Theory and the Experimental Confirmation of the Local Electronic Structure of the Multiferroic PbVO3, a New Member of PbTiO3Family, Studied by X-ray Near Edge Absorption Structure: I

Abstract

Recently, an interesting multiferroic system PbVO 3 [A. A. Belik et al. : Chem. Mater. 17 (2005) 269] has been successfully prepared using a high-pressure and high-temperature technique. The crystallographic features of PbVO 3 were reported. In this note, we concentrate on the theoretical and the experimental X-ray near edge absorption structure (XANES) spectra by considering the K-edge of Vanadium. The tetragonality ( c / a =1.229 at 300 K) of PbVO 3 is the largest in the PbTiO 3 family of compounds. Thus, one is led naturally to examine the effects of the changes in the tetragonality and axial oxygen position on the electronic structure (i.e., XANES spectrum). We study these effects in two ways. At a given temperature, we vary the tetragonality and the axial oxygen position, and quantify the changes in terms of the XANES difference spectrum. Secondly, we compute the XANES spectra at three different temperatures, namely, 90, 300, and 530 K, and quantify the changes in terms of the difference spectrum. We note that in this compound the tetragonality increases almost monotonically with temperature from 12 to 570 K, without transition to the cubic phase under ambient pressure. A key objective of the current investigation is to gain an understanding of various absorption features in the vicinity of the K-edge of V, in terms of valence, local site symmetry, local coordination geometry, local bond distances, charge transfer, and local projected density of states. We consider both the polarized and unpolarized XANES spectra, theoretically. The experiment was performed on the polycrystalline material after the theoretical investigation. In short, we have performed a local electronic study, theoretical as well as experimental, which complements the crystallographic features reported recently for PbVO 3 . The local electronic study given here is supplemented and enhanced by the O-K edge results indicated in the accompanying Paper II, which gives both the experimental and theoretical analyses of the XES, XAS, and fundamental band gap of PbVO 3 , which is found to be 1.2 eV.