X-ray absorption spectroscopy of Ru-doped relaxor ferroelectrics with a perovskite-type structure

Abstract

X-ray absorption near-edge structure and extended x-ray absorption fine structure spectroscopy at the Ru K edge of Ru-doped PbSc 0.5 Ta 0.5 O 3 (PST-Ru), PbSc 0.5 Nb 0.5 O 3 (PSN-Ru), and 0.9PbZn 1/3 Nb 2/3 O 3 -0.1PbTiO 3 (PZN-0.1PT-Ru) as well as at the Ta L 3 edge of PST-Ru and the Nb K edge of PSN-Ru was applied to study the short-and intermediate-range atomic arrangements in perovskite-type (ABO 3 ) relaxor ferroelectrics. The compounds were also analyzed by complementary Raman scattering, visible/near-visible absorption spectroscopy, and synchrotron x-ray single-crystal diffraction. The results show that Ru is octahedrally coordinated in all three relaxor host matrices but the average oxidation state of Ru in PST-Ru and PSN-Ru is ß4.4, whereas it is ß3.8 in PZN-0.1PT-Ru. In PbSc 0.5 B 0.5 O 3 (B = Ta, Nb) Ru substitutes for the B cations in the form of isolated point defects, while in PZN-0.1PT-Ru Ru replaces adjacent A and B sites, forming a chainlike structural species of face-sharing elongated octahedra. Chemical 1:1 B-site order as well as dynamic BO 6 tilting is observed around both the Ru dopant and the major B cation in PST-Ru and PSN-Ru regardless of the fact that according to x-ray diffraction at ambient conditions, the average structure is cubic with weak or no long-range chemical order. Pb cations are off-center displaced from the prototypic cubic A site for all three compounds and in Ru-doped PbSc 0.5 B 0.5 O 3 the BO 6 tilt angle correlates with the degree of coherent B-Pb distances.

Synthesis of (Li2Fe1–yMny)SO Antiperovskites with Comprehensive Investigations of (Li2Fe0.5Mn0.5)SO as Cathode in Li-ion Batteries

“…As known, the position of the absorption edge E 0 in transition metal oxides correlates with the metal valence state . To determine the absorption edge E 0 , two different approaches are usually used: either as the energy corresponding to the maximum of the energy derivative of μ­( E ) or as the energy at the X-ray absorption coefficient μ­( E ) = 0.8 of normalized postedge intensities . We defined the absorption edge E 0 as the energy at μ­( E ) = 0.8, since in this case, the energy positions for (Li 2 Fe)­SO, (Li 2 Fe 0.5 Mn 0.5 )­SO, and FeO are nearly the same, pointing the oxidation state of Fe in antiperovskites close to +2, what is expected from the stoichiometry obtained from the chemical analysis.…”

Comparison of Layered Li(Li0.2Rh0.8)O2 and LiRhO2 upon Li Removal: Stabilizing Effect of Li Substitution

“…It is known for 3d and 4d transition-metal oxides that the position of the absorption edge E 0 correlates with the metal valence state . The absorption edge E 0 can be defined as either the energy at the X-ray absorption coefficient μ­( E ) = 0.8 of normalized postedge intensities or the energy corresponding to the maximum of the energy derivative of μ­( E ), which is coincident with the inflection point of the absorption edge. , While a chemical shift of about 3 eV between the absorption edge positions of oxide materials with M n + and M ( n +1)+ is usually observed for 3d transition-metal oxides with Co, for 4d metal oxides, a chemical shift of about 1.5–2 V is smaller, as, for example, was shown for different ruthenium oxides …”

“…24 The absorption edge E0 can either be defined as the energy at the x-ray absorption coefficient μ(E) = 0.8 of normalized post-edge intensities, or as the energy corresponding to the maximum of the energy derivative of μ(E), which is in coincidence with the inflection point of the absorption edge. [24][25] While a chemical shift of about 3 eV between absorption edge positions of oxide materials with M n+ and M (n+1)+ is usually observed for 3d transition metal oxides with Co, 26 for 4d metal oxides the chemical shift of about 1.5-2 V is smaller, as for example it was shown for different Ru-oxides. 25 The XAS measurements on the Rh-K edge revealed a shift of about 1.5 eV towards higher energies during delithiation of Li(Li0.2Rh0.8)O2 to Lix0(Li0.2Rh0.8)O2, and back during subsequent material lithiation, see Fig.…”

“…[24][25] While a chemical shift of about 3 eV between absorption edge positions of oxide materials with M n+ and M (n+1)+ is usually observed for 3d transition metal oxides with Co, 26 for 4d metal oxides the chemical shift of about 1.5-2 V is smaller, as for example it was shown for different Ru-oxides. 25 The XAS measurements on the Rh-K edge revealed a shift of about 1.5 eV towards higher energies during delithiation of Li(Li0.2Rh0.8)O2 to Lix0(Li0.2Rh0.8)O2, and back during subsequent material lithiation, see Fig. 6, thus confirming significant participation of Rh in the redox process.…”

Operation Mechanism in Hybrid Mg–Li Batteries with TiNb2O7 Allowing Stable High-Rate Cycling

“…It is well-known that the position of the absorption edge E0 in 3d and 4d transition metal oxides correlates with the metal valence state. 36 The absorption edge E0 can be defined using various approaches: either as the energy corresponding to the maximum of the energy derivative of μ(E), which is in coincidence with the inflection point of the absorption edge, 37 or as the energy at the x-ray absorption coefficient μ(E) = 0.8 of normalized post-edge intensities, 38 that often provide the same adsorption edge energy.…”