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Effect of zirconium titanium ratio on some physical properties of low temperature sintered PZT − PZN − pmnn ceramics

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  • Save International Journal of M aterials and Chemistry 2013, 3(2): 39-43 DOI: 10.5923/j.ijmc.20130302.04 Effect of Zr/Ti Ratio Content on Some Physical Properties of Low Temperature Sintering PZT−PZN−PMnN Ceramics Le Dai Vuong*, Phan Dinh Gio, Truong Van Chuong, Dung Thi Hoai Trang, Duong Viet Hung, Nguyen Trung Duong Department of Physics, College of Sciences, Hue University, 77 Nguyen Hue street, Hue city, Vietnam Abstract Low-temperature sintering of 0.8Pb(ZrxTi1-x)]O3 – 0.125Pb(Zn1/3Nb2/3)O3 – 0.075Pb(Mn1/3Nb2/3)O3 + 0.7 % wt Li2CO3 (PZT-PZN-PMnN) ceramics was prepared by using Li2CO3 as the sintering aid. Their structure and physical properties were investigated according to the Zr/Ti rat io content. Fro m X-ray diffract ion patterns showed that samples formed a phase perovskite structure without secondary phases. The electro mechanical coupling factor (kp), the maximu m d ielectric constant (εmax), the piezoelectric constant (d31) and the mechanical quality factor (Qm) increased with the increase of Zr/Ti ratio content and reaches to the highest value at the ratio content of Zr/Ti = 48/52. At this ratio content, the ceramic has the optima l e lectro mechanical p roperties: the εmax = 19500, the k p = 0.62, the d31 = 140 p C/N and the Qm = 1112. Keywords Crystal Structure, Dielectrics, Piezoelectrics, Electro mechanical Coupling Factor 1. Introduction Last several decades have witnessed extensive study on t h e relaxo r ferro elect rics s ince t heir d is cov ery by Smolenskii et al.[1], owing to their significant technical importance on the application of electro mechanical devices such as mu lt ilay er ceramic capacitors , elect rostrict ive t ra nsdu c e rs , mic ro d is p la ce me n t pos it ion e rs . Pb(Mn1/3Nb2/3)O3 (PMnN) and Pb(Zn1/3Nb2/3)O3 (PZN) a re members of lead-based relaxo r ferroelectric family with different cations on the B-site of perovskite lattice. These materials are ferroelectric materials that have characteristics as high dielectric constant, the temperature at the broad ph ase t rans it io n po int bet ween t he ferro elect ric and paraelectric phase (the d iffuse phase transition) and the strong frequency dependency of the dielectric properties. Gao Feng et al.[2] investigated 0.8PZT – (0.2– x)PZN – xPM n N cera mics wit h co mp o s it io n s clo s e t o t h e morphotropic phase boundary (MPB). The optimized results of kp (0.57), ε (842) and Qm (1020) were obtained at 0.075 mo l Pb (Mn1/3Nb2/3)O3, which is a new p ro mising material for p iezoelectric transformer. The Zr/Ti ratio is known to affect some properties strongly such as the elastic constant, the permittiv ity, the coupling factor, etc. These properties * Corresponding author: (Le Dai Vuong) Published online at Copyright © 2013 Scientific & Academic Publishing. All Rights Reserved take extreme values when Zr/Ti rat io corresponds to the composition of the MPB which separates the tetragonal (T) and rhombohedral (R) phases towards Ti-rich and Zr-rich sides, respectively[3,4]. Rangson Muanghlua et al.[5]. studied the effect of Zr/Ti rat io on the structure and ferroelect ric p ropert ies o f 0.07Pb(Mn1/3Nb2/3)O3-0.6Pb(Ni1/3 Nb2/3)O3-0.87Pb(ZrxTi1-x)O3 ceramics. Fro m XRD analysis and ferroelectric properties measurements indicated the existence of the MPB co mposition between x = 0.50. At this composition, the ceramics exh ibits the highest ferroelectric properties. Yoo and Lee[6] also reported that the PZT-PNN-PMnN ceramics were strongly influence by the Zr/Ti ratio. They found that the electromechanical coupling factor kp, the piezoelectric constant d33 and the mechanical quality factor Qm increased with the increase of Zr/Ti rat io and then decreased after the ratio exceeded 50/50. Recently, Fares Kahoul et al.[7] studied the structure and electrical properties of Pb0.98Sm0.02[(Zrx,Ti1-x)0.98 (Fe1/2Nb1/2)0.02]O3 ceramics with the composition near the MPB. They found that the kp, d31 and Qm of the ceramics are enhanced with the increase of Zr/Ti ratio. At Zr/Ti ratio of 55/45, the ceramics has the optima l e lectro mechanical properties, k p = 0.631, d31 = 120.10-12C/N, Qm = 462. The research results of the above authors clearly showed the significance of Zr/Ti rat io in controlling the electro mechanical properties of the PZT-based ceramics. In this paper, we investigated the effect of Zr/Ti rat io content on some physical properties of the low temperature sintering PZT-PZN-PMnN ceramics. 40 Le Dai Vuong et al.: Eff ect of Zr/Ti Ratio Content on Some Physical Properties of Low Temperature Sintering PZT−PZN−PMnN Ceramics 2. Experimental Procedure The general formu la of the material was 0.8Pb(ZrxTi1-x)O3 – 0.125Pb (Zn1/3Nb2/3)O3 – 0.075Pb (Mn1/3 Nb2/3)O3 + 0.7 wt% Li2 CO3, where x is 0.46, 0.47, 0.48, 0.49, 0.50 and 0.51. They are denoted by M46, M47, M48, M49, M50 and M51, respectively. The raw materials including powders (purity of 99%) of ZrO2, TiO2, Nb2O5, ZnO and MnO2 for the given composition were weighted by mole ratio and the powders were mixed and milled (the PM 400/2 milling machine) for 8 h using ziconia balls and ethanol as the mediu m, then were calcined. Thereafter, Pb O was added and milled again. Powders were calcined at 850oC for 2 h, then the sintering aid, Li2 CO3 was added[8] and milled again for 16h. The ground materials were pressed into disk 12mm in diameter and 1.5mm in thickness under 100 MPa. The samples were sintered in a sealed alu mina crucible with PbZrO3 coated powder at temperature 950o C for 2h. The crystalline phase was analyzed using an X-ray diffacto meter (XRD, D8 ADVANCE). The microstructure of the samples was examined by using a scanning electron microscope (SEM ). The density of samples was measured by Archimedes method. The samp les were poled in a silicone oil bath at 120oC by applying 30 kVcm−1 for 20 min, then cooled at this electric field. They were aged for 24h p rior to testing. The piezoelectric properties were determined by the resonance and antiresonance technique using an impedance analyzer (Agilent 4396B and RLC HIOKI 3532). The calculation equations are as follows: kp =[2.51(fp-fs)/fp]1/2 and Qm = f p2[2πZ C min s fs( f 2 p − f 2 s )]−1 , where fs and fp are resonant and antiresonant frequencies (Hz), and Zmin and Cs are resonant impedance (ohms) and electrical capacitance (farads). The dielectric p roperties were measured by RLC HIOKI 3532. content. All the samples showed a tetragonal perovskite phase without any secondary phase. The lattice parameters for various compositions were calcu lated using the least square method fro m the double (002) and (200) peaks of tetragonal structure and results for the tetragonality c/a of perovskite phase are shown in Figure 2. The c/a rat io decreases with increasing Zr/Ti ratio content, indicating that the tetragonality of PZT-PZN-PMnN ceramics decreased when Zr increased. Figure 2. The tetragonality c/a of the ceramics as a function of Zr/T i ratio M46 M47 M48 M49 3. Results and Discussion 3.1. Phase Analysis and Microstruc ture M50 M51 Figure 3. Microstructures of samples with the different Zr/T i ratio cont ent s Figure 1. X-ray diffraction patterns of the ceramics with different Zr/Ti ratio contents Figure. 1 shows X-ray diffract ion patterns (XRD) of the PZT–PZN–PMnN ceramics with the variation of Zr/Ti rat io Figure 3 shows the SEM image of the fractured surface of PZT–PZN–PMnN ceramics at different Zr/Ti ratio contents. It is observed fro m the micrographs that the average grain size of samp les are increased with the increasing amount of Zr/Ti ratio (Table 1). It is exp lained that the initial and intermediate stages of sintering, densification and grain International Journal of M aterials and Chemistry 2013, 3(2): 39-43 41 growth occur through liquid-phase diffusion (Li2CO3)[8], and then the liquid phase at the intergranular boundaries gradually dissolves into the grains with grain growth[9,10]. However, figure 3 also shows that further increasing the Zr/Ti content to 51/ 49 gives rise to an abnormal grain boundary, and the average grain size is reduced. Table 1. The average grain size of ceramic samples Samples M46 M47 M48 M49 M50 M51 Average grain size (µm) 0.80 0.90 1.18 1.16 1.02 1.00 characteristics of a relaxo r material in wh ich the phase transition temperature occurs within a broad temperature range. This is one of the characteristics of ferroelectrics with disordered perovskite structure. The maximu m dielectric constant εmax increases with increasing Zr/Ti ratio content, and at Zr/Ti = 48/ 52, the highest dielectric constant εmax of about 19500 and then sharply decreases beyond this point. This can be exp lained by the increase of grain size effect[10]. The dielectric loss tanδ shows the reversed trend, this appropriate to the characteristics of dielectrics[11]. 3.2. The Ceramic Density The densities of the samples containing different amounts of Zr/Ti ratio were measured, and the results are shown in Figure 4. As seen, the densities of the ceramics are in the range fro m 7.80g/cm3 to 7.86g/cm3 (94-97 % theoretical density) and dependent on Zr/Ti ratio content. When Zr/Ti ratio content increases, the density of samp les increases and achieves the highest value (7.86g/c m3) at the ratio of Zr/Ti = 48/ 52, and then decreases. This may be explained fro m microstructures of ceramic samp les. When the amount of Zr/Ti rat io increased, the ceramic samples became mo re dense, and at Zr/Ti = 48/52, the ceramic samp le was almost fully dense (fig. 3). When the further increasing the Zr/Ti ratio content to 49/51 and above, a large number of pores were present, giving rise to an abnormal grain boundary. Hence, the densities of the ceramics are decreased. The variation in density of the ceramic samples is in good accordance with the microstructure. Figure 5. Temperature dependence of the dielectric constant and dielectric loss t anδ at 1 kHz of ceramic In Figure 6, the change of Curie temperature TC with the Zr/Ti ratio is shown. With the increase in Zr amount, the Curie temperature decreases because the Curie temperature of PbZrO3 is about 232oC and it is lo wer than that of PbTiO3, 490oC[11,12]. Figure 4. The density of PZT-PZN-PMnN samples as a function of the Zr/T i content 3.3. Dielectric Properties The change of Zr/Ti content also significantly affects the piezoelectric and dielectric properties of PZT–PZN–PMnN cera mics . Figure 5 shows the dependence of dielectric constant εand dielectric loss tanδ of the ceramic on temperature at 1 kHz. As observed, the dielectric properties exh ibited Figure 6. The Curie temperature TC of PZT-PZN- PMnN ceramics with different amounts of Zr/Ti ratio Figure 7 shows the temperature dependence of the dielectric constant ε and dielectric loss tanδ of the M48 sample measured at frequency of 1kHz, 10kHz, 100kHz and 1MHz, respectively. It show that the shape of the ε peaks was broad, which is typical of a case diffuse transition with frequency dispersion. When the measured frequency increased, the maximu m of εmax was decreased and shifted to higher temperature wh ile dielectric loss increased near the Curie point, which is typical of a re la xor material[13]. 42 Le Dai Vuong et al.: Eff ect of Zr/Ti Ratio Content on Some Physical Properties of Low Temperature Sintering PZT−PZN−PMnN Ceramics Figure 7. Temperature dependence of relative dielectric constant ε and dielect ric loss tanδ of M48 sample at different frequencies 3.4. Piezoelectric Properties To determine piezoelectric property of ceramics, resonant vibration spectrum of samples were measured at room temperature in Figure 8. Figure 8. Spectrum of radial resonance of M48 sample Fro m these resonant spectra, electro mechanical coefficients kp, piezoelectric coefficients d31, mechanical quality factor Qm and dielectric loss tanδ were determined. Figure 9 shows the changing in the electromechanical coupling factor (kp), the piezoelectric constant (d31), mechanical quality factor Qm and dielectric loss tanδ as a function of the amount of Zr/Ti ratio. As can be seen, both kp and d31 show a similar variation with increasing Zr/Ti rat io content. When the amount of Zr/Ti ratio is lower than 48/52, the kp and the d31 are rapidly increased with increasing Zr/Ti ratio content, while the mechanica l quality factor Qm and the dielectric loss tanδ are desreased. The optimized values for kp of 0.62, d31 of 140.10-12C/N, Qm of 1112 and tanδ of 0.005 were obtained at Zr/Ti = 48/52. This is probably related to characteristics of the increasing grain size. As well known, the increased grain size makes domain reorientation easier and severely promotes domain wall motion, which could increase the piezoelectric propert ies[13]. Ho wever, the further increasing of Zr/Ti ratio content gives rise to an abnormal grain boundary and the average grain size is also reduced as shown in Fig. 3. Therefore, electrical properties of PZT-PZN-PMnN ceramics are reduced. Figure 9. The values of kp, d31, Qm, and tanδ of the PZT-PZN-PMnN ceramic samples 4. Conclusions We have investigated some physical properties of the low temperature s in ter in g 0.8 Pb(Z rxT i1-x)O3–0. 125Pb (Zn1/3Nb2/3)O3 – 0.075(Mn1/3Nb2/3)O3 + 0.7 wt% Li2 CO3 ceramics. Results of this study are summarized as follows: - All the specimens displayed a tetragonal perovskite structure without secondary phase. With increasing the Zr/Ti ratio content, the tetragonality c/a was decreased. - At the Zr/Ti rat io content of 48/ 52 and sintering temperature (Ts) of 950oC, the density, the electromechanical coupling factor k p, the dielectric constant εmax, the piezoelectric constant d31, the dielectric loss tanδ and the mechanical quality factor Qm showed the optimu m values of 7.86g/cm3, 0.62, 19500, 140 p C/N, 0.005 and 1112, respectively. Therefore, they are a promising candidate material used in high power p iezoelectric devices. REFERENCES [1] Smolenskii. G. A., V. A. Isupov and A. I. Agranovskaya New ferroelectrics of complex composition of the type A22+(BI3+,BII5+)O6 . I. Sov. Phys.Solid State, 1, 1959 150-151. [2] F. Gao., L. Cheng, Hong R., J. Liu, C. Wang and C. 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