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Comparison of electronic structure of LiInO2 with NaInO2
Journal of Alloys and Compounds 359 (2003) 278–280
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Comparison of electronic structure of LiInO 2 with NaInO 2 a a a a a, Shintaro Kawakami , Masakuni Sasaki , Hiroshi Tabata , Hirokazu Shimooka , Shigemi Kohiki *, b c c Shigenori Matsushima , Masaoki Oku , Toetsu Shishido a
Department of Materials Science, Kyusyu Institute of Technology, Kita-kyusyu 804 -8550, Japan b Kitakyushu National College of Technology, Kita-kyusyu 803 -0985, Japan c Institute for Materials Research, Tohoku University, Sendai 980 -8577, Japan Received 27 July 2002; accepted 16 January 2003
Abstract Electronic structure of NaCl type LiInO 2 was compared experimentally and theoretically with that of a-NaFeO 2 type NaInO 2 to clarify the influences of Li–In direct interaction peculiar to LiInO 2 . Ultraviolet–visible diffuse reflectance spectrum of LiInO 2 , with the onset of absorption at 3.7 eV, was rather more simple than that of NaInO 2 accompanied by two small peaks in the band gap of 3.7 eV. Discrete variational-Xa calculations for the [Li 10 In 9 O 44 ] 512 and [Na 7 In 12 O 44 ] 452 model clusters depicted well the features of absorption spectra of LiInO 2 and a-NaInO 2 , respectively. The calculations also revealed that higher valence bands of LiInO 2 and NaInO 2 were dominated, respectively, by the Li 2s–In 5s bonding orbital with a large overlap population and the Na 3s,p–O 2p bonding orbital with a small overlap population, however, lower conduction bands in both LiInO 2 and NaInO 2 were formed by the In 5s–O 2p antibonding orbital. The experimental valence band spectrum of LiInO 2 , simply peaked at |4 eV below the valence band maximum, can be ascribed to overlapping of the Li 2s–In 5s bonding orbital with the In 5p–O 2p bonding orbital at around 23 eV in the density of states. 2003 Elsevier B.V. All rights reserved. Keywords: Crystal structure; Electronic structure; Discrete variational-Xa calculation
1. Introduction Electronic structure of the general formula ABO 2 (A5 alkali metal and B5trivalent metal) compounds is of interest in view of correlation between crystal structure and physical properties of solids. LiInO 2 (A5Li and B5In) crystal has the NaCl layer type structure with the I4 1 /amd space group [1]. In the tetragonal system Li, In, and O atoms occupy Wyckoff positions 8e (z /c50.5299), 4a (z /c50), and 8e (z /c50.2313), respectively [1]. In this splitting case the site occupancy of Li is 0.5. As illustrated in Fig. 1, the splitting case can be approximated well by the ideal case where Li atoms occupy 4b (z /c50.5) site with full-occupancy [1]. It is expected that direct interaction between Li and In atoms on the identical layer in the hexagonal system of LiInO 2 crystal adds peculiar characteristics to its electronic structure formed basically by the Li–O 6 and In–O 6 octahedral coordination fields. As also shown in Fig. 1 for convenience of comparison, *Corresponding author. Tel.: 181-93-884-3310; fax: 181-93-8843300. E-mail address: [email protected] (S. Kohiki). 0925-8388 / 03 / $ – see front matter 2003 Elsevier B.V. All rights reserved. doi:10.1016 / S0925-8388(03)00179-8
NaInO 2 (A5Na and B5In) crystallizes in the a-NaFeO 2 structure with the R3m [2] space group. In the hexagonal system Na, In, and O atoms occupy Wyckoff positions 3a,
Fig. 1. Schematic representation of (a) LiInO 2 and (b) NaInO 2 crystals.
S. Kawakami et al. / Journal of Alloys and Compounds 359 (2003) 278–280
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3b, and 6c, respectively [2]. Alternating layers of Na and In atoms, separated by a layer of O atoms, appear at every 0.5c in the c-axis direction. The electronic structure of NaInO 2 mirrors the Na–O 6 and In–O 6 octahedral coordination fields. Syntheses of LiInO 2 were reported [1,3,4], however, no report has been available on the electronic structure of LiInO 2 . We have already reported synthesis and characterization of NaInO 2 [5]. Thus, we compare experimentally and theoretically the electronic structure of LiInO 2 with that of NaInO 2 as a first step for development of new functional materials.
2. Experimental Single-phase LiInO 2 sample was synthesized by calcination of an equimolar mixture of In 2 O 3 and Li 2 CO 3 for 1 h at 1000 8C in air. We could not find any other peaks from LiInO 2 crystal in the X-ray diffraction pattern using a Rigaku CN2013 diffractometer with Cu Ka radiation. The ˚ which are in lattice constants were a54.3 2 and b59.3 4 A, ˚ reported agreement with those (a54.307 and b59.329 A) for LiInO 2 single crystal [1]. As shown in Fig. 2, the optical absorption spectrum of the LiInO 2 sample is rather more simple than that of NaInO 2 as a reference. LiInO 2 is transparent in visible region since there is no absorption below the absorption edge located at 3.7 eV, though NaInO 2 should reflect the absorption at around 2.4 and 3.3 eV in the band gap (3.7 eV). The valence band spectrum of the LiInO 2 sample in Fig. 3 showed no occupied state in the band gap and a single peaked structure at |4 eV below the valence band maximum. Thus, the simple absorption spectrum should correspond to the electron transition from the valence band to the conduction band of LiInO 2 crystal. A first-principles molecular orbital cluster calculation by the discrete variational (DV)-Xa method [6] was employed to clarify origins of the difference between the absorption spectra of LiInO 2 and NaInO 2 . The electronic structure of the model clusters was self-consistently calculated using numerical atomic basis functions. Used mini-
Fig. 2. Ultraviolet–visible diffuse reflectance spectrum of the (a) LiInO 2 sample by a JASCO V-550 spectrometer with a resolution of 0.002 eV, and (b) that of NaInO 2 reproduced from Ref. [5] for comparison.
Fig. 3. Valence band spectrum of the LiInO 2 sample by a Surface Science Laboratories SSX-100 spectrometer with monochromatized Al Ka source.
mal basis sets were 1s–2p for O, 1s–5p for In, 1s–2p for Li, and 1s–3p for Na. The cluster models with 63 atoms, [Li 10 In 9 O 44 ] 512 and [Na 7 In 12 O 44 ] 452 , were constructed on the basis of the crystal structures of NaCl and a-NaFeO 2 types, respectively. The lattice constants used were a5 ˚ for LiInO 2 [1], and a53.235 and 4.307 and b59.329 A ˚ b516.35 A for NaInO 2 [2]. The number of the sampling points was 500 per atom. The clusters were embedded in a Madelung potential generated by point charges outside the clusters. Total density of states (TDOS) and partial DOS (PDOS) were made by broadening the discrete energy eigenvalues with Gaussian functions of full width at halfmaximum of 0.3 eV.
3. Results and discussion TDOS and PDOS for [Li 10 In 9 O 44 ] 512 and [Na 7 In 12 O 44 ] 452 clusters are shown in Fig. 4(a) and (b), respectively. Energies are aligned so that the highest
Fig. 4. Total density of states (TDOS) and partial DOS (PDOS) of (a) [Li 10 In 9 O 44 ] 512 and (b) [Na 7 In 12 O 44 ] 452 clusters.
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occupied molecular orbital (HOMO) is set to zero. The DOS with negative and positive energies denote occupied and unoccupied levels, respectively. The valence band of LiInO 2 and NaInO 2 is dominated by the O 2p orbital component. The conduction band of LiInO 2 lower than 5 eV is mainly formed by the In 5s orbital components at 3.7 and 5 eV. The lower energy component at 3.7 eV of the DOS corresponds to the experimental band gap (3.7 eV) of LiInO 2 . The conduction band of NaInO 2 lower than 5 eV is formed by the components of the In 5s and 5p orbitals. The In 5s components at 2.0 and 2.7 eV mirror the experimental absorption peaks at around 2.4 and 3.3 eV, and the In 5p component at 4.0 eV reflects the experimental absorption begun at 3.7 eV. The calculated DOS for the [Li 10 In 9 O 44 ] 512 and [Na 7 In 12 O 44 ] 452 clusters depicted well the features of experimental absorption spectra of LiInO 2 and a-NaInO 2 , respectively. We have calculated the overlap population to examine in detail the electronic structure of LiInO 2 . The overlappopulation diagrams indicating the bonding contribution (right) and the antibonding contribution (left) of the [Li 10 In 9 O 44 ] 512 and [Na 7 In 12 O 44 ] 452 clusters are shown in Fig. 5(a) and (b), respectively. In both clusters the In–O interaction formed a bonding contribution in the upper
valence band and an antibonding contribution in the lower conduction band. Energy splitting between the In–O bonding and antibonding orbitals of the [Li 10 In 9 O 44 ] 512 cluster is |4 eV, which is much larger than that (¯2 eV) of the [Na 7 In 12 O 44 ] 452 cluster. For the [Na 7 In 12 O 44 ] 452 cluster the energy splitting between the In–O bonding and antibonding interaction corresponds to the onset of optical absorption. For the [Li 10 In 9 O 44 ] 512 cluster it is peculiar that the Li–In bonding interaction forms the HOMO component shallower than the In–O bonding component, thus the onset of optical absorption corresponds to the energy difference (¯3.5 eV) between the Li–In bonding and In–O antibonding orbitals. The population of the Li–In bonding component is almost equivalent to that of the In–O bonding component in the region of 21 to 25 eV. Therefore, the experimental valence band spectrum of LiInO 2 , simply peaked at |4 eV below the valence band maximum, can be ascribed to overlapping of the Li 2s–In 5s bonding orbital with the In 5p–O 2p bonding orbital at around 23 eV in the density of states. Judging from the shallowest Li–In bonding component with relatively large population in LiInO 2 crystal, substitution by trivalent 3d and / or 4f ions of In 31 ions may bring about spin glass and / or superparamagnetic behavior depending on the magnetic ion concentration since the magnetic ions can randomly distribute at the sites of non-magnetic cations.
Acknowledgements S.K. acknowledges the support of The Ogasawara Foundation for the Promotion of Science and Engineering for this study. Part of this work was performed under the inter-university cooperate research program of the Laboratory for Advanced Materials, the Institute for Materials Research, Tohoku University.
References
Fig. 5. Overlap-population diagrams of the (a) [Li 10 In 9 O 44 ] 512 and (b) [Na 7 In 12 O 44 ] 452 clusters.
[1] H. Glaum, S. Voigt, R. Hoppe, Z. Anorg. Allg. Chem. 598 / 599 (1991) 129. [2] G.E. Peterson, P.M. Bridenbaugh, J. Chem. Phys. 51 (1969) 2610. [3] R. Hoppe, B. Schepers, Z. Anorg. Allg. Chem. 295 (1958) 233. [4] M. Shimode, Y. Hayashi, M. Sasaki, K. Mukaida, J. Solid State Chem. 151 (2000) 16. [5] K. Fukuzaki, S. Kohiki, S. Matsushima, M. Oku, T. Hideshima, T. Watanabe, S. Takahashi, H. Shimooka, J. Mater. Chem. 10 (2000) 779. [6] H. Adachi, M. Tsukada, C. Satoko, J. Phys. Soc. Jpn. 45 (1978) 875.
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www.elsevier.com / locate / jallcom
Comparison of electronic structure of LiInO 2 with NaInO 2 a a a a a, Shintaro Kawakami , Masakuni Sasaki , Hiroshi Tabata , Hirokazu Shimooka , Shigemi Kohiki *, b c c Shigenori Matsushima , Masaoki Oku , Toetsu Shishido a
Department of Materials Science, Kyusyu Institute of Technology, Kita-kyusyu 804 -8550, Japan b Kitakyushu National College of Technology, Kita-kyusyu 803 -0985, Japan c Institute for Materials Research, Tohoku University, Sendai 980 -8577, Japan Received 27 July 2002; accepted 16 January 2003
Abstract Electronic structure of NaCl type LiInO 2 was compared experimentally and theoretically with that of a-NaFeO 2 type NaInO 2 to clarify the influences of Li–In direct interaction peculiar to LiInO 2 . Ultraviolet–visible diffuse reflectance spectrum of LiInO 2 , with the onset of absorption at 3.7 eV, was rather more simple than that of NaInO 2 accompanied by two small peaks in the band gap of 3.7 eV. Discrete variational-Xa calculations for the [Li 10 In 9 O 44 ] 512 and [Na 7 In 12 O 44 ] 452 model clusters depicted well the features of absorption spectra of LiInO 2 and a-NaInO 2 , respectively. The calculations also revealed that higher valence bands of LiInO 2 and NaInO 2 were dominated, respectively, by the Li 2s–In 5s bonding orbital with a large overlap population and the Na 3s,p–O 2p bonding orbital with a small overlap population, however, lower conduction bands in both LiInO 2 and NaInO 2 were formed by the In 5s–O 2p antibonding orbital. The experimental valence band spectrum of LiInO 2 , simply peaked at |4 eV below the valence band maximum, can be ascribed to overlapping of the Li 2s–In 5s bonding orbital with the In 5p–O 2p bonding orbital at around 23 eV in the density of states. 2003 Elsevier B.V. All rights reserved. Keywords: Crystal structure; Electronic structure; Discrete variational-Xa calculation
1. Introduction Electronic structure of the general formula ABO 2 (A5 alkali metal and B5trivalent metal) compounds is of interest in view of correlation between crystal structure and physical properties of solids. LiInO 2 (A5Li and B5In) crystal has the NaCl layer type structure with the I4 1 /amd space group [1]. In the tetragonal system Li, In, and O atoms occupy Wyckoff positions 8e (z /c50.5299), 4a (z /c50), and 8e (z /c50.2313), respectively [1]. In this splitting case the site occupancy of Li is 0.5. As illustrated in Fig. 1, the splitting case can be approximated well by the ideal case where Li atoms occupy 4b (z /c50.5) site with full-occupancy [1]. It is expected that direct interaction between Li and In atoms on the identical layer in the hexagonal system of LiInO 2 crystal adds peculiar characteristics to its electronic structure formed basically by the Li–O 6 and In–O 6 octahedral coordination fields. As also shown in Fig. 1 for convenience of comparison, *Corresponding author. Tel.: 181-93-884-3310; fax: 181-93-8843300. E-mail address: [email protected] (S. Kohiki). 0925-8388 / 03 / $ – see front matter 2003 Elsevier B.V. All rights reserved. doi:10.1016 / S0925-8388(03)00179-8
NaInO 2 (A5Na and B5In) crystallizes in the a-NaFeO 2 structure with the R3m [2] space group. In the hexagonal system Na, In, and O atoms occupy Wyckoff positions 3a,
Fig. 1. Schematic representation of (a) LiInO 2 and (b) NaInO 2 crystals.
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3b, and 6c, respectively [2]. Alternating layers of Na and In atoms, separated by a layer of O atoms, appear at every 0.5c in the c-axis direction. The electronic structure of NaInO 2 mirrors the Na–O 6 and In–O 6 octahedral coordination fields. Syntheses of LiInO 2 were reported [1,3,4], however, no report has been available on the electronic structure of LiInO 2 . We have already reported synthesis and characterization of NaInO 2 [5]. Thus, we compare experimentally and theoretically the electronic structure of LiInO 2 with that of NaInO 2 as a first step for development of new functional materials.
2. Experimental Single-phase LiInO 2 sample was synthesized by calcination of an equimolar mixture of In 2 O 3 and Li 2 CO 3 for 1 h at 1000 8C in air. We could not find any other peaks from LiInO 2 crystal in the X-ray diffraction pattern using a Rigaku CN2013 diffractometer with Cu Ka radiation. The ˚ which are in lattice constants were a54.3 2 and b59.3 4 A, ˚ reported agreement with those (a54.307 and b59.329 A) for LiInO 2 single crystal [1]. As shown in Fig. 2, the optical absorption spectrum of the LiInO 2 sample is rather more simple than that of NaInO 2 as a reference. LiInO 2 is transparent in visible region since there is no absorption below the absorption edge located at 3.7 eV, though NaInO 2 should reflect the absorption at around 2.4 and 3.3 eV in the band gap (3.7 eV). The valence band spectrum of the LiInO 2 sample in Fig. 3 showed no occupied state in the band gap and a single peaked structure at |4 eV below the valence band maximum. Thus, the simple absorption spectrum should correspond to the electron transition from the valence band to the conduction band of LiInO 2 crystal. A first-principles molecular orbital cluster calculation by the discrete variational (DV)-Xa method [6] was employed to clarify origins of the difference between the absorption spectra of LiInO 2 and NaInO 2 . The electronic structure of the model clusters was self-consistently calculated using numerical atomic basis functions. Used mini-
Fig. 2. Ultraviolet–visible diffuse reflectance spectrum of the (a) LiInO 2 sample by a JASCO V-550 spectrometer with a resolution of 0.002 eV, and (b) that of NaInO 2 reproduced from Ref. [5] for comparison.
Fig. 3. Valence band spectrum of the LiInO 2 sample by a Surface Science Laboratories SSX-100 spectrometer with monochromatized Al Ka source.
mal basis sets were 1s–2p for O, 1s–5p for In, 1s–2p for Li, and 1s–3p for Na. The cluster models with 63 atoms, [Li 10 In 9 O 44 ] 512 and [Na 7 In 12 O 44 ] 452 , were constructed on the basis of the crystal structures of NaCl and a-NaFeO 2 types, respectively. The lattice constants used were a5 ˚ for LiInO 2 [1], and a53.235 and 4.307 and b59.329 A ˚ b516.35 A for NaInO 2 [2]. The number of the sampling points was 500 per atom. The clusters were embedded in a Madelung potential generated by point charges outside the clusters. Total density of states (TDOS) and partial DOS (PDOS) were made by broadening the discrete energy eigenvalues with Gaussian functions of full width at halfmaximum of 0.3 eV.
3. Results and discussion TDOS and PDOS for [Li 10 In 9 O 44 ] 512 and [Na 7 In 12 O 44 ] 452 clusters are shown in Fig. 4(a) and (b), respectively. Energies are aligned so that the highest
Fig. 4. Total density of states (TDOS) and partial DOS (PDOS) of (a) [Li 10 In 9 O 44 ] 512 and (b) [Na 7 In 12 O 44 ] 452 clusters.
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S. Kawakami et al. / Journal of Alloys and Compounds 359 (2003) 278–280
occupied molecular orbital (HOMO) is set to zero. The DOS with negative and positive energies denote occupied and unoccupied levels, respectively. The valence band of LiInO 2 and NaInO 2 is dominated by the O 2p orbital component. The conduction band of LiInO 2 lower than 5 eV is mainly formed by the In 5s orbital components at 3.7 and 5 eV. The lower energy component at 3.7 eV of the DOS corresponds to the experimental band gap (3.7 eV) of LiInO 2 . The conduction band of NaInO 2 lower than 5 eV is formed by the components of the In 5s and 5p orbitals. The In 5s components at 2.0 and 2.7 eV mirror the experimental absorption peaks at around 2.4 and 3.3 eV, and the In 5p component at 4.0 eV reflects the experimental absorption begun at 3.7 eV. The calculated DOS for the [Li 10 In 9 O 44 ] 512 and [Na 7 In 12 O 44 ] 452 clusters depicted well the features of experimental absorption spectra of LiInO 2 and a-NaInO 2 , respectively. We have calculated the overlap population to examine in detail the electronic structure of LiInO 2 . The overlappopulation diagrams indicating the bonding contribution (right) and the antibonding contribution (left) of the [Li 10 In 9 O 44 ] 512 and [Na 7 In 12 O 44 ] 452 clusters are shown in Fig. 5(a) and (b), respectively. In both clusters the In–O interaction formed a bonding contribution in the upper
valence band and an antibonding contribution in the lower conduction band. Energy splitting between the In–O bonding and antibonding orbitals of the [Li 10 In 9 O 44 ] 512 cluster is |4 eV, which is much larger than that (¯2 eV) of the [Na 7 In 12 O 44 ] 452 cluster. For the [Na 7 In 12 O 44 ] 452 cluster the energy splitting between the In–O bonding and antibonding interaction corresponds to the onset of optical absorption. For the [Li 10 In 9 O 44 ] 512 cluster it is peculiar that the Li–In bonding interaction forms the HOMO component shallower than the In–O bonding component, thus the onset of optical absorption corresponds to the energy difference (¯3.5 eV) between the Li–In bonding and In–O antibonding orbitals. The population of the Li–In bonding component is almost equivalent to that of the In–O bonding component in the region of 21 to 25 eV. Therefore, the experimental valence band spectrum of LiInO 2 , simply peaked at |4 eV below the valence band maximum, can be ascribed to overlapping of the Li 2s–In 5s bonding orbital with the In 5p–O 2p bonding orbital at around 23 eV in the density of states. Judging from the shallowest Li–In bonding component with relatively large population in LiInO 2 crystal, substitution by trivalent 3d and / or 4f ions of In 31 ions may bring about spin glass and / or superparamagnetic behavior depending on the magnetic ion concentration since the magnetic ions can randomly distribute at the sites of non-magnetic cations.
Acknowledgements S.K. acknowledges the support of The Ogasawara Foundation for the Promotion of Science and Engineering for this study. Part of this work was performed under the inter-university cooperate research program of the Laboratory for Advanced Materials, the Institute for Materials Research, Tohoku University.
References
Fig. 5. Overlap-population diagrams of the (a) [Li 10 In 9 O 44 ] 512 and (b) [Na 7 In 12 O 44 ] 452 clusters.
[1] H. Glaum, S. Voigt, R. Hoppe, Z. Anorg. Allg. Chem. 598 / 599 (1991) 129. [2] G.E. Peterson, P.M. Bridenbaugh, J. Chem. Phys. 51 (1969) 2610. [3] R. Hoppe, B. Schepers, Z. Anorg. Allg. Chem. 295 (1958) 233. [4] M. Shimode, Y. Hayashi, M. Sasaki, K. Mukaida, J. Solid State Chem. 151 (2000) 16. [5] K. Fukuzaki, S. Kohiki, S. Matsushima, M. Oku, T. Hideshima, T. Watanabe, S. Takahashi, H. Shimooka, J. Mater. Chem. 10 (2000) 779. [6] H. Adachi, M. Tsukada, C. Satoko, J. Phys. Soc. Jpn. 45 (1978) 875.