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 are present in one valence state (III) on the octahedral sites of the spinel structure. The high-pressure behavior of 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 The high-pressure phase is metastable down to normal pressure. The ratio reduces from 1.62 to 1.10 above and remains nearly pressure independent in the high-pressure phase. The transition is attributed to the changes in electron configuration of the ions. According to the crystal field theory, the electron of octahedrally coordinated is either in the orbital or in the In the first configuration the 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 electrons of the ions is moved to the level, which is revealed as an abrupt fall of observed magnitude of the distortion of the bulk crystal above
- Received 16 June 1999
DOI:https://doi.org/10.1103/PhysRevB.60.12651
©1999 American Physical Society