[en] The structural transformations in the spinel LiMn₂O₄ were investigated using powder synchrotron radiation diffraction. Structure refinement by the Rietveld profile analysis, based on the synchrotron radiation X-ray diffraction data collected at 300, 250, and 10 K was performed on a stoichiometric lithium-manganese spinel oxide sample. Investigations on the distribution of Mn³⁺ and Mn⁴⁺ ions over the cationic sites of orthorhombic unit cell of LiMn₂O₄ were carried out at 250 and 10 K. The results of Rietveld analysis explain the effect of the anisotropic lattice parameter changes as a function of temperature. The changes in Mn³⁺ distribution over octahedral sites with decreasing temperature were found to be the cause of LiMn₂O₄ lattice parameters changes

[en] Two research groups of Poznan University pretend to be seen as a cradle of Polish powder crystallography. Both of them published their first X-ray diffraction results in early 1930s, what can suggest the first experiments as early as in 1920s. Some historical background based on documents and relations of scientists lets us better know our science heritage. (author)

[en] Structural phase transitions of the spinel lithium-manganese oxide, LiMn₂O₄ (Fd3m at room temperature) in the temperature range of 300-20 K, were investigated using synchrotron and laboratory X-ray powder diffraction. Splitting of the spinel X-ray lines 311, 400, 440, 531, 533 and 622, recorded during the test, evidenced the reversible formation of cubic, orthorhombic and tetragonal structures. The first transformation starts at ∼290 K as a cubic (Fd3m)→orthorhombic (Fddd) symmetry reduction, and both phases coexist down to 260 K. Below 100 K a second structural transition, orthorhombic→tetragonal (F4₁/ddm) was observed, with the coexistence of these two phases down to ∼40 K. The supercell corresponding to 3ax3axa (a, spinel unit-cell constant) has been considered for both orthorhombic and tetragonal polymorphs of LiMn₂O₄, based on the appearance of (2.10.0) superstructure X-ray reflection

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[en] Typically, wavelength instabilities at synchrotron beams are largely due to thermomechanical phenomena at the primary-beam monochromators and fluctuations of the synchrotron orbit. Although they are small, they may have a negative influence on some kinds of diffraction experiments, for example in thermal expansion studies. Using a wavelength calibration procedure is a natural way of solving or at least reducing this problem. Diamond can be used as a calibration material because of its known low-thermal expansion and low X-ray absorption. Low-temperature X-ray powder diffraction measurements were carried out at the powder diffractometer at the B2 beamline at Hasylab/DESY (Hamburg). The cryostat ensured a good temperature stability and accuracy. Unit-cell parameters for cubic (spinel-type) silicon nitride, c-Si₃N₄, and for copper indium selenide, CuInSe₂, were determined in the temperature range from 14 up to 302 K. An improvement of the data quality due to elimination of the wavelength fluctuation effect is demonstrated

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