Victor Pardo

Reduction of the bulk modulus at high pressure in CrN

Nitride coatings are increasingly demanded in the cutting- and machining-tool industry owing to their hardness, thermal stability and resistance to corrosion. These properties derive from strongly covalent bonds; understanding the bonding is a requirement for the design of superhard materials with improved capabilities. Here, we report a pressure-induced cubic-to-orthorhombic transition at approximately 1 GPa in CrN. High-pressure X-ray diffraction and ab initio calculations show an unexpected reduction of the bulk modulus, K0, of about 25% in the high-pressure (lower volume) phase. Our combined theoretical and experimental approach shows that this effect is the result of a large exchange striction due to the approach of the localized Cr:t3 electrons to becoming molecular-orbital electrons in Cr-Cr bonds. The softening of CrN under pressure is a manifestation of a strong competition between different types of chemical bond that are found at a crossover from a localized to a molecular-orbital electronic transition.

Half-metallic semi-Dirac-point generated by quantum confinement in TiO2/VO2 nanostructures.

Multilayer VO_{2}/TiO_{2} nanostructures (d;{1}-d;{0} interfaces with no polar discontinuity) are studied with first-principles density functional methods including structural relaxation. Quantum confinement of the half-metallic VO2 slab within insulating TiO2 produces an unexpected and unprecedented two-dimensional new state, with a (semi-Dirac) point Fermi surface: spinless charge carriers are effective-mass-like along one principal axis but are massless along the other. Effects of interface imperfection are addressed.

Magnetism driven by anion vacancies in superconducting α -FeSe 1 − x

To study the microscopic electronic and magnetic interactions in the substoichiometric iron chalcogenide

Magnetism from 2p states in alkaline earth monoxides : Trends with varying N impurity concentration

{\text{FeSe}}_{1\ensuremath{-}x}

Compensated magnetism by design in double perovskite oxides

which is observed to superconduct at

Enhanced pressure dependence of magnetic exchange in A2+[V2]O4 spinels approaching the itinerant electron limit

x\ensuremath{\approx}\frac{1}{8}

Dielectric properties and magnetostriction of the collinear multiferroic spinel CdV 2 O 4

up to

Pressure-induced metal-insulator and spin-state transition in low-valence layered nickelates

{T}_{c}=27\text{ }\text{K}

Evidence for magnetic clusters in Ba Co O 3

, we use first principles methods to study the Se vacancy in this nearly magnetic FeSe system. The vacancy forms a ferrimagnetic cluster of eight Fe atoms, which for the ordered

Electronic structure of CrN: A comparison between different exchange correlation potentials

x=\frac{1}{8}