Covalency effects in transition-metal perovskitelike compounds: Partial densities of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>p</mml:mi></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>d</mml:mi></mml:math>states and photoelectron valence-band spectra

Abstract

The evolution of x-ray-photoelectron (XPS) valence-band spectra for the series of perovskitelike compounds BaTi${\mathrm{O}}_{3}$, KNb${\mathrm{O}}_{3}$, KTa${\mathrm{O}}_{3}$, W${\mathrm{O}}_{3}$, and Re${\mathrm{O}}_{3}$ gives evidence for quite important covalency effects due to the spatial overlap of metal $\mathrm{md}$ and oxygen $2p$ states. Theoretical partial densities of states of $d$ and $p$ character allow an explanation of the experimental results when transition-matrix-element effects are taken into account. These are introduced by using atomic cross sections for the corresponding partial transition probabilities in a simple model which is justified in the XPS regime. We discuss the cross-section values and the atomic-population analysis. The uv-photoelectron valence-band spectrum of W${\mathrm{O}}_{3}$ compared to the XPS one confirms the validity of the calculated partial densities of states. The case of Re${\mathrm{O}}_{3}$ already given in the literature is included in this work; the theoretical density of states is computed again with slight modifications in order to improve the agreement with published experimental results and to test the influence of two different population analyses.