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Single crystal growth and structure refinement of Li4Ti5O12
ARTICLE IN PRESS
Journal of Physics and Chemistry of Solids 69 (2008) 1454–1456 www.elsevier.com/locate/jpcs
Single crystal growth and structure refinement of Li4Ti5O12 Kunimitsu Kataokaa,b,, Yasuhiko Takahashia, Norihito Kijimaa, Junji Akimotoa, Ken-ichi Ohshimab a
National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305 8565, Japan b Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305 8573, Japan Received 30 June 2007; received in revised form 5 October 2007; accepted 30 October 2007
Abstract Single crystal of Li4Ti5O12 was synthesized by a flux method using LiCl flux. The obtained Li4Ti5O12 single crystal is colorless and has ¯ a ¼ 8.352 (4) A˚, V ¼ 583.6 (8) A˚3, and the shape of a rod. Li4Ti5O12 crystallizes in the cubic spinel type structure, space group Fd 3m, Z ¼ 8. The structure was determined by a single-crystal X-ray study and refined to the conventional values of R ¼ 3.6% and wR ¼ 3.3% for 209 independent observed reflections. r 2007 Elsevier Ltd. All rights reserved. Keywords: A. Oxides; B. Crystal growth; C. X-ray diffraction; D. Crystal structure
1. Introduction
2. Experimental
Lithium-titanium oxide ceramics are important industrial materials. In recent years, Li4Ti5O12 is used as a negative electrode material in advanced lithium–ion batteries. Single-crystal growth and structural characterization of Li4Ti5O12 were originally determined by Deschanvres et al. [1]. However, the precise structural properties including the anisotropic atomic displacement parameters have not been determined yet. In all the experimental studies of Li4Ti5O12 reported to date, powder and/or thin-film samples were used although single crystals were needed in order to investigate the structural and electrochemical lithium–ion intercalation/deintercalation properties precisely. In the present study, Li4Ti5O12 single-crystals are successfully grown by flux method, and the crystal structure is refined by single-crystal X-ray diffraction (XRD) method.
Li4Ti5O12 polycrystalline sample was synthesized by the solid-state reaction of Li2CO3 (99.9%) and TiO2 (99.9%). The starting mixture was filled in alumina crucibles, and was heated in air at 973 K for 12 h and was subsequently heated at 1123 K for 24 h. The products were examined with X-ray powder diffraction data measured by Cu Ka radiation using a Rigaku RINT2550 V diffractometer (operating condition: 40 kV, 200 mA) equipped with a curved graphite monochromator. All observed peaks were well indexed to the reported XRD data [2]. Single crystals of Li4Ti5O12 were synthesized by a flux method using LiCl flux. Flux method is one of the crystal growth techniques where the sample is dissolved in a flux solution and crystal growth takes place at relatively low temperatures. The Li4Ti5O12 powder was mixed with LiCl (99.9%) in order to form a flux material with a normal weight ratio of Li4Ti5O12:LiCl ¼ 1:10. The mixture was filled in Au crucible, heated in air at 1223 K for 70 h, and was cooled naturally. The products were easily separated from the frozen flux by rinsing the crucible in hot water for several hours. The shape of products was observed by scanning electron microscope (SEM, JEOL JSM-5400). Integrated
Corresponding author at: Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305 8573, Japan. Fax: +81 29 861 9214. E-mail address: [email protected] (K. Kataoka).
0022-3697/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2007.10.134
ARTICLE IN PRESS K. Kataoka et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1454–1456
intensity data were collected on Rigaku AFC-7S four-circle diffractometer at 295 K. 3. Results and discussions 3.1. Crystal growth Rod-shaped colorless crystals with a maximum size of 0.05 0.05 0.50 mm3 were grown in the upper pert of the frozen flux, as shown in Fig. 1. X-ray powder diffraction data obtained using the pulverized rod specimens confirmed that the product was a single-phase of Li4Ti5O12, and no other phases existed. The lattice parameters, determined by a least-squares refinement using 2y values of 25 strong reflections in the range of 20–301 and Mo Ka radiation (l ¼ 0.71069 A˚) on the four-circle diffractometer at 295 K, were a ¼ 8.352(4) A˚, and V ¼ 583.6(8) A˚3. These values were in good agreement with the reported values (a ¼ 8.35894 A˚, V ¼ 584.0548 A˚3) [3]. The size of obtained crystals in the present study was not enough to measure the physical properties. In order to grow lager crystals of Li4Ti5O12, we changed the growing temperature and the flux amount; however, the crystal morphology could not be improved in the present study. A further investigation should be performed to obtain much lager single crystals. 3.2. Structure refinement A small rod-shaped crystal, with a dimension of 0.05 0.05 0.20 mm3, was used for the structure analysis. The intensity data were collected by the 2y–o scan method with a scan rate of 1.01/min at 295 K on the four-circle diffractometer (operating condition: 50 kV, 40 mA) using graphite monochromatized Mo Ka radiation (l ¼ 0.71069 A˚). The fluctuations of the intensities, monitored by examining a set of three standard reflections ((4 0 0), (0 4 0), (0 0 4)) obtained after every 150 measurements, were
Fig. 1. SEM photograph of as-grown Li4Ti5O12 single crystals.
1455
Table 1 Experiment and crystallographic data of Li4Ti5O12 Structural formula
Li4Ti5O12
Temperature (K) Crystal system Space group Lattice parameters a (A˚) V (A˚3) Z Dx (g/cm3) Crystal size (mm) Maximum 2y (deg) Absorption correction Transmission factors: min and max Measured reflections Rint Independent reflections Observed reflections (43s) Number of variables R wR [w ¼ 1/s2F]
295 Cubic Fd3¯ m 8.352(4) 583.6(8) 8 3.48 0.05 0.05 0.20 135 Gaussian integration 0.660 and 0.804 1144 0.067 209 297 8 0.036 0.033
Table 2 Atomic coordinates and equivalent isotropic displacement parameters (A˚2) for Li4Ti5O12 Atom Site Population x
y
z
Ueq
Li1 Li2 Ti1 O1
0.125 0.5 0.5 0.2626 (1)
0.125 0.5 0.5 0.2626 (1)
0.0097 (8) 0.01055 (6) 0.01055 (6) 0.0092 (1)
8a 16d 16d 32e
1.00 1.667 0.833 1.00
0.125 0.5 0.5 0.2626 (1)
Table 3 Anisotropic displacement parameters (A˚2) for Li4Ti5O12 Atom
U11
U22
U33
U12
U13
U23
Li1 Li2 Ti1 O1
0.010(1) 0.0106(1) 0.0106(1) 0.0092(2)
U11 U11 U11 U11
U11 U11 U11 U11
0 0.0012(1) 0.0012(1) 0.0017(3)
0 U12 U12 U12
0 U12 U12 U12
within 2%. A total of 1144 reflections were obtained within the limit of 2yo1351. All calculations were carried out using the Xtal3.5 program [4]. Structure factors were obtained after averaging the equivalent Bragg intensities, which were corrected for Lorentz and polarization factors, scale factors, and absorption and extinction effected. Neutral atomic scattering factors for all atoms were applied in the refinement. Table 1 summarizes the crystallographic and experimental data. In the following structure analysis, the space group with ¯ confirmed by the successful refinement, was adopted. Fd 3m The refinement was initiated with the reported atomic coordinates for Li4Ti5O12 [1]. The final atomic coordinates and the displacement parameters are listed in Tables 2 and 3, respectively.
ARTICLE IN PRESS 1456
K. Kataoka et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1454–1456
XRD [3,5]. In the present single-crystal study, the tetrahedral Li1–O1 and octahedral Ti1/Li2–O1 distances were determined to be 1.9963(6) and 1.9854(9) A˚, respectively. It should be noted that the U11 value (0.0106(1) A˚) for the octahedral Ti/Li2 atom, listed in Table 3, was slightly larger than that (0.00639(6) A˚) for the Ti atom in the spinel-type LiTi2O4 [6]. This fact may be explained by the Li substitution for the octahedral site.
References [1] A. Deschanvres, B. Raveau, Z. Sekkal, Mat. Res. Bull. 6 (1971) 699–704. [2] D. Tsubone, T. Hashimoto, K. Igarashi, T. Shimizu, J. Ceram. Soc. Japan 102 (1994) 180–184. [3] S. Scharner, W. Weppner, P. Schmid-Beurmann, J. Solid State Chem. 134 (1997) 170–181. [4] S.R. Hall, D.J. du Boulay, R. Olthof-Hazekamp (Eds.), Xtal3.5 System, University of Western Australia, Australia, 2000. [5] M. Nakayama, Y. Ishida, H. Ikuta, M. Wakihara, Solid State Ionics 117 (1999) 265–271. [6] Y. Takahashi, Y. Gotoh, J. Akimoto, J. Phys. Chem. Solid 63 (2002) 987–990. Fig. 2. Crystal structure of Li4Ti5O12.
The crystal structure of Li4Ti5O12 is shown in Fig. 2. The refined oxygen coordination parameter, x(O) ¼ 0.2626(1), was well consistent with the previous reports by powder
Journal of Physics and Chemistry of Solids 69 (2008) 1454–1456 www.elsevier.com/locate/jpcs
Single crystal growth and structure refinement of Li4Ti5O12 Kunimitsu Kataokaa,b,, Yasuhiko Takahashia, Norihito Kijimaa, Junji Akimotoa, Ken-ichi Ohshimab a
National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305 8565, Japan b Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305 8573, Japan Received 30 June 2007; received in revised form 5 October 2007; accepted 30 October 2007
Abstract Single crystal of Li4Ti5O12 was synthesized by a flux method using LiCl flux. The obtained Li4Ti5O12 single crystal is colorless and has ¯ a ¼ 8.352 (4) A˚, V ¼ 583.6 (8) A˚3, and the shape of a rod. Li4Ti5O12 crystallizes in the cubic spinel type structure, space group Fd 3m, Z ¼ 8. The structure was determined by a single-crystal X-ray study and refined to the conventional values of R ¼ 3.6% and wR ¼ 3.3% for 209 independent observed reflections. r 2007 Elsevier Ltd. All rights reserved. Keywords: A. Oxides; B. Crystal growth; C. X-ray diffraction; D. Crystal structure
1. Introduction
2. Experimental
Lithium-titanium oxide ceramics are important industrial materials. In recent years, Li4Ti5O12 is used as a negative electrode material in advanced lithium–ion batteries. Single-crystal growth and structural characterization of Li4Ti5O12 were originally determined by Deschanvres et al. [1]. However, the precise structural properties including the anisotropic atomic displacement parameters have not been determined yet. In all the experimental studies of Li4Ti5O12 reported to date, powder and/or thin-film samples were used although single crystals were needed in order to investigate the structural and electrochemical lithium–ion intercalation/deintercalation properties precisely. In the present study, Li4Ti5O12 single-crystals are successfully grown by flux method, and the crystal structure is refined by single-crystal X-ray diffraction (XRD) method.
Li4Ti5O12 polycrystalline sample was synthesized by the solid-state reaction of Li2CO3 (99.9%) and TiO2 (99.9%). The starting mixture was filled in alumina crucibles, and was heated in air at 973 K for 12 h and was subsequently heated at 1123 K for 24 h. The products were examined with X-ray powder diffraction data measured by Cu Ka radiation using a Rigaku RINT2550 V diffractometer (operating condition: 40 kV, 200 mA) equipped with a curved graphite monochromator. All observed peaks were well indexed to the reported XRD data [2]. Single crystals of Li4Ti5O12 were synthesized by a flux method using LiCl flux. Flux method is one of the crystal growth techniques where the sample is dissolved in a flux solution and crystal growth takes place at relatively low temperatures. The Li4Ti5O12 powder was mixed with LiCl (99.9%) in order to form a flux material with a normal weight ratio of Li4Ti5O12:LiCl ¼ 1:10. The mixture was filled in Au crucible, heated in air at 1223 K for 70 h, and was cooled naturally. The products were easily separated from the frozen flux by rinsing the crucible in hot water for several hours. The shape of products was observed by scanning electron microscope (SEM, JEOL JSM-5400). Integrated
Corresponding author at: Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305 8573, Japan. Fax: +81 29 861 9214. E-mail address: [email protected] (K. Kataoka).
0022-3697/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2007.10.134
ARTICLE IN PRESS K. Kataoka et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1454–1456
intensity data were collected on Rigaku AFC-7S four-circle diffractometer at 295 K. 3. Results and discussions 3.1. Crystal growth Rod-shaped colorless crystals with a maximum size of 0.05 0.05 0.50 mm3 were grown in the upper pert of the frozen flux, as shown in Fig. 1. X-ray powder diffraction data obtained using the pulverized rod specimens confirmed that the product was a single-phase of Li4Ti5O12, and no other phases existed. The lattice parameters, determined by a least-squares refinement using 2y values of 25 strong reflections in the range of 20–301 and Mo Ka radiation (l ¼ 0.71069 A˚) on the four-circle diffractometer at 295 K, were a ¼ 8.352(4) A˚, and V ¼ 583.6(8) A˚3. These values were in good agreement with the reported values (a ¼ 8.35894 A˚, V ¼ 584.0548 A˚3) [3]. The size of obtained crystals in the present study was not enough to measure the physical properties. In order to grow lager crystals of Li4Ti5O12, we changed the growing temperature and the flux amount; however, the crystal morphology could not be improved in the present study. A further investigation should be performed to obtain much lager single crystals. 3.2. Structure refinement A small rod-shaped crystal, with a dimension of 0.05 0.05 0.20 mm3, was used for the structure analysis. The intensity data were collected by the 2y–o scan method with a scan rate of 1.01/min at 295 K on the four-circle diffractometer (operating condition: 50 kV, 40 mA) using graphite monochromatized Mo Ka radiation (l ¼ 0.71069 A˚). The fluctuations of the intensities, monitored by examining a set of three standard reflections ((4 0 0), (0 4 0), (0 0 4)) obtained after every 150 measurements, were
Fig. 1. SEM photograph of as-grown Li4Ti5O12 single crystals.
1455
Table 1 Experiment and crystallographic data of Li4Ti5O12 Structural formula
Li4Ti5O12
Temperature (K) Crystal system Space group Lattice parameters a (A˚) V (A˚3) Z Dx (g/cm3) Crystal size (mm) Maximum 2y (deg) Absorption correction Transmission factors: min and max Measured reflections Rint Independent reflections Observed reflections (43s) Number of variables R wR [w ¼ 1/s2F]
295 Cubic Fd3¯ m 8.352(4) 583.6(8) 8 3.48 0.05 0.05 0.20 135 Gaussian integration 0.660 and 0.804 1144 0.067 209 297 8 0.036 0.033
Table 2 Atomic coordinates and equivalent isotropic displacement parameters (A˚2) for Li4Ti5O12 Atom Site Population x
y
z
Ueq
Li1 Li2 Ti1 O1
0.125 0.5 0.5 0.2626 (1)
0.125 0.5 0.5 0.2626 (1)
0.0097 (8) 0.01055 (6) 0.01055 (6) 0.0092 (1)
8a 16d 16d 32e
1.00 1.667 0.833 1.00
0.125 0.5 0.5 0.2626 (1)
Table 3 Anisotropic displacement parameters (A˚2) for Li4Ti5O12 Atom
U11
U22
U33
U12
U13
U23
Li1 Li2 Ti1 O1
0.010(1) 0.0106(1) 0.0106(1) 0.0092(2)
U11 U11 U11 U11
U11 U11 U11 U11
0 0.0012(1) 0.0012(1) 0.0017(3)
0 U12 U12 U12
0 U12 U12 U12
within 2%. A total of 1144 reflections were obtained within the limit of 2yo1351. All calculations were carried out using the Xtal3.5 program [4]. Structure factors were obtained after averaging the equivalent Bragg intensities, which were corrected for Lorentz and polarization factors, scale factors, and absorption and extinction effected. Neutral atomic scattering factors for all atoms were applied in the refinement. Table 1 summarizes the crystallographic and experimental data. In the following structure analysis, the space group with ¯ confirmed by the successful refinement, was adopted. Fd 3m The refinement was initiated with the reported atomic coordinates for Li4Ti5O12 [1]. The final atomic coordinates and the displacement parameters are listed in Tables 2 and 3, respectively.
ARTICLE IN PRESS 1456
K. Kataoka et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1454–1456
XRD [3,5]. In the present single-crystal study, the tetrahedral Li1–O1 and octahedral Ti1/Li2–O1 distances were determined to be 1.9963(6) and 1.9854(9) A˚, respectively. It should be noted that the U11 value (0.0106(1) A˚) for the octahedral Ti/Li2 atom, listed in Table 3, was slightly larger than that (0.00639(6) A˚) for the Ti atom in the spinel-type LiTi2O4 [6]. This fact may be explained by the Li substitution for the octahedral site.
References [1] A. Deschanvres, B. Raveau, Z. Sekkal, Mat. Res. Bull. 6 (1971) 699–704. [2] D. Tsubone, T. Hashimoto, K. Igarashi, T. Shimizu, J. Ceram. Soc. Japan 102 (1994) 180–184. [3] S. Scharner, W. Weppner, P. Schmid-Beurmann, J. Solid State Chem. 134 (1997) 170–181. [4] S.R. Hall, D.J. du Boulay, R. Olthof-Hazekamp (Eds.), Xtal3.5 System, University of Western Australia, Australia, 2000. [5] M. Nakayama, Y. Ishida, H. Ikuta, M. Wakihara, Solid State Ionics 117 (1999) 265–271. [6] Y. Takahashi, Y. Gotoh, J. Akimoto, J. Phys. Chem. Solid 63 (2002) 987–990. Fig. 2. Crystal structure of Li4Ti5O12.
The crystal structure of Li4Ti5O12 is shown in Fig. 2. The refined oxygen coordination parameter, x(O) ¼ 0.2626(1), was well consistent with the previous reports by powder