Microphase separation in Pr0.67Ca0.33MnO3 by small angle neutron scattering

We have evidenced by small angle neutron scattering at low temperature the coexistence of ferromagnetism (F) and antiferromagnetism (AF) in Pr0.67Ca0.33MnO3. The results are compared to those obtained in Pr0.80Ca0.20MnO3 and Pr0.63Ca0.37MnO3, which are F and AF respectively. Quantitative analysis shows that the small angle scattering is not due to a mesoscopic mixing but to a nanoscopic electronic and magnetic ''red cabbage'' structure, in which the ferromagnetic phase exists in form of thin layers in the AF matrix (stripes or 2D ''sheets'').Comment: 4 figure

Phase Behavior and Relative Stability of Malonamide Polymorphs

International audienceThe three known polymorphs of malonamide have been characterized by thermal analysis and X-ray powder diffraction. The melting thermodynamic characteristics of the three forms are thus proposed in the present paper. From these data, the relative thermodynamic stability of these three solid forms has been determined. It appears that an enantiotropic behavior is established between the bmonoclinic and the orthorhombic phases while the quadratic one is monotropic with respect to the other two

Decomposition behavior of the NaH2 (PO4)0.48(AsO4)0.52 H2O compound above room temperature shown by the study of Raman X- ray powder and ac-conductivity

International audienceThe mixed compound NaH2(PO4)0.48(AsO4)0.52.H2O, which has been examined by Raman spectroscopy, XRD powder and dielectric, exhibits solid-solid phase transitions and one reversible solid-liquid phase transition. Besides, the investigation of dehydration behavior of sodium dihydrogenate phosphate-arsenate monohydrate was undertaken in the temperature range of 253 K to 333 K. The onset temperature of dehydration was determined from changes in ionic conductivity and X-ray powder on heating. It was confirmed by the Raman study not only in the disappearance of the vibrations assigned to the PO4, AsO4 stretching O***O bridge vibrations and the O***H-O vibrations, but also in the appearance of the new vibrations attributed to the (PO3), which constitutes the P-O-P chain, giving a polymer (with) the formula: NaH2(P2O7)x(As2O7)(1-x). The important variation was observed in all studies at 313 K whi ch co uld correspond to the transformation of the NDAP compounds of a solid crystal into a liquid form

Mechanical Properties of ZTA: Correlation with Structural Properties and Influence of Ageing

We report the mechanical and thermal properties of industrial Zirconia Toughened Alumina (ZTA) composites for different compositions of zirconia and yttria, paying a special attention to possible ageing. As a result a correlation between the structural properties and the in-fine performances is obtained; in particular, depending on mechanical properties expected by the customer, optimum composites compositions are indicated

Structural evolution of ZTA composites during synthesis and processing

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Experimental electron densities of neutral and zwitterionic forms of piroxicam drug

International audienceThe electron and electrostatic properties of piroxicam (PX) were derived from high resolution X-ray diffraction experiments carried out at 100 K. Two forms of the piroxicam molecule have been investigated in their crystalline states. One molecule is neutral (nPX) in form I (monoclinic) of piroxicam, while the second found in the hydrated pseudopolymorph (triclinic) is zwitterionic (zPX). In the zPX crystal, the asymmetric unit is formed by two PX molecules with different conformations. The experimental electron density was refined using the Hansen-Coppens multipole model. The electron densities were carefully analyzed using the Atoms in Molecules approach of Richard Bader. Integrated atomic charges compare well for the nPX and zPX molecules. The negative electrostatic potential is found more extended for the zPX molecules than in the nPX one, probably due to the presence of the water molecules connected via hydrogen bonds. The electrostatic potential values on the molecular surface (isodensity of 0.007 eÅ-3) were statistically analyzed in order to reveal local polarity, variances of the positive and negative regions, charge separation etc. In the nPX crystal, the molecular dipole is found equal to 9.12 D with a local dipole of 9.28 D for the SO2CN fragment. The two molecules in the asymmetric unit of the zPX crystal display dipole moment magnitudes respectively equal to 6.83 D and 22.69 D; the corresponding SO2CN sulfonyl cyanide fragment dipoles are 10.88 D and 13.64 D. Comparisons were made for the same fragment in the sulfathiazole molecule. Hence, we have also studied the polymorphs III and IV of the sulfathiazole; the asymmetric unit for polymorph III contains two molecules. The resulted SO2CN dipole moment values are 11.19 D and 11.18 D found for the two molecules in polymorph III and 12.34 D for polymorph IV of the sulfathiazole. The intermolecular electrostatic interaction and the empirical packing energies are estimated to characterize the crystal packing of the two forms of piroxicam

Influence of the substrate on the phase composition and electrical properties of 0.65PMN-0.35PT thick films

International audienceThick films with the nominal composition 0.65Pb(Mg1/3Nb2/3)O-3-0.35PbTiO(3) (0.65PMN-0.35PT) were produced by screen-printing and firing paste prepared from an organic vehicle and pre-reacted powder. The films were fired for 2 h at 950 degrees C on alumina (Al2O3), platinum (Pt), aluminium nitride (AlN) and 0.65PMN-0.35PT substrates. The films were then characterized using scanning electron microscopy, X-ray diffraction and dielectric constant measurements. The X-ray analysis did not detect the presence of any undesirable pyrochlore phase, and the differences in the phase compositions were determined with a Rietveld refinement. The variations of the cell parameters vs. the temperature for the monoclinic and tetragonal phases were calculated. It was demonstrated that under similar processing conditions the microstructures, phase compositions and dielectric properties strongly depended on the stress in the thick films due to the different temperature expansion coefficients of the thick films and the substrates. The 0.65PMN-0.35PT thick films under compressive stresses (for the case of the Al2O3 and Pt substrates) exhibited a tetragonal phase in addition to the monoclinic one. The films were sintered to a high density and with a coarse microstructure. These microstructures favour a high dielectric constant. In contrast, for the films under a tensile stress, like the films on AlN substrates, the films were sintered to a lower density and the microstructure consisted of smaller grains. The X-ray analysis showed mainly a monoclinic phase, while the tetragonal phase was not detected. These results indicate the importance of the stresses in 0.65PMN-0.35PT thick films and their influence on the structural and electrical characteristics of the films