- Email: [email protected]
PT multilayered thin films prepared by sol–gel process
Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Q1 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Nanostructured PZT/PT multilayered thin films prepared by sol–gel process Radhapiyari Laishram n, O.P. Thakur Solid State Physics Laboratory Lucknow Road, Timarpur, Delhi 110054, India
art ic l e i nf o
a b s t r a c t
Article history: Received 22 May 2014 Accepted 22 August 2014
The morphological progression of PZT thin films (Zr/Ti: 53/47) prepared by sol–gel method has been studied by annealing the films at 650 1C for different durations. FESEM analysis could detect the presence of very small amount of pyrochlore phase (showing different morphologies) in the films annealed for 30 min, 1 h, 3 h and 4 h. However, the very small percentage of the pyrochlore phase present in the 1-h annealed film could not be detected by XRD. The annealing duration was optimized to 2 h with no evidence of any pyrochlore phase in the FESEM microstructure but only grains corresponding to pure perovskite phase. The present study reveals the presence of the pyrochlore phase as the reason for degraded properties in PZT films which have been otherwise characterized as pure perovskite phase by XRD. & 2014 Published by Elsevier B.V.
Keywords: Sol–gel preparation Dielectrics Microstructure Piezoelectric materials
1. Introduction
2. Experimental
Due to large piezoelectric properties, high sensitivity, wide frequency bandwidth, and fast responses, PZT thin films are widely used for micro-electromechanical systems’ (MEMS) applications, such as in the areas of transducers [1], micromirrors [2], switches [3], gas sensors [4], pyroelectric sensors [5], energy harvesting devices [6], tactile sensors [7], and intracochlear devices [8]. Details of the growth techniques for PZT thin films are available in the literature [9–11]. One major difficulty in the PZT system is to get a pure perovskite phase, devoid of the unwanted pyrochlore phase, which requires a precise control of compositional stoichiometry. Precise control of stoichiometry in the PZT system is however a difficult task due to the volatility of lead at higher temperatures (4 600 1C), which is required for the crystallization of the films. If there is deficiency or excess of lead in the final composition, the pyrochlore phase appears, which eventually degrades the ferroelectric properties [12]. So it is of utmost importance to prepare the PZT system by precisely controlling the stoichiometry in order to obtain pure perovskite phase by inhibiting the growth of competitive pyrochlore phase. The present paper is an effort to find the optimal thermal conditions for the deposition of pure perovskite PZT films by controlling the growth of unwanted pyrochlore phase.
PbZr0.53Ti0.47O3 (PZT) and PbTiO3 (PT) sols of 0.4 M concentration were prepared by using lead acetate trihydrate, zirconium n-propoxide, titanium isopropoxide, acetic acid and 2-methoxyethanol (Sigma Aldrich) solvents. 10 mol% extra lead was added in order to compensate the lead loss during annealing of the film (for both PZT and PT sols). The films of PZT with PbTiO3 seed layers were coated on a platinized silicon substrate by multiple spin coating at 3000 rpm for 30 s and each layer was pyrolyzed at 350 1C for 5 min. After getting the desired thickness, the films were finally annealed at 650 1C for different durations (30 min, 1 h, 2 h, 3 h and 4 h). The structural characterization of the films was done with XRD system (Philips Diffractometer PW 3020) using CuKα radiation. The surface morphology of the films was observed by FESEM (ZEISS Supra™ 55) microscopy. The dielectric properties were measured using an LCR meter (Agillent 4284A) and the P–E hysteresis behavior was studied using a ferroelectric test system (RT 66A, USA).
n
Corresponding author. Fax: þ 91 11 23913609. E-mail address: [email protected] (R. Laishram).
3. Results and discussion Fig. 1 shows the variations in the surface morphology of the PZT films annealed for different durations, as obtained from FESEM. The micrographs for the films annealed for 30 min and 1 h (Fig. 1a and b) show two different types of morphologies: one, with ultrafine grains of sizes 5–10 nm, and the other, with tightly packed larger grains of size 100 nm; the spherulitic granules represent the perovskite phase whereas the agglomeration of fine grains represents the
http://dx.doi.org/10.1016/j.matlet.2014.08.121 0167-577X/& 2014 Published by Elsevier B.V.
Please cite this article as: Laishram R, Thakur OP. Nanostructured PZT/PT multilayered thin films prepared by sol–gel process. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.08.121i
2
30 min
1h
3h
4h
2h
(Py ) (111)
(101)(110)
1h
(Py )
(200) (002)
(Py ) (001)(100)
Intensity (a.u.)
30min
(Py )
2h 3h 4h
20
25
30
35
40
45
50
2θ (degrees) Fig. 2. X-ray diffraction patterns of the films annealed for 30 min, 1 h, 2 h, 3 h and 4 h. 60 2h
40
1h 30 min
20 2
pyrochlore phase. The FESEM result illustrates clear evidence of the coexistence of the secondary phase along with the perovskite phase of PZT. A similar result has been reported by other workers also [13]. The existence of this mixed (perovskite and lead excess pyrochlore) phase is due to the lack of a complete compensation of the extra lead left out as a result of a shorter annealing time. Such lead excess pyrochlore phase has been reported by other workers [14]. The fraction of agglomerated fine grains corresponding to the pyrochlore phase is found to decrease in film with a 1 h annealing period (Fig. 1b). When the annealing duration is increased to 2 h, all the agglomerated fine grains disappear and only the spherulitic grains associated with the perovskite phase are seen (Fig. 1c). As the annealing duration increases to 3 h, the pyrochlore phase re-appears; instead of grain growth enhancement, grains bigger in size start getting ruptured and at this rupture site, ultrafine nanograins ( 10 nm) corresponding to lead deficient pyrochlore phase appear. The rupture of bigger grains is a consequence of the volatization of lead out of the film surface, felicitated by the higher vapor pressure of lead-oxide. These results are clearly depicted in the FESEM micrograph captured at higher magnification (Fig. 1d). The morphology of the film annealed for the still longer duration of 4 h (Fig. 1e) shows the pyrochlore phase as a major phase and pores appear due to lead volatilization, and therefore lead-deficient stoichiometry of pyrochlore phase is observed in this case. Im and Choo [15] also observed pyrochlore phase formation (lead-deficient and leadexcess) at the expense of the perovskite phase. Fig. 2 shows the XRD patterns of the films annealed for different durations. The films annealed for 1 h and 2 h show a single phase perovskite phase with no traces of pyrochlore; the films annealed for 30 min, 3 h and 4 h show a perovskite phase with traces of pyrochlore. However, FESEM shows the presence of the pyrochlore phase for the samples annealed for 30 min, 1 h, 3 h and 4 h, while pure perovskite phase can be observed only in 2 h annealed film. In the case of 1 h annealed film, the small amount of pyrochlore phase present on the surface of PZT films remains undetected by XRD but is detected by FESEM. The grain boundaries around the pyrochlore (lead rich) nanograins contain excess of lead, rendering a liquid/ amorphous phase along the grain boundary and the area covered by the grain boundary is higher owing to nano-crystalline nature of the films. Therefore, the pyrochlore phase is shielded by an amorphous phase and is invisible in the XRD pattern [16,17]. Similar observations have been reported in other lead-based systems by Gyeong-Su and Chung [13] and others [18–20]. Reaney et al. [21] reported that the
(Py )
Fig. 1. FESEM photographs of the films annealed for (a) 30 min, (b) 1 h, (c) 2 h, (d) 3 h, and (e) 4 h.
P (μC/cm )
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 Q2 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
R. Laishram, O.P. Thakur / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
0 -20 -40 -60 -300
-200
-100
0
100
200
300
E (kV/cm) Fig. 3. Ferroelectric hysteresis loops for the films annealed at different durations.
conventional lead-deficient pyrochlore phase present on the surface of the PZT films cannot be removed by heat treatments; however the lead excess pyrochlore phase can be transformed to the stable perovskite phase by suitable heat treatment. The ferroelectric hysteresis loops for the films annealed at different durations are shown in Fig. 3 (hysteresis loops of pyrochlore phase dominant films are not shown). The remnant polarization (Pr) is increased when the sample is annealed for longer durations. The ferroelectric, dielectric and electrical properties of the films are tabulated in
Please cite this article as: Laishram R, Thakur OP. Nanostructured PZT/PT multilayered thin films prepared by sol–gel process. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.08.121i
R. Laishram, O.P. Thakur / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45
Table 1 Various properties of PZT films. Annealing period
Remnant polarization, Pr (μC/cm2)
Coercive field, Ec (kV/cm)
Dielectric constant (ε)
Dissipation factor (tan δ)
DC resistivity (Ω cm)
30 min 1h 2h
15 22.5 27
68 80 73
305 425 555
0.053 0.047 0.038
5 1010 1.0 1011 1.5 1010
Table 1 (electrical properties of pyrochlore phase dominant films are not depicted). The 2 h annealed film shows superior properties owing to better crystallinity and absence of pyrochlore phase. The electrical and ferroelectric properties are degraded for the films having a small percentage of pyrochlore content [22]. This degradation in the ferroelectric properties is due to the centro-symmetric characteristics of the pyrochlore phase which forbids spontaneous polarization [15,18,21]. 4. Conclusions PZT films deposited by the sol–gel route were annealed at the same temperature (650 1C) but for different durations. The structural and microstructural analyses of the films show that lead-excess pyrochlore phase is present in films which are annealed for a shorter period whereas lead-deficient pyrochlore is present for films annealed for a longer duration. The film annealed at 650 1C for 2 h is observed to be of purely perovskite phase and does not contain any pyrochlore phase. The ferroelectric and electrical properties were observed to be the best for this purely perovskite phase film. FESEM, in contrast to the XRD technique, seems to be the suitable one in order to confirm the presence of the minor pyrochlore phase in PZT films. Acknowledgments The authors are thankful to Mr. Anand for FESEM measurements of our samples and also to the Director, SSPL, for his constant support and interest in the present work. References [1] Gutierrez CA, Meng E. Parylene-based electrochemical-MEMS transducers. J Microelectromech Syst 2010;19:1352–61.
3
[2] Bakke T, Vogl A, Zero O, Tyholdt F, Johansen IR, Wang D. A novel ultra-planar, long-stroke and low-voltage piezoelectric micromirror. J Micromech Microeng 2010;20:064010. [3] Guerre R, Drechsler U, Bhattacharyya D, Rantakari P, Stutz R, Wright RV, et al. Wafer-level transfer technologies for PZT-based RF MEMS switches. J Microelectromech Syst 2010;19:548–60. [4] Ko FH, Hsu YC, Wang MT, Huang GWS. Fabrication of a gas sensor with a piezoelectric PZT film deposited by a novel hydrothermal microwave-assisted annealing. Microelectron Eng 2007;84:1300–4. [5] Liu WG, Ko JS, Zhu WG. Influences of thin Ni layer on the electrical and absorption properties of PZT thin film pyroelectric IR sensors. Infrared Phys Technol 2000;41:169–73. [6] Lee BS, Lin SC, Wu WJ, Wang XY, Chang PZ, Lee CK. Piezoelectric MEMS generators fabricated with an aerosol deposition PZT thin film. J Micromech Microeng 2009;19:065014. [7] Dahiya RS, Cattin D, Adami A, Collini C, Barboni L, Valle M, et al. Towards tactile sensing system on chip for robotic applications. IEEE Sens J 2011;11:3216–26. [8] Luoa C, Caob GZ, Shena IY. Development of a lead–zirconate–titanate (PZT) thin-film microactuator probe for intracochlear applications. Sens Actuators A 2013;201:1–9. [9] Jorel C, Colder H, Galdi A, Méchin L. Epitaxial PZT thin films on YSZ-buffered Si (001) substrates for piezoelectric MEMS or NEMS applications. Mater Sci Eng 2012;41:012012. [10] Tseng HJ, Tian WC, Wu WJ. Flexible PZT thin film tactile sensor for biomedical monitoring. Sensors 2013;13:5478–92. [11] Izyumskaya N, Alivov YI, Cho SJ, Morkoç H, Lee H, Kang YS. Processing, structure, properties, and applications of PZT thin films. Crit Rev Solid State Mater Sci 2007;32:111–202. [12] Ghard NB. Dielectric and piezoelectric nonlinearities in oriented perovskite thin films. (Ph.D. thesis)The Pennsylvania State University; 2005. [13] Gyeong-Su P, Chung II-Sub. Characterization of secondary phases in lead zirconate titanate film surface deposited with excess lead content. Jpn J Appl Phys 2002;41:1519–22. [14] Young P, Won JK, Tae SJ. Effect of excess Pb on fatigue properties of PZT thin films prepared by rf-magnetron sputtering. Mater Lett 2002;56:481–5. [15] Im KV, Choo WK. The perovskite phase formation of 0.4Pb(Yb1/2Nb1/2)O3– 0.6PbTiO3 thin films prepared on Pt/Ti electrode by reactive magnetron sputtering. J Eur Ceram Soc 2001;21:1553–6. [16] Straumal BB, et al. Ferromagnetism of nanostructured zinc oxide films. Phys Q3 Metal Metallogr 2012;113:1244–56. [17] Straumal BB, et al. Ferromagnetic behavior of Fe-doped ZnO nanograined films. Beilstein J Nanotechnol 2013;4:361–9. [18] Carim AH, Tuttle BA, Doughty DH, Martinez SL. Microstructure of solutionprocessed lead zirconate titanate (PZT) thin films. J Am Ceram Soc 1991;74:1455–8. [19] Thountom S, Nakasata M, Tunkasiri T, Thavornyutikarn P. Phase evolution and electrical properties of lead zirconate titanate thin films grown by using a triol sol–gel route. Ceram Int 2009;35:147–9. [20] Alshareef HN, Bellur KR, Auciello O, Kingon AI. Effect of electrodes on the phase evolution and microstructure of PZT thin films. Ferroelectrics 1994;152:85–90. [21] Reaney IM, Taylor DV, Brooks KG. Ferroelectric PZT films by the sol–gel deposition. J Sol Gel Sci Technol 1998;13:813–20. [22] Etin A, Shter GE, Grader GS. Surface composition and imprint in CSD based PZT films. J Am Ceram Soc 2007;90:3800–3.
Please cite this article as: Laishram R, Thakur OP. Nanostructured PZT/PT multilayered thin films prepared by sol–gel process. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.08.121i
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Q1 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Nanostructured PZT/PT multilayered thin films prepared by sol–gel process Radhapiyari Laishram n, O.P. Thakur Solid State Physics Laboratory Lucknow Road, Timarpur, Delhi 110054, India
art ic l e i nf o
a b s t r a c t
Article history: Received 22 May 2014 Accepted 22 August 2014
The morphological progression of PZT thin films (Zr/Ti: 53/47) prepared by sol–gel method has been studied by annealing the films at 650 1C for different durations. FESEM analysis could detect the presence of very small amount of pyrochlore phase (showing different morphologies) in the films annealed for 30 min, 1 h, 3 h and 4 h. However, the very small percentage of the pyrochlore phase present in the 1-h annealed film could not be detected by XRD. The annealing duration was optimized to 2 h with no evidence of any pyrochlore phase in the FESEM microstructure but only grains corresponding to pure perovskite phase. The present study reveals the presence of the pyrochlore phase as the reason for degraded properties in PZT films which have been otherwise characterized as pure perovskite phase by XRD. & 2014 Published by Elsevier B.V.
Keywords: Sol–gel preparation Dielectrics Microstructure Piezoelectric materials
1. Introduction
2. Experimental
Due to large piezoelectric properties, high sensitivity, wide frequency bandwidth, and fast responses, PZT thin films are widely used for micro-electromechanical systems’ (MEMS) applications, such as in the areas of transducers [1], micromirrors [2], switches [3], gas sensors [4], pyroelectric sensors [5], energy harvesting devices [6], tactile sensors [7], and intracochlear devices [8]. Details of the growth techniques for PZT thin films are available in the literature [9–11]. One major difficulty in the PZT system is to get a pure perovskite phase, devoid of the unwanted pyrochlore phase, which requires a precise control of compositional stoichiometry. Precise control of stoichiometry in the PZT system is however a difficult task due to the volatility of lead at higher temperatures (4 600 1C), which is required for the crystallization of the films. If there is deficiency or excess of lead in the final composition, the pyrochlore phase appears, which eventually degrades the ferroelectric properties [12]. So it is of utmost importance to prepare the PZT system by precisely controlling the stoichiometry in order to obtain pure perovskite phase by inhibiting the growth of competitive pyrochlore phase. The present paper is an effort to find the optimal thermal conditions for the deposition of pure perovskite PZT films by controlling the growth of unwanted pyrochlore phase.
PbZr0.53Ti0.47O3 (PZT) and PbTiO3 (PT) sols of 0.4 M concentration were prepared by using lead acetate trihydrate, zirconium n-propoxide, titanium isopropoxide, acetic acid and 2-methoxyethanol (Sigma Aldrich) solvents. 10 mol% extra lead was added in order to compensate the lead loss during annealing of the film (for both PZT and PT sols). The films of PZT with PbTiO3 seed layers were coated on a platinized silicon substrate by multiple spin coating at 3000 rpm for 30 s and each layer was pyrolyzed at 350 1C for 5 min. After getting the desired thickness, the films were finally annealed at 650 1C for different durations (30 min, 1 h, 2 h, 3 h and 4 h). The structural characterization of the films was done with XRD system (Philips Diffractometer PW 3020) using CuKα radiation. The surface morphology of the films was observed by FESEM (ZEISS Supra™ 55) microscopy. The dielectric properties were measured using an LCR meter (Agillent 4284A) and the P–E hysteresis behavior was studied using a ferroelectric test system (RT 66A, USA).
n
Corresponding author. Fax: þ 91 11 23913609. E-mail address: [email protected] (R. Laishram).
3. Results and discussion Fig. 1 shows the variations in the surface morphology of the PZT films annealed for different durations, as obtained from FESEM. The micrographs for the films annealed for 30 min and 1 h (Fig. 1a and b) show two different types of morphologies: one, with ultrafine grains of sizes 5–10 nm, and the other, with tightly packed larger grains of size 100 nm; the spherulitic granules represent the perovskite phase whereas the agglomeration of fine grains represents the
http://dx.doi.org/10.1016/j.matlet.2014.08.121 0167-577X/& 2014 Published by Elsevier B.V.
Please cite this article as: Laishram R, Thakur OP. Nanostructured PZT/PT multilayered thin films prepared by sol–gel process. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.08.121i
2
30 min
1h
3h
4h
2h
(Py ) (111)
(101)(110)
1h
(Py )
(200) (002)
(Py ) (001)(100)
Intensity (a.u.)
30min
(Py )
2h 3h 4h
20
25
30
35
40
45
50
2θ (degrees) Fig. 2. X-ray diffraction patterns of the films annealed for 30 min, 1 h, 2 h, 3 h and 4 h. 60 2h
40
1h 30 min
20 2
pyrochlore phase. The FESEM result illustrates clear evidence of the coexistence of the secondary phase along with the perovskite phase of PZT. A similar result has been reported by other workers also [13]. The existence of this mixed (perovskite and lead excess pyrochlore) phase is due to the lack of a complete compensation of the extra lead left out as a result of a shorter annealing time. Such lead excess pyrochlore phase has been reported by other workers [14]. The fraction of agglomerated fine grains corresponding to the pyrochlore phase is found to decrease in film with a 1 h annealing period (Fig. 1b). When the annealing duration is increased to 2 h, all the agglomerated fine grains disappear and only the spherulitic grains associated with the perovskite phase are seen (Fig. 1c). As the annealing duration increases to 3 h, the pyrochlore phase re-appears; instead of grain growth enhancement, grains bigger in size start getting ruptured and at this rupture site, ultrafine nanograins ( 10 nm) corresponding to lead deficient pyrochlore phase appear. The rupture of bigger grains is a consequence of the volatization of lead out of the film surface, felicitated by the higher vapor pressure of lead-oxide. These results are clearly depicted in the FESEM micrograph captured at higher magnification (Fig. 1d). The morphology of the film annealed for the still longer duration of 4 h (Fig. 1e) shows the pyrochlore phase as a major phase and pores appear due to lead volatilization, and therefore lead-deficient stoichiometry of pyrochlore phase is observed in this case. Im and Choo [15] also observed pyrochlore phase formation (lead-deficient and leadexcess) at the expense of the perovskite phase. Fig. 2 shows the XRD patterns of the films annealed for different durations. The films annealed for 1 h and 2 h show a single phase perovskite phase with no traces of pyrochlore; the films annealed for 30 min, 3 h and 4 h show a perovskite phase with traces of pyrochlore. However, FESEM shows the presence of the pyrochlore phase for the samples annealed for 30 min, 1 h, 3 h and 4 h, while pure perovskite phase can be observed only in 2 h annealed film. In the case of 1 h annealed film, the small amount of pyrochlore phase present on the surface of PZT films remains undetected by XRD but is detected by FESEM. The grain boundaries around the pyrochlore (lead rich) nanograins contain excess of lead, rendering a liquid/ amorphous phase along the grain boundary and the area covered by the grain boundary is higher owing to nano-crystalline nature of the films. Therefore, the pyrochlore phase is shielded by an amorphous phase and is invisible in the XRD pattern [16,17]. Similar observations have been reported in other lead-based systems by Gyeong-Su and Chung [13] and others [18–20]. Reaney et al. [21] reported that the
(Py )
Fig. 1. FESEM photographs of the films annealed for (a) 30 min, (b) 1 h, (c) 2 h, (d) 3 h, and (e) 4 h.
P (μC/cm )
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 Q2 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66
R. Laishram, O.P. Thakur / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
0 -20 -40 -60 -300
-200
-100
0
100
200
300
E (kV/cm) Fig. 3. Ferroelectric hysteresis loops for the films annealed at different durations.
conventional lead-deficient pyrochlore phase present on the surface of the PZT films cannot be removed by heat treatments; however the lead excess pyrochlore phase can be transformed to the stable perovskite phase by suitable heat treatment. The ferroelectric hysteresis loops for the films annealed at different durations are shown in Fig. 3 (hysteresis loops of pyrochlore phase dominant films are not shown). The remnant polarization (Pr) is increased when the sample is annealed for longer durations. The ferroelectric, dielectric and electrical properties of the films are tabulated in
Please cite this article as: Laishram R, Thakur OP. Nanostructured PZT/PT multilayered thin films prepared by sol–gel process. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.08.121i
R. Laishram, O.P. Thakur / Materials Letters ∎ (∎∎∎∎) ∎∎∎–∎∎∎
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45
Table 1 Various properties of PZT films. Annealing period
Remnant polarization, Pr (μC/cm2)
Coercive field, Ec (kV/cm)
Dielectric constant (ε)
Dissipation factor (tan δ)
DC resistivity (Ω cm)
30 min 1h 2h
15 22.5 27
68 80 73
305 425 555
0.053 0.047 0.038
5 1010 1.0 1011 1.5 1010
Table 1 (electrical properties of pyrochlore phase dominant films are not depicted). The 2 h annealed film shows superior properties owing to better crystallinity and absence of pyrochlore phase. The electrical and ferroelectric properties are degraded for the films having a small percentage of pyrochlore content [22]. This degradation in the ferroelectric properties is due to the centro-symmetric characteristics of the pyrochlore phase which forbids spontaneous polarization [15,18,21]. 4. Conclusions PZT films deposited by the sol–gel route were annealed at the same temperature (650 1C) but for different durations. The structural and microstructural analyses of the films show that lead-excess pyrochlore phase is present in films which are annealed for a shorter period whereas lead-deficient pyrochlore is present for films annealed for a longer duration. The film annealed at 650 1C for 2 h is observed to be of purely perovskite phase and does not contain any pyrochlore phase. The ferroelectric and electrical properties were observed to be the best for this purely perovskite phase film. FESEM, in contrast to the XRD technique, seems to be the suitable one in order to confirm the presence of the minor pyrochlore phase in PZT films. Acknowledgments The authors are thankful to Mr. Anand for FESEM measurements of our samples and also to the Director, SSPL, for his constant support and interest in the present work. References [1] Gutierrez CA, Meng E. Parylene-based electrochemical-MEMS transducers. J Microelectromech Syst 2010;19:1352–61.
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Please cite this article as: Laishram R, Thakur OP. Nanostructured PZT/PT multilayered thin films prepared by sol–gel process. Mater Lett (2014), http://dx.doi.org/10.1016/j.matlet.2014.08.121i