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Crystals 2018, 8(2), 15; https://doi.org/10.3390/cryst8020015

Theoretical and Experimental Investigations into Novel Oxynitride Discovery in the GaN-TiO2 System at High Pressure

1
Department of Chemistry, State University of New York, Stony Brook, NY 11794, USA
2
Department of Geosciences, State University of New York, Stony Brook, NY 11794, USA
3
Center for Materials by Design, Institute for Advanced Computational Science, State University of New York, Stony Brook, NY 11794, USA
4
Mineral Physics Institute, Stony Brook University, Stony Brook, New York 11794, USA
5
Skolkovo Institute of Science and Technology, Skolkovo Innovation Center, 3 Nobel Street, Moscow 143026, Russia
6
Department of Problems of Physics and Energetics, Moscow Institute of Physics and Technology, 9 Institutskiy Lane, Dolgoprudny City, Moscow 141700, Russia
7
International Center for Materials Design, Northwestern Polytechnical University, Xi’an 710072, China
*
Authors to whom correspondence should be addressed.
Received: 31 December 2017 / Revised: 19 January 2018 / Accepted: 19 January 2018 / Published: 23 January 2018
(This article belongs to the Special Issue Non-Ambient Crystallography)
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Abstract

We employed ab initio evolutionary algorithm USPEX to speed up the discovery of a novel oxynitride in the binary system of GaN-TiO2 using high-pressure synthesis. A 1:2 mixture of GaN and nanocrystalline TiO2 (anatase) was reacted under 1 GPa of pressure and at 1200 °C in a piston cylinder apparatus to produce a mixture of TiO2 (rutile) and an unknown phase. From the initial analysis of high resolution neutron and X-ray diffraction data, it is isomorphic with monoclinic V2GaO5 with a unit cell composition of Ga10Ti8O28N2 with the following parameters: monoclinic, space group C2/m, a = 17.823(1) Å, b = 2.9970(1) Å, c = 9.4205(5) Å, β = 98.446(3)°; Volume = 497.74(3) Å3. Further, a joint rietveld refinement revealed two distinct regimes—A Ti-rich block and a Ga-rich block. The Ti-rich block consists of four edge-shared octahedra and contains a site which is about 60% occupied by N; this site is bonded to four Ti. The remainder of the block consists of edge linked Ti-octahedral chains linked to the TiN/TiO fragments at octahedral corners partially occupied by nitrogen. The Ga-block contains two symmetry independent octahedral sites, occupied mostly by Ga, and a pure Ga-centered tetrahedral site bonded mostly to oxygen. View Full-Text
Keywords: oxynitrides; water splitting; high pressure; crystal structure prediction; USPEX oxynitrides; water splitting; high pressure; crystal structure prediction; USPEX
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    Description: The COD entry 3000168 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via http://www.crystallography.net/cod/search.html.
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James, A.; Esfahani, M.M.D.; Woerner, W.R.; Sinclair, A.; Ehm, L.; Oganov, A.R.; Parise, J.B. Theoretical and Experimental Investigations into Novel Oxynitride Discovery in the GaN-TiO2 System at High Pressure. Crystals 2018, 8, 15.

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