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Preparation and crystal structure of BaTiO3 thin film on LaAlO3 substrates by a coating-pyrolysis process
January 2002
Materials Letters 52 Ž2002. 169–172 www.elsevier.comrlocatermatlet
Preparation and crystal structure of BaTiO 3 thin film on LaAlO 3 substrates by a coating-pyrolysis process Seungwon Kim a,) , T. Manabe b, I. Yamaguchi b, T. Kumagai b, S. Mizuta b a
Department of Chemical Engineering, Yosu National UniÕersity, Yosu 550-749, South Korea National Institute of Materials and Chemical Research, Tsukuba, Ibaraki 305-8565, Japan
b
Received 17 February 2001; accepted 12 April 2001
Abstract An epitaxial BaTiO 3 thin film was prepared on LaAlO 3 substrates using metal naphthenates by coating-pyrolysis ŽCP. process. The amorphous films pyrolyzed were crystallized by heat treatment under low oxygen partial pressure at 950 8C. Crystallinity, epitaxy, and crystal structure of the BaTiO 3 thin film on the LaAlO 3 substrates were measured by XRD ur2 u scan, b scan and reciprocal space map. The epitaxial BaTiO 3 thin film on the LaAlO 3 substrates showed a-domain of tetragonal phase with lattice constants of a Hs 0.3997 nm and a Is 0.4037 nm. The surface of the epitaxial BaTiO 3 thin film on the LaAlO 3 substrates consisted of round-shaped grains of diameter about 0.1 mm. q 2002 Elsevier Science B.V. All rights reserved. Keywords: BaTiO 3 ; LaAlO 3 ; Thin film; Tetragonal coating-pyrolysis; Naphthenates; Epitaxy; Crystal structure
1. Introduction Ferroelectric BaTiO 3 thin films having a perovskite structure are of interest for electronic device applications. Because of their useful ferroelectricity, high dielectric constant and large electro-optic coefficient, they are used in non-volatile memory devices, thin film condensers and sensors w1,2x. Especially, epitaxial BaTiO 3 thin films having a low propagation loss are applied to the various nonlinear optical devices w3x. The BaTiO 3 thin films were prepared by the various processing techniques such as metal-organic
) Corresponding author. Tel.: q82-61-659-3292; fax: q82-61653-3659. E-mail address: [email protected] ŽS. Kim..
chemical vapor deposition ŽMOCVD. w4,5x, laser ablation w6x, radio-frequency sputtering w7,8x, pulsed laser deposition w9–11x and reactive evaporation w12x. Especially, the preparation of the epitaxial BaTiO 3 thin films must consider the lattice misfits between the thin films and the substrates. The various substrates such as MgO Ž100., LaAlO 3 Ž100., SrTiO 3 Ž100., MgOrGaAs Ž100. and PtrMgO Ž100. were used. The lattice constant of LaAlO 3 Žpseudo-cubic structure. is 0.3705 nm, while tetragonal BaTiO 3 Žperovskite structure. has the lattice constants of a s 0.3994 nm and c s 0.4038 nm. The lattice misfits between LaAlO 3 and tetragonal BaTiO 3 are 5.3% and 6.5% along the a- and c-axis, respectively. These misfit values are larger than those between BaTiO 3 and SrTiO 3 Ž2.3% and 3.4%. or MgO Ž5.2% and 4.2%. substrates. So it is considered to be more
00167-577Xr02r$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 0 1 . 0 0 3 8 6 - X
170
S. Kim et al.r Materials Letters 52 (2002) 169–172
difficult to prepare the epitaxial BaTiO 3 films on the LaAlO 3 than on the SrTiO 3 or MgO substrates. Recently, we have succeeded in the fabricating of the epitaxial BaTiO 3 thin films on the SrTiO 3 and MgO substrates by the coating-pyrolysis ŽCP. process w13,14x. The chemical solution processes such as the coating-pyrolysis process, metal-organic deposition w16x and sol–gel process w17x have the following advantages: it is a simple and low-cost chemical process and is easily applicable to the substrates with any shape and size. The crystal structures of the epitaxial BaTiO 3 thin films on SrTiO 3 and MgO substrates were pseudo-cubic w13x and cubic structure w15x, respectively. In this paper, BaTiO 3 thin films on the LaAlO 3 Ž100. substrates were prepared by the CP process using a mixed metal-naphthenate solution. The crystallinity, in-plane alignment, crystal structure and surface morphology of the epitaxial BaTiO 3 thin films were investigated.
2. Experimental A coating solution for the preparing of the BaTiO 3 thin films used a mixed solution of commercial barium- and titanium-naphthenates. LaAlO 3 Ž100. was used as a substrate for the preparing of BaTiO 3 thin films. The molar ratio of BarTi in the coating solution was set as 1.0. This solution was diluted with toluene to adjust a concentration and viscosity for a spin coating. The metal concentration of the coating solution was about 0.2 mmolrg. The solution was spin-coated on the LaAlO 3 Ž100. substrates at 2000 rpm for 5 s. The coated films were pyrolyzed at 470 8C for 10 min in air to eliminate the organic components in the coating solution. The coating and pyrolysis conditions were the same as those for the preparation of the epitaxial BaTiO 3 films on the SrTiO 3 and MgO substrates in our previous papers w13,14x. The pyrolyzed films were heat-treated in a tube furnace at 950 8C for 2 h under a gas mixture of argon and oxygen with oxygen partial pressure of 2 = 10y4 atm. A flow rate of the gas mixture was set as 300 mlrmin. The pŽO 2 . was checked by zirconia-type oxygen analyzer at an outlet of the tube furnace. Crystallinity, alignment and crystal structure of the BaTiO 3 thin film on the LaAlO 3 Ž100. substrates were examined by X-ray diffraction ŽXRD.
ur2 u scans, b scans and reciprocal-space mapping using Cu K a radiation with graphite bent crystal monochromator. The surface morphology of the BaTiO 3 thin film was observed by scanning electron microscope ŽSEM..
3. Results and discussion The thermal decomposition of barium and titanium naphthenates to BaCO 3 and TiO 2 were completed at about 470 8C by the thermogravimetric analysis w18x. Therefore, the spin-coated films on the LaAlO 3 Ž100. substrates were pyrolyzed at 470 8C. The pyrolyzed films were amorphous according to the XRD ur2 u scan results, as shown as Fig. 1Ža., similar to the pyrolyzed films prepared on the SrTiO 3 and MgO substrates w13,14x. The pyrolyzed films were crystallized by heat-treatment at high temperatures under low oxygen partial pressure. The thickness of the final films was about 0.3 mm, confirmed by the observation of a cross-section of the films with the scanning electron microscope. The BaTiO 3 thin film heat-treated at 900 8C were still amorphous, not shown here. Fig. 1Žb. shows the XRD pattern of the BaTiO 3 thin film heat-treated at 950 8C. The XRD pattern showed the strong BaTiO 3 Ž h00 . reflections and trace peaks attributable to BaTiO 3 Ž101. and Ž111.. However, the trace peaks are considered negligibly small. The result of XRD
Fig. 1. XRD u r2 u scans of the pyrolyzed films Ža. and the BaTiO 3 thin film Žb. heat-treated under low oxygen partial pressure at 950 8C.
S. Kim et al.r Materials Letters 52 (2002) 169–172
171
pattern suggests that the BaTiO 3 thin film consisted of mainly Ž h00 . oriented BaTiO 3 grains. The amorphous pyrolyzed films on the SrTiO 3 and MgO substrates were crystallized by heat treatment at 700 8C and at 900 8C under low oxygen partial pressure w13,14x. This means that the larger the lattice misfits between films and substrate such as 3.4%, 4.2%, 6.5% for the SrTiO 3 , MgO and LaAlO 3 substrates, the higher the heat-treatment temperatures required for the preparation of the BaTiO 3 thin films. Using the substrate LaAlO 3 Ž200. peak as an internal calibration standard, the lattice constant Ž a H . perpendicular to the substrate surface for the thin film heat-treated at 950 8C was estimated to be 0.3997 nm. These value is close to the a-axis value Ž a 0 s 0.3994 nm. of the bulk tetragonal BaTiO 3 and that Ž0.3999 nm. of the BaTiO 3 thin film on the SrTiO 3 substrates w13x. The in-plane alignment of the BaTiO 3 thin film on the LaAlO 3 substrates was investigated by XRD b scans using the Schulz reflection method of BaTiO 3 Ž101.rŽ110. reflections. The BaTiO 3 thin film was rotated from b s 08 to 3608 at a tilted angles of a s 458. As shown in Fig. 2, the four
Fig. 3. A bird’s eye view Ža. and contour map Žb. of the resulting 2 u r v versus D v mappings.
Fig. 2. XRD b scans of the BaTiO 3 Ž101.rŽ110. reflections Ža. and LaAlO 3 Ž101. reflections Žb. in the BaTiO 3 films.
sharp peaks of the BaTiO 3 Ž101. reflections were observed at every 908 in the line profiles of the b scan and agreed with those of the LaAlO 3 Ž101. reflections. The X-ray pole-figure measured at the tilted angle from 308 to 608 displayed the four sharp spots of the BaTiO 3 Ž101. reflections at every 908, not shown here. This result indicates that the BaTiO 3 thin film was epitaxially grown on the LaAlO 3 substrates and the relationship between BaTiO 3 and LaAlO 3 was BaTiO 3 Ž100. I LaAlO 3 Ž100. and BaTiO 3 w001x I LaAlO 3 w001x. To evaluate the lattice constant Ž a I . along the in-plane directions of the thin film, a reciprocal-space mapping was measured for the BaTiO 3 thin film by an asymmetric XRD 2 urv scans, in which u and v angles with the same rotation axes refer to symmetric and asymmetric Bragg reflections, respectively. Fig. 3Ža. and Žb. display a bird’s eye view and a contour map of the resulting 2 urv versus D v mappings, respectively. A strong peak derived from LaAlO 3 Ž303. reflection of the substrate and another
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S. Kim et al.r Materials Letters 52 (2002) 169–172
was epitaxially grown on the LaAlO 3 Ž100. substrates. The epitaxial BaTiO 3 thin film had the a-domain of the tetragonal phase having the lattice constants with a H s 0.3997 nm and a Is 0.4037 nm. The epitaxial BaTiO 3 thin film on the LaAlO 3 substrates displayed the surface with round-shaped grains of diameter about 0.1 mm. Acknowledgements
Fig. 4. Surface morphology of the epitaxial BaTiO 3 film on the LaAlO 3 substrates.
peak derived from BaTiO 3 Ž303. reflection of the BaTiO 3 thin film are recognized at 2 u s 119.508 and 110.358, respectively, in these mapping graphs. The lattice constant Ž a I . of the thin film along the in-plane directions was calculated from the lattice constant Ž a H s 0.3997 nm., perpendicular to the substrate surface and the top positions of BaTiO 3 Ž303. and LaAlO 3 Ž303. reflection peaks. The lattice constant Ž a I . calculated was 0.4037 nm, which is close to the c-axis value Ž c 0 s 0.4038 nm. of the bulk tetragonal BaTiO 3 . The results of the ur2 u scan and the asymmetric 2 urv scan indicate that the epitaxial BaTiO 3 thin film on the LaAlO 3 substrates showed a-domain of the tetragonal phase. Fig. 4 shows the surface morphology of the epitaxial BaTiO 3 thin film on the LaAlO 3 substrates observed by SEM. Although some cracks were interspersed among grains, the surface of the epitaxial BaTiO 3 thin film was consistent with round-shaped grains of diameter about 0.1 mm.
4. Conclusions The epitaxial BaTiO 3 thin films were prepared on the LaAlO 3 Ž100. substrates by CP process using metal naphthenate solution. The amorphous films pyrolyzed at 470 8C were crystallized to BaTiO 3 phase by heat treatment under oxygen partial pressure of 2 = 10y4 atm at 950 8C. The result of XRD 2 u and b scans showed that the BaTiO 3 thin film
This work was partially supported by the RRC program of MOST and KOSEF through the Research and Development Center for Facility Automation and Information Systems ŽFAIS. at YOSU National University. References w1x D. Dimos, Annu. Rev. Mater. Sci. 25 Ž1995. 273. w2x A.J. Moulson, J.M. Herbert, Electoceramics, Chapman & Hall, London, 1990, p. 147. w3x A.M. Glass, Science 235 Ž1987. 1003. w4x D.L. Kaiser, M.D. Vaudin, L.D. Lotter, Z.L. Wang, J.P. Cline, C.S. Hwang, R.B. Marinenko, J.G. Gillen, Appl. Phys. Lett. 66 Ž1995. 2801. w5x L.A. Wills, B.W. Wessels, D.S. Richeson, T.J. Marks, Appl. Phys. Lett. 60 Ž1992. 41. w6x T. Nose, H.T. Kim, H. Uwe, Jpn. J. Appl. Phys. 33 Ž1994. 5259. w7x S. Kim, S. Hishita, Y.M. Kang, S. Baik, J. Appl. Phys. 78 Ž1995. 5604. w8x K. Fujimoto, Y. Kobayashi, K. Kubota, Thin Solid Films 169 Ž1989. 249. w9x D.H. Kim, H.S. Kwok, Appl. Phys. Lett. 67 Ž1995. 1803. w10x V. Srikant, E.J. Tarsa, D.R. Clarke, J.S. Speck, J. Appl. Phys. 77 Ž1995. 1517. w11x M.G. Norton, K.P.B. Cracknell, C.B. Carter, J. Am. Ceram. Soc. 75 Ž1992. 1999. w12x Y. Yano, K. Iijima, Y. Daitoh, T. Terashima, Y. Bando, Y. Watanabe, H. Kasatani, H. Terauchi, J. Appl. Phys. 76 Ž1994. 7833. w13x S. Kim, T. Manabe, I. Yamaguchi, T. Kumagai, S. Mizuta, J. Mater. Res. 12 Ž1997. 1141. w14x S. Kim, T. Manabe, I. Yamaguchi, T. Kumagai, S. Mizuta, Thin Solid Films 310 Ž1997. 199. w15x S. Kim, O.Y. Kwon, S.W. Choi, T. Manabe, I. Yamaguchi, T. Kumagai, S. Mizuta, J. Korean Crystal Growth 10 Ž2000. 378. w16x W.O. Benomar, S.S. Xue, R.A. Lessard, A. Singh, Z.L. Wu, P.K. Kuo, J. Mater. Res. 9 Ž1994. 970. w17x M.N. Kamalasanan, N.D. Kumar, S. Chandra, J. Appl. Phys. 74 Ž1993. 5679. w18x S. Kim, O.Y. Kwon, Korean J. Chem. Eng. 16 Ž1999. 40.
Materials Letters 52 Ž2002. 169–172 www.elsevier.comrlocatermatlet
Preparation and crystal structure of BaTiO 3 thin film on LaAlO 3 substrates by a coating-pyrolysis process Seungwon Kim a,) , T. Manabe b, I. Yamaguchi b, T. Kumagai b, S. Mizuta b a
Department of Chemical Engineering, Yosu National UniÕersity, Yosu 550-749, South Korea National Institute of Materials and Chemical Research, Tsukuba, Ibaraki 305-8565, Japan
b
Received 17 February 2001; accepted 12 April 2001
Abstract An epitaxial BaTiO 3 thin film was prepared on LaAlO 3 substrates using metal naphthenates by coating-pyrolysis ŽCP. process. The amorphous films pyrolyzed were crystallized by heat treatment under low oxygen partial pressure at 950 8C. Crystallinity, epitaxy, and crystal structure of the BaTiO 3 thin film on the LaAlO 3 substrates were measured by XRD ur2 u scan, b scan and reciprocal space map. The epitaxial BaTiO 3 thin film on the LaAlO 3 substrates showed a-domain of tetragonal phase with lattice constants of a Hs 0.3997 nm and a Is 0.4037 nm. The surface of the epitaxial BaTiO 3 thin film on the LaAlO 3 substrates consisted of round-shaped grains of diameter about 0.1 mm. q 2002 Elsevier Science B.V. All rights reserved. Keywords: BaTiO 3 ; LaAlO 3 ; Thin film; Tetragonal coating-pyrolysis; Naphthenates; Epitaxy; Crystal structure
1. Introduction Ferroelectric BaTiO 3 thin films having a perovskite structure are of interest for electronic device applications. Because of their useful ferroelectricity, high dielectric constant and large electro-optic coefficient, they are used in non-volatile memory devices, thin film condensers and sensors w1,2x. Especially, epitaxial BaTiO 3 thin films having a low propagation loss are applied to the various nonlinear optical devices w3x. The BaTiO 3 thin films were prepared by the various processing techniques such as metal-organic
) Corresponding author. Tel.: q82-61-659-3292; fax: q82-61653-3659. E-mail address: [email protected] ŽS. Kim..
chemical vapor deposition ŽMOCVD. w4,5x, laser ablation w6x, radio-frequency sputtering w7,8x, pulsed laser deposition w9–11x and reactive evaporation w12x. Especially, the preparation of the epitaxial BaTiO 3 thin films must consider the lattice misfits between the thin films and the substrates. The various substrates such as MgO Ž100., LaAlO 3 Ž100., SrTiO 3 Ž100., MgOrGaAs Ž100. and PtrMgO Ž100. were used. The lattice constant of LaAlO 3 Žpseudo-cubic structure. is 0.3705 nm, while tetragonal BaTiO 3 Žperovskite structure. has the lattice constants of a s 0.3994 nm and c s 0.4038 nm. The lattice misfits between LaAlO 3 and tetragonal BaTiO 3 are 5.3% and 6.5% along the a- and c-axis, respectively. These misfit values are larger than those between BaTiO 3 and SrTiO 3 Ž2.3% and 3.4%. or MgO Ž5.2% and 4.2%. substrates. So it is considered to be more
00167-577Xr02r$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 5 7 7 X Ž 0 1 . 0 0 3 8 6 - X
170
S. Kim et al.r Materials Letters 52 (2002) 169–172
difficult to prepare the epitaxial BaTiO 3 films on the LaAlO 3 than on the SrTiO 3 or MgO substrates. Recently, we have succeeded in the fabricating of the epitaxial BaTiO 3 thin films on the SrTiO 3 and MgO substrates by the coating-pyrolysis ŽCP. process w13,14x. The chemical solution processes such as the coating-pyrolysis process, metal-organic deposition w16x and sol–gel process w17x have the following advantages: it is a simple and low-cost chemical process and is easily applicable to the substrates with any shape and size. The crystal structures of the epitaxial BaTiO 3 thin films on SrTiO 3 and MgO substrates were pseudo-cubic w13x and cubic structure w15x, respectively. In this paper, BaTiO 3 thin films on the LaAlO 3 Ž100. substrates were prepared by the CP process using a mixed metal-naphthenate solution. The crystallinity, in-plane alignment, crystal structure and surface morphology of the epitaxial BaTiO 3 thin films were investigated.
2. Experimental A coating solution for the preparing of the BaTiO 3 thin films used a mixed solution of commercial barium- and titanium-naphthenates. LaAlO 3 Ž100. was used as a substrate for the preparing of BaTiO 3 thin films. The molar ratio of BarTi in the coating solution was set as 1.0. This solution was diluted with toluene to adjust a concentration and viscosity for a spin coating. The metal concentration of the coating solution was about 0.2 mmolrg. The solution was spin-coated on the LaAlO 3 Ž100. substrates at 2000 rpm for 5 s. The coated films were pyrolyzed at 470 8C for 10 min in air to eliminate the organic components in the coating solution. The coating and pyrolysis conditions were the same as those for the preparation of the epitaxial BaTiO 3 films on the SrTiO 3 and MgO substrates in our previous papers w13,14x. The pyrolyzed films were heat-treated in a tube furnace at 950 8C for 2 h under a gas mixture of argon and oxygen with oxygen partial pressure of 2 = 10y4 atm. A flow rate of the gas mixture was set as 300 mlrmin. The pŽO 2 . was checked by zirconia-type oxygen analyzer at an outlet of the tube furnace. Crystallinity, alignment and crystal structure of the BaTiO 3 thin film on the LaAlO 3 Ž100. substrates were examined by X-ray diffraction ŽXRD.
ur2 u scans, b scans and reciprocal-space mapping using Cu K a radiation with graphite bent crystal monochromator. The surface morphology of the BaTiO 3 thin film was observed by scanning electron microscope ŽSEM..
3. Results and discussion The thermal decomposition of barium and titanium naphthenates to BaCO 3 and TiO 2 were completed at about 470 8C by the thermogravimetric analysis w18x. Therefore, the spin-coated films on the LaAlO 3 Ž100. substrates were pyrolyzed at 470 8C. The pyrolyzed films were amorphous according to the XRD ur2 u scan results, as shown as Fig. 1Ža., similar to the pyrolyzed films prepared on the SrTiO 3 and MgO substrates w13,14x. The pyrolyzed films were crystallized by heat-treatment at high temperatures under low oxygen partial pressure. The thickness of the final films was about 0.3 mm, confirmed by the observation of a cross-section of the films with the scanning electron microscope. The BaTiO 3 thin film heat-treated at 900 8C were still amorphous, not shown here. Fig. 1Žb. shows the XRD pattern of the BaTiO 3 thin film heat-treated at 950 8C. The XRD pattern showed the strong BaTiO 3 Ž h00 . reflections and trace peaks attributable to BaTiO 3 Ž101. and Ž111.. However, the trace peaks are considered negligibly small. The result of XRD
Fig. 1. XRD u r2 u scans of the pyrolyzed films Ža. and the BaTiO 3 thin film Žb. heat-treated under low oxygen partial pressure at 950 8C.
S. Kim et al.r Materials Letters 52 (2002) 169–172
171
pattern suggests that the BaTiO 3 thin film consisted of mainly Ž h00 . oriented BaTiO 3 grains. The amorphous pyrolyzed films on the SrTiO 3 and MgO substrates were crystallized by heat treatment at 700 8C and at 900 8C under low oxygen partial pressure w13,14x. This means that the larger the lattice misfits between films and substrate such as 3.4%, 4.2%, 6.5% for the SrTiO 3 , MgO and LaAlO 3 substrates, the higher the heat-treatment temperatures required for the preparation of the BaTiO 3 thin films. Using the substrate LaAlO 3 Ž200. peak as an internal calibration standard, the lattice constant Ž a H . perpendicular to the substrate surface for the thin film heat-treated at 950 8C was estimated to be 0.3997 nm. These value is close to the a-axis value Ž a 0 s 0.3994 nm. of the bulk tetragonal BaTiO 3 and that Ž0.3999 nm. of the BaTiO 3 thin film on the SrTiO 3 substrates w13x. The in-plane alignment of the BaTiO 3 thin film on the LaAlO 3 substrates was investigated by XRD b scans using the Schulz reflection method of BaTiO 3 Ž101.rŽ110. reflections. The BaTiO 3 thin film was rotated from b s 08 to 3608 at a tilted angles of a s 458. As shown in Fig. 2, the four
Fig. 3. A bird’s eye view Ža. and contour map Žb. of the resulting 2 u r v versus D v mappings.
Fig. 2. XRD b scans of the BaTiO 3 Ž101.rŽ110. reflections Ža. and LaAlO 3 Ž101. reflections Žb. in the BaTiO 3 films.
sharp peaks of the BaTiO 3 Ž101. reflections were observed at every 908 in the line profiles of the b scan and agreed with those of the LaAlO 3 Ž101. reflections. The X-ray pole-figure measured at the tilted angle from 308 to 608 displayed the four sharp spots of the BaTiO 3 Ž101. reflections at every 908, not shown here. This result indicates that the BaTiO 3 thin film was epitaxially grown on the LaAlO 3 substrates and the relationship between BaTiO 3 and LaAlO 3 was BaTiO 3 Ž100. I LaAlO 3 Ž100. and BaTiO 3 w001x I LaAlO 3 w001x. To evaluate the lattice constant Ž a I . along the in-plane directions of the thin film, a reciprocal-space mapping was measured for the BaTiO 3 thin film by an asymmetric XRD 2 urv scans, in which u and v angles with the same rotation axes refer to symmetric and asymmetric Bragg reflections, respectively. Fig. 3Ža. and Žb. display a bird’s eye view and a contour map of the resulting 2 urv versus D v mappings, respectively. A strong peak derived from LaAlO 3 Ž303. reflection of the substrate and another
172
S. Kim et al.r Materials Letters 52 (2002) 169–172
was epitaxially grown on the LaAlO 3 Ž100. substrates. The epitaxial BaTiO 3 thin film had the a-domain of the tetragonal phase having the lattice constants with a H s 0.3997 nm and a Is 0.4037 nm. The epitaxial BaTiO 3 thin film on the LaAlO 3 substrates displayed the surface with round-shaped grains of diameter about 0.1 mm. Acknowledgements
Fig. 4. Surface morphology of the epitaxial BaTiO 3 film on the LaAlO 3 substrates.
peak derived from BaTiO 3 Ž303. reflection of the BaTiO 3 thin film are recognized at 2 u s 119.508 and 110.358, respectively, in these mapping graphs. The lattice constant Ž a I . of the thin film along the in-plane directions was calculated from the lattice constant Ž a H s 0.3997 nm., perpendicular to the substrate surface and the top positions of BaTiO 3 Ž303. and LaAlO 3 Ž303. reflection peaks. The lattice constant Ž a I . calculated was 0.4037 nm, which is close to the c-axis value Ž c 0 s 0.4038 nm. of the bulk tetragonal BaTiO 3 . The results of the ur2 u scan and the asymmetric 2 urv scan indicate that the epitaxial BaTiO 3 thin film on the LaAlO 3 substrates showed a-domain of the tetragonal phase. Fig. 4 shows the surface morphology of the epitaxial BaTiO 3 thin film on the LaAlO 3 substrates observed by SEM. Although some cracks were interspersed among grains, the surface of the epitaxial BaTiO 3 thin film was consistent with round-shaped grains of diameter about 0.1 mm.
4. Conclusions The epitaxial BaTiO 3 thin films were prepared on the LaAlO 3 Ž100. substrates by CP process using metal naphthenate solution. The amorphous films pyrolyzed at 470 8C were crystallized to BaTiO 3 phase by heat treatment under oxygen partial pressure of 2 = 10y4 atm at 950 8C. The result of XRD 2 u and b scans showed that the BaTiO 3 thin film
This work was partially supported by the RRC program of MOST and KOSEF through the Research and Development Center for Facility Automation and Information Systems ŽFAIS. at YOSU National University. References w1x D. Dimos, Annu. Rev. Mater. Sci. 25 Ž1995. 273. w2x A.J. Moulson, J.M. Herbert, Electoceramics, Chapman & Hall, London, 1990, p. 147. w3x A.M. Glass, Science 235 Ž1987. 1003. w4x D.L. Kaiser, M.D. Vaudin, L.D. Lotter, Z.L. Wang, J.P. Cline, C.S. Hwang, R.B. Marinenko, J.G. Gillen, Appl. Phys. Lett. 66 Ž1995. 2801. w5x L.A. Wills, B.W. Wessels, D.S. Richeson, T.J. Marks, Appl. Phys. Lett. 60 Ž1992. 41. w6x T. Nose, H.T. Kim, H. Uwe, Jpn. J. Appl. Phys. 33 Ž1994. 5259. w7x S. Kim, S. Hishita, Y.M. Kang, S. Baik, J. Appl. Phys. 78 Ž1995. 5604. w8x K. Fujimoto, Y. Kobayashi, K. Kubota, Thin Solid Films 169 Ž1989. 249. w9x D.H. Kim, H.S. Kwok, Appl. Phys. Lett. 67 Ž1995. 1803. w10x V. Srikant, E.J. Tarsa, D.R. Clarke, J.S. Speck, J. Appl. Phys. 77 Ž1995. 1517. w11x M.G. Norton, K.P.B. Cracknell, C.B. Carter, J. Am. Ceram. Soc. 75 Ž1992. 1999. w12x Y. Yano, K. Iijima, Y. Daitoh, T. Terashima, Y. Bando, Y. Watanabe, H. Kasatani, H. Terauchi, J. Appl. Phys. 76 Ž1994. 7833. w13x S. Kim, T. Manabe, I. Yamaguchi, T. Kumagai, S. Mizuta, J. Mater. Res. 12 Ž1997. 1141. w14x S. Kim, T. Manabe, I. Yamaguchi, T. Kumagai, S. Mizuta, Thin Solid Films 310 Ž1997. 199. w15x S. Kim, O.Y. Kwon, S.W. Choi, T. Manabe, I. Yamaguchi, T. Kumagai, S. Mizuta, J. Korean Crystal Growth 10 Ž2000. 378. w16x W.O. Benomar, S.S. Xue, R.A. Lessard, A. Singh, Z.L. Wu, P.K. Kuo, J. Mater. Res. 9 Ž1994. 970. w17x M.N. Kamalasanan, N.D. Kumar, S. Chandra, J. Appl. Phys. 74 Ž1993. 5679. w18x S. Kim, O.Y. Kwon, Korean J. Chem. Eng. 16 Ž1999. 40.