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Materials science

The hardest known oxide

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Abstract

A material as hard as diamond or cubic boron nitride has yet to be identified1,2,3,4,5,6, but here we report the discovery of a cotunnite-structured titanium oxide which represents the hardest oxide known. This is a new polymorph of titanium dioxide, where titanium is nine-coordinated to oxygen in the cotunnite (PbCl2) structure. The phase is synthesized at pressures above 60 gigapascals (GPa) and temperatures above 1,000 K and is one of the least compressible and hardest polycrystalline materials to be described.

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Figure 1: Example of profile-fitted X-ray diffraction data obtained from a cotunnite-structured TiO2 sample (space group Pnma, Z = 4, a = 5.163(2) Å, b = 2.989(1) Å, c = 5.966(2) Å, Ti (0.264(1); 0.25; 0.110(1)), O1 (0.346(1); 0.25; 0.422(1)), O2 (0.012(2); 0.75; 0.325(1)); numbers in parentheses, s.d.).

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Correspondence to L. S. Dubrovinsky.

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Dubrovinsky, L., Dubrovinskaia, N., Swamy, V. et al. The hardest known oxide. Nature 410, 653–654 (2001). https://doi.org/10.1038/35070650

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