Communication pubs.acs.org/IC
High-Pressure Polymorph of NaBiO3 Octavianti Naa,† Nobuhiro Kumada,*,† Akira Miura,‡ Takahiro Takei,† Masaki Azuma,§ Yoshihiro Kusano,∥ and Kengo Oka⊥ †
Center for Crystal Science and Technology, University of Yamanashi, 7-32 Miyamae-cho, Kofu 400-8511, Japan Faculty of Engineering, Hokkaido University, Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan § Materials and Structural Laboratory, Tokyo Institute of Technology 4259 Nagatsuta, Midori-ku Yokohama, Kanagawa 226-8503, Japan ∥ Department of Applied Arts and Design, Kurashiki University of Science and the Arts, 2640 Nishinoura, Tsurajima-cho, Kurashiki, Okayama 712-8505, Japan ⊥ Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan ‡
S Supporting Information *
The starting compound NaBiO3 with the ilmenite-type structure was prepared by heating NaBiO3·nH2O (Kanto Chemicals Co. Ltd.) in air at 200 °C for 3 h. The starting compound was charged into a gold capsule, treated at 6 GPa and 600 °C for 30 min with a cubic-anvil-type high-pressure apparatus. A small amount (0.1 mass%) of an oxidizing agent, KClO4, was added to prevent reduction of Bi5+. The pressure was calibrated by monitoring the electrical resistivity change of Bi and Ba.9 The temperature during the synthesis was measured with a Pt−Pt/Rh thermocouple. The products were identified by powder X-ray diffraction (XRD) using monochromated Cu Kα radiation. Electron diffraction patterns were taken with a Topcon EM-002B diffractometer. Synchrotron powder X-ray diffraction (SXRD) measurements were performed using beamline BL02B2 at the SPring-8 facility. The data were collected with a constant wavelength (λ = 0.42274 Å) at room temperature. RIETAN-FP10 was used for crystal structure refinement, and crystal structures were drawn using VESTA.11 Diffuse-reflectance spectra of the powder samples were measured with a JASCO V-550 spectrometer. The photocatalytic activities were examined for decomposition of phenol (20 ppm solution) under visible light with a cutoff wavelength of 420 nm. Time dependence of the phenol concentration was checked by liquid chromatography (Prominence LC-20AT, Shimadzu). The color of the sample changed from yellow ocher to dark red during high-pressure treatment. Figure 1 shows the electron diffraction patterns of β-NaBiO3. These patterns could be indexed with a hexagonal cell of a ≈ 10.0 Å and c ≈ 3.50 Å, and no
ABSTRACT: A new high-pressure polymorph of NaBiO3 (hereafter β-NaBiO3) was synthesized under the conditions of 6 GPa and 600 °C. The powder X-ray diffraction pattern of this new phase was indexed with a hexagonal cell of a = 9.968(1) Å and c = 3.2933(4) Å. Crystal structure refinement using synchrotron powder X-ray diffraction data led to RWP = 8.53% and RP = 5.55%, and the crystal structure was closely related with that of Ba 2 SrY6 O 12. No photocatalytic activity for phenol decomposition was observed under visible-light irradiation in spite of a good performance for its mother compound, NaBiO3. The optical band-gap energy of β-NaBiO3 was narrower than that of NaBiO3, which was confirmed with density of states curves simulated by first-principles density functional theory calculation.
T
he AMO3 ilmenite-type oxides are known to have two kinds of chemical compositions: A2+M4+O3 and A+M5+O3.1 The mineral ilmenite FeTiO3 is the former group, and most ilmenitetype oxides belong to this group. The latter group contains NaBiO3,2 NaSbO3,3 NaNbO3,4 etc. NaBiO3 is prepared by dehydration of NaBiO3·nH2O, and the crystal structure of the ilmenite polymorph of NaBiO3 was refined using neutron diffraction data.5 Although NaNbO3 has an orthorhombic perovskite-type structure, an ilmenite-type polymorph can be prepared by hydrothermal reaction.4 In the case of CdTiO3, an ilmenite-type structure is a low-temperature form, and it transforms to a perovskite-type structure at about 900 °C.6 Ilmenite-type NaSbO3 transforms to a perovskite-type structure under high pressure at 10.5 GPa and 1150 °C.7 The mediumsized cations, Na+ and Cd2+, whose Shannon ionic radii are 1.02 and 0.95 Å,8 respectively, for six-coordination, can be found in both ilmenite- and perovskite-type structures. We expected to obtain a perovskite-type NaBiO3 under high-pressure conditions; however, a new polymorphic form actually appeared. In this paper, we will describe the preparation and crystal structure for a high-pressure polymorph of NaBiO3 and compare the photocatalytic activities of the ilmenite-type and high-pressure polymorph of NaBiO3. © XXXX American Chemical Society
Figure 1. Electron diffraction patterns of β-NaBiO3. Received: April 18, 2016
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DOI: 10.1021/acs.inorgchem.6b00947 Inorg. Chem. XXXX, XXX, XXX−XXX
Communication
Inorganic Chemistry systematic absence was observed. Rietveld refinements of βNaBiO3 were carried out for eight possible space groups: P6, P6̅, P6/m, P622, P6mm, P6̅m2, P6̅2m, and P6/mmm. Reasonable R values (RWP = 8.53%; RP = 5.55%) using SXRD data were found by using the space group P6̅ (No. 174), and refinement with the other space groups was unsuccessful. The Rietveld refinement profile of β-NaBiO3 is shown in Figure S1. The lattice parameters were calculated to be a = 9.968(1) Å and c = 3.2933(4) Å. The density (6.74 g/cm3) of β-NaBiO3 is higher than that (6.50 g/ cm3) of the ilmenite-type structure. In the case of NaSbO3, the density (5.706 g/cm3) of the perovskite-type structure is significantly higher than that (4.976 g/cm3) of the ilmenitetype one.7 The crystal data are summarized in Table S1, and the atomic parameters and selected interatomic distances are shown in Tables S2 and S3, respectively. The crystal structure of βNaBiO3 is shown in Figure 2a. This compound has a tunnel
The mother compound, NaBiO3, had good photocatalytic activity for phenol decomposition under visible-light irradiation;14 however, β-NaBiO3 exhibited no photocatalytic activity under the same experimental conditions as those shown in Figure 3. Figure 4 indicates optical absorption spectra for NaBiO3 and β-
Figure 3. Photocatalytic activities of NaBiO3 and β-NaBiO3.
Figure 4. UV−vis absorption spectra (a) and Tauc plot for the estimation (b) for NaBiO3 and β-NaBiO3.
NaBiO3. The band-gap energies were estimated from the dependence of (αhν)2 on energy and hν (Tauc plot) on the assumption of direct transitions.14b The Tauc plot estimation of the band-gap energy for polycrystalline samples was reported to give accurate values for monazite-type oxides.15 The band-gap energies for NaBiO3 and β-NaBiO3 were calculated to be 2.4 and 1.7 eV, respectively. This difference corresponds to the change of color during the high-pressure treatment. The disappearance of photocatalytic activity is thought to be caused by a decrease of the band-gap energy. This result is confirmed with the density of states (DOS) calculation, as shown in Figure S2. The calculated band-gap energy in β-NaBiO3 is smaller than that in NaBiO3. A similar band-gap collapse by high-pressure phase transition is observed in NaSbO37 and InTaO4.16 Recently, we reported photocatalytic activity for new bismuthates containing Bi5+.17,18 Two types of cadmium bismuthates exhibited no photocatalytic activity,14 although calcium and lead bismuthates and their thermally treated samples had photocatalytic activity.18 The band-gap energies of the former compounds were 1.0 and 1.2 eV, and those of the latter compounds ranged from 1.8 to 2.5 eV. Those compounds have PbSb2O6-type or fluorite-type structure, which is quite different from that of β-NaBiO3. It is likely that the range of 1.7−1.8 eV for the band-gap energy is the threshold value for photocatalytic activity of bismuthates containing Bi5+.
Figure 2. Crystal structures of β-NaBiO3 (a) and BaSr2Y6O12 (b).
structure formed by edge-sharing of (Bi2/3Na1/3)O6 octahedra, and two types of tunnels are running along the c axis. These edgesharing octahedra are strongly distorted compared with those in the mother compound or trirutile-type MgBi2O6.12 A Na atom is sited at one of the two tunnels, and another larger tunnel has no atom. This crystal structure is similar to that of BaSr2Y6O12,13 in which the tunnel structure is formed by edge-sharing of YO6 octahedra, and the Ba and Sr atoms are sited at two types of tunnels, as shown in Figure 2. Although two types of tunnels are fully occupied by two types of alkaline-earth metals in BaSr2Y6O12, a larger tunnel in β-NaBiO3 is vacant. β-NaBiO3 possesses no large atoms, which can be accommodated in the larger tunnel. Two types of crystallographic sites for Na atoms are surrounded by six O atoms with trigonal-prism coordination. The interatomic distances between the Na and O atoms are 2.24(9) and 2.60(6) Å. The mean interatomic distances between the Bi or Na and O atoms in two types of octahedral sites are 2.19 and 2.26 Å. These values are slightly longer than that (2.116 Å) of the Bi−O distance in the mother compound. This comes from the incorporation of a Na atom in the octahedral sites. B
DOI: 10.1021/acs.inorgchem.6b00947 Inorg. Chem. XXXX, XXX, XXX−XXX
Communication
Inorganic Chemistry
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(15) Errandonea, D.; Muňoz, A.; Rodríguez-Hernández, P.; Proctor, J. E.; Sapiňa, F.; Bettinelli, M. Inorg. Chem. 2015, 54, 7524−7535. (16) Errandonea, D.; Popescu, C.; Garg, A. B.; Botella, P.; MartinezGarcía, D.; Pellicer-Porres, J.; Rodríguez-Hernández, P.; Muňoz, A.; Cuenca-Gotor, V.; Sans, J. Phys. Rev. B: Condens. Matter Mater. Phys. 2016, 93, 035204-1−035204-12. (17) Kumada, N.; Miura, A.; Takei, T.; Nishimoto, S.; Kameshima, Y.; Miyake, M.; Kuroiwa, Y.; Moriyoshi, C. J. Asian Ceram. Soc. 2015, 3, 251−254. (18) Kumada, N.; Xu, N.; Miura, A.; Takei, T. J. Ceram. Soc. Jpn. 2014, 122, 509−512.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b00947. Crystallographic data, Rietveld refinement profile, and DOS calculation for β-NaBiO3 (PDF) CIF file (CIF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Author Contributions
N.K. conducted this research work in collaboration with A.M., T.T., and M.A. O.N. prepared powder samples and performed laboratory XRD measurements. Y.K. performed TEM observation. O.N. performed high-pressure experiments with help from M.A. and K.O. O.N., M.A., and K.O. performed SXRD measurements. T.T. performed computational calculations. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The experiments at SPring-8 were performed with the approval of the Japan Synchrotron Radiation Research Institute (Proposal 2013A1299). This work was partially supported by the Collaborative Research Project of Materials and Structures Laboratory, Tokyo Institute of Technology, and by JSPS KAKENHI Grant 26420678.
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REFERENCES
(1) Wells, A. F. Structural Inorganic Chemistry ,4th ed.; Oxford University Press: Oxford, U.K., 1975; p 479. (2) (a) Aurivillius, B.; Malmström, B. G.; Haraldsen, H.; Prydz, H. Acta Chem. Scand. 1955, 9, 1219−1221. (b) Kumada, N.; Kinomura, N.; Muto, F. Nippon Seramikkusu Kyokai Gakujutsu Ronbunshi 1990, 98, 384−388. (3) Wang, B.; Chen, S. C.; Greenblatt, M. J. Solid State Chem. 1994, 108, 184−188. (4) (a) Kinomura, N.; Kumata, N.; Muto, F. Mater. Res. Bull. 1984, 19, 299−304. (b) Modeshia, D. R.; Darton, R. J.; Ashbrook, S. E.; Walton, R. I. Chem. Commun. 2009, 68−70. (5) Kumada, N.; Kinomura, N.; Sleight, A. W. Mater. Res. Bull. 2000, 35, 2397−2402. (6) (a) Posnjak, E.; Barth, T. F. W. Z. Kristallogr. - Cryst. Mater. 1934, 88, 271−280. (b) Kennedy, B. J.; Zhou, Q.; Avdeev, M. J. Solid State Chem. 2011, 184, 2987−2993. (7) Mizoguchi, H.; Woodward, P. M.; Byeon, S. H.; Parise, J. B. J. Am. Chem. Soc. 2004, 126, 3175−3184. (8) Shannon, R. D. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, 32, 751−767. (9) Encyclopedia of Inorganic and Bioinorganic Chemistry; John Wiley and Sons, Inc.: New York, 2014. (10) Izumi, F.; Momma, K. Solid State Phenom. 2007, 130, 15−20. (11) Momma, K.; Izumi, F. J. Appl. Crystallogr. 2008, 41, 653−658. (12) Kumada, N.; Takahashi, N.; Kinomura, N.; Sleight, A. W. Mater. Res. Bull. 1997, 32, 1003−1008. (13) Schulze, A. R.; Mueller-Buschbaum, H. Z. Naturforsch., B: J. Chem. Sci. 1981, 36, 837−839. (14) (a) Kako, T.; Zou, Z.; Katagiri, M.; Ye, J. Chem. Mater. 2007, 19, 198−202. (b) Takei, T.; Haramoto, R.; Dong, Q.; Kumada, N.; Yonesaki, Y.; Kinomura, N.; Mano, T.; Nishimoto, S.; Kameshima, Y.; Miyake, M. J. Solid State Chem. 2011, 184, 2017−2022. C
DOI: 10.1021/acs.inorgchem.6b00947 Inorg. Chem. XXXX, XXX, XXX−XXX
