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See detailRole of vacancies in metal-insulator transitions of crystalline phase-change materials
Zhang, Wei; Thiess, Alex; Zalden, Peter et al

in Nature Materials (2012), 11(11), 952-956

The study of metal-insulator transitions (MITs) in crystalline solids is a subject of paramount importance, both from the fundamental point of view and for its relevance to the transport properties of ... [more ▼]

The study of metal-insulator transitions (MITs) in crystalline solids is a subject of paramount importance, both from the fundamental point of view and for its relevance to the transport properties of materials. Recently, a MIT governed by disorder was observed in crystalline phase-change materials. Here we report on calculations employing density functional theory, which identify the microscopic mechanism that localizes the wavefunctions and is driving this transition. We show that, in the insulating phase, the electronic states responsible for charge transport are localized inside regions having large vacancy concentrations. The transition to the metallic state is driven by the dissolution of these vacancy clusters and the formation of ordered vacancy layers. These results provide important insights on controlling the wavefunction localization, which should help to develop conceptually new devices based on multiple resistance states. © 2012 Macmillan Publishers Limited. All rights reserved. [less ▲]

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See detailCoupling of three lattice instabilities
Ghosez, Philippe ULg; Triscone, Jean-Marc

in Nature Materials (2011), 10

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See detailUltradispersity of diamond at the nanoscale
Raty, Jean-Yves ULg; Galli, G.

in Nature Materials (2003), 2(12), 792-795795

Nanometre-sized diamond has been found in meteorites, protoplanetary nebulae, and interstellar dusts, as well as in residues of detonation and in diamond films. Remarkably, the size distribution of ... [more ▼]

Nanometre-sized diamond has been found in meteorites, protoplanetary nebulae, and interstellar dusts, as well as in residues of detonation and in diamond films. Remarkably, the size distribution of diamond nanoparticles seems to be peaked around 2-5 nm, and to be largely independent of preparation conditions. We have carried out ab initio calculations of the stability of nanodiamond as a function of surface hydrogen coverage and of size. We have found that at about 3 nm, and for a broad range of pressures and temperatures, particles with bare, reconstructed surfaces become thermodynamically more stable than those with hydrogenated surfaces, thus preventing the formation of larger grains. Our findings provide an explanation of the size distribution of extraterrestrial and of terrestrial nanodiamond found in ultradispersed and ultracrystalline diamond films. They also provide an atomistic structural model of these films, based on the topology and structure of 2-3 nm diamond clusters consisting of a diamond core surrounded by a fullerene-like carbon network [less ▲]

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