New Superhard Phases for 3D C60-based Fullerites

We have explored new possible phases of 3D C60-based fullerites using semiempirical potentials and ab-initio density functional methods. We have found three closely related structures - two body centered orthorhombic and one body centered cubic - having 52, 56 and 60 tetracoordinated atoms per molecule. These 3D polymers result in semiconductors with bulk moduli near 300 GPa, and shear moduli around 240 GPa, which make them good candidates for new low density superhard materials.Comment: To be published in Physical Review Letter

High Pressure Effects on Superconductivity

The review is devoted to a discussion of the effects of high pressure imposed on superconducting materials. Low-temperature superconductors, high-temperature superconducting cuprates, and some unconventional superconducting compounds are investigated. Experimental as well as theoretical results regarding the pressure effects on Tc and other interesting properties are summarized.Comment: To be published in: "Frontiers in Superconducting Materials", Edt. A. Narlikar, Springer Verla

BASAL THERMAL CONDUCTIVITY OF TiSe2

We present the first results on the thermal conductivity of TiSe2. For this semimetal the heat transport is found to occur only through phonons within the investigated temperature range (1.65 - 150 K). At lower temperatures, possible origins for the nearly T2 observed law are analyzed. The other features of K(T) are also examined

Low field magnetism and cationic distribution in quasi-stoichiometric Li1-xNi1+xO2

International audienceThe low field magnetic susceptibility and X-band ESR spectra of quasi-stoichiometric Li1−xNi1+xO2 samples have been measured. The anomaly around 240 K, observed in Li0.98Ni1.02O2 under a 1 mT field, disappears under the conventional magnetic fields used in ESR or susceptibility measurements. We comment on the distribution of extra Ni ions in the lithium planes depending on the synthesis conditions. The departure of x from the exact stoichiometry determined by Rietveld refinements is not the single parameter which determines the magnetic and therefore the electrochemical properties of Li1−xNi1+xO2 samples

Experimental consequences of quantum critical points at high temperatures

We study the Cr1-xRex phase diagram finding that its phase transition temperature towards an antiferromagnetic order TN follows a quantum [(xc-x)/xc]ψ law, with ψ=1/2, from the quantum critical point (QCP) at xc=0.25 up to TN≈600K. We compare this system to others in order to understand why this elemental material is affected by the QCP up to such unusually high temperatures. We determine a general criterion for the crossover, as a function of an external parameter such as concentration, from the region controlled solely by thermal fluctuations to that where quantum effects become observable. The properties of materials with low coherence lengths will thus be altered far away from the QCP.Fil: Freitas, D. C.. Université Grenoble Alpes; Francia. Centro Brasileiro de Pesquisas Físicas; BrasilFil: Rodiere, P.. Université Grenoble Alpes; FranciaFil: Nuñez, Matias. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Garbarino, G.. European Synchrotron Radiation Facility; FranciaFil: Sulpice, A.. Université Grenoble Alpes; FranciaFil: Marcus, J.. Université Grenoble Alpes; FranciaFil: Gay, F.. Université Grenoble Alpes; FranciaFil: Continentino, M. A.. Centro Brasileiro de Pesquisas Físicas; BrasilFil: Regueiro Nuñez, Manuel. Université Grenoble Alpes; Franci