Determination of Space Group and Refinement of Structure Parameters for La₂CuO_4-δ Crystals

Abstract

The space group in the orthorhombic phase of La2CuO4-δ was confirmed to be Cmca for both as grown and deoxygenated crystals by using conventional and convergent beam electron diffraction together with high resolution neutron powder diffraction methods. The Rietveld refinements of neutron powder diffraction data determined the structural parameters. Slight differences in lattice constants, positional parameters and occupation factor for oxygen atoms were found between the two crystals.

Electrochemically Induced Phase Changes in La2CuO4 During Cathodic Electrocatalysis

“…The expansion of unit cell volume following anodization of LCO and the loss of Cu II observed by XPS confirm that this copper‐based redox process is associated with the insertion of interstitial oxygen ions . Comparison of the unit cell dimensions with previously reported structures for LCO suggests that anodization of the pristine La 2 CuO 4+0.12 yields a comparable La 2 CuO 4+0.11 at 1.3 V and an expanded La 2 CuO 4+0.15 at 1.9 V . The voltammetric characterization below this region is not well documented; we find LCO to be functionally stable when limited to voltages between −0.4 and 1.1 V vs. RHE.…”

“…The as‐prepared material exists in an orthorhombic layered perovskite structure (space group Cmce, ICSD#56528) for which Rietveld refinement indicates unit cell dimensions of 5.3818, 5.4285 and 13.2095 Å (Figure A). LCO accommodates both interstitial oxygen and oxygen vacancies and is often presented as La 2 CuO 4+δ , with wide range of positive and negative δ values reported (Table S1) . The low relative molecular weight of oxygen makes it difficult to directly quantify δ in materials such as La 2 CuO 4 using laboratory powder X‐ray diffraction experiments.…”

“…Early synthesis of this superconducting phase relied on high temperatures and pressures under oxidizing environments, but electrochemical oxidation at moderate potentials in aqueous solutions was later shown to be a facile route to install the requisite interstitial oxygen atoms . While oxygen deficient LCO has been synthesized, details regarding the cathodic electrochemistry of LCO and potential phase changes have not received similar scrutiny. Nonetheless, LCO and related doped phases have been directly employed as catalysts for electrocatalytic reduction reactions including photocatalytic HER, ORR and ECR .…”

Electron microscopic study on SrGdMnO4

“…In the copper-bearing K 2 NiF 4 -type structures, i.e., La 2 MO 4 (M = Cu, Ni) [14][15][16][17] and La 2−x Ba x CuO 4 [18,19], various space groups have been reported so far. We have noticed that our electron diffraction data are essentially the same as those of La 1.9 Ba 0.1 CuO 4 [19] with the orthorhombic Pccm structure.…”

Spontaneous Reactivity of La2CuO4 toward CO2 Diagnosed Using Variable Temperature Raman Spectroscopy

“…The possible role of oxygen vacancies on reactivity of samples with CO 2 was probed by cycling the environment between O 2 , N 2 , and CO 2 at 600 °C. Oxygen nonstoichiometry values (δ in La 2 CuO 4‑δ ) have been reported between −0.1 and 0.2 and can be manipulated in numerous was, including chemical reduction, electrochemical reduction, or heating in oxygen deficient atmospheres. ,− Gas cycling experiments on LCNO and LNO show these structures to be resistant to reaction with CO 2 . Both N 2 and CO 2 atmospheres cause strong growth of a peak at 700 cm –1 for LCNO, which rapidly decays when the atmosphere is changed back to O 2 (Figure S6).…”