Compressibility of CaMnO 3 : A study using a large-volume diffraction press

International audienceCaMnO3 is a parent compound for various manganite systems exhibiting useful physical properties. Therefore, its structural and elastic properties are of general interest. In this paper, P–V equation of state of stoichiometric CaMnO3 is determined using energy dispersive X-ray diffraction. The measurements were carried out at a synchrotron beamline F2.1 (Hasylab, DESY) with samples compressed in a cubic-anvil diffraction press, MAX80, for pressures ranging up to 4.84 GPa. The experimental bulk modulus of CaMnO3, derived from the variation in the unit-cell volume with pressure by fitting the Birch–Murnaghan equation of state, is 154.4(3.3) GPa. The results are discussed on the basis of experimental and theoretical data for CaMnO3 and related compounds

Lattice parameters and orthorhombic distortion of CaMnO 3

International audienceCaMnO3 is a parent compound for numerous multicomponent manganese perovskite oxides. Its crystallographic data are of primary importance in the science and technology of functional CaMnO3-based materials. In the present study, data were collected for a CaMnO3 sample at 302 K. The crystal structure refinement yields accurate absolute values of lattice parameters, a=5.281 59(4) Å, b=7.457 30(4) Å, and c=5.267 48(4) Å, leading to orthorhombic distortion of (c/a, √2c/b)=(0.997 33,0.998 95). The orthorhombic distortion of the CaMnO3 structure is discussed on the basis of comparison of our unit-cell size with data already published. At a graphical representation of the distortion, it is observed that there is a considerable scatter of the distortion values among the literature data but, interestingly, a considerable fraction of experimental results (including the present one) for stoichiometric samples are grouped around the distortion (c/a, √2c/b)=(0.9973,0.9990), which lies close to a maximum in the extent of orthorhombicity. The influence of off-stoichiometry on the orthorhombic distortion is discussed on the basis of available experimental data. Simulations, employing a mean-field approach for low temperatures, predict an increase in cell volume and structural distortions with the concentration of oxygen vacancies when the additional electrons are localized on the manganese. A simple model of delocalization produced the opposite effect, which is expected to combine with lattice vibrations to recover the cubic phase at high temperatures

Lattice parameters and orthorhombic distortion of CaMnO 3

International audienceCaMnO3 is a parent compound for numerous multicomponent manganese perovskite oxides. Its crystallographic data are of primary importance in the science and technology of functional CaMnO3-based materials. In the present study, data were collected for a CaMnO3 sample at 302 K. The crystal structure refinement yields accurate absolute values of lattice parameters, a=5.281 59(4) Å, b=7.457 30(4) Å, and c=5.267 48(4) Å, leading to orthorhombic distortion of (c/a, √2c/b)=(0.997 33,0.998 95). The orthorhombic distortion of the CaMnO3 structure is discussed on the basis of comparison of our unit-cell size with data already published. At a graphical representation of the distortion, it is observed that there is a considerable scatter of the distortion values among the literature data but, interestingly, a considerable fraction of experimental results (including the present one) for stoichiometric samples are grouped around the distortion (c/a, √2c/b)=(0.9973,0.9990), which lies close to a maximum in the extent of orthorhombicity. The influence of off-stoichiometry on the orthorhombic distortion is discussed on the basis of available experimental data. Simulations, employing a mean-field approach for low temperatures, predict an increase in cell volume and structural distortions with the concentration of oxygen vacancies when the additional electrons are localized on the manganese. A simple model of delocalization produced the opposite effect, which is expected to combine with lattice vibrations to recover the cubic phase at high temperatures

Compressibility of CaMnO 3 : A study using a large-volume diffraction press

International audienceCaMnO3 is a parent compound for various manganite systems exhibiting useful physical properties. Therefore, its structural and elastic properties are of general interest. In this paper, P–V equation of state of stoichiometric CaMnO3 is determined using energy dispersive X-ray diffraction. The measurements were carried out at a synchrotron beamline F2.1 (Hasylab, DESY) with samples compressed in a cubic-anvil diffraction press, MAX80, for pressures ranging up to 4.84 GPa. The experimental bulk modulus of CaMnO3, derived from the variation in the unit-cell volume with pressure by fitting the Birch–Murnaghan equation of state, is 154.4(3.3) GPa. The results are discussed on the basis of experimental and theoretical data for CaMnO3 and related compounds

Equation of state of CaMnO3: a combined experimental and computational study

International audienceElastic properties of CaMnO3 are of primary importance in the science and technology of CaMnO3-based perovskites. From X-ray diffraction experiments performed at pressures up to 100 kbar using a diamond-anvil cell to hydrostatically compress our sample, a bulk modulus, K 0, of 1734(96) kbar was obtained after fitting parameters to the third-order Birch–Murnaghan equation of state. Mean field, semiclassical simulations predict, for the first time, the third-order equation-of-state parameters and show how the bulk modulus increases with pressure (the zero pressure value being 2062.1 kbar) and decreases with the extent of nonstoichiometry caused by the formation of oxygen vacancies. These trends are amplified for the shear modulus. A more accurate model that allows for the explicit reduction of Mn ions, or localization of excess electrons, yields qualitatively similar results. The experimental and calculated axial ratios show the same trends in their variation with rising pressure

Equation of state of CaMnO3: a combined experimental and computational study

International audienceElastic properties of CaMnO3 are of primary importance in the science and technology of CaMnO3-based perovskites. From X-ray diffraction experiments performed at pressures up to 100 kbar using a diamond-anvil cell to hydrostatically compress our sample, a bulk modulus, K 0, of 1734(96) kbar was obtained after fitting parameters to the third-order Birch–Murnaghan equation of state. Mean field, semiclassical simulations predict, for the first time, the third-order equation-of-state parameters and show how the bulk modulus increases with pressure (the zero pressure value being 2062.1 kbar) and decreases with the extent of nonstoichiometry caused by the formation of oxygen vacancies. These trends are amplified for the shear modulus. A more accurate model that allows for the explicit reduction of Mn ions, or localization of excess electrons, yields qualitatively similar results. The experimental and calculated axial ratios show the same trends in their variation with rising pressure

Tailoring Magnetic Properties of Fe0.65Co0.35 Nanoparticles by Compositing with RE2O3 (RE = La, Nd, and Sm)

Fe-Co alloys are the most important soft magnetic materials, which are successfully used for a wide range of applications. In this work, the magnetic properties of lanthanide-substituted (Fe0.65Co0.35)0.95(RE2O3)0.05 (RE = La, Nd, and Sm) nanoparticles, prepared by mechanical alloying, are reported. Our comprehensive studies (X-ray diffraction, Mössbauer spectroscopy, scanning electron microscopy with X-ray energy dispersive spectrometry, SQUID magnetometry and differential scanning calorimetry) have revealed different properties, depending on the dopant type. The RE2O3 addition led to a decrease in the crystallite size and to an increase in the internal microstrain. Moreover, because of the high grain fragmentation tendency of RE2O3, the cold welding between Fe–Co ductile particles was minimized, indicating a significant decrease in the average particle size. The parent Fe0.65Co0.35 alloy is known for its soft ferromagnetism. For the La-substituted sample, the magnetic energy product was significantly lower (0.450 MG·Oe) than for the parent alloy (0.608 MG·Oe), and much higher for the Sm-substituted compound (0.710 MG·Oe). The processing route presented here, seems to be cost-effective for the large-scale production of soft magnetic materials

The Impact of Hydrogenation on Structural and Superconducting Properties of FeTe0.65Se0.35 Single Crystals

Properties of FeTe0.65Se0.35 single crystals, with the onset of critical temperature (Tconset) at 15.5 K, were modified via hydrogenation performed for 10–90 h, at temperatures ranging from 20 to 250 °C. It was found that the tetragonal matrix became unstable and crystal symmetry lowered for the samples hydrogenated already at 200 °C. However, matrix symmetry was not changed and the crystal was not destroyed after hydrogenation at 250 °C. Bulk Tcbulk, determined at the middle of the superconducting transition, which is equal to 12–13 K for the as grown FeTe0.65Se0.35, rose by more than 1 K after hydrogenation. The critical current density studied in magnetic field up to 70 kOe increased 4–30 times as a consequence of hydrogenation at 200 °C for 10 h. Electron paramagnetic resonance measurements also showed higher values of Tcbulk for hydrogenated crystals. Thermal diffusion of hydrogen into the crystals causes significant structural changes, leads to degeneration of crystal quality, and significantly alters superconducting properties. After hydrogenation, a strong correlation was noticed between the structural changes and changes in the parameters characterizing the superconducting state