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Ferroelectric, dielectric and piezoelectric properties of potassium lanthanum bismuth titanate K0.5La0.5Bi4Ti4O15 ceramics
Materials Chemistry and Physics 110 (2008) 402–405
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Ferroelectric, dielectric and piezoelectric properties of potassium lanthanum bismuth titanate K0.5 La0.5 Bi4 Ti4 O15 ceramics Chun-Ming Wang a,∗ , Jin-Feng Wang a , Zhi-Gang Gai a , Ming-Lei Zhao a , Liang Zhao a , Jian-Xiu Xu a , Na Yin a , Cheng-Ju Zhang a , Shang-Qian Sun a , Guo-Zhong Zang b , Rui-Qing Chu b , Zhi-Jun Xu b a b
School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, PR China College of Materials Science and Engineering, Liaocheng University, Liaocheng 252000, PR China
a r t i c l e
i n f o
Article history: Received 26 October 2007 Received in revised form 17 February 2008 Accepted 24 February 2008 PACS: 77.84.−s 77.84.Dy 77.65.Bn 77.80.Bh 77.80.Dj
a b s t r a c t The Aurivillius type bismuth layer-structured compound potassium lanthanum bismuth titanate (K0.5 La0.5 Bi4 Ti4 O15 ) is synthesized using conventional solid-state processing. The phase analysis is performed by X-ray diffraction (XRD) and the microstructural morphology is conducted by scanning electron microscopy (SEM). The ferroelectric, dielectric and piezoelectric properties of K0.5 La0.5 Bi4 Ti4 O15 (KLBT) ceramics are investigated in detail. The remnant polarization (Pr ) and coercive field (Ec ) are found to be 8.6 C cm−2 and 60 kV cm−1 , respectively. The Curie temperature Tc and piezoelectric coefficient d33 are 413 ◦ C and 18 pC N−1 , respectively. © 2008 Elsevier B.V. All rights reserved.
Keywords: Ferroelectrics Piezoelectricity
1. Introduction The most widely used ferroelectric and piezoelectric materials in the field of electronic ceramics are the lead-based perovskitetype oxide ceramics [1–8]. These lead-based perovskite ceramics exhibit outstanding piezoelectric and electromechanical properties close to the morphotropic phase boundary (MPB) [6–8]. Nevertheless, the lead-based ceramics contain 60–70% lead by weight, due to the high toxicity of lead, there is a strong demand to develop environmentally friendly ceramics whose electrical properties are comparable to those of the lead-based perovskite-type ferroelectrics. Under such a situation, bismuth layer-structured ferroelectrics (BLSFs) are expected to be as promising as the lead-free ceramics. In the past several years, the BLSFs have been intensively studied for use in non-volatile random access memories (NvRAMs) [9–15] and in piezoelectric devices suitable for use at high frequencies and high temperatures [16–27], due to their high Curie temperature Tc , low dielectric constant, and anisotropies in the electromechanical coupling factor k (such as, kt /kp , k33 /k31 ) as com-
pared to the lead oxide-based perovskites. The structural formula of the BLSFs is generally described as (Bi2 O2 )2+ (Am−1 Bm O3m+1 )2− , which consists of pseudo-perovskite (Am−1 Bm O3m+1 )2− layers interleaved with (Bi2 O2 )2+ layers along the c-axis, where A is a mono-, di-, and tri-valent ion or combination of them allowing dodecahedral coordination, B is a combination of cations well suited to octahedral coordination, and m is an integer usually in the range of 1–5. While the pseudo-perovskite-like layers offer large possibilities in terms of compositional flexibility, the cation sites in the interleave (Bi2 O2 ) layers are almost exclusively occupied by Bi3+ cations forming (Bi2 O2 )2+ slabs. Recently, a number of pure and modified BLSFs have been investigated with a view to their dielectric and ferroelectric properties, especially high temperature piezoelectric characteristics [21–31]. In this work, the structural analysis of a new BLSF K0.5 La0.5 Bi4 Ti4 O15 (KLBT) is performed by X-ray diffraction (XRD) and the microstructural morphology is conducted by scanning electron microscopy (SEM). The ferroelectric, dielectric and piezoelectric properties of the KLBT ceramics are investigated, and high piezoelectric coefficient d33 = 18 pC N−1 is obtained. 2. Experimental procedure
∗ Corresponding author. Tel.: +86 531 8837 7035x8322; fax: +86 531 8837 7031. E-mail address: [email protected] (C.-M. Wang). 0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2008.02.032
The BLSF potassium lanthanum bismuth titanate ceramics were produced using a standard mixed oxide processing route procedure. The starting materials used
C.-M. Wang et al. / Materials Chemistry and Physics 110 (2008) 402–405
403
Fig. 1. X-ray diffraction patterns for the KLBT piezoelectric ceramic powder.
were analytical grades K2 CO3 (99.9% purity), La2 O3 (99.9%), Bi2 O3 (99.9%), and TiO2 (99.9%). The weighed chemicals were wet-milled in polyethylene bottles with ZrO2 balls for 12 h in ethanol. The milled powders were dried and calcined at 780 ◦ C for 2 h with heating rates of 4 ◦ C min−1 . After calcinations, the mixture was wet-milled again in the same conditions. The milled powders were dried, ground and granulated with polyvinyl alcohol (PVA) binder. The granulated powder was pressed into discs 15 mm in diameter by 2.0 mm in thickness at a pressure of 150 MPa. After burning out the PVA at 650 ◦ C, the green compacts were put into the sealed Al2 O3 crucibles and fully surrounded with the powder of matching compositions. By the ordinarily firing method, the samples were sintered for 3 h at 1100 ◦ C with heating rates of 4 ◦ C min−1 , and then cooled to room temperature freely. The size of final samples is about 13 mm in diameter and 0.6 mm in thickness. The XRD patterns for the KLBT ceramic powders were obtained with an X-ray ˚ radidiffractometer (D8 Advance, Bruker AXS GMBH) using Cu K␣1 ( = 1.540596 A) ation. Microstructure characterization of the sintered ceramics was conducted by SEM (JEOL JXA-840). For room temperature electrical and dielectric properties measurement, silver electrodes (1 cm2 ) are fixed on both surfaces of the sintered pellets and fired at 650 ◦ C for 20 min in air. Samples were pooled in silicone oil at 180 ◦ C for 15 min under a dc electric field of 12.5 kV mm−1 . The dielectric spectra measurements were performed with 4294A impedance analyzer using 100 kHz and 1 MHz frequency with an amplitude voltage of 0.5 V as a function of temperature. The piezoelectric coefficient d33 was measured using a quasi-static d33 meter (Institute of Acoustics, Academia Sinica, ZJ-2). The electromechanical coupling factors were determined using the impedance analyzer according to IEEE standard.
3. Results and discussion Fig. 1 shows the X-ray powder diffraction pattern of the KLBT piezoelectric ceramics. The analysis of the XRD pattern reveals the presence of only a bismuth oxide layer type structure with m = 4 within the composition. The highest intensity of diffraction peak is the (1 1 9) in the XRD pattern, which is consistent with the fact that the most intense reflection of BLSFs are all of the type of (112m + 1) [32]. By the analysis of XRD data, the lattice parameters for the tetramolecular orthorhombic cell (a, b, and c) were obtained, where ˚ b = 5.440 A, ˚ and c = 41.217 A. ˚ According to XRD, the thea = 5.433 A, oretical density (t ) of the KBT compound was obtained, where t = 7.483 g cm−3 . Related to theoretical density, the relative density of KLBT is comparative high, and higher than 97% of the theoretical density. Fig. 2 shows the SEM micrograph of the surface of the KLBT piezoelectric ceramics. It is found that the grain growth is structurally highly anisotropic and the length l of the plate-like grain is much bigger than the thickness t, due to the high grain growth rate in the direction perpendicular to the c-axis of the BLSFs crystal. The typical sizes of plate-like grain are 3 m in length l and 500 nm in thickness t, as marked in Fig. 2. Since the BLSF ceramics are ordinarily sintered, the mixed different orientation plate grains stacked together. Fig. 3 shows the polarization hysteresis measured as a function of electric field at 1 Hz frequency. In order to clearly show the polarization hysteresis at different maxima drive electric field (Em ), Fig. 4
Fig. 2. SEM photographs for the surface of KLBT piezoelectric ceramics.
also presents the polarization hysteresis measured at respective maxima drive field. The inset parts of Fig. 4 give the remnant polarization (Pr ) and coercive field (Ec ) values determined at respective maxima drive field. From Fig. 4, one can see, with the maxima drive field increasing to 90 kV cm−1 , the polarization hysteresis is completely open and trends to saturation. The remnant polarization and coercive field determined at a maxima drive field of 90 kV cm−1 were found to be 8.6 C cm−2 and 60 kV cm−1 , respectively. Fig. 5 shows the relative dielectric constant (εr ) and dielectric loss (tan ı) measured at 100 kHz and 1 MHz as a function of temperature for the KLBT piezoelectric ceramics. The maximum of dielectric constant corresponding to the ferro-paraelectric phase transition is clearly observed at Tc = 413 ◦ C (Curie temperature). The peak value of the dielectric constant is about five times higher than the value of room temperature constant. The dielectric loss is very low, especially when the temperature is lower than 300 ◦ C. With the temperature increasing, the dielectric loss slightly increases, and then drops at a specific temperature. With the temperature further increasing, the dielectric loss sharply increases. Fig. 6 shows the frequency dependence of the impedance |Z| and the conductance G measured at room temperature in the piezoelectric radial–extensional vibration mode, the kp mode. The calculated electromechanical factor kp and the mechanical quality factor Qmp were 2.21% and 1974, respectively. The electromechanical factor and mechanical quality factor of the thickness-extensional (kt ) vibration mode was also measured. The calculated electromechanical
Fig. 3. Polarization hysteresis versus electric field for KLBT ceramics measured at 1 Hz frequency.
404
C.-M. Wang et al. / Materials Chemistry and Physics 110 (2008) 402–405
Fig. 4. Polarization hysteresis for KLBT ceramics measured at respective maxima drive field.
Fig. 5. Temperature dependence of dielectric constant and dielectric loss for KLBT piezoelectric ceramics.
factor kt and the mechanical quality factor Qmt were 12.8% and 419, respectively. The detailed room temperature dielectric, ferroelectric and piezoelectric properties for the KLBT piezoceramics are characterized and listed in Table 1. The room temperature relative dielectric constant at 1 kHz is 258, and the dielectric loss is very low, only 0.7%. The Curie temperature Tc is found to be 413 ◦ C. The piezoelectric coefficient d33 is found to be 18 pC N−1 , higher than the d33 values of most reported stoichiometric BLSF systems. Table 2 lists the electromechanical coupling factors kp , kt , k33 , k31 , where kt /kp ≈ 6, k33 /k31 ≈ 9, indicating that the KLBT presents strong anisotropic electromechanical coupling factors. Compared with other BLSF alkali bismuth titanate ceramics, such as
Fig. 6. Frequency dependence of impedance and conductance for planar mode. Table 1 Dielectric, ferroelectric and piezoelectric properties of potassium lanthanum bismuth titanate Sample εr tan ı (%) Tc (◦ C) Ec (C cm−2 ) Pr (kV cm−1 ) d33 (pC N−1 )
KLBT 258 0.7 413 8.6 60 18
Na0.5 Bi4.5 Ti4 O15 , K0.5 Bi4.5 Ti4 O15 , they have similar electromechanical coupling factors kp in the order of 2% and kt in the order of 10%. The mechanical quality factor Qmp and Qmt are found to be 1974 and 419, respectively. Planar frequency constants (Np ) and thick-
Table 2 Electromechanical coupling factors, mechanical quality factor and frequency constant of potassium lanthanum bismuth titanate compared with other bismuth layer-structured ferroelectric alkali bismuth titanate ceramics Sample
kp (%)
Qmp
kt (%)
Qmt
KLBT Na0.5 Bi4.5 Ti4 O15 K0.5 Bi4.5 Ti4 O15
2.21 2.1 2.23
1974 4200 1602
12.8 15 9.2
419 – –
k33 (%) 13 – 9
k31 (%) 1.4 1.3 1.4
Np (Hz m)
Nt (Hz m)
Ref.
2481 – –
2258 – –
This work [28,33] [33,34]
C.-M. Wang et al. / Materials Chemistry and Physics 110 (2008) 402–405
ness frequency constant (Nt ) for the KLBT ceramics are found to be higher than 2481 and 2258 Hz m, respectively. 4. Conclusion The potassium lanthanum bismuth titanate material was synthesized using conventional solid-state processing. The remnant polarization (Pr ) and coercive field (Ec ) were found to be 8.6 C cm−2 and 60 kV cm−1 , respectively. The Curie temperature Tc and piezoelectric coefficient d33 were 413 ◦ C and 18 pC N−1 . The electromechanical coupling factors kp , kt , and the mechanical quality factor Qmp , Qmt , are 2.21%, 12.8%, 1974 and 419, respectively. Planar frequency constants (Np ) and thickness frequency constant (Nt ) for the KLBT ceramics are found to be 2481 and 2258 Hz m. Acknowledgments This research was supported by the National Natural Science Foundation of China under the Grant Nos. 50572056 and 50702030 and the Specialized Research Fund for the Doctoral Program of Higher Education of China under Grant No. 20070422059. References [1] S.L. Swartz, T.R. Shrout, W.A. Schulze, L.E. Cross, J. Am. Ceram. Soc. 67 (1984) 311. [2] S.-E. Park, T.R. Shrout, J. Appl. Phys. 82 (1997) 1804. [3] R.E. Eitel, C.A. Randall, T.R. Shrout, P.W. Rehrig, W. Hackenberger, S.E. Park, Jpn. J. Appl. Phys. 40 (2001) 5999. [4] R.E. Eitel, C.A. Randall, T.R. Shrout, S.E. Park, Jpn. J. Appl. Phys. 41 (2002) 2099. [5] S. Zhang, C.A. Randall, T.R. Shrout, Appl. Phys. Lett. 83 (2003) 3150.
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[6] B. Noheda, N. Cereceda, T. Iglesias, G. Lifante, J.A. Gonzalo, H.T. Chen, Y.L. Wang, Phys. Rev. B 51 (1995) 16388. [7] B. Noheda, D.E. Cox, G. Shirane, J.A. Gonzalo, L.E. Cross, S.E. Park, Appl. Phys. Lett. 74 (1999) 2059. [8] R. Guo, L.E. Cross, S.E. Park, B. Noheda, D.E. Cox, G. Shirane, Phys. Rev. Lett. 84 (2000) 5423. [9] B.H. Park, B.S. Kang, S.D. Bu, T.W. Noh, J. Lee, W. Jo, Nature 401 (1999) 682. [10] U. Chon, K.-B. Kim, H.M. Jang, G.-C. Yi, Appl. Phys. Lett. 79 (2001) 3137. [11] U. Chon, H.M. Jang, M.G. Kim, C.H. Chang, Phys. Rev. Lett. 89 (2002) 087601. [12] U. Chon, J.S. Shim, H.M. Jang, J. Appl. Phys. 93 (2003) 4769. [13] A. Garg, Z.H. Barber, M. Dawber, J.F. Scott, A. Snedden, P. Lightfoot, Appl. Phys. Lett. 83 (2003) 2414. [14] A. Garg, A. Snedden, P. Lightfoot, J.F. Scott, X. Hu, Z.H. Barber, J. Appl. Phys. 96 (2004) 3408. [15] C.A.P. de Araujo, J.D. Cuchiaro, L.D. McMillan, M.C. Scott, J.F. Scott, Nature 374 (1995) 627. [16] E.C. Subbarao, J. Phys. Chem. Solids 23 (1962) 665. [17] C.-M. Wang, J.-F. Wang, Appl. Phys. Lett. 89 (2006) 202905. [18] C.-M. Wang, J.-F. Wang, Z.-G. Gai, Scripta Mater. 57 (2007) 789. [19] T. Takenaka, K. Sakata, Jpn. J. Appl. Phys. 19 (1980) 31. [20] T. Takenaka, K. Sakata, J. Appl. Phys. 55 (1984) 1092. [21] T. Takeuchi, T. Tani, Y. Saito, Jpn. J. Appl. Phys. 38 (1999) 5553. [22] T. Takeuchi, T. Tani, Y. Saito, Jpn. J. Appl. Phys. 39 (2000) 5577. [23] R. Aoyagi, H. Takeda, S. Okamura, T. Shiosaki, Jpn. J. Appl. Phys. 40 (2001) 5671. [24] R. Aoyagi, H. Takeda, S. Okamura, T. Shiosaki, Mater. Res. Bull. 38 (2003) 25. [25] M. Matsushita, R. Aoyagi, H. Takeda, S. Okamura, T. Shiosaki, Jpn. J. Appl. Phys. 43 (2004) 7164. [26] H. Takeda, C. Fujioka, R. Aoyagi, S. Okamura, T. Shiosaki, Appl. Phys. A 82 (2006) 741. [27] H. Yan, M.J. Reece, J. Liu, Z. Shen, Y. Kan, P. Wang, J. Appl. Phys. 100 (2006) 076103. [28] H. Takeda, R. Aoyagi, M. Matsushita, T. Shiosaki, Appl. Phys. A 76 (2003) 295. [29] R. Aoyagi, S. Inai, Y. Hiruma, T. Takenaka, Jpn. J. Appl. Phys. 44 (2005) 7055. [30] R. Aoyagi, H. Takeda, S. Okamura, T. Shiosaki, Mater. Sci. Eng. B 116 (2005) 156. [31] H. Takeda, C. Fujioka, R. Aoyagi, S. Okamura, T. Shiosaki, Appl. Phys. A 81 (2005) 131. [32] X. Du, I.W. Chen, J. Am. Ceram. Soc. 81 (1998) 3253. [33] S. Ikegami, I. Ueda, Jpn. J. Appl. Phys. 13 (1974) 1572. [34] C.M. Wang, J.F. Wang, J. Am. Ceram. Soc. 91 (2008) 918.
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Ferroelectric, dielectric and piezoelectric properties of potassium lanthanum bismuth titanate K0.5 La0.5 Bi4 Ti4 O15 ceramics Chun-Ming Wang a,∗ , Jin-Feng Wang a , Zhi-Gang Gai a , Ming-Lei Zhao a , Liang Zhao a , Jian-Xiu Xu a , Na Yin a , Cheng-Ju Zhang a , Shang-Qian Sun a , Guo-Zhong Zang b , Rui-Qing Chu b , Zhi-Jun Xu b a b
School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, PR China College of Materials Science and Engineering, Liaocheng University, Liaocheng 252000, PR China
a r t i c l e
i n f o
Article history: Received 26 October 2007 Received in revised form 17 February 2008 Accepted 24 February 2008 PACS: 77.84.−s 77.84.Dy 77.65.Bn 77.80.Bh 77.80.Dj
a b s t r a c t The Aurivillius type bismuth layer-structured compound potassium lanthanum bismuth titanate (K0.5 La0.5 Bi4 Ti4 O15 ) is synthesized using conventional solid-state processing. The phase analysis is performed by X-ray diffraction (XRD) and the microstructural morphology is conducted by scanning electron microscopy (SEM). The ferroelectric, dielectric and piezoelectric properties of K0.5 La0.5 Bi4 Ti4 O15 (KLBT) ceramics are investigated in detail. The remnant polarization (Pr ) and coercive field (Ec ) are found to be 8.6 C cm−2 and 60 kV cm−1 , respectively. The Curie temperature Tc and piezoelectric coefficient d33 are 413 ◦ C and 18 pC N−1 , respectively. © 2008 Elsevier B.V. All rights reserved.
Keywords: Ferroelectrics Piezoelectricity
1. Introduction The most widely used ferroelectric and piezoelectric materials in the field of electronic ceramics are the lead-based perovskitetype oxide ceramics [1–8]. These lead-based perovskite ceramics exhibit outstanding piezoelectric and electromechanical properties close to the morphotropic phase boundary (MPB) [6–8]. Nevertheless, the lead-based ceramics contain 60–70% lead by weight, due to the high toxicity of lead, there is a strong demand to develop environmentally friendly ceramics whose electrical properties are comparable to those of the lead-based perovskite-type ferroelectrics. Under such a situation, bismuth layer-structured ferroelectrics (BLSFs) are expected to be as promising as the lead-free ceramics. In the past several years, the BLSFs have been intensively studied for use in non-volatile random access memories (NvRAMs) [9–15] and in piezoelectric devices suitable for use at high frequencies and high temperatures [16–27], due to their high Curie temperature Tc , low dielectric constant, and anisotropies in the electromechanical coupling factor k (such as, kt /kp , k33 /k31 ) as com-
pared to the lead oxide-based perovskites. The structural formula of the BLSFs is generally described as (Bi2 O2 )2+ (Am−1 Bm O3m+1 )2− , which consists of pseudo-perovskite (Am−1 Bm O3m+1 )2− layers interleaved with (Bi2 O2 )2+ layers along the c-axis, where A is a mono-, di-, and tri-valent ion or combination of them allowing dodecahedral coordination, B is a combination of cations well suited to octahedral coordination, and m is an integer usually in the range of 1–5. While the pseudo-perovskite-like layers offer large possibilities in terms of compositional flexibility, the cation sites in the interleave (Bi2 O2 ) layers are almost exclusively occupied by Bi3+ cations forming (Bi2 O2 )2+ slabs. Recently, a number of pure and modified BLSFs have been investigated with a view to their dielectric and ferroelectric properties, especially high temperature piezoelectric characteristics [21–31]. In this work, the structural analysis of a new BLSF K0.5 La0.5 Bi4 Ti4 O15 (KLBT) is performed by X-ray diffraction (XRD) and the microstructural morphology is conducted by scanning electron microscopy (SEM). The ferroelectric, dielectric and piezoelectric properties of the KLBT ceramics are investigated, and high piezoelectric coefficient d33 = 18 pC N−1 is obtained. 2. Experimental procedure
∗ Corresponding author. Tel.: +86 531 8837 7035x8322; fax: +86 531 8837 7031. E-mail address: [email protected] (C.-M. Wang). 0254-0584/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2008.02.032
The BLSF potassium lanthanum bismuth titanate ceramics were produced using a standard mixed oxide processing route procedure. The starting materials used
C.-M. Wang et al. / Materials Chemistry and Physics 110 (2008) 402–405
403
Fig. 1. X-ray diffraction patterns for the KLBT piezoelectric ceramic powder.
were analytical grades K2 CO3 (99.9% purity), La2 O3 (99.9%), Bi2 O3 (99.9%), and TiO2 (99.9%). The weighed chemicals were wet-milled in polyethylene bottles with ZrO2 balls for 12 h in ethanol. The milled powders were dried and calcined at 780 ◦ C for 2 h with heating rates of 4 ◦ C min−1 . After calcinations, the mixture was wet-milled again in the same conditions. The milled powders were dried, ground and granulated with polyvinyl alcohol (PVA) binder. The granulated powder was pressed into discs 15 mm in diameter by 2.0 mm in thickness at a pressure of 150 MPa. After burning out the PVA at 650 ◦ C, the green compacts were put into the sealed Al2 O3 crucibles and fully surrounded with the powder of matching compositions. By the ordinarily firing method, the samples were sintered for 3 h at 1100 ◦ C with heating rates of 4 ◦ C min−1 , and then cooled to room temperature freely. The size of final samples is about 13 mm in diameter and 0.6 mm in thickness. The XRD patterns for the KLBT ceramic powders were obtained with an X-ray ˚ radidiffractometer (D8 Advance, Bruker AXS GMBH) using Cu K␣1 ( = 1.540596 A) ation. Microstructure characterization of the sintered ceramics was conducted by SEM (JEOL JXA-840). For room temperature electrical and dielectric properties measurement, silver electrodes (1 cm2 ) are fixed on both surfaces of the sintered pellets and fired at 650 ◦ C for 20 min in air. Samples were pooled in silicone oil at 180 ◦ C for 15 min under a dc electric field of 12.5 kV mm−1 . The dielectric spectra measurements were performed with 4294A impedance analyzer using 100 kHz and 1 MHz frequency with an amplitude voltage of 0.5 V as a function of temperature. The piezoelectric coefficient d33 was measured using a quasi-static d33 meter (Institute of Acoustics, Academia Sinica, ZJ-2). The electromechanical coupling factors were determined using the impedance analyzer according to IEEE standard.
3. Results and discussion Fig. 1 shows the X-ray powder diffraction pattern of the KLBT piezoelectric ceramics. The analysis of the XRD pattern reveals the presence of only a bismuth oxide layer type structure with m = 4 within the composition. The highest intensity of diffraction peak is the (1 1 9) in the XRD pattern, which is consistent with the fact that the most intense reflection of BLSFs are all of the type of (112m + 1) [32]. By the analysis of XRD data, the lattice parameters for the tetramolecular orthorhombic cell (a, b, and c) were obtained, where ˚ b = 5.440 A, ˚ and c = 41.217 A. ˚ According to XRD, the thea = 5.433 A, oretical density (t ) of the KBT compound was obtained, where t = 7.483 g cm−3 . Related to theoretical density, the relative density of KLBT is comparative high, and higher than 97% of the theoretical density. Fig. 2 shows the SEM micrograph of the surface of the KLBT piezoelectric ceramics. It is found that the grain growth is structurally highly anisotropic and the length l of the plate-like grain is much bigger than the thickness t, due to the high grain growth rate in the direction perpendicular to the c-axis of the BLSFs crystal. The typical sizes of plate-like grain are 3 m in length l and 500 nm in thickness t, as marked in Fig. 2. Since the BLSF ceramics are ordinarily sintered, the mixed different orientation plate grains stacked together. Fig. 3 shows the polarization hysteresis measured as a function of electric field at 1 Hz frequency. In order to clearly show the polarization hysteresis at different maxima drive electric field (Em ), Fig. 4
Fig. 2. SEM photographs for the surface of KLBT piezoelectric ceramics.
also presents the polarization hysteresis measured at respective maxima drive field. The inset parts of Fig. 4 give the remnant polarization (Pr ) and coercive field (Ec ) values determined at respective maxima drive field. From Fig. 4, one can see, with the maxima drive field increasing to 90 kV cm−1 , the polarization hysteresis is completely open and trends to saturation. The remnant polarization and coercive field determined at a maxima drive field of 90 kV cm−1 were found to be 8.6 C cm−2 and 60 kV cm−1 , respectively. Fig. 5 shows the relative dielectric constant (εr ) and dielectric loss (tan ı) measured at 100 kHz and 1 MHz as a function of temperature for the KLBT piezoelectric ceramics. The maximum of dielectric constant corresponding to the ferro-paraelectric phase transition is clearly observed at Tc = 413 ◦ C (Curie temperature). The peak value of the dielectric constant is about five times higher than the value of room temperature constant. The dielectric loss is very low, especially when the temperature is lower than 300 ◦ C. With the temperature increasing, the dielectric loss slightly increases, and then drops at a specific temperature. With the temperature further increasing, the dielectric loss sharply increases. Fig. 6 shows the frequency dependence of the impedance |Z| and the conductance G measured at room temperature in the piezoelectric radial–extensional vibration mode, the kp mode. The calculated electromechanical factor kp and the mechanical quality factor Qmp were 2.21% and 1974, respectively. The electromechanical factor and mechanical quality factor of the thickness-extensional (kt ) vibration mode was also measured. The calculated electromechanical
Fig. 3. Polarization hysteresis versus electric field for KLBT ceramics measured at 1 Hz frequency.
404
C.-M. Wang et al. / Materials Chemistry and Physics 110 (2008) 402–405
Fig. 4. Polarization hysteresis for KLBT ceramics measured at respective maxima drive field.
Fig. 5. Temperature dependence of dielectric constant and dielectric loss for KLBT piezoelectric ceramics.
factor kt and the mechanical quality factor Qmt were 12.8% and 419, respectively. The detailed room temperature dielectric, ferroelectric and piezoelectric properties for the KLBT piezoceramics are characterized and listed in Table 1. The room temperature relative dielectric constant at 1 kHz is 258, and the dielectric loss is very low, only 0.7%. The Curie temperature Tc is found to be 413 ◦ C. The piezoelectric coefficient d33 is found to be 18 pC N−1 , higher than the d33 values of most reported stoichiometric BLSF systems. Table 2 lists the electromechanical coupling factors kp , kt , k33 , k31 , where kt /kp ≈ 6, k33 /k31 ≈ 9, indicating that the KLBT presents strong anisotropic electromechanical coupling factors. Compared with other BLSF alkali bismuth titanate ceramics, such as
Fig. 6. Frequency dependence of impedance and conductance for planar mode. Table 1 Dielectric, ferroelectric and piezoelectric properties of potassium lanthanum bismuth titanate Sample εr tan ı (%) Tc (◦ C) Ec (C cm−2 ) Pr (kV cm−1 ) d33 (pC N−1 )
KLBT 258 0.7 413 8.6 60 18
Na0.5 Bi4.5 Ti4 O15 , K0.5 Bi4.5 Ti4 O15 , they have similar electromechanical coupling factors kp in the order of 2% and kt in the order of 10%. The mechanical quality factor Qmp and Qmt are found to be 1974 and 419, respectively. Planar frequency constants (Np ) and thick-
Table 2 Electromechanical coupling factors, mechanical quality factor and frequency constant of potassium lanthanum bismuth titanate compared with other bismuth layer-structured ferroelectric alkali bismuth titanate ceramics Sample
kp (%)
Qmp
kt (%)
Qmt
KLBT Na0.5 Bi4.5 Ti4 O15 K0.5 Bi4.5 Ti4 O15
2.21 2.1 2.23
1974 4200 1602
12.8 15 9.2
419 – –
k33 (%) 13 – 9
k31 (%) 1.4 1.3 1.4
Np (Hz m)
Nt (Hz m)
Ref.
2481 – –
2258 – –
This work [28,33] [33,34]
C.-M. Wang et al. / Materials Chemistry and Physics 110 (2008) 402–405
ness frequency constant (Nt ) for the KLBT ceramics are found to be higher than 2481 and 2258 Hz m, respectively. 4. Conclusion The potassium lanthanum bismuth titanate material was synthesized using conventional solid-state processing. The remnant polarization (Pr ) and coercive field (Ec ) were found to be 8.6 C cm−2 and 60 kV cm−1 , respectively. The Curie temperature Tc and piezoelectric coefficient d33 were 413 ◦ C and 18 pC N−1 . The electromechanical coupling factors kp , kt , and the mechanical quality factor Qmp , Qmt , are 2.21%, 12.8%, 1974 and 419, respectively. Planar frequency constants (Np ) and thickness frequency constant (Nt ) for the KLBT ceramics are found to be 2481 and 2258 Hz m. Acknowledgments This research was supported by the National Natural Science Foundation of China under the Grant Nos. 50572056 and 50702030 and the Specialized Research Fund for the Doctoral Program of Higher Education of China under Grant No. 20070422059. References [1] S.L. Swartz, T.R. Shrout, W.A. Schulze, L.E. Cross, J. Am. Ceram. Soc. 67 (1984) 311. [2] S.-E. Park, T.R. Shrout, J. Appl. Phys. 82 (1997) 1804. [3] R.E. Eitel, C.A. Randall, T.R. Shrout, P.W. Rehrig, W. Hackenberger, S.E. Park, Jpn. J. Appl. Phys. 40 (2001) 5999. [4] R.E. Eitel, C.A. Randall, T.R. Shrout, S.E. Park, Jpn. J. Appl. Phys. 41 (2002) 2099. [5] S. Zhang, C.A. Randall, T.R. Shrout, Appl. Phys. Lett. 83 (2003) 3150.
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