Electron energy-loss spectroscopy study of the metal-insulator transition in (V_1-xCr_x)₂O₃ (x = 0.012)

Electron energy-loss spectra of (V_1-xCr_x)₂O₃ (x = 0.012) at the antiferromagnetic insulating (AFI), paramagnetic metallic (PM) and paramagnetic insulating (PI) phases have been measured using a high-resolution transmission electron energy-loss spectroscopy (EELS) microscope. The changes in the EELS spectra at the transition from the PM phase to the AFI phase are interpreted in a similar manner to the case of V₂O₃ [Jpn. J. Appl. Phys. 37 (1998) 584]. The change in the electronic structure at the transition from the PM phase to the PI phase (Mott transition) was revealed for the first time. A sharp peak observed at 1.0 cV in the PM phase did not appear in the PI phase. The t_2g peak of the O 1s → V 3d(t_2g) EELS spectra shows an energy increase of 0.5 eV at the transition from the PM phase to the PI phase. This increase is interpreted to occur by the splitting of the bonding e_g^π band, which is partially filled in the PM phase, into the fully occupied lower band and the unoccupied upper band, and by the lifting of the unoccupied band to an energy higher than the Fermi level in the PM phase. The r_2g peak also shows a decrease in intensity but an increase in the full width at half-maximum (FWHM) at the transition. The decrease in intensity occurs due to the decrease of the hybridization of the V 3d with the O 2p Orbitals resulting from an increase of the V-O distance. The increase in the FWHM results from the lifting of the a_1g band due to the decrease of the lattice constant c_H and the splitting of the e_g^π and e_g^π, bands each into two bands due to electron correlation.