Experimental and Theoretical Study of the Electronic Structures of Lanthanide Indium Perovskites LnInO₃

Abstract

Ternary lanthanide indium oxides LnInO 3 (Ln = La, Pr, Nd, Sm) were synthesized by high-temperature solid-state reaction and characterized by Xray powder diffraction. Rietveld refinement of the powder patterns showed the LnInO 3 materials to be orthorhombic perovskites belonging to the space group Pnma, based on almost-regular InO 6 octahedra and highly distorted LnO 12 polyhedra. Experimental structural data were compared with results from density functional theory (DFT) calculations employing a hybrid Hamiltonian. Valence region X-ray photoelectron and K-shell X-ray emission and absorption spectra of the LnInO 3 compounds were simulated with the aid of the DFT calculations. Photoionization of lanthanide 4f orbitals gives rise to a complex final-state multiplet structure in the valence region for the 4f n compounds PrInO 3 , NdInO 3 , and SmInO 3 , and the overall photoemission spectral profiles were shown to be a superposition of final-state 4f n−1 terms onto the cross-section weighted partial densities of states from the other orbitals. The occupied 4f states are stabilized in moving across the series Pr−Nd−Sm. Band gaps were measured using diffuse reflectance spectroscopy. These results demonstrated that the band gap of LaInO 3 is 4.32 eV, in agreement with DFT calculations. This is significantly larger than a band gap of 2.2 eV first proposed in 1967 and based on the idea that In 4d states lie above the top of the O 2p valence band. However, both DFT and X-ray spectroscopy show that In 4d is a shallow core level located well below the bottom of the valence band. Band gaps greater than 4 eV were observed for NdInO 3 and SmInO 3 , but a lower gap of 3.6 eV for PrInO 3 was shown to arise from the occupied Pr 4f states lying above the main O 2p valence band.

Toward Zero-Strain Mixed Conductors: Anomalously Low Redox Coefficients of Chemical Expansion in Praseodymium-Oxide Perovskites

“…Nonetheless, when O-2p holes are filled ( U = 10 eV), the CCE is an order of magnitude smaller than when Pr-4f holes are filled ( U = 4 eV). While the exact positions of the Pr-4f and O-2p states are not known from the experiment, we were able to find PES data for the related compound PrInO 3, which shares the same Pbnm space group as PrGaO 3 , and the data indicate that the Pr-4f states are located slightly above the O states (see Figure S11a). This suggests that a U value roughly in the range of 6–8 eV may reasonably describe PGM in our simulations.…”

Investigation of the Solution Chemistry of Hybrid Organic–Inorganic Indium Halides for New Material Discovery

“…Understanding the absorption origin of the 281 nm band is assisted by first performing a comprehensive survey of the different coordination environments that indium could form in the various solid-state products. − According to the survey results, several possible geometries were selected for DFT calculations (see Figure ). In fact, the most reported indium halide crystal structures are based on tetrahedra, octahedra, or a combination of the two within one crystal structure. − A few representative examples include InBr 2 , which is based on InBr 4 – tetrahedral building blocks. , For CsInBr 3 , indium adopts an octahedral InBr 6 3– coordination . Unusual for most metals, crystal structures of In 4 Br 7 and (C 4 H 14 N 2 ) 2 In 2 Br 10 contain a combination of the InBr 4 – tetrahedral and InBr 6 3– octahedral anions. , …”

Highly Active Hydrogen‐rich Photothermal Reverse Water Gas Shift Reaction on Ni/LaInO3 Perovskite Catalysts with Near‐unity Selectivity

“…The spin‐polarized total and partial density of states (TDOS and PDOS) reveal that the conduction band and valence band of LaInO 3 are mainly constructed by the La‐d and O‐p states, respectively (Figure S9). A strong DOS distribution at the Fermi level (0 eV) after Ni NPs loading indicates a significant increase of the d‐band center, leading to a faster charge transfer rate [40, 41] . Thus, we propose a photoinduced charge transfer (PCT) process to explain the shifts of the binding energy of O 1s, La 3d and Ni 3p, in which the photoexcited electron of O atoms transfer to Ni NPs and La atoms.…”