Critical behavior and spontaneous magnetization estimation in La0.5Sr0.5MnO3 compound

International audienc

Crystal structure, phase transitions, and magnetic properties of titanium doped La0.5Sr0.5MnO3 perovskites

International audienceThe current paper investigates the effect of titanium substitution on the structure as well as the magnetic properties of La0.5Sr0.5Mn1−xTixO3 (0≤x≤0.5) polycrystalline powder. The samples studied crystallize in a distorted perovskite structures of tetragonal (space group I4/mcm) symmetry with octahedral tilting scheme ( a 0 a 0 c − ), leading to the absence of octahedral tilting all along two perovskite main directions and to an out-of-phase along the third direction, or rhombohedral (space group R 3 ¯ c) symmetry with octahedral tilting scheme ( a − a − a − ) yielding to out-of-phase along the three perovskite main directions. As the Ti content increases, a better matching of the (Mn/Ti)–O distances and (Mn/Ti)–O–(Mn/Ti) bond angle occurs. This phenomenon is created by an elongation of the (Mn/Ti)–O distance, as Mn4+ is substituted by the larger ion Ti4+. In the whole compositional range, the symmetry-adapted to atomic displacements, responsible for the out-of-phase tilting of the (Mn/Ti)O6 octahedra, stays active, anticipating tetragonal-to-rhombohedral phase transition. Taking in to account what has been explained above, measurements of magnetic properties show a decrease of magnetic ordering temperature when Ti content increases, which in turn leads to the diminution of the exchange interaction caused by reducing the FM coupling and the replacement of neighboring manganese Mn3+–O–Mn4+ by Mn3+–O–Ti4+ bonds. This phenomenon results in broadening of the paramagnetic to ferromagnetic phase transition range. Further changes in magnetic properties with the increase in Ti concentration are studied

Above room temperature conduction mechanism of Ti doped LaSrMnO perovskite

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Above room temperature conduction mechanism of Ti doped LaSrMnO perovskite

International audienc

The structural, magnetic and above room temperature magnetocaloric properties of La0.5Sr0.5MnO3 compound

International audienc

X-ray evidence for a new phase in ammonium hydrogen oxalate hemihydrate under pressure

Using an X-ray diamond anvil cell, we have found superlattice reflections, characteristic of the high pressure-low temperature phase III of NH 4HC2O4, 1/2 H2O. At 77 K and 0.75 GPa, these peaks are located around each Bragg peaks of phase I at position ( h, k, 1 ± δ) with δ ≃ 0.25.Les diagrammes de diffraction obtenus à l'aide d'une cellule à enclumes de diamant ont permis d'identifier, à haute pression et basse température, les taches de surstructure caractéristiques de la phase III de NH4HC 2O4' 1/2 H2O. A 77 K et 0,75 GPa, les taches trouvées entourent les pics de Bragg de la phase I et sont situées à (h, k, 1 ± δ) avec δ ≃ 0,25

Differential scanning calorimetry and X-ray diffraction study of water confined in silica gel for several levels of hydration

Differential scanning calorimetry (DSC) and X-ray scattering measurements on water confined in silica gel is studied for several levels of hydration at room temperature and down to 77 K. The DSC analysis of water confined in silica gel in function of the level of hydration shows that the solidification of water inside the pore is sensitive to the pore opening but the fusion is closely related to the curve of the pore. The X-ray pair correlation function showed the presence of a distorted tetrahedral-like hydrogen-bonded network of water characterized by the peaks at ~2.8, ~4.1 and ~4.9 Å. This distortion is caused by the competition between confinement effect and silica-water interaction. To eliminate the contribution of the water-silica gel interaction we have determined the structure of confined water by subtraction of the feebly hydrated silica gel from that strongly hydrated sample. The pair correlation function of extracted water show an oxygen-oxygen correlation at 3.8 Å. A similar peak is observed in the case of water confined in polyHEMA, in charcoal and at vicinity of myoglobin

Critical Behavior of La0.67Ba0.33Mn0.95Fe0.05O3 Manganite

National audienc

Étude des modifications structurales de l'eau confinée dans le gel de silice

Les modifications structurales de l'eau confinée dans le gel de silice en poudre en fonction du taux d'hydratation sont étudiées par calorimétrie différentielle à balayage et par diffusion des rayons X. L'analyse thermique par DSC a permis de montrer que pour les faibles taux d'hydratation ($\le 50\%$) l'eau est complètement confinée dans les pores alors que pour les forts taux d'hydratation ($>50\%$) l'eau se trouve aussi bien dans les pores qu'autour des grains de la silice. L'apparition de la glace cubique lors du refroidissement de l'eau confinée dans le gel de silice prouve que l'interaction eau-silice ne peut être négligée lors de la détermination du signal de l'eau. L'extraction du signal, diffusé uniquement par l'eau confinée, à partir des intensités diffusées par le gel de silice à deux taux d'hydratation distincts, révèle dans les fonctions de corrélation de paire un pic à 3.7Å qui ne peut être attribué qu'à une corrélation oxygène-oxygène inexistante dans l'eau massique et résultant de la déformation du réseau tétraédrique des molécules d'eau sous l'effet du confinement et de la proximité d'une surface