tm of the MP ceramic samples increases with increasing PZT content and in the range of 206 oC to 275 oC and εmax increased to a maximum value of 18371 when the PZT is 0.8 mol and then decreased. Because of the different phase transformation temperatures of PZN (Tm ≈ 140oC) [25], [74] and PZT (TC ≈ 390oC) [74], so the phase transition temperature of the PZT–PZN–PMnN ceramics should exhibit a significant dependence on PZT content [74]. For MZ sample groups, with the increasing Zr content, the maximum of εmax increase and reach biggest (εmax = 19473) at the Zr/Ti ratio is 48/52. The Curie temperature decreases with the increasing Zr content because the Curie temperature of PbZrO3 is about 232oC [71] and it is lower than that of PbTiO3, 490oC [3], [74]. (a) M P90 → γ6 = 1.70 M P85→ γ5 = 1.77 M P80 → γ4 = 1.83 M P75→ γ3 = 1.85 Ln(1/ε−1/εmax ) Ln(1/ε−1/εmax) (b) MZ46 → γ1 = 1.74 MZ47 → γ1 = 1.83 MZ48 → γ1 = 1.85 MZ49 → γ1 = 1.93 MZ50 → γ1 = 1.94 M P70→ γ2 = 1.86 MZ51 → γ1 = 1.90 M P65→ γ1 = 1.88 Fit Fit -1 0 1 2 3 Ln(T-T m ) 4 5 -1 0 1 2 3 4 5 Ln(T-T m ) Figure 3.2 Plot of ln (1/ε – 1/εm) versus ln(T - Tm) of MP (a), MZ (b) sample groups 3.1.3. The dependence of the dielectric properties versus the frequency Figure 3.3, 3.4 show the temperature dependence of the dielectric constant ε and dielectric loss tanδ of the MP80 and M48 samples measured at frequency of 1kHz, 10kHz, 100kHz and 1MHz, respectively. We can see that the shape of the ε peaks was broad, which is typical of a case diffuse transition with frequency dispersion. When the measured frequency 10 increased, the maximum of εmax was decreased and shifted to higher temperature while dielectric loss increased near the Curie point, which is typical of a relaxor material [81]. 20000 1kH z 10kH z 100kH z 1000kH z 14000 12000 0 .5 0 .4 10000 0 .3 8000 6000 0 .2 4000 2000 0 .1 0.40 18000 MZ48 16000 1kHz 10kHz 100kHz 1000kHz 14000 12000 0.35 0.30 0.25 10000 0.20 8000 6000 0.15 4000 0.10 2000 0.05 0 0 Dielectric loss, tanδ M P80 16000 Dielectric constant, ε 0 .6 18000 Dielectric loss, tanδ D ielectric constant, ε 20000 0.00 0 50 100 150 200 250 50 0 .0 350 300 100 150 200 250 300 350 0 Temperature ( C) 0 T em perature ( C ) Figure 3.3. Temperature dependence of dielectric constant ε and dielectric loss tanδ of MP sample group at different frequencies Figure 3.4. Temperature dependence of dielectric constant ε and dielectric loss tanδ of MZ sample group at different frequencies MP80 MP75 50 MP85 2 30 20 10 MP70 MP90 MP65 0 -25 -20 -15 -10 -5 Polarization, P (µC/cm ) 40 MP65 MP70 MP75 MP80 MP85 MP90 2 Polarization, P (µC/cm ) 3.2. Ferroelectric properties of PZT – PZN – PMnN ceramics 3.2.1 The effect of PZT content and Zr/Ti ratio on ferroelectric properties of PZT – PZN – PMnN ceramics at room temperature Figure 3.7, 3.8 show the forms of ferroelectric hysteresis loops of the sample groups measured at room temperature. From ferroelectric hysteresis loops of the sample groups, the remanent polarization Pr and the coercive field Ec were determined, as shown in figure 3.9. The Pr reaches the highest value (34.5 µC/cm2) at PZT content of 0.8 mol and Zr/Ti ratio of 48/52. At contents, the coercive field Ec reaches value 9.0 kV/cm. This result is in good agreement with the studied dielectric properties of the samples. 0 5 10 15 20 25 -10 -20 -30 -40 Field, E (kV/cm) Figure 3.7 Hysteresis loops of MP sample group M Z 46 M Z 47 M Z 48 M Z 49 M Z 50 M Z 51 40 30 20 10 0 -30 -25 -20 -15 -10 -5 0 -10 5 10 15 20 25 30 -20 -30 -40 -50 Field, E (kV/cm ) Figure 3.8 Hysteresis loops of MZ sample group 25 12 20 11 10 15 9 10 0.60 8 0.65 0.70 0.75 0.80 0.85 0.90 0.95 40 (b) 35 30 25 20 15 10 0.45 0.46 0.47 PZT content (mol) 0.48 0.49 0.50 0.51 18 17 16 15 14 13 12 11 10 9 8 7 6 0.52 Coercive field, E c(kV/cm) 13 2 14 (a) Remanent polarization, P r (µC/cm ) 30 Coercive field, E c(kV/cm) 2 Remanent polarization, P r (µC/cm ) 11 Zr content (mol) Figure 3.9. The Pr and the Ec as a function of PZT contents (a) and Zr/Ti ratios (b) 3.2.2 The temperature dependence of ferroelectric properties of PZT – PZN – PMnN ceramics The effect of temperature on ferroelectric properties of ceramics is studied by hysteresis loops of the MZ48 sample (Figure 3.10) measured at different temperatures from 30 oC to 280 oC. When the temperature increased from room temperature to 120 °C, the remanent polarization Pr increased. When the temperature rises above 120 °C, the remanent polarization Pr and the coercive field Ec decreased (Figure 3.11). The reason is when the temperature increases, the oxygen vacancies in the perovskite structure will move and significantly increase the conductivity of the material which should increase the dielectric loss. The size of the hysteresis loops depend on dielectric loss of the material. Therefore, the dielectric loss increases, the size of the hysteresis loops increases, the remanent polarization Pr and the coercive field Ec increases[81]. When the temperature increases (above 120 oC), large thermal motion energy, bipolar disorder increased, the hysteresis loops narrowed, the remanent polarization Pr and the coercive field Ec decreases. 2 20 -2 0 -1 0 0 10 -2 0 -4 0 -6 0 20 140 160 180 200 220 240 260 280 o C C C o C o C o C o C o C 30 o o F ie ld , E (k V /c m ) Figure 3.10 Hysteresis loops of MZ48 45 18 40 Pr 16 35 EC 14 30 12 25 20 10 15 8 10 6 5 4 0 0 50 100 150 200 250 300 Coercive field, E c (kV/cm ) 2 P olarization, P (µC /cm ) 40 0 -3 0 R em anent polarization, P r (µC/cm ) 60 o 30 C o 40 C o 50 C o 60 C o 80 C o 100 C o 120 C 2 o T e m p e ra tu re ( C ) Figure 3.11. Temperature dependence of 12 3.3. Piezoelectric properties PZT- PZN-PMnN ceramics To determine piezoelectric properties of ceramics, resonant vibration spectrum of sample groups were measured at room temperature. From these resonant spectra, electromechanical coefficients kp, kt, k31, piezoelectric coefficients d31, mechanical quality factor Qm were determined (Figure 3.16). As seen in Figure 3.16 (a), piezoelectric properties were strongly influenced by the composition of the ceramics. As the increase in PZT content not only enhanced the electrical properties, but also increased the mechanical properties of ceramics. The values of kp, kt, k31, d31 and Qm reach maximum (kp = 0.58, kt = 0.48, k31 = 0.34, d31 = 130 and Qm = 1034) at 0.8 mol PZT, and then rapidly decreased with increasing x content. These results are consistent with the literature [74]. 1000 0.4 900 0.3 kp kt k31 800 d31 700 Qm 600 0.7 0.8 PZT content (mol) 0.9 140 120 100 80 60 1600 (b) 0.6 1400 0.5 1200 0.4 0.3 kp kt 0.2 0.45 1000 d31 Qm k31 800 0.46 0.47 0.48 0.49 0.50 0.51 160 140 120 100 80 60 0.52 Zr content (mol) Figure 3.16 The values of kp, kt, k31, d31, Qm and tanδ of the PZT-PZN-PMnN ceramic as a function of PZT contents (a) and Zr/Ti ratios (b) Piezoelectric coefficients, d 31 (pC/N) 1100 0.7 Mechanical quality factor, Q m 1200 Electromechanical coefficients, kp, kt, k31 1300 0.5 0.2 0.6 160 (a) Piezoelectric coefficients, d 31 (pC/N) 1400 0.6 Mechanical quality factor, Q m Electromechanical coefficients, kp, kt, k31 For MZ sample group (Figure 3.16 (b)), when the amount of Zr/Ti ratio is lower than 48/52, the kp, kt, k31, d31 are rapidly increased with increasing Zr/Ti ratio, while the mechanical quality factor Qm and the dielectric loss tanδ are lightly decreased. This is probably related to characteristics of the increasing grain size. As is well known, the increased grain size makes domain reorientation easier and severely promotes domain wall motion, which could increase the piezoelectric properties [81]. 13 Chapter 4. STUDY THE EFFECTS OF CuO, Fe2O3 ON PROPERTIES OF PZT–PZN–PMnN CERAMICS 4.1. Effect of Fe2O3 on properties of PZT-PZN-PMnN ceramics To improve the mechanical quality factor Qm and dielectric loss tanδ of PZT-PZN-PMnN ceramics, Fe2O3 doping were mixed into the PZT-PZNPMnN ceramics. 4.1.1. Effect of Fe2O3 on structure, microstructure of PZT-PZN-PMnN ceramics 4 .1 2 4 .0 4 a c 40 1 .0 1 0 202 220 112 211 102 201 111 30 1 .0 1 5 6 (0 0 2 ) T (2 0 0 ) T (2 0 0 ) R M6 M5 M4 M3 M2 5 4 3 2 1 0 R 111 002 200 0 .0 0 .1 0 .2 0 .3 0 .4 F e 2 O 3 c o n te n t (% w t) 1 .0 2 0 Intensity (a.u.) c /a c/a ratio o a,c ( A ) 4 .0 6 4 .0 0 (b ) 1 .0 2 5 4 .0 8 4 .0 2 001 100 20 1 .0 3 0 4 .1 0 300 (a ) 101 M F0 M F1 M F2 M F3 M F4 M F5 M F6 110 0 1 2 3 4 5 6 R 100 Intensity (a.u.) Figure 4.1 shows X-ray diffraction patterns (XRD) of the PZT–PZN– PMnN ceramics at the different contents of Fe2O3. All samples have perovskite phase with tetragonal structure. When increasing of Fe2O3 content, the tetragonality c/a ratio increases as shown in insert figure 4.1(a). It can be determined from the (002)T and (200)T double peaks at 2θ ≈ 44.5o (figure 4.1(b)). 50 2 θ (D e g re e ) 60 70 M1 M0 4 3 .0 4 3 .5 4 4 .0 4 4 .5 4 5 .0 2 θ (D e g re e ) 4 5 .5 4 6 .0 4.1 The patterns of PZT–PZN–PMnN ceramics Figure Figure 4.3 shows theXRD SEM micrographs of the fracture surface of the samples as Fe2O3 addition. It is seen from the micrographs that the grain size grows with the increase of Fe2O3 addition. Below the 0.25 wt% Fe2O3, the grain sizes increase and the grain boundaries present regular shapes. However, when the addition of Fe2O3 is higher than 0.25 wt%, a few cavities appeared between the grains (MF5, MF6 samples). 14 MF0 MF2 MF3 MF4 MF5 MF6 Figure 4.3 Microstructures of samples with the different Fe2O3 contents 4.1.2. Effect of Fe2O3 on dielectric properties of PZT-PZN-PMnN ceramics 0.35 0.30 0.25 10000 0.20 5000 0.15 4 0.10 3 0 0.05 o Curie temperature, T m ( C ) 15000 260 0.40 MF0 MF1 MF2 MF3 MF4 MF5 MF6 20000 Dielectric loss, tanδ Dielectric constant, ε 25000 250 240 230 220 50 100 150 200 250 Temperature (oC) 300 350 0.0 0.1 0.2 0.3 0.4 Fe 2 O 3 content (%wt) Figure 4.4 Temperature dependence of the dielectric constant and dielectric loss at 1 kHz of samples Figure 4.5 The temperature Tm of Fe2O3-doped PZT–PZN–PMnN ceramic samples Figure 4.4 shows the dependence of dielectric constant  and dielectric loss tan of the ceramics versus temperature at frequency of 1 kHz. With increasing Fe2O3 doping, the εmax increased to a maximum value of (24500) when the Fe2O3 content is 0.25wt% and then decreased. This can be explained by increasing grain size effect [81]. Corresponding Fe2O3 content increases, Tm temperature of ceramics lightly decreased from 244 to 234 oC (Figure 4.5). 274 700 274 272 680 700 145 200 140 190 A1(1TO) A1(1TO) 268 266 266 264 264 262 660 680 640 660 -1 1 150 210 E(2TO ) 1 145 200 270 268 -1 -1 E(2TO1) (cm-1) E(2TO1) (cm-1) A1(2TO) (cm ) M6 -1 M6 (b) 272270 E + B1 (cm ) -1 E + B1 (cm ) Silent E +B1 155 220 Silent E +B1 150 210 E(2TO ) A1(2TO) (cm ) Rh R A 1 (3 L O ) h A 1 (3L O ) R1 E (4 L O ) E (4L O ) R1 A 1 (2T O ) E (2L O ) E (2 L O ) (a ) E(4LO), R1 (cm ) -1 E(4LO), R1 (cm ) 230 R1 A 1 (2 T O ) E + B 1 E + BE1 (2T O ) E (2A T1 (1T O)O) A 1 (1(a.u T O )) In ten sity In te n s ity (a .u ) 160 160 230 155 220R1 620 640 600 620 580 600 15 0 54 51 48 45 -4 -1 FW H M (cm ) Ln(1/ε-1/ε m ) -8 -1 2 M 0 → γ 0 = 1.88 -1 6 M 1 → γ 0 = 1.90 -2 0 M 3 → γ 0 = 1.93 M 2 → γ 0 = 1.91 M 4 → γ 0 = 1.94 M 5 → γ 0 = 1.79 -2 4 M 6 → γ 0 = 1.67 E(4LO ) 104 102 100 98 R1 55 54 53 52 51 (E+B 1 ) 72 71 70 69 E(2TO 1 ) 3 1 .4 3 1 .2 3 1 .0 3 0 .8 3 0 .6 A 1 (1TO ) 0 .0 F it 0 .1 0 .2 0 .3 0 .4 Fe 2 O 3 content (% w t) -2 8 0 1 2 3 4 5 Ln(T -T m ) Figure 4.9 Ln(1/ −1/max) as a function of ln(T−T max) of samples FWHM of the PZT-PZN-PMnN samples as a function of Fe2O3 Figure 4.8(a) shows the Raman scattering spectra of Fe2O3-doped PZT– PZN-PMnN ceramics measured at room temperature. Compared with PbTiO3 [1] and Pb(Zr,Ti)O3 [64], the vibration bands in the Raman scattering spectra of Fe2O3-doped PZT–PZN–PMnN samples seem wider and more dispersive. It can be seen from this figure that the silent mode at about 268 cm-1 shifts to a low frequency as the Fe2O3 doping increases. Dilsom [18] assumed that the decrease in frequency with increasing Fe2O3 contents is due to the difference in the atomic mass of Zr (91.22 g), Ti (47.87 g), Nb (92.90 g), Zn (65.39 g), and Mn (54.94 g) when they are replaced by Fe (56 g) in the B site. The shift of the silent mode to a low frequency due to Fe2O3 content increases the average energy of the B–O bonding hence Tm of the ceramics are decreased [91]. The value of γ gives information on the phase transition diffuse characterized. The values of γ increases with increase of Fe2O3 contents 16 (Figure 4.9(a)). It is found that the full width at half maximum (FWHM) of the B–O vibrations exhibit an obvious increase, leading to a strong composition disorder (Figure 4.9(b)). However, when the Fe2O3 content is higher than 0.25 wt%, the value of γ and FWHM decreases. This can be explained by the solubility limit of Fe ion in the PZT-PZN-PMnN ceramics. 4.1.3. Effect of Fe2O3 on piezoelectric properties of PZT-PZN-PMnN ceramics To determine piezoelectric properties of ceramics, resonant vibration spectra of samples were measured at room temperature (Figure 4.11). From these resonant spectra, piezoelectric parameters of samples were determined (Figure 4.12). 6 5 10 4 10 3 10 2 10 1 10 0 80 7000 60 6000 40 0 -2 0 -4 0 -6 0 -8 0 -1 0 0 200 210 220 230 240 F re q u e n cy, f (kH z) 250 (b ) 5000 20 Z (Ω) Z (Ω) 10 8000 100 (a ) θ (D egree) 10 4000 3000 2000 1000 0 1 2 3 4 5 6 7 8 F re q u e n c y, f (M H z) Figure 4.11. Spectrum of radial resonance (a) and thick resonance (b) of MF4 sample Figure 4.12 shows the electromechanical coupling factor (kp, kt), the piezoelectric constant (d31), the mechanical quality factor Qm and dielectric loss tanδ change as a function of the amount of Fe2O3. The mechanical quality factor (Qm) and the dielectric loss (tanδ) of the Fe2O3-doped PZT– PZN–PMnN ceramics markedly improved, as shown in Fig. 4.12. As the Fe2O3 content in the PZT–PZN–PMnN ceramics was increased up to 0.25 wt%, the Qm value increased steadily up to 1450 while dielectric loss tanδ decreased steadily down to the lowest value (tanδ =0.003) because the Fe ions at the (Ti, Zr, Nb) sites in the lattice acted as acceptors. As can be seen in Figure. 4.12, the kp, kt and the d31 show a similar variation with increasing Fe2O3 content. When the content of Fe2O3 is lower than 0.25 wt%, the kp, kt and the d31 were increased with increasing Fe2O3 content. The optimized values for kp of 0.64, kt of 0.51 and d31 of 155 pC/N were obtained at content Fe2O3 = 0.25 wt%. This is probably related to characteristics of the increasing grain size. 0.010 0.008 0.006 0.004 0.002 0.64 1800 kp 1600 Qm 1400 0.60 0.56 1200 0.52 0.48 kt 0.44 Tanδ 1000 800 0.40 600 0.0 0.1 0.2 0.3 160 140 120 100 80 60 60 50 MF 40 30 2 2000 d31 0.68 P (µC/cm ) 0.012 0.72 The piezoelectric constant d31 (pC/N) Dielectric loss tanδ 0.014 The mechanical quality factor, Qm 0.016 Electromechanical coupling factor, kp, kt 17 20 10 0 -30 -25 -20 -15 -10 -5 -10 0 5 10 15 -30 -40 -50 0.4 20 25 30 MF1 MF2 MF3 MF4 MF5 MF6 -20 -60 E (kV/cm ) Fe2O3 content (%wt) Figure 4.12. The kp, kt, d31, Qm, and tanδ Figure 4.13 Hysteresis loops of Fe2O3doped PZT-PZN-PMnN ceramics as a function of Fe2O3 contents 4.1.4. Effect of Fe2O3 on ferroelectric properties of PZT-PZN-PMnN ceramics From the form of feroelectric hysteresis loops of the Fe2O3 doped PZTPZN-PMnN samples measured at room temperature, the remanent polarization Pr and the coercive field Ec were determined, as shown in Table 4.5. Table 4.5. The characterize parameters of ferroelectric properties (Pr, Ec) of Fe2O3 doped PZT-PZN-PMnN Samples MF0 MF1 MF2 MF3 MF4 MF5 MF6 EC (kV/cm) 9,8 9,8 8,4 9,0 8,6 8,7 10,5 34,5 34,1 35,6 36,0 37,0 35,0 26,0 2 Pr (µC/cm ) A sharp increase in Pr was observed for MF0-MF4 samples, reaches the highest value (37 µC/cm2) with MF4 sample, and then decreases. This result is in good agreement with the studied dielectric and piezoelectric properties of the samples. While, the coercive field Ec decreases with increasing of Fe2O3 content. The minimum value of the Ec is 8.6 kV/cm were obtained at content of Fe2O3 = 0.25 wt%. 4.2. Effect of CuO on the sintering behavior and electrical properties of PZT–PZN–PMnN ceramics 4.2.1. Effect of CuO on the sintering behavior of PZT–PZN–PMnN ceramics Many material scientists are interested in research [29], [34], [64], [87] in PZT−PZN−PMnN ceramics due to their large dielectric constant ε, large electromechanical coefficient kp, large polarization Pr, high mechanical quality 18 factor Qm, and suitability for the application of ultrasound transducers. However, the sintering temperature of this ceramic system is quite high (1150 °C), [29], [64]. The most common and effective method to reduce the sintering temperature of PZT based ceramics is using various additives such as BiFeO3, CuO, CuO-ZnO, Li2CO3, Bi2O3, LiBiO2, B2O3, CuO-PbO, Cu2OPbO to create low-temperature liquid phases of ceramics [5], [13], [15], [16], [20], [23], [33], [35], [41], [44], [53]. In this section, we have chosen the CuO doped 0,8Pb(Zr0,48Ti0,52)O3 0,125Pb(Zn1/3Nb2/3)O3 0,075Pb(Mn1/3Nb2/3)O3 ceramics sintered at 800 oC; 830 oC; 850 oC and 870 oC. Table 4.7. The density, , tan, kp of M0-1150 sample Sample D ε tanδ kp M0-1150 (g/cm3) Figure 2.14. The density of PZT-PZNPMnN ceramics with diff erent amounts of CuO additive sintered at 800 oC, 830 oC, 850 oC, 870 oC M01 7,85 1217 0,007 0,57 M02 7,83 1108 0,007 0,56 M03 7,81 1209 0,006 0,55 M04 7,85 1168 0.007 0,55 TB 7,83 1219 0,007 0,56 Figure 2.14 shows the densities as a function of sintering temperature for PZT-PZN-PMnN ceramics with various CuO additions. With increasing sintering temperature and CuO content, the density increases and reaches the maximum value (7.91 g/cm3) at 850oC and 0.125 wt % CuO content, before the density starts to decrease. The sintering temperature of undoped PZTPZN-PMnN ceramics was higher 1150 °C (the density of 7.83 g/cm3). From the phase diagram of Hitoshi Kitaguchi [17] has shown that CuO and PbO form the liquid phase at point eutectic 789°C. So when CuO doped in PZTPZN-PMnN ceramics, CuO reacted with PbO and formed a liquid phase during the sintering, which assisted the densification of the specimens. Thus, the addition of CuO improved the sinterability, reduced the sintering
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