Doping Evolution of the Local Electronic and Structural Properties of the Double Perovskite Ba₂Na_1–xCa_xOsO₆

Abstract

We present a combined experimental and computational study of the effect of charge doping in the osmium based double perovskite Ba 2 Na 1– x Ca x OsO 6 for 0 ≤ x ≤ 1 in order to provide a structural and electronic basis for understanding this complex Dirac–Mott insulator material. Specifically, we investigate the effects of the substitution of monovalent Na with divalent Ca, a form of charge doping or alloying that nominally tunes the system from Os 7+ with a 5d 1 configuration to Os 6+ with 5d 2 configuration. After an X-ray diffraction characterization, the local atomic and electronic structure has been experimentally probed by X-ray absorption fine structure at all the cation absorption edges at room temperature; the simulations have been performed using ab initio density functional methods. We find that the substitution of Na by Ca induces a linear volume expansion of the crystal structure which indicates an effective alloying due to the substitution process in the whole doping range. The local structure corresponds to the expected double perovskite one with rock-salt arrangement of Na/Ca in the B site and Os in the B′ one for all the compositions. X-ray absorption near edge structure measurements show a smooth decrease of the oxidation state of Os from 7+ (5d 1 ) to 6+ (5d 2 ) with increasing Ca concentration, while the oxidation states of Ba, Na, and Ca are constant. This indicates that the substitution of Na by Ca gives rise to an effective electron transfer from the B to the B′ site. The comparison between X-ray absorption measurements and ab initio simulations reveals that the expansion of the Os–O bond length induces a reduction of the crystal field splitting of unoccupied Os derived d states.

Discerning phase-matrices for individual nitride inclusions within ultra-high-strength steel: experiment driven DFT investigation

“…The Brillouin zone was sampled with a 3×3×3 k-mesh grid for the structure optimization step. The obtained lattice parameters of austenite were a=b=c=3.646 Å, that of ferrite were a=b=c=2.839 Å, and that of Fe 3 C were a=4.491 Å, b=5.030 Å, c= 6.739 Å, which agreed well with previous theoretical and experimental results [18,19]. For the calculation of XAS spectrum, the super-cell core-hole method as implemented in VASP code was used [16].…”

“…where E tot is the total energy of the system, E Fe , E N , E B , E Al , E Ti , and E C correspond to the total energy per atom (the energy of a single atom in the bulk structure) of Fe, N, B, Al, Ti, and C elements, respectively. The values of the formation energies of bare matrixes are well match reference data [18]. energy was scanned at a 0.2 eV step for B K-edge and N K-edge and a step of 0.1 eV was set for L 2,3-edge.…”

CryoEXAFS: X-ray absorption spectroscopy station with cryogenic or in-beam operando electrochemistry sample conditions at BESSY II

“…• In-situ characterization of materials under catalysis conditions with low-temperature data collection (freeze-quench approach, Klingan et al, 2018;Pasquini et al, 2019, Bergmann et al, 2020Smith et al, 2017) • Operando XAS on films for water oxidation reaction (OER) under electrochemistry conditions at room temperature (Smith et al, 2017;González-Flores et al, 2018) • XAS on dilute-solution (1 mM) protein samples at cryogenic conditions (Reschke et al, 2019) • Rapid-scan EXAFS (redox transitions and catalytic processes during cyclic voltammetry) • EXAFS as a function of chemical composition and/or temperature dependent EXAFS (Kesavan et al, 2020) 3 Technical data (a) XAS experiments at cryogenic (cryostat) or operando (electrochemistry) conditions can be performed in parallel using two energy-resolving detectors. (b) Rapid data readout/transfer (e.g.…”

Pressure Dependence of Structural Behavior and Electronic Properties in Double Perovskite Ba2SmSbO6

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