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Issue 8, 2016
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Stabilizing metastable tetragonal HfO2 using a non-hydrolytic solution-phase route: ligand exchange as a means of controlling particle size

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Abstract

There has been intense interest in stabilizing the tetragonal phase of HfO2 since it is predicted to outperform the thermodynamically stable lower-symmetry monoclinic phase for almost every application where HfO2 has found use by dint of its higher dielectric constant, bandgap, and hardness. However, the monoclinic phase is much more thermodynamically stable and the tetragonal phase of HfO2 is generally accessible only at temperatures above 1720 °C. Classical models comparing the competing influences of bulk free energy and specific surface energy predict that the tetragonal phase of HfO2 ought to be stable at ultra-small dimensions below 4 nm; however, these size regimes have been difficult to access in the absence of synthetic methods that yield well-defined and monodisperse nanocrystals with precise control over size. In this work, we have developed a modified non-hydrolytic condensation method to precisely control the size of HfO2 nanocrystals with low concentrations of dopants by suppressing the kinetics of particle growth by cross-condensation with less-reactive precursors. This synthetic method enables us to stabilize tetragonal HfO2 while evaluating ideas for critical size at which surface energy considerations surpass the bulk free energy stabilization. The phase assignment has been verified by atomic resolution high angle annular dark field images acquired for individual nanocrystals.

Graphical abstract: Stabilizing metastable tetragonal HfO2 using a non-hydrolytic solution-phase route: ligand exchange as a means of controlling particle size

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Publication details

The article was received on 11 Apr 2016, accepted on 03 May 2016 and first published on 03 May 2016


Article type: Edge Article
DOI: 10.1039/C6SC01601D
Chem. Sci., 2016,7, 4930-4939
  • Open access: Creative Commons BY license
    All publication charges for this article have been paid for by the Royal Society of Chemistry

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    Stabilizing metastable tetragonal HfO2 using a non-hydrolytic solution-phase route: ligand exchange as a means of controlling particle size

    G. R. Waetzig, S. W. Depner, H. Asayesh-Ardakani, N. D. Cultrara, R. Shahbazian-Yassar and S. Banerjee, Chem. Sci., 2016, 7, 4930
    DOI: 10.1039/C6SC01601D

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