Abstract
Transmission electron microscopy (polycrystalline electron diffraction, nanoelectron diffraction, and energy dispersive x-ray spectroscopy) was used to determine the dispersion of crystal phase and Nb dopants in mixed-phase (anatase and rutile) Ti1−xNbyO2 thin films prepared by reactive sputtering. When co-sputtering mixed-phase TiO2 with a dopant, it is unclear how the crystal phases are distributed within thin film structures, what the dominant interfaces are, and how the dopant is distributed within the crystal phases. In the Ti1−xNbyO2 films, anatase and rutile grains were found to be homogeneously dispersed indicating that anatase/rutile interfaces are the dominant interfaces. Anatase/rutile interfaces are a critical feature of mixed-phase materials which impart high reactivity to the composite. Nb homogeneously dispersed at low concentrations, but at high concentrations, Nb segregated in the rutile phase. There is an apparent threshold beyond which Nb segregates according to its higher solubility in rutile due to a better lattice fit.
Similar content being viewed by others
References
G.H. Li and K.A. Gray: The solid-solid interface: Explaining the high and unique photocatalytic reactivity of TiO2-based nanocomposite materials. Chem. Phys. 339, 173 (2007).
G.H. Li, L. Chen, M.E. Graham, and K.A. Gray: A comparison of mixed phase titania photocatalysts prepared by physical and chemical methods: The importance of the solid-solid interface. J. Mol. Catal. A: Chem. 275, 30 (2007).
G.H. Li, S. Ciston, Z.V. Saponjic, L. Chen, N.M. Dimitrijevic, T. Rajh, and K.A. Gray: Synthesizing mixed-phase TiO2 nanocomposites using a hydrothermal method for photo-oxidation and photoreduction applications. J. Catal. 253, 105 (2008).
L. Chen, M.E. Graham, G.H. Li, and K.A. Gray: Fabricating highly active mixed phase TiO2 photocatalysts by reactive dc magnetron sputter deposition. Thin Solid Films 515, 1176 (2006).
D.C. Hurum, K.A. Gray, T. Rajh, and M.C. Thurnauer: Recombination pathways in the Degussa P25 formulation of TiO2: Surface versus lattice mechanisms. J. Phys. Chem. B 109, 977 (2005).
D.C. Hurum, A.G. Agrios, K.A. Gray, T. Rajh, and M.C. Thurnauer: Explaining the enhanced photocatalytic activity of Degussa P25 mixed-phase TiO2 using EPR. J. Phys. Chem. B 107, 4545 (2003).
L. Chen, M.E. Graham, and K.A. Gray: Nitrogen stabilized reactive sputtering of optimized TiO2-x photocatalysts with visible light reactivity. J. Vac. Sci. Technol. A 27, 712 (2009).
P.A. DeSario, L. Chen, M.E. Graham, and K.A. Gray: Non-stoichiometric mixed-phase titania thin films: Red-shifted photoresponse and enhanced reactivity. J. Vac. Sci. Technol. A 29 (2011).
P.A. DeSario, M.E. Graham, R.M. Gelfand, and K.A. Gray: The effect of Nb substitution on the synthesis and photo-response of TiO2 thin films prepared by direct current magnetron sputtering. Thin Solid Films 519, 3562 (2011).
M. Yang, D. Kim, H. Jha, K. Lee, J. Paul, and P. Schmuki: Nb doping of TiO2 nanotubes for an enhanced efficiency of dye-sensitized solar cells. Chem. Commun. 47, 2032 (2011).
D. Kurita, S. Ohta, K. Sugiura, H. Ohta, and K. Koumoto: Carrier generation and transport properties of heavily Nb-doped anatase TiO2 epitaxial films at high temperatures. J. Appl. Phys. 100, 096105 (2006).
Y. Furubayashi, T. Hitosugi, Y. Yamamoto, K. Inaba, G. Kinoda, Y. Hirose, T. Shimada, and T. Hasegawa: A transparent metal: Nb-doped anatase TiO2. Appl. Phys. Lett. 86, 252101 (2005).
M. Sacerdoti, M.C. Dalconi, M.C. Carotta, B. Cavicchi, M. Ferroni, S. Colonna, and M.L. Di Vona: XAS investigation of tantalum and niobium in nanostructured TiO2 anatase. J. Solid State Chem. 177, 1781 (2004).
J. Arbiol, J. Cerda, G. Dezanneau, A. Cirera, F. Peiro, A. Cornet, and J.R. Morante: Effects of Nb doping on the TiO2 anatase-to-rutile phase transition. J. Appl. Phys. 92, 853 (2002).
M.A. Gillispie, M. van Hest, M.S. Dabney, J.D. Perkins, and D.S. Ginley: Rf magnetron sputter deposition of transparent conducting Nb-doped TiO2 films on SrTiO3. J. Appl. Phys. 101, 033125 (2007).
Y. Gao: In-situ IR and spectroscopic ellipsometric analysis of growth process and structural properties of Ti1-xNbxO2 thin films by metal-organic chemical vapor deposition. Thin Solid Films 346, 73 (1999).
L.E. Depero, L. Sangaletti, B. Allieri, E. Bontempi, R. Salari, M. Zocchi, C. Casale, and M. Notaro: Niobium-titanium oxide powders obtained by laser-induced synthesis: Microstructure and structure evolution from diffraction data. J. Mater. Res. 13, 1644 (1998).
D. Morris, Y. Dou, J. Rebane, C.E.J. Mitchell, R.G. Egdell, D.S.L. Law, A. Vittadini, and M. Casarin: Photoemission and STM study of the electronic structure of Nb-doped TiO2. Phys. Rev. B 61, 13445 (2000).
L. Sheppard, T. Bak, J. Nowotny, C.C. Sorrell, S. Kumar, A.R. Gerson, M.C. Barnes, and C. Ball: Effect of niobium on the structure of titanium dioxide thin films. Thin Solid Films 510, 119 (2006).
Y. Furubayashi, N. Yamada, Y. Hirose, Y. Yamamoto, M. Otani, T. Hitosugi, T. Shimada, and T. Hasegawa: Transport properties of d-electron-based transparent conducting oxide: Anatase Ti1-xNbxO2. J. Appl. Phys. 101, 093705 (2007).
Y. Furubayashi, T. Hitosugi, Y. Yamamoto, Y. Hirose, G. Kinoda, K. Inaba, T. Shimada, and T. Hasegawa: Novel transparent conducting oxide: Anatase Ti1-xNbxO2. Thin Solid Films 496, 157 (2006).
A.M. Ruiz, G. Dezanneau, J. Arbiol, A. Cornet, and J.R. Morante: Insights into the structural and chemical modifications of Nb additive on TiO2 nanoparticles. Chem. Mater. 16, 862 (2004).
Y. Gao, Y. Liang, and S.A. Chambers: Synthesis and characterization of Nb-doped TiO2(110) surfaces by molecular beam epitaxy. Surf. Sci. 348, 17 (1996).
S.A. Chambers, Y. Gao, S. Thevuthasan, Y. Liang, N.R. Shivaparan, and R.J. Smith: Molecular beam epitaxial growth and characterization of mixed (Ti,Nb)O2 rutile films on TiO2(100). J. Vac. Sci. Technol. A 14, 1387 (1996).
M. Valigi, D. Cordischi, G. Minelli, P. Natale, P. Porta, and C.P. Keijzers: A structural, thermogravimetric, magnetic, electron-spin resonance, and optical reflectance study of the NbO2-TiO2 system. J. Solid State Chem. 77, 255 (1988).
A. Ghicov, M. Yamamoto, and P. Schmuki: Lattice widening in niobium-doped TiO2 nanotubes: Efficient ion intercalation and swift electrochromic contrast. Angew. Chem. Int. Ed. 47, 7934 (2008).
S.A. Chambers, Y. Gao, Y.J. Kim, M.A. Henderson, S. Thevuthasan, S. Wen, and K.L. Merkle: Geometric and electronic structure of epitaxial NbxTi1-xO2 on TiO2(110). Surf. Sci. 365, 625 (1996).
D. Das Mulmi, T. Sekiya, N. Kamiya, S. Kurita, Y. Murakami, and T. Kodaira: Optical and electric properties of Nb-doped anatase TiO2 single crystal. J. Phys. Chem. Solids 65, 1181 (2004).
W.D. Sproul, M.E. Graham, M.S. Wong, S. Lopez, D. Li, and R.A. Scholl: Reactive direct-current magnetron sputtering of aluminium-oxide coatings. J. Vac. Sci. Technol. A 13, 1188 (1995).
L. Chen, M.E. Graham, G.H. Li, D.R. Gentner, N.M. Dimitrijevic, and K.A. Gray: Photoreduction of CO2 by TiO2 nanocomposites synthesized through reactive direct current magnetron sputter deposition. Thin Solid Films 517, 5641 (2009).
K. Sakata: Study of phase transition in NbxTi1-xO2. J. Phys. Soc. Jpn. 26, 1067 (1969).
B.O. Marinder and A. Magneli: Rutile-type phases in some systems of mixed transition metal dioxides. Acta Chem. Scand. 12, 1345 (1958).
M.R. Antonio, I. Song, and H. Yamada: Coordination and valence of niobium in TiO2–NbO2 solid-solutions through x-ray absorption-spectroscopy. J. Solid State Chem. 93, 183 (1991).
C.N. Zhang, M. Ikeda, T. Uchikoshi, J.G. Li, T. Watanabe, and T. Ishigaki: High-concentration niobium (V) doping into TiO2 nanoparticles synthesized by thermal plasma processing. J. Mater. Res. 26, 658 (2011).
H.Z. Zhang and J.F. Banfield: Phase transformation of nanocrystalline anatase-to-rutile via combined interface and surface nucleation. J. Mater. Res. 15, 437 (2000).
P.I. Gouma and M.J. Mills: Anatase-to-rutile transformation in titania powders. J. Am. Ceram. Soc. 84, 619 (2001).
S.B. Aldabergenova, A. Ghicov, S. Albu, J.M. Macak, and P. Schmuki: Smooth titania nanotubes: Self-organization and stabilization of anatase phase. J. Non-Cryst. Solids 354, 2190 (2008).
Acknowledgments
The financial support provided for this study from the NSF Grant no. CBET-0829146 is gratefully acknowledged. The characterization (XRD, TEM, and SEM) was performed in the JB Cohen x-ray facility and the NUANCE research centers at Northwestern University. We also thank Matthew K. Waltz for his assistance with image processing.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
DeSario, P.A., Wu, J., Grahm, M.E. et al. Nanoscale structure of Ti1−xNbyO2 mixed-phase thin films: Distribution of crystal phase and dopants. Journal of Materials Research 27, 944–950 (2012). https://doi.org/10.1557/jmr.2011.449
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1557/jmr.2011.449