Effect of the Ca content on the electronic structure of Pb1−xCaxTiO3 perovskites

Abstract

This study performs O K-and Ti L 3,2-edge x-ray absorption near-edge structure ͑XANES͒ measurements and first-principles pseudopotential calculations for the electronic structures of ABO 3-type Pb 1Ϫx Ca x TiO 3 (xϭ0-1) perovskites. The features in the O K-edge XANES spectra are found to be contributed primarily by hybridization between O 2p and Ti 3d, Pb 6p, and Ca 3d orbitals. The O K-edge XANES spectra reveal that partial substitution of A cations, Pb, by Ca not only decreases O 2p-Pb 6p but also O 2p-Ti 3d hybridization. The Ti L 3,2-edge measurements find that the off-center displacement of Ti, and hence, ferroelectricity persist up to a Ca concentration between 0.3 and 0.4.

Electronic structure of Pb1−xLaxTiO3 ferroelectric materials from Ti 2p and O 1s soft x-ray absorption spectroscopy

“…12 These authors observed that this splitting disappeared in the samples containing high concentrations of Ca and suggested a restoration of the Ti ion to the center of the octahedron. Thus, they correlated the changes observed in the L 3 e g peak to the structural changes in the first oxygen atoms around titanium atoms.…”

“…18 The separation between the L 3 and L 2 edges is attributed to Ti 2p 3/2 ͑L 3 ͒ and 2p 1/2 ͑L 2 ͒ spin orbit splitting, which is around 5.3 eV and is comparable to that observed in TiO 2 and other mixed perovskite compounds. [8][9][10][11][12][13][14] The crystal field at both the L 3 and L 2 edges splits the 3d band into t 2g and e g subbands. 21 The split observed at the D peak, shown in greater detail in Fig.…”

“…16,17 Different features observed in the O K-edge spectra of mixed perovskite ferroelectric compounds have also been interpreted in terms of hybridization between O 2p and Ti 3d, and O 2p and Pb 6p orbitals. 12 On the other hand, the features observed at the Ti L 3,2 edges in different ABO 3 and in mixed perovskite compounds have been attributed to various factors, some of which are controversial. [18][19][20] To better understand the structural results obtained from the Ti K edge, we conducted an experimental study of the electronic structure of the Pb 1−x La x TiO 3 system for x ranging from 0 to 30 at.…”

“…7 Although the use of x-ray absorption spectroscopy to study ABO 3 and mixed perovskite compounds has been limited mainly to the analysis of K-edge spectra, the electronic structure of the transition metals in these compounds has recently been studied by soft x-ray absorption spectroscopy measurements of Ti L 3,2 and O K edges. [8][9][10][11][12][13][14] When applied to mixed perovskite compounds, these studies proved very useful in shedding light on how compositional substitution influences the electronic structure of these systems. [11][12][13]15 Theoretical calculations have shown that hybridized states of Ti 3d and O 2p and covalent bonding of Pb-O crucially affect ferroelectric stability in the PbTiO 3 compound.…”

“…[8][9][10][11][12][13][14] When applied to mixed perovskite compounds, these studies proved very useful in shedding light on how compositional substitution influences the electronic structure of these systems. [11][12][13]15 Theoretical calculations have shown that hybridized states of Ti 3d and O 2p and covalent bonding of Pb-O crucially affect ferroelectric stability in the PbTiO 3 compound. 16,17 Different features observed in the O K-edge spectra of mixed perovskite ferroelectric compounds have also been interpreted in terms of hybridization between O 2p and Ti 3d, and O 2p and Pb 6p orbitals.…”