3 years ago

First-principles modeling of hafnia-based nanotubes

First-principles modeling of hafnia-based nanotubes
Andrei V. Bandura, Robert A. Evarestov, Alexey V. Kovalenko, Vitaly V. Porsev
Hybrid density functional theory calculations were performed for the first time on structure, stability, phonon frequencies, and thermodynamic functions of hafnia-based single-wall nanotubes. The nanotubes were rolled up from the thin free layers of cubic and tetragonal phases of HfO2. It was shown that the most stable HfO2 single-wall nanotubes can be obtained from hexagonal (111) layer of the cubic phase. Phonon frequencies have been calculated for different HfO2 nanolayers and nanotubes to prove the local stability and to find the thermal contributions to their thermodynamic functions. The role of phonons in stability of nanotubes seems to be negligible for the internal energy and noticeable for the Helmholtz free energy. Zone folding approach has been applied to estimate the connection between phonon modes of the layer and nanotubes and to approximate the nanotube thermodynamic properties. It is found that the zone-folding approximation is sufficiently accurate for heat capacity, but less accurate for entropy. The comparison has been done between the properties of TiO2, ZrO2, and HfO2. © 2017 Wiley Periodicals, Inc. Metal-oxide nanotubes of hafnia, with a small diameter, are expected to improve the sensitivity of chemical sensors and reinforce thermal stability and toughness of the materials analogous to carbon nanotubes. In this work, we perform the theoretical study of the structure and stability of various single-wall nanotubes obtained by folding of different hafnia layers. Calculations of phonon frequencies for nanotubes and parent nanolayer provide the analysis of thermal contributions to nanotube stability.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/jcc.24849

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