Showing papers by "Leif Gerward published in 1999"
TL;DR: In this article, the high-pressure behavior of manganese ions was investigated up to 52 GPa using the energy-dispersive x-ray diffraction technique and synchrotron radiation.
Abstract: X-ray photoelectron spectroscopy, magnetic measurements, and a single-crystal x-ray structure determination at normal pressure have shown that Jahn-Teller active manganese ions in ${\mathrm{ZnMn}}_{2}{\mathrm{O}}_{4}$ are present in one valence state (III) on the octahedral sites of the spinel structure. The high-pressure behavior of ${\mathrm{ZnMn}}_{2}{\mathrm{O}}_{4}$ was investigated up to 52 GPa using the energy-dispersive x-ray diffraction technique and synchrotron radiation. The structural first-order phase transition from the body-centered to primitive-tetragonal cell takes place at ${P}_{c}=23\mathrm{GPa}.$ The high-pressure phase is metastable down to normal pressure. The $c/a$ ratio reduces from 1.62 to 1.10 above ${P}_{c}$ and remains nearly pressure independent in the high-pressure phase. The transition is attributed to the changes in electron configuration of the ${\mathrm{Mn}}^{3+}$ ions. According to the crystal field theory, the ${e}_{g}$ electron of octahedrally coordinated ${\mathrm{Mn}}^{3+}$ is either in the ${d}_{z}^{2}$ orbital or in the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}.$ In the first configuration the ${\mathrm{MnO}}_{6}$ octahedron will be elongated and this is the case at normal pressure, while the second configuration gives the flattened octahedron. In the high-pressure phase some proportion of the ${e}_{g}$ electrons of the ${\mathrm{Mn}}^{3+}$ ions is moved to the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$ level, which is revealed as an abrupt fall of observed magnitude of the distortion of the bulk crystal above ${P}_{c}.$
108 citations
01 Jan 1999
23 citations
TL;DR: In this paper, the authors investigated the compressibility of nanostructured FeCu materials prepared by mechanical milling using in-situ high-pressure x-ray diffraction using synchrotron radiation.
15 citations
TL;DR: In this article, the discovery of gamma rays by the relatively unknown French physicist Paul Villard is described in its historical context, where the discovery was largely overlooked by the scientific community, due to the fact that they did not fit into the picture that contemporary scientists had on the material nature of atomic radiations.
Abstract: The discovery of gamma rays by the relatively unknown French physicist Paul Villard is described in its historical context. From the beginning Villard gave a correct interpretation of the new rays, but his discovery was largely overlooked by the scientific community. A major reason for the small interest in gamma rays at the time was that they apparently did not fit into the picture that contemporary scientists had on the material nature of atomic radiations.
14 citations