Determination of N and O – Atom and N2(A) Metastable Molecule Densities in the Afterglows of N2 and N2‐O2 Microwave Discharges

Early afterglows of N₂ and N₂‐O₂ flowing microwave discharges are characterized by optical emission spectroscopy. The N and O atom and N₂(A) metastable molecule densities are determined by optical emission spectroscopy after calibration by NO titration for N‐atoms and measurements of NO and N₂ band intensities for O‐atoms and N₂(A) metastable molecules. By using N₂ tanks with 50 and 10 ppm impurity, it is determined in the afterglow an O‐ atom impurity of 150‐200 ppm. Variations of the N and O‐atom and N₂(A) metastable molecule densities are obtained in the early afterglow of N₂–(9·10^–5–3·10^–3)O₂ gas mixtures. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

In‐situ X‐ray photoelectron spectroscopy of trimethyl aluminum and water half‐cycle treatments on HF‐treated and O3‐oxidized GaN substrates

We have investigated the effect of trimethyl aluminum (TMA) and water (H₂O) half‐cycle treatments on HF‐treated, and O₃‐oxidized GaN surfaces at 300 °C. The in‐situ X‐ray photoelectron spectroscopy results indicate no significant re‐growth of Ga–O–N or self‐cleaning on HF‐treated and O₃‐oxidized GaN substrates with exposure to water and TMA. This result is different from the self‐cleaning effect of Ga₂O₃ seen on sulfur‐treated GaAs or InGaAs substrates. O₃ causes aggressive oxidation of GaN substrate and direct O–N bonding compared to H₂O. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of N‐carbamoylamino acid nitrosation by {NO + O2} in the solid‐gas phase. Effects of NOx speciation and kinetic evidence for a multiple‐stage process

Nitrosation of N‐carbamoylamino acids (CAA) by gaseous NO + O₂, an interesting synthetic pathway to amino acid N‐carboxyanhydrides (NCA), alternative to the phosgene route, was investigated on N‐carbamoyl‐valine either in acetonitrile suspension or solventless conditions, and compared to the classical nitrosating system NaNO₂ + CF₃COOH (TFA), the latter being quite less efficient in terms of either rate, stoichiometric demand, or further tractability of the product. The rate and efficiency of the NO + O₂ reaction mainly depends on the O₂/NO ratio. Evaluation of the contribution of various nitrosating species (N₂O₃, N₂O₄, HNO₂) through stoichiometric balance showed the reaction to be effected mostly by N₂O₃ for O₂/NO ratios below 0.3, and by N₂O₄ for O₂/NO ratios above 0.4. The relative contribution of (subsequently formed) HNO₂ always remains minor. Differential scanning calorimetry (DSC) monitoring of the reaction in the solid phase by either HNO₂ (from NaNO₂ + TFA), gaseous N₂O₄ or gaseous N₂O₃, provides the associated rate constants (ca. 0.1, 2 and 10⁸ s^?1 at 25°C, respectively), showing that N₂O₃ is by far the most reactive of these nitrosating species. From the DSC measurement, the latent heat of fusion of N₂O_3, 2.74 kJ · mol^?1 at ?105 °C is also obtained for the first time. The kinetics was investigated under solventless conditions at 0°C, by either quenching experiments or less tedious, rough calorimetric techniques. Auto‐accelerated, parabolic‐shaped kinetics was observed in the first half of the reaction course, together with substantial heat release (temperature increase of ca. 20°C within 1–2 min in a 20‐mg sample), followed by pseudo‐zero‐order kinetics after a sudden, important decrease in apparent rate. This kinetic break is possibly due to the transition between the initial solid‐gas system and a solid‐liquid‐gas system resulting from water formation. Overall rate constants increased with parameters such as the specific surface of the solid, the O₂/NO ratio, or the presence of moisture (or equivalently the hydrophilicity of the involved CAA), however without precise relationship, while the last two parameters may directly correlate to the increasing acidity of the medium. Copyright © 2007 John Wiley & Sons, Ltd.     

Vibrational Excitation of N2(B,C) and N+2(B) States in N2 and N2 – H2 Flowing Microwave Discharges

The ro‐vibrational spectra of N₂ microwave discharges have been analysed by emission spectroscopy. It is deduced the rotational and vibrational temperatures of N₂ states. The characteristic of vibrational temperature Θ₁ of the N₂ (X, v) ground state has been specifically determined.It has been found that the N₂ (C, B, v') and N⁺₂ (B, v') radiative states are directly excited by electron collisions on the N₂ (X,v) ground state at a N₂ gas pressure of 0.1 Torr (discharge tube of 5 mm I.D, microwave power 100 Watt) with a Θ₁ value near 10⁴ K. At higher gas pressure up to 5 Torr, the N₂ (C, v') states remain alone to be mainly excited by electron collisions on N₂ (X, v). It is considered the excitations of the N₂ (B, v') states by collisions of electrons and N₂ (X,v > 4) vibrational molecules on the N₂ (A) metastable states.With x < 9% H₂ into N₂, it is observed an increase of N₂, 2^nd pos intensity, resulting of an increase of high energy electrons. Inversely, the N₂, 1^st pos intensity decreased, partly following the decrease of low energy electrons (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal structures of 3‐methyl‐2(1H)‐quinoxalinone and three substituted derivatives

3‐Methyl‐2(1H)‐quinoxalinone and three derivatives (3,7‐dimethyl‐2(1H)‐quinoxalinone, 3‐methyl‐6,7‐dichloro‐2(1H)‐quinoxalinone and 3‐methyl‐7‐nitro‐2(1H)‐quinoxalinone) have been synthesised and analysed by ¹H NMR and IR spectral spectroscopies. The crystal structures have been determined at room temperature from X‐ray single crystal diffraction data for three of them and from powder diffraction data for the nitro derivative. 3‐Methyl‐2(1H)‐quinoxalinone crystallises in the P2₁/c monoclinic system, 3,7‐dimethyl‐2(1H)‐quinoxalinone in the Pbca orthorhombic system and the two others compounds in the P$\overline {1} $ triclinic system. For the nitro derivative, C? H$\cdots $ N short contacts are established between the carbon of the methyl and the double bounded nitrogen of the ring. For the three other compounds N? H$\cdots $ O hydrogen bonds involve the atoms of the heterocyclic ring. Copyright © 2011 John Wiley & Sons, Ltd.     

Electronic structure and enhanced visible‐light absorption of N,B‐codoped TiO2

We present GGA+U calculations to investigate the electronic structure and visible‐light absorption of N,B‐codoped anatase TiO₂. The N_sB_i (substitutional N, interstitial B) codoped TiO₂ produces significant Ti 3d and N 2p mid‐gap states when the distance of N and B atoms is far, whereas the N_iB_i (interstitial N and B) and N_sB_s (substitutional N and B) codoped TiO₂ prefer to form localized p states at 0.3–1.2 eV above the valence band maximum. Further, the optical band edges of the three codoped systems shift slightly to the visible region, but only the far‐distance N_sB_i codoped TiO₂ clearly shows an optical transition. These results indicate that N_sB_i codoped TiO₂ has a dominant contribution to the optical absorption of N,B‐codoped TiO₂. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Acid‐base properties and supramolecular structure of N‐[(hydroxymethyl)triazolyl]triflamides: DFT,ab initio,and FTIR study

For N‐{[2‐(hydroxymethyl)‐2H‐1,2,3‐triazolyl‐4‐yl]methyl}triflamide 1 , N‐{[2‐(hydroxymethyl)‐2H‐1,2,3‐triazolyl‐4‐yl]methyl}‐N‐phenyltriflamide 2 , and N,N‐bis{[2‐(hydroxymethyl)‐2H‐1,2,3‐triazolyl‐4‐yl]methyl}triflamide 3 , the proton affinities of the triazole nitrogen atoms and the hydroxy and sulfonyl oxygen atoms as well as the energies of formation of the conformers with intramolecular H‐bonds and dimers with intermolecular NH?N, OH?N, OH?O═S, and NH?O═S H‐bonds were calculated by density functional theory and second‐order Møller‐Plesset perturbation methods. Quantum Theory of Atoms in Molecules analysis was performed to investigate the nature of H‐bonds. According to Fourier transform infrared spectroscopy, in CH₂Cl₂ solution, the monomeric molecules of 1 to 3 exist in the equilibrium with cyclic dimers having the OH?N hydrogen bonds.     

Emission spectroscopy detection of N2 active species in plasma nitriding process

The present paper is a review of recent works related to the optical emission spectroscopy applied to the determination of ground state densities of N atoms in Ar-N₂ flowing post-discharges. The effect of small quantities of H₂ in the Ar-N₂ discharge on N atom densities within the post-discharge has been analysed. The authors demonstrate that optical emission of Na impurity may be applied to the determination of the vibrational temperature of N₂(X,v) states at the temperatures usual for nitriding of metals in Ar-N₂ post-discharge. From the diagnostic of Ar-N₂ post-discharges, it is clearly specified that nitriding of iron base alloys in a flowing post-discharge reactor is originating in N atoms, especially when a few H₂ molecules are admixed into the Ar-N₂ discharge. Finally, correlation between the N-atom density and the thickness of the iron nitrided layers when H₂ is introduced into the Ar-N₂ discharge are given. Dedicated to Prof. Jan Janča on the occasion of his 60^th birthday.     

A combined experimental and density functional study of 1‐(arylsulfonyl)‐2‐R‐4‐chloro‐2‐butenes reactivity towards the allylic chlorine

Nucleophilic substitution and dehydrochlorination reactions of a number of the ring‐substituted 1‐(arylsulfonyl)‐2‐R‐4‐chloro‐2‐butenes are studied both experimentally and theoretically. The developed synthetic procedures are characterized by a general rapidity, cheapness, and simplicity providing moderate to high yields of 1‐arylsulfonyl 1,3‐butadienes (48–95%), 1‐(arylsulfonyl)‐2‐R‐4‐(N,N‐dialkylamino)‐2‐butenes (31–53%), 1‐(arylsulfonyl)‐2‐R‐2‐buten‐4‐ols (37–61%), and bis[4‐(arylsulfonyl)‐3‐R‐but‐2‐enyl]sulfides (40–70%). The density functional theory B3LYP/6‐311++G(2d,2p) calculations of the intermediate allylic cations in acetone revealed their high stability occurring from a resonance stabilization and hyperconjugation by the SO₂Ar group. The reactivity parameters estimated at the bond critical points of the diene/allylic moiety display a high correlation (R² > 0.97) with the Hammett (σ_p) constants. 1‐Arylsulfonyl 1,3‐butadienes are characterized by a partly broken π conjugated system, which follows from analysis of the two‐centered delocalization (δ) and localization (λ) index values. The highest occupied molecular orbital energies of 1‐arylsulfonyl 1,3‐butadienes are lower than those of 1,3‐butadiene explaining their low reactivity towards the Diels–Alder condensation. Copyright © 2015 John Wiley & Sons, Ltd.     

Rotational disorder in 2‐piperidyl‐5‐nitro‐6 ‐methylpyridine: structural phase transition and its vibrational characteristics

X‐ray diffraction (XRD) studies have shown that 2‐piperidyl‐5‐nitro‐6‐methylpyridine, C₁₁H₁₅N₃O₂, undergoes a structural phase transition at T = 240 K. The room temperature structure is tetragonal, space group I4₁/a, with the unit‐cell dimensions a = 13.993(2) and c = 23.585(5) Å. The pyridine ring takes trans conformation with respect to the piperidine unit. While pyridine is well ordered, the piperidine moiety shows apparent disorder resulting from a libration about the linking N C bond. The low‐temperature phase is monoclinic, space group I2/a. Contraction of the unit‐cell volume by 2.3% at 170 K enables the C H···O linkage between the molecules of the neighbouring stacks. As result, the asymmetric unit becomes bi‐molecular. The thermal librations of the piperidine and methyl groups become considerably reduced at 170 K and nearly fully reduced at about 100 K. The IR spectra and polarised Raman spectra agree with the X‐ray structure and confirm the disorder effect on the piperidine ring. The assignment of the bands observed was made on the basis of DFT chemical quantum calculations. Copyright © 2008 John Wiley & Sons, Ltd.     

Detection of small amounts of H2O in CO2‐rich fluid inclusions using Raman spectroscopy

Raman spectroscopic analysis at low (−100 °C) or high (100–200 °C) temperature is shown to be effective for detecting small amounts of H₂O in CO₂‐rich fluid inclusions from the deep lithosphere, which have previously been thought to be water‐free. Copyright © 2009 John Wiley & Sons, Ltd.     

Silicon surface passivation by atomic‐layer‐deposited Al2O3 facilitated in situ by the combination of H2O and O3 as reactants

We investigate the effect of O₃ and H₂O oxidant pre‐pulse prior to Al₂O₃ atomic layer deposition for Si surface passivation. Interfacial oxide SiO_x formed by the O₃ pre‐pulse is more beneficial than that by H₂O to a high level of surface passivation. The passivation of thinner H₂O–Al₂O₃ films is more improved by this O₃ pre‐pulse. O₃ pre‐pulse for 10 nm H₂O–Al₂O₃ reduces saturation current density in boron emitter to 18 fA cm^–2 by a factor of 1.7. Capacitance–voltage measurements reveal this interfacial oxide plays a role of decreasing interface trap density without detrimental effect to negative charge density of Al₂O₃. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Identification of epidermal L‐tryptophan and its oxidation products by in vivo FT‐Raman Spectroscopy further supports oxidative stress in patients with vitiligo

In the past, non‐invasive in vivo FT‐Raman spectroscopy has been used to detect H₂O₂‐mediated oxidation of methionine to methionine sulfoxide and methionine sulfone, as well as cysteine to cysteic acid, in the sequence of proteins in the epidermis of patients with vitiligo. L ‐tryptophan (Trp) is another potential target for this oxidation. Owing to the presence of 10⁻³M epidermal albumin which contains one Trp residue, it was tempting to follow the oxidation of this amino acid. Using in vivo and in vitro FT‐Raman spectroscopy, we show for the first time that epidermal Trp is oxidised in patients with vitiligo, yielding 5‐OH‐Trp at 930 cm⁻¹ and other oxidation products (i.e. N‐formyl kynurenine and kynurenine) from indole ring oxidation peaking at 1050 cm⁻¹. On the basis of detailed in vitro results, we could conclude that 5‐OH‐Trp as well as formyl kynurenine and kynurenine are formed via H₂O₂‐mediated Fenton chemistry. These results once again bring out the strength of non‐invasive in vivo FT‐Raman Spectroscopy in dermatology to follow the effect of oxidative stress in the skin of patients with vitiligo. Copyright © 2008 John Wiley & Sons, Ltd.     

Effect of microheterogeneity of CF3CH2OH–H2O mixed solvent on reactions of carbocations from 1,2,2,3‐tetramethyl‐1,2‐dihydroquinoline

Carbocations are key intermediates in many important organic reactions. The remarkable effect of the solvent composition on the kinetic parameters of the carbocation decay and product composition was found in the photolysis of 1,2,2,3‐tetramethyl‐1,2‐dihydroquinoline ( 1 ) in 2,2,2‐trifluoroethanol (TFE)–H₂O mixtures. The rate constant of the intermediate carbocation decay has a maximum, and the activation energy is minimal in the TFE–H₂O mixture 3 : 7 (v/v). In the steady‐state photolysis, products of oligomerization of 1 with n up to 8 and their adducts with TFE and H₂O were identified at this solvent composition. The results were rationalized in terms of TFE clustering in aqueous mixtures, with the maximum of cluster formation at 30 vol % TFE. The clusters form a pseudo‐phase, in which the molecules of 1 are concentrated and the carbocations are generated. TFE, H₂O and 1 compete in the combination reaction with the photogenerated carbocation to afford the products. This effect was not observed for 1,2,2,4‐tetramethyl‐1,2‐dihydroquinoline ( 2 ), the isomer of 1 , due to steric hindrance at C(4) carbon atom of the heterocycle, the active site of the intermediate carbocation, which makes impossible for the carbocation from 2 to react further with 2 . Thus, the kinetic parameters and the product composition in the photolysis of 1 in TFE–H₂O mixtures reflect the changes in the microstructure of the binary solvent. Copyright © 2013 John Wiley & Sons, Ltd.     

Solvation structure of magnesium,zinc, and alkaline earth metal ions in N,N‐dimethylformamide,N,N‐dimethylacetamide,and their mixtures studied by means of Raman spectroscopy and DFT calculations—Ionic size and electronic effects on steric congestion

The solvation structure of magnesium, zinc(II), and alkaline earth metal ions in N,N‐dimethylformamide (DMF) and N,N‐dimethylacetamide (DMA), and their mixtures has been studied by means of Raman spectroscopy and DFT calculations. The solvation number is revealed to be 6, 7, 8, and 8 for Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺, respectively, in both DMF and DMA. The δ (O C N) vibration of DMF shifts to a higher wavenumber upon binding to the metal ions and the shift Δν(= ν_bound − ν_free) becomes larger, when the ionic radius of the metal ion becomes smaller. The ν (N CH₃) vibration of DMA also shifts to a higher wavenumber upon binding to the metal ions. However, the shift Δν saturates for small ions, as well as the transition‐metal (II) ions, implying that steric congestion among solvent molecules takes place in the coordination sphere. It is also indicated that, despite the magnesium ion having practically the same ionic radius as the zinc(II) ion of six‐coordination, their solvation numbers in DMA are significantly different. DFT calculations for these metalsolvate clusters of varying solvation numbers revealed that not only solvent–solvent interaction through space but also the bonding nature of the metal ion plays an essential role in the steric congestion. The individual solvation number and the Raman shift Δν in DMF–DMA mixtures indicate that steric congestion is significant for the magnesium ion, but not appreciable for calcium, strontium, and barium ions, despite the solvation number of these metal ions being large. Copyright © 2006 John Wiley & Sons, Ltd.     

Experimental and theoretical FT‐IR and FT‐Raman spectroscopic analysis of N1‐methyl‐2‐chloroaniline

In this work, the experimental and theoretical vibrational spectra of N1‐methyl‐2‐chloroaniline (C₇H₈NCl) were studied. FT‐IR and FT‐Raman spectra of the title molecule in the liquid phase were recorded in the region 4000–400 cm^?1 and 3500–50 cm^?1, respectively. The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional method (B3LYP) with the 6‐311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FT‐IR and FT‐Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. ¹³C and ¹H NMR chemical shifts results were compared with the experimental values. The optimized geometric parameters (bond lengths and bond angles) were given and are in agreement with the corresponding experimental values of aniline and p‐methyl aniline. Copyright © 2008 John Wiley & Sons, Ltd.     

N‐protonated and O‐protonated tautomers of 1‐azabicyclo[3.3.1]nonan‐2‐one: observation of individual 13C‐NMR carbonyl peaks and comparisons with protonated tautomers of planar and other distorted lactams

An earlier study fit calculated dynamic ¹³C‐NMR spectra in trifluoroacetic acid (TFA) (with added sulfuric acid) to slow exchange between N‐protonated and O‐protonated tautomers of 1‐azabicyclo[3.3.1]nonan‐2‐one. The present study reports simultaneous observation of both carbonyl ¹³C peaks in 40% sulfuric acid/60% TFA at ?40 °C. This furnishes the only example in which experimental carbonyl ¹³C chemical shifts may be compared with a neutral lactam (in TFA or CDCl₃) with its N‐protonated and O‐protonated derivatives. The seemingly anomalous upfield chemical shifts (experimental and computational) of the ¹³C carbonyl peaks in this N‐protonated lactam (and other twisted N‐protonated lactams) relative to the free bases are compared with data for unstrained protonated lactams and amides. The results are rationalized through conventional resonance structures. Copyright © 2012 John Wiley & Sons, Ltd.     

Solvent‐dependent structural dynamics of 2(1H)‐pyridinone in light absorbing S4(ππ*) state

The B‐band resonance Raman spectra of 2(1H)‐pyridinone (NHP) in water and acetonitrile were obtained, and their intensity patterns were found to be significantly different. To explore the underlying excited state tautomeric reaction mechanisms of NHP in water and acetonitrile, the vibrational analysis was carried out for NHP, 2(1D)‐pyridinone (NDP), NHP–(H₂O)_n (n = 1, 2) clusters, and NDP–(D₂O)_n (n = 1, 2) clusters on the basis of the FT‐Raman experiments, the B3LYP/6‐311++G(d,p) computations using PCM solvent model, and the normal mode analysis. Good agreements between experimental and theoretically predicted frequencies and intensities in different surrounding environments enabled reliable assignments of Raman bands in both the FT‐Raman and the resonance Raman spectra. The results indicated that most of the B‐band resonance Raman spectra in H₂O was assignable to the fundamental, overtones, and combination bands of about ten vibration modes of ring‐type NHP–(H₂O)₂ cluster, while most of the B‐band resonance Raman spectra in CH₃CN was assigned to the fundamental, overtones, and combination bands of about eight vibration modes of linear‐type NHP–CH₃CN. The solvent effect of the excited state enol‐keto tautomeric reaction mechanisms was explored on the basis of the significant difference in the short‐time structural dynamics of NHP in H₂O and CH₃CN. The inter‐molecular and intra‐molecular ESPT reaction mechanisms were proposed respectively to explain the Franck–Condon region structural dynamics of NHP in H₂O and CH₃CN.Copyright © 2015 John Wiley & Sons, Ltd.     

Solvatochromic properties of long alkyl chain π* indicators: comparison of N,N‐dialkyl‐4‐nitroanilines and alkyl 4‐nitrophenyl ethers

Hydrophobic forms of the N,N‐dialkyl‐4‐nitroaniline (DNAP) (p‐O₂NC₆H₄NR₂) ( 1a–f ) and alkyl‐4‐nitrophenyl ether (p‐O₂NC₆H₄OR) ( 2a–c ) solvatochromic π* indicators have been characterized and compared with respect to: (a) solvatochromic bandshape, (b) sensitivity expressed as ?s , ( / d π * ), and (c) trends in ? s with increasing length of alkyl chain(s) on the probe molecule. ? Octyl 4‐nitrophenyl ether (p‐O₂NC₆H₄OC₈H₁₇) ( 2b ) and ? decyl 4‐nitrophenyl ether (p‐O₂N C₆H₄ OC₁₀H₂₁) ( 2c ) were synthesized and their solvatochromic UV/Vis absorption bands were found to maintain a Gausso‐Lorentzian bandshape for the indicators in non‐polar and alkyl substituted aromatic solvents, for example, hexane(s) and mesitylene. Corresponding absorption bands for 1a–f display increasing deviation from a Gausso‐Lorentzian shape in the same solvents as the alkyl chains on the indicator are increased in length all the way to C₁₀ and C₁₂, for example, N,N‐didecyl‐4‐nitroaniline (p‐O₂NC₆H₄N (C₁₀H₂₁)₂) and N,N‐didodecyl‐4‐nitroaniline (p‐O₂NC₆H₄N (C₁₂H₂₅)₂) ( 1d–f ). A plot of ? s versus C_n follows a 1st order decay for the DNAP indicators but is linear for the alkyl 4‐nitrophenyl ethers. A discussion of how the long alkyl chains on the two types of indicators affect the orientation and overlap of n and π * orbitals, and resulting solvatochromic bands is presented. For DNAP, overextending the alkyl chains to obtain greater hydrophobic character may cause the alkane component to dominate solute‐solvation processes at the expense of the probe's fundamental solvatochromic character. Copyright © 2007 John Wiley & Sons, Ltd.     

Interrelation between inhomogeneity and cyclability in O3‐NaFe1/2Co1/2O2

O3‐NaFe_1/2Co_1/2O₂ shows initial capacity of 160 mAh/g and an average operating voltage of 3.1 V (vs. Na) with good cyclability, and is a promising candidate of the cathode materials for sodium‐ion secondary batteries (SIBs). Here, we found that the cyclability of the slowly‐cooled sample is much worse than that of quenched one, even though the former sample keeps the O3‐type structure. The energy dispersive X‐ray spectroscopy (EDX) images suggest that the slow‐cooled sample (Na_x Fe_1–yCo_y O₂) is inhomogeneous in the Fe concentration (1 – y), perhaps triggered by the Na deficiency (1 – x). We ascribed the poor cyclability in the slowly‐cooled sample to the concentration inhomogeneity (Δy). The Δy is further responsible for the fluctuation of the lattice constants (a and c), as revealed by the Williamson–Hall plot. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)