Size-Dependent Pressure-Induced Amorphization in Nanoscale ${\mathrm{TiO}}_{2}$

Size-Dependent Pressure-Induced Amorphization in Nanoscale ${TiO}_{2}$

Varghese Swamy, Alexei Kuznetsov, Leonid S. Dubrovinsky, Paul F. McMillan, Vitali B. Prakapenka, Guoyin Shen, and Barry C. Muddle

Phys. Rev. Lett. 96, 135702 – Published 5 April 2006

Abstract

We investigated the size-dependent high-pressure phase transition behavior of nanocrystalline anatase ${TiO}_{2}$ with synchrotron x-ray diffraction and Raman spectroscopy to 45 GPa at ambient temperature. Pressure-induced amorphization results in a high-density amorphous (HDA) form when the starting crystallite size is $< 10 nm$ . The HDA- ${TiO}_{2}$ transforms to a low-density amorphous form at lower pressures. Harnessing the nanometer length scale thus provides a new window for experimental investigation of amorphization in poor glass formers and a synthesis route for new amorphous materials.

Received 16 January 2006

DOI:https://doi.org/10.1103/PhysRevLett.96.135702

Authors & Affiliations

Varghese Swamy^1,*, Alexei Kuznetsov², Leonid S. Dubrovinsky², Paul F. McMillan^3,†, Vitali B. Prakapenka⁴, Guoyin Shen⁴, and Barry C. Muddle¹

¹Department of Materials Engineering, Monash University, P.O. Box 69M, Victoria 3800, Australia
²Bayerisches Geoinstitut, Universität Bayreuth, Bayreuth D-95440, Germany
³Department of Chemistry and Materials Chemistry Centre, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom
⁴Consortium for Advanced Radiation Sources, University of Chicago, Chicago, Illinois 60637, USA

^*Corresponding author. Electronicaddress:Varghese.Swamy@eng.monash.edu.au
^†Also at Davy-Faraday Research Laboratory, Royal Institution, 21 Albemarle Street, London W1X 4BS, UK.

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Vol. 96, Iss. 13 — 7 April 2006

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Figure 1
(a) Size-dependent pressure stability of $n c − t − {TiO}_{2}$ (modified after Ref. 7). The average transition pressures of the three phase transition regimes are shown. Nanocrystals of size $< 10 nm$ undergo PIA and remain amorphous ( $a − {TiO}_{2}$ ) upon further compression and decompression. Approximately $12 - 50 nm$ crystallites transform to $m − {TiO}_{2}$ upon compression, which then transforms to $o − {TiO}_{2}$ on decompression. Coarser crystallites transform directly to $o − {TiO}_{2}$ . The compression-decompression paths of the two samples of this study are indicated. (b) Known stable $P − T$ relations [9, 19, 20, 21] in the bulk ${TiO}_{2}$ system.Reuse & Permissions
Figure 2
Synchrotron XRD data obtained during compression and decompression of $n c − t − {TiO}_{2}$ particles. (a) PIA takes place in sample B (8 nm particles) at $\sim 20 GPa$ (left column). The amorphous phase is recovered to ambient conditions, but subtle changes in the XRD pattern, including increased ordering at low pressures, are observed upon decompression (right column). (b) Integrated XRD data of sample B during compression or decompression runs. Anatase ( $t − {TiO}_{2}$ ) reflections are indicated by “up” arrow; arrows labeled “ $o$ ” and “ $g$ ” represent $o − {TiO}_{2}$ and Au diffraction positions at 0 GPa. (c) Integrated XRD data of sample A (4 nm) obtained during decompression. Calculated XRD spectra (for wavelength $λ = 0.3344 Å$ ) of $o − {TiO}_{2}$ and $m − {TiO}_{2}$ are given for comparison. The 0 GPa (outside the DAC) spectrum of pressure-amorphized sample A exhibits diffuse scattering background characteristic of a highly disordered material, with perhaps structural similarity to $o − {TiO}_{2}$ . Electron diffraction (d), however, confirms the amorphous nature of the material at a length scale of that of a crystalline unit cell ( $\sim 1 nm$ ).Reuse & Permissions
Figure 3
Raman spectra of sample A measured during compression and decompression. (a) Compression. The bottom three spectra show the pressure evolution of anatase ( $n c − t − {TiO}_{2}$ ) Raman modes. PIA occurs at $P > 20 GPa$ . (b) During decompression, spectral changes indicate structural modification within the $a − {TiO}_{2}$ materials produced via PIA.Reuse & Permissions
Figure 4
Comparison of low- and high- $P$ Raman spectra of $a − {TiO}_{2}$ with those of crystalline polymorphs. (a) Raman spectrum of $a − {TiO}_{2} / LDA$ (sample B) decompressed to 0 GPa. (b) Raman spectrum of $a − {TiO}_{2} / HDA$ (sample A) at 34 GPa. (c) Raman spectrum of $n c − o − {TiO}_{2}$ ( $\sim 11 nm$ ) at 0 GPa. (d) Raman spectrum of $n c − m − {TiO}_{2}$ ( $\sim 30 nm$ ) obtained at 34 GPa [26].Reuse & Permissions

Physical Review Letters

Size-Dependent Pressure-Induced Amorphization in Nanoscale TiO2

Varghese Swamy, Alexei Kuznetsov, Leonid S. Dubrovinsky, Paul F. McMillan, Vitali B. Prakapenka, Guoyin Shen, and Barry C. Muddle

Phys. Rev. Lett. 96, 135702 – Published 5 April 2006

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Size-Dependent Pressure-Induced Amorphization in Nanoscale ${TiO}_{2}$