Synthesis under pressure and characterizations through optical spectroscopy of Jahn-Teller cations (LS Ni~(3+), IS Co~(3+)) as probes diluted in a perovskite matrix

摘要

The objective is to explore through optical spectroscopy and magnetic measurements the coordination and electronic structures of transition-metal ions introduced as impurities with unusual valence states in the oxide perovskite LaAlO_(3). The selected transition-metal ions Ni~(3+)(3d~(7)) and Co~(3+)(3d~(6)) are characterized by an electronic configuration likely leading to an orbital degenerate E state in Oh symmetry, and thus electron-lattice coupling due to the Jahn-Teller effect may induce low symmetry distortion around the impurity oxygen octahedron. We show that a sol-gel process followed by high oxygen pressure treatments yields stabilization of trivalent state in oxide perovskite. Information about the coordination, electronic structure and aggregation around the magnetic impurity was obtained from X-ray diffraction, FTIR and optical spectroscopy. Finally, evidence on the possible existence of intermediate spin state in Co~(3+) is under consideration.