P and SK-edge XANES of transition-metal phosphates and sulfates

Electronic structures of several 3d transition-metal phosphates and sulfates have been studied using total-electron-yield X-ray absorption near-edge structure (TEY-XANES) spectroscopy. In P and S K-edge XANES spectra that relate to the electron transitions from P and S Is to P and S 3p-dominant unoccupied states, respectively, two peaks are observed when the number of 3d electrons of cations is less than nine, whereas only one peak is observed when the number is ten. With the increase of the number of the 3d electrons, the lower-energy peak (pre-edge peak) decreases in intensity and shifts to the lower-energy side with discontinuity at five 3d electrons, and the higher-energy peak (main peak) simply shifts to the lower-energy side without such discontinuity. The changes of the pre-edge peak indicate that the density and energy level of the P or S 3p-dominant unoccupied states relate to the number of the 3d electrons, which suggests that P and S 3p states hybridize with 3d states of the cations. The shift of the main peak, which would be associated with the hybridization of the P or S 3p states with 4s states of the cations, can be explained by the depression of the energy levels of the cations with the increase of core electrons. (C) 1999 Elsevier Science B.V. All rights reserved.