The hardest known oxide

Dubrovinsky, Leonid; Dubrovinskaia, Natalia; Swamy, Varghese; Muscat, J.; Harrison, N. M.; Ahuja, Rajeev; Holm, B.; Johansson, Börje

doi:10.1038/35070650

Cited by 321 publications

(274 citation statements)

References 12 publications

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“…Among new III-group high-pressure phases, noteworthy are those of the TiO 2 , RuO 2 , OsO 2 and ZrO2 oxides with the high values of moduli and the hardness of 20 -40 GPa [40] (Fig.15a,b). Examples of superhard high-pressure phases also are provided by new modifications of TaN and ReC (H~ 25 GPa and 35 GPa, respectively) [26].…”

Section: Superhard Materials: More Equal Than Othersmentioning

confidence: 99%

High-pressure synthesized materials: treasures and hints

Бражкин

2007

High Pressure Research

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The present review covers the production of new materials under high pressures. A primary limitation on the use of pressures higher than 1 GPa is a small volume and mass of a produced material. Therefore, despite an extremely wide range of new high-pressure synthesized substances with unique properties, synthesis on an commercial scale is applied up to now only to obtain superhard materials, this real treasure of today's industry. At the same time, high-pressure experiments often give material scientists a hint at what new intriguing substances can exist in principle. This is true for new superhard, semiconducting, magnetic, superconducting and optical materials already synthesized under pressure, and as well as for a large number of hypothetic new polymers from low-Z elements. Many of new materials, including the above polymers, may exist in the metastable form at normal pressure at sufficiently high temperatures.Keywords: high pressure, materials synthesis, metastable phases 1 IntroductionThe synthesis of materials under high pressure is a vast area of physics, chemistry and engineering. Should you browse the Internet to search "high pressure synthesis", the web search engines, for example, Google, would respond with over 10 mln links, making it absolutely impossible to write any comprehensive review on this topic. For this same reason, neither it is possible to list all relevant references. The purpose of this paper is to present the author's personal view on the state of art and prospects of the production of new materials by using highpressure synthesis, and to complement already existing reviews, for example [1,2]. It should be noted that a number of publications, for example [2], discuss a comparatively narrow range of materials synthesized under pressure. Other publications, for example [1], also focus on anomalous properties of materials in a strongly compressed state, although most of materials with such properties cannot be retained at normal pressure, hence, they are not directly related to the subject under consideration. In addition, the behavior of materials in a strongly compressed state has also been extensively covered in scientific literature (for example, see [3]).For physicists, the history of a high-pressure research is first of all associated with P.W. Bridgman, a 1946 Nobel Prize Laureate "for the invention of an apparatus to produce extremely high pressures, and for the discoveries he made therewith in the field of high pressure physics". Nowadays high-pressure synthesis of new materials is primarily associated with a successful synthesis of superhard materials -diamond and cubic boron nitride -in the second half of the 20 th century. At the same time, the pressures 1 -10 3 MPa have been already in use for more than a century in chemistry for the industrial production of materials. What's more, the development of relevant engineering procedures has been more than once rewarded with a Nobel Prize in chemistry. In 1918, F. Haber won the Nobel Prize "for the synthesis of ammonia from its el...

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Section: Superhard Materials: More Equal Than Othersmentioning

confidence: 99%

High-pressure synthesized materials: treasures and hints

Бражкин

2007

High Pressure Research

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“…2 Stoichiometric TiO 2 has four polymorphs: rutile, anatase, brookite and cotunnite. 3 Nearly stoichiometric rutile shows two homologous series of planar bulk defects that self-assemble into crystallographic shear planes: Ti n O 2n À 1 with (4 o n o 10) based on {121} directed planes, and (16 o n o B37) based on {132}. [4][5][6] Stable reduced phases down to Ti 4 O 7 , a crystal structure with promising electrical characteristics, 7 can also be formed.…”

Section: Introductionmentioning

confidence: 99%

Surface and interstitial Ti diffusion at the rutile TiO2(110) surface

Mulheran

Nolan

Browne

et al. 2010

Phys. Chem. Chem. Phys.

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Diffusion of Ti through the TiO 2 (110) rutile surface plays a key role in the growth and reactivity of TiO 2 . To understand the fundamental aspects of this important process, we present an analysis of the diffusion of Ti ad-species at the stoichiometric TiO 2 (110) surface using complementary computational methodologies of density functional theory corrected for on-site Coulomb interactions (DFT + U) and a charge equilibration (QEq) atomistic potential to identify minimum energy pathways. We find that diffusion of Ti from the surface to subsurface (and vice versa) follows an interstitialcy exchange mechanism, involving exchange of surface Ti with the 6-fold coordinated Ti below the bridging oxygen rows. Diffusion in the subsurface between layers also follows an interstitialcy mechanism. The diffusion of Ti is discussed in light of continued attempts to understand the re-oxidation of non-stoichiometric TiO 2 (110) surfaces.

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“…14,15 There are other methods to determine the DOS experimentally, especially electron and x-ray spectroscopic methods, [16][17][18] and theoretical ab initio calculations can be used too. [19][20][21][22] A detailed knowledge of the DOS is especially interesting for EC materials, since the coloration in the visible wavelength region involves electron excitations between filled and empty states by, for example, an intervalence charge transfer mechanism. 23 The accuracy of the methods for determining D and the DOS may be severely limited in the presence of side reactions.…”

Section: Introductionmentioning

confidence: 99%

Determination of solid phase chemical diffusion coefficient and density of states by electrochemical methods: Application to iridium oxide-based thin films

Backholm

Georén

Niklasson

2008

Journal of Applied Physics

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Potentiostatic intermittent titration technique ͑PITT͒ and electrochemical impedance spectroscopy ͑EIS͒ were investigated as methods to determine solid phase chemical diffusion coefficient ͑D͒ and electronic density of states ͑DOS͒. These techniques were then applied to iridium oxide ͑IrOx͒ and iridium-tantalum oxide ͑IrTaOx͒ thin films prepared by sputter deposition. The experiments, performed in 1M propionic acid between −0.2 and 0.8 V vs Ag/ AgCl, showed effects of interfacial side reactions, whose contribution to the electrochemical response could be identified and corrected for in the case of PITT as well as EIS. It was found that D is strongly underestimated when using PITT with the common Cottrell formalism, which follows from non-negligible interfacial charge transfer and Ohmic resistances. EIS indicated an anomalous diffusion mechanism, and D was determined to be in the 10 −11 -10 −10 cm 2 / s range for IrOx and IrTaOx. Both PITT and EIS showed that the intercalated charge as a function of potential exhibits a shape that resembles the theoretical DOS of crystalline iridium oxide, especially for IrTaOx.

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The hardest known oxide

Cited by 321 publications

References 12 publications

High-pressure synthesized materials: treasures and hints

High-pressure synthesized materials: treasures and hints

Surface and interstitial Ti diffusion at the rutile TiO2(110) surface

Determination of solid phase chemical diffusion coefficient and density of states by electrochemical methods: Application to iridium oxide-based thin films

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