POLARIZED XAS STUDIES OF TERNARY NICKEL OXIDES

Polarized Ni K-edge x-ray-absorption spectroscopy (XAS) results on La2-xSrxNiO4 (x=0.2 1.3) are presented and interpreted with the aid of polarized Cu K-edge results on the high-Tc analog material La1.85Sr0.15CuO4. The Sr-substitution-induced reduction in the disparity between the Ni-O apical and in-plane distances is seen to result in the collapse of the energy splitting 4p and 4p spectral features in the polarized Ni K-edge XAS (mainly by shifting the 4p feature to higher energies). The 4p feature identifications used in previous Cu and Ni compound studies are clarified and the chemical shift estimates of the d hole count variation in the La2-xSrxNiO4 system are revised in the light of this observed continuous 4p-4p splitting collapse. The area increase in the 1s 3d quadrupole transition is quantitatively correlated with the Sr content of the compound. The magnitude of the area increase of this feature suggests that in addition to an increase in Ni d hole count there is also an increase in Ni-p/Ni-d hybridization which opens a dipole-allowed transition channel. Finally the dramatic appearance and growth of a prominent high-energy feature and its correlation with the increase in Ni d hole count is described and discussed. © 1995 The American Physical Society.