High-resolution synchrotron x-ray diffraction measurements were performed on single crystalline and powder samples of BiMn 2 O 5 . A linear temperature dependence of the unit cell volume was found between T N = 38 and 100 K, suggesting that a low-energy lattice excitation may be responsible for the lattice expansion in this temperature range. Between T* ϳ 65 K and T N , all lattice parameters showed incipient magnetoelastic effects, due to short-range spin correlations. An anisotropic strain along the a direction was also observed below T*. Below T N , a relatively large contraction of the a parameter following the square of the average sublattice magnetization of Mn was found, indicating that a second-order spin Hamiltonian accounts for the magnetic interactions along this direction. On the other hand, the more complex behaviors found for b and c suggest additional magnetic transitions below T N and perhaps higher-order terms in the spin Hamiltonian. Polycrystalline samples grown by distinct routes and with nearly homogeneous crystal structure above T N presented structural phase coexistence below T N , indicating a close competition amongst distinct magnetostructural states in this compound.
Poster Sessions distribution maps obtained from the maximum entropy method (MEM) describe that 13.4 % of protons exist at inter-layer space. Proton diffusion constants were estimated as 1.9(1) 10-10 m 2 /s at 393 K and 2.1(3) 10-10 m 2 /s at 413 K respectively. The structural change corresponds to a rotational mode of SeO4 tetrahedra, which is led from the group theoretical analysis from R3m to C2/c. A diffusive spectrum was observed around 0 meV at the L-point (0.5 2 0) above TC as an over dumped phonon mode. The rotational mode of SeO4 tetrahedra drives the improper ferroelastic phase transition, and assists the disconnection and reconstruction of hydrogen bonds in the high temperature phase.
During the summer scholarship program in the Brazilian Synchrotron Light Laboratory, the XAFS2 beamline was adapted to perform X-ray Diffraction measurement. This beamline instrumentation allows us to open a new possibilities on the usual XAFS experiments, which is specially useful for combine the techniques to obtaining structural information on short and long range order. We explore both techniques performing in situ studies with a capillary micro-reactor [1] at the same time the hydrogen desorption was measured with mass spectroscopy on metal hydrides (MgCo compounds) during a thermal treatment under helium atmosphere. The possibility of changing the experimental setup between XAFS and XRD within minutes a complete description of the material changes in various operating conditions, were obtained. Indeed, this is a very promising set up combination to explore catalysts or functional materials, which increase the research possibilities of the beamline.
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