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Electron-pinned defect-dipoles for high-performance colossal permittivity materials

Abstract

The immense potential of colossal permittivity (CP) materials for use in modern microelectronics as well as for high-energy-density storage applications has propelled much recent research and development. Despite the discovery of several new classes of CP materials, the development of such materials with the required high performance is still a highly challenging task. Here, we propose a new electron-pinned, defect-dipole route to ideal CP behaviour, where hopping electrons are localized by designated lattice defect states to generate giant defect-dipoles and result in high-performance CP materials. We present a concrete example, (Nb+In) co-doped TiO2 rutile, that exhibits a largely temperature- and frequency-independent colossal permittivity (> 104) as well as a low dielectric loss (mostly < 0.05) over a very broad temperature range from 80 to 450 K. A systematic defect analysis coupled with density functional theory modelling suggests that ‘triangular’ In23+VO••Ti3+ and ‘diamond’ shaped Nb25+Ti3+ATi (A = Ti3+/In3+/Ti4+) defect complexes are strongly correlated, giving rise to large defect-dipole clusters containing highly localized electrons that are together responsible for the excellent CP properties observed in co-doped TiO2. This combined experimental and theoretical work opens up a promising feasible route to the systematic development of new high-performance CP materials via defect engineering.

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Figure 1: Frequency dependences of the dielectric properties.
Figure 2: Temperature dependences of the dielectric and conductive properties.
Figure 3: Valence states and defect characterizations of (Nb+In) doped TiO2.
Figure 4: Structure of the In and Nb defect complexes.

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Acknowledgements

W.H., Y.L., R.L.W., A.S. and J.W.L. acknowledge the supports of the Australian Research Council (ARC) in the form of Discovery and Linkage Projects, and of the Australian National University Connect Ventures in the form of Discovery Translation Fund. Y.L. and T.J.F. also appreciate support from the ARC Future Fellowships program. The DFT calculations performed in this work were undertaken using the NCI National Facility in Canberra, Australia, which is supported by the Australian Commonwealth Government. The authors acknowledge AMMRF facilities.

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W.H., Y.L., R.L.W. and T.J.F. contributed to the preparation of manuscript. Y.L. initiated this research, and planned and coordinated all experimental works. Y.L. and R.L.W. were involved in all discussions regarding the data interpretation, structural analyses and development of the defect model. W.H., A.S. and M.K. were involved in the fabrication of the samples with different compositions and synthesizing conditions. W.H. conducted the characterization of the dielectric and conductive properties. W.H. and P.S. performed EPR measurement and analysis. W.H. and B.G. carried out XPS measurement and analysis. T.J.F. performed the DFT calculation and defect modelling. L.N. contributed to the defect design. J.S. contributed to the discussion about the defect model. W.H. carried out the microstructural analysis via SEM with backscattering image and a careful EDX analysis with the assistance of H.C. and F.B. W.H., J.W-L. and Y.L. carried out the dielectric measurements down to ~ 10 K.

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Correspondence to Yun Liu.

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Hu, W., Liu, Y., Withers, R. et al. Electron-pinned defect-dipoles for high-performance colossal permittivity materials. Nature Mater 12, 821–826 (2013). https://doi.org/10.1038/nmat3691

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