Search results for "spinel"
showing 10 items of 103 documents
Cation Distribution in Ferrites with Spinel Structure Measured by Anomalous Powder Diffraction
1998
The Poisson Ratio in CoFe2O4Spinel Thin Films
2012
The response of epitaxial CoFe2O4 thin films to biaxial compressive stress imposed by MgAl2O4 and SrTiO3 single crystalline substrates is studied using X-ray diffraction and Raman spectroscopy. It is found that the Poisson ratio ν signals a non-auxetic behavior and depends on the substrate used. The Raman modes show an increase in frequency when increasing compressive strain by reducing film thickness; this is due to the shrinking of the unit cell volume. Such behavior is in qualitative agreement with recent ab initio calculations, although the measured values are significantly smaller than predictions. In contrast, the measured Poisson ratio is found to be in good agreement with expectatio…
Post-spinel transformations and equation of state inZnGa2O4: Determination at high pressure byin situx-ray diffraction
2009
Room-temperature angle-dispersive x-ray diffraction measurements on spinel ZnGa{sub 2}O{sub 4} up to 56 GPa show evidence of two structural phase transformations. At 31.2 GPa, ZnGa{sub 2}O{sub 4} undergoes a transition from the cubic spinel structure to a tetragonal spinel structure similar to that of ZnMn{sub 2}O{sub 4}. At 55 GPa, a second transition to the orthorhombic marokite structure (CaMn{sub 2}O{sub 4}-type) takes place. The equation of state of cubic spinel ZnGa{sub 2}O{sub 4} is determined: V{sub 0} = 580.1(9) {angstrom}{sup 3}, B{sub 0} = 233(8) GPa, B'{sub 0} = 8.3(4), and B''{sub 0} = -0.1145 GPa{sup -1} (implied value); showing that ZnGa{sub 2}O{sub 4} is one of the less comp…
Apparent magic numbers in embedded Ti-O clusters
2003
Stable clusters constituted of four ${\mathrm{TiO}}_{2}$ entities have been evidenced in nanometer-sized spinel oxides by a combination of diffraction and x-ray-absorption experiments. Contrary to free clusters, the size of the embedded clusters is strongly determined by the constraints imposed by the surrounding matrix so that the magic number of four is in fact specific to the matrix and only then apparent.
Structural and vibrational properties of CdAl2S4 under high pressure: Experimental and theoretical approach
2014
The behavior of defect chalcopyrite CdAl2S4 at high pressures and ambient temperature has been investigated in a joint experimental and theoretical study. High-pressure X-ray diffraction and Raman scattering measurements were complemented with theoretical ab initio calculations. The equation of state and pressure dependences of the structural parameters of CdAl2S4 were determined and compared to those of other AB(2)X(4) ordered-vacancy compounds. The pressure dependence of the Raman-active mode frequencies is reported, as well as the theoretical phonon dispersion curves and phonon density of states at 1 atm. Our measurements suggest that defect chalcopyrite CdAl2S4 undergoes a phase transit…
AB$$_{2}$$O$$_{4}$$ Compounds at High Pressures
2014
In this chapter, we present an overview of the effects of pressure on the crystalline structure and physical properties of oxygen-based spinels and other related oxides. Recent X-ray diffraction and Raman spectroscopy studies are summarized. A brief description of pressure-driven transitions and post-spinel structures is also provided. We also compare the response to high-pressure of several spinel oxides. We conclude with an examination of elastic and magnetic properties.
Effect of coatings on long term behaviour of a commercial stainless steel for solid oxide electrolyser cell interconnect application in H2 /H2O atmos…
2014
Abstract K41X (AISI 441) stainless steel evidenced a high electrical conductivity after 3000 h ageing in H 2 /H 2 O side when used as interconnect for solid oxide electrolyser cells (SOEC) working at 800 °C. Perovskite (La 1 − x Sr x MnO 3 − δ ) and spinel (Co 3 O 4 ) oxides coatings were applied on the surface of the ferritic steel for ageing at 800 °C for 3000 h. Both coatings improved the behaviour of the steel and give interesting opportunities to use the K41X steel as interconnect for hydrogen production via high temperature steam electrolysis. Co 3 O 4 reduced into Co leading to a very good Area Specific Resistance (ASR) parameter, 0.038 Ω cm 2 . Despite a good ASR (0.06 Ω cm 2 ), La …
FeCr2O4 synthetic spinel: heating experiments and oxidation kinetics
2011
Il dibattito sul federalismo nel secondo dopoguerra
2018
Il Movimento Federalista Europeo viene fondato a Milano nel 1943 da Altiero Spinelli con un gruppo di antifascisti, come movimento di idee e di azione, con l’obiettivo di dare vita ad una federazione di Stati Uniti d’Europa. Per Altiero Spinelli, che del movimento fu l’ideatore principale, lo scopo prioritario della lotta politica era quello di assicurare stabilmente al vecchio continente i valori irrinunciabili della pace, della libertà, della democrazia e della giustizia sociale. Sulla scia di tale orientamento si sviluppò un intenso dibattito che, prima ancora della fondazione del Movimento Federalista Europeo, aveva trovato un riscontro teorico nel “Manifesto di Ventotene”, originariame…
Synthesis and host properties of tetragonal Li2Mn2O4 and Li2Co0.4Mn1.6O4
2000
Abstract This paper presents synthesis and electrochemical properties of tetragonal lithium manganese dioxide, Li2Mn2O4 and its cobalt doped analogue Li2Co0.4Mn1.6O4. The materials are compared as host materials for lithium insertion and the behavior during the initial lithium extraction as well as on repeated cycling is presented. These materials show an initial lithium extraction capacity between 200 and 270 mAh/g. On repeated cycling, they are converted into spinel-like lattices with reversible capacities in the range 82–90 mAh/g. As they are chemically compatible with the manganese spinel, they will be well suited as additives compensating for the capacity loss during the initial formin…