Nickelocene as precursor of microporous organometallic-derived carbon and nickel oxide-carbon nanocomposite

Microporous flower-like and spherical carbon particles, made of graphene-like layers, have been obtained via chlorination of nickelocene (Ni(C₅H₅)₂). Their mechanism of formation, in terms of morphology and micro-nanostructure, has been followed from 200 to 900°C. Conventional transmission electron microscopy and high-resolution-TEM observations allow determining that their structure is made of highly disordered graphene-like layers. The Raman spectrum of the high temperature sample exhibits the characteristics D and G bands. The peak positions, the ratio of their intensities (I_D/I_G) and full width at half maximum suggest a high degree of disorder in the nanostructures. The calculated in-plane correlation length of these graphene-like layers is 1.15nm. In all the carbon particles, electron energy-loss spectroscopy shows sp² carbon bonding content higher than 95% and mass density in the range of 1.0-1.6g/cm³. Textural studies show Type I adsorption isotherms with surface area of 922m²/g for the sample produced at 900°C. In addition, the basic hydrothermal treatment of the sample chlorinated at 600°C yields a composite material with NiO nanoparticles well dispersed within the carbon matrix.

High pressure synthesis of polar and non-polar cation-ordered polymorphs of Mn2ScSbO6

Two new Mn₂ScSbO₆ polymorphs are presented: an antiferromagnetic double perovskite (DPv) and a multiferroic Ni₃TeO₆-type (NTO) induced by site-selective disorder.

Strain-induce shift of the crystal-field splitting of SrTiO₃ embedded in scandate multilayers

Strained SrTiO₃ layers have become of interest, since the paraelectric-to-ferroelectric transition temperature can be increased to room temperature. A linear relationship between strain and energy splitting of the fundamental transitions in the fine structure of Ti L(₂,₃) and O K edges is observed, that can be exploited to measure strain from electronic transitions, complementary to measuring local strain directly via high-resolution transmission electron microscopy (HRTEM) images. In particular, for both methods, the geometrical phase analysis performed on high-resolution images and the measurement of the energy splitting by energy loss spectroscopy, tensile strain of SrTiO₃ layers was measured when grown on DyScO₃ and GdScO₃ substrates. The effect of strain on the electron loss near edge structure (ELNES) of the Ti L(₂,₃) edge in comparison to unstrained samples is analyzed. Ab initio calculations of the Ti L(₂,₃) and O K edge show a linear variation of the crystal field splitting with strain. Calculated and experimental values of the crystal field splitting show a very good agreement.