Beiträge zu den Eigenschaften von Titanaten mit Ilmenitstruktur. I. Aspekte eines Hochtemperaturphasenübergangs in NiTiO3

Contributions to the Properties of Titanates with Ilmenite Structure. I. Aspects of a High Temperature Phase Transition in NiTiO₃ NiTiO₃ (Ilmenite structure) shows an anomalous increase of the electrical conductivity in the temperature range between 1 250°C and 1 290°C. The temperature dependence of the Seebeck coefficient is also found to be anomalous in this region. DTA experiments are consistent with a phase transition; the transition enthalpy was estimated to Δ_uH_m = 17 ± 3 kJmol^?1. NiTiO₃ powders and single crystals were quenched from 1 350°C and 1 200°C to room temperature; in principle no differences of the lattice parameters or atomic positions could be detected. The determination of the distribution of cations using x-ray powder methods failt because of strong texture effects. Structure refinements with single crystal methods suggest an ordered Ilmenite structure independent of the quenching temperature. The results are in agreement with a reversible order-disorder transition of higher order. It seems to be impossible to quench the high temperature phase by conventional methods.     

Oberflächenzusammensetzung,Löslichkeit und Ionenaktivitätsprodukt von Calcit in fremdionenhaltigen Lösungen

Surface Composition, Solubility, and the Ion Activity Product of Calcite in Solutions with Auxiliary Ions Using the method of simultaneous ion and isotope exchange the chemical composition of the surface layer of calcite powder in equilibrium with solutions of varying Me/Ca molar ratios is determined (Me = Mg²⁺, Co²⁺, Ni²⁺, and Fe²⁺ ions). The ion exchange isotherms show a marked bend in the surface reactivity when a surface molar ration of ～1 and ～3 is reached. The solubility of calcite initially decreases on the addition of Co²⁺ or Ni²⁺ ions to the solution whereas it increases in the presence of Mg²⁺ or Fe²⁺ ions. The activity product of the pseudo compound, Ca_xMe_(1–x)CO₃, decreases in the Ni²⁺, Co²⁺ or Fe²⁺ exchange experiments, however, it increases considerably in those with Mg²⁺ ions.     

Phase relations and exsolution phenomena in the system NiOTiO2

The phase relations in the system NiOTiO₂ were studied between 1000 and 1600°C using quenched powder specimens, DTA runs, and single crystal diffusion couples. Quenching experiments establish the stable phases TiO₂ (rutile), NiTiO₃ an ilmenite structure type, Ni_2(1+x)Ti_1?xO₄ (x ≥ 0.16), a cation-excess spinel, and Ni_1?2xTi_xO (rocksalt structure type). DTA runs reveal the existence of an additional nonstoichiometric ilmenite phase Ni_1?2xTi_1+xO₃ (x ≤ 0.03) above 1260°C. In quenched (1500, 1450°C) or slowly cooled single crystal diffusion couples, mutual oriented exsolutions occur in the rutile crystal and in the ilmenite diffusion zone. Orientation relations are: {101}_rutile{1120}_ilmenite; ∥010〉_rutile∥00.1〉_ilmenite. The cation-excess spinel decomposes below 1375°C into oriented intergrowth of NiTiO₃ (ilmenite) and NiO: {111}_NiO{0001}_NiTiO3; ∥110〉_NiO∥21.0〉_NiTiO3.     

Verbindungen der L-Ascorbinsäure mit Metallen. I. Zur Darstellung von Ascorbatkomplexen einiger 3d-Elemente

Compounds of L-Ascorbic Acid with Metals. I. Preparation of Ascorbate Complexes of Some Elements of the First Transition Series From a systematic investigation of the factors impairing the preparation of pure ascorbate complexes of transition elements a general procedure for their preparation is derived, and the synthesis of hitherto unknown ascorbate complexes of TiO²⁺, Cr³⁺, Mn²⁺, Co²⁺, Ni²⁺, and Zn²⁺ is described.     

Solid state reactivity and mechanisms in oxide systems

Starting from oxalate mixed crystals Ni_xMn_3?x(C₂O₄)₃·6H₂O thermal decomposition at reduced oxygen partial pressure (po₂= 2%) leads to the formation of NiMn₂O₄ (x = 1) at metastable conditions. Ni_1.5Mn_1.5O₄ (x = 1.5) existing in the metastable state only has been also prepared. The spinel compounds both are of the highly inversed type. Following a sol-gel preparation route Mg₂TiO₄ has been also found to be formed in the metastable state. Annealing results in decomposition of the compounds providing NiMnO₃ and 1/2α-Mn₂O₃ or NiMnO₃ only or MgTiO₃ and MgO, respectively. The reaction rates observed are lower for NiMn₂O₄ and Ni_1.5Mn_1.5O₄ than for Mg₂TiO₄ decomposition. The reverse reaction of NiMn₂O₄ formation above 730°C shows an endothermic enthalpy of +61 kJ·mol^?1. For Mg₂TiO₄ formation above 1050°C an endothermic enthalpy of +19.3 kJ·mol^?1 is found. The results are discussed in terms of structural features of the oxides.     

纯相和镍取代的Co_3O_4尖晶石催化剂用于N_2O直接分解(英文)

A series of NixCo1-xCo2O4(0 ≤ x ≤ 1) spinel catalysts were prepared by the co-precipitation method and used for direct N2O decomposition. The decomposition pathway of the parent precipitates was characterized by thermal analysis. The catalysts were calcined at 500 °C for 3 h and characterized by powder X-ray diffraction, Fourier transform infrared, and N2 adsorption-desorption. Nickel cobaltite spinel was formed in the solid state reaction between NiO and Co3O4. The N2O decomposition measurement revealed significant increase in the activity of Co3O4 spinel oxide catalyst with the partial replacement of Co2+ by Ni2+. The activity of this series of catalysts was controlled by the degree of Co2+ substitution by Ni2+, spinel crystallite size, catalyst surface area, presence of residual K+, and calcination temperature.     

Metallkomplexe der Phosphinsäuren. XVII. Untersuchungen zur Oligomerisation von NiII- und CoII-Komplexen bifunktioneller Dithiophosphinsäuren HS(S)P(R)-R′-(R)P(S)SH [2]

Metal Complexes of Phosphinic Acids. XVII. Investigations on the Oligomerisation of Ni^II and Co^II Complexes of Bifunctional Dithiophosphinic Acids Alkali or ammonium salts of bifunctional dithiophosphinic acids react with Ni²⁺ or Co²⁺ to give complexes [S₂P(R)? (CH₂)_n? (R)PS₂M]_m or _x (R = 4-methoxyphenyl; M = Ni²⁺, Co²⁺; n = 4? 10) some of which are soluble in organic solvents and of low molecular weight (m), while others are insoluble (x). According to magnetic and spectroscopic measurements all of them contain planar NiS₄ or tetrahedral CoS₄ chromophors. While the insoluble compounds are regarded as coordination polymers, it is shown by osmometric measurements and by ³¹P{¹H} spectroscopy, that there exists the equilibrium monomers (ansa type) ? oligomers in solutions of the soluble complexes. The influence of n on the solubility and the equilibrium is discussed. The association can be explained by simple statistic considerations.     

NixCo3-xO4表面修饰对CdSe/TiO2纳米管阵列光电化学氧化水活性的影响

利用氨挥发诱导法在CdSe/TiO2纳米管阵列表面负载一层NixCo3-xO4。采用SEM、XRD、XPS、UV-Vis对样品进行表征,通过线性扫描伏安法测定光阳极的释氧电势来评价其光电水氧化活性。结果表明:表面NixCo3-xO4是尖晶石结构;相对于CdSe/TiO2纳米管阵列光阳极,NixCo3-xO4/CdSe/TiO2光阳极能将光电氧化水的过电势降低430 mV。Ni离子的引入使得NixCo3-xO4表面富含三价阳离子(Ni3+,Co3+),从而促进CdSe/TiO2光阳极光电水氧化的进行。     

Zur Thermochemie und Struktur von Berylliumchlorid

Thermochemistry and Structure of Beryllium Chloride BeCl₂ is dimorphous, with a transition point at 405°C. The transition enthalpy and transition entropy have been determined by solution calorimetry: Δ_UH° = 2.9 kJmol^?1 and Δ_US° = 9.7 JK^?1mol^?1. The previously known SiS₂-type structure of BeCl₂ is that of the high temperature phase. The structure of the phase stable at room temperature has been determined from single crystal data. a = 1 062.4(6) pm, c = 1 804(2) pm, I4₁/acd, Z = 32, R = 0.038 (Mg(NH₂)₂-type). The structure consists of P₄O₁₀-like [Be₄Cl₆Cl_4/2]-units, connected by their terminal anions.     

Farbe und Konstitution bei anorganischen Feststoffen, 7. Mitt.: Die Lichtabsorption des zweiwertigen Nickels in oxidischen Koordinationsgittern vom Ilmenittyp

Zusammenfassung Die Systeme NiTiO₃/CdTiO₃ und MgTiO₃/CdTiO₃ werden röntgenographisch und spektralphotometrisch untersucht. Es zeigt sich, daß nur begrenzte Mischkristallbildung vorhanden ist. Im Gitter von CdTiO₃ können nur etwa 0,05 Cd²⁺ durch Ni²⁺ bei 890°C und 0,03 Cd²⁺ bei 600°C isomorph ausgetauscht werden. Eine isomorphe Substitution von Ni²⁺ durch Cd²⁺ im NiTiO₃ kann nicht nachgewiesen werden.Die Ni-haltige CdTiO₃-Phase (I) ist rot, die NiTiO₃-Phase (II) gelb. Die drei Hauptabsorptionsbanden von I sind gegenüber denen von II stark nach IR verschoben infolge des schwächeren Kristallfeldes am Ort des eingebauten Ni²⁺. Während also der Feldparameter beim Übergang III abnimmt, ändert sich derRacah-ParameterB nicht.Um das System MgTiO₃/CdTiO₃ spektralphotometrisch zu untersuchen, wird mit Ni²⁺ als optischem Indikator dotiert. Es zeigt sich, daß in CdTiO₃ mehr als 0,1 Cd²⁺ durch Mg²⁺ isomorph ersetzt werden können. Die Einbaugrenze dürfte bei 0,2 Mg²⁺ liegen.Die Ergebnisse bestätigen erneut, daß die Hauptabsorptions-banden eines farbgebenden Kations nach Einbau in ein Wirtsgitter mit nur einer Art von kationischen Gitterpositionen in Richtung IR verschoben werden, wenn das Wirtsgitter durch isomorphen Einbau größerer Kationen aufgeweitet wird.

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The systems NiTiO₃/CdTiO₃ and MgTiO₃/CdTiO₃ were investigated by X-rays and spectrophotometrically. There is only a limited formation of mixed crystals. In the lattice of CdTiO₃ (ilmenite structure) only about 0,05 Cd²⁺ can be substituted isomorphously by Ni²⁺ at 890°C and 0,03 Cd²⁺ at 600°C respectively. An isomorphous substitution of Ni²⁺ by Cd²⁺ in NiTiO₃ could not be proved. The Ni²⁺ containing CdTiO₃ phase (I) is red, the NiTiO₃ phase (II) yellow. The three main absorption bands of (I) compared with those of (II) are considerably shifted towards IR on account of the weaker crystal field at the spot where Ni²⁺ is incorporated. Whereas the crystal field parameter decreases by the transition (I) (II), theRacah parameter B does not change.To investigate the system MgTiO₃/CdTiO₃ spectrophotometrically the lattices are doped with Ni²⁺ as an optical indicator.In CdTiO₃ more than 0,1 Cd²⁺ can be substituted isomorphously by Mg²⁺. The limit may be about 0,2 Mg²⁺.The results confirm again, that the main absorption bands of a colouring cation after the incorporation into a host lattice with only one kind of cationic sites are shifted towards IR if this lattice will be expanded by isomorphous incorporation of larger cations.

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Mit 6 Abbildungen

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6. Mitt.:O. Schmitz-DuMont undNorbert Moulin, Z. anorg. allgem. Chem.,330 259 (1964).     

Farbe und Konstitution bei anorganischen Feststoffen, 12. Mitt.: Die Lichtabsorption des zweiwertigen Kobalts in oxidischen Koordinationsgittern vom Ilmenittyp

Zusammenfassung Die Systeme Co _x Mg _1-x TiO₃ (I) und Co _x Cd _1-x TiO₃ (II) wurden röntgenographisch und spektralphotometrisch untersucht. I stellt eine lückenlose Mischkristallreihe dar. Mit wachsendemx nehmen bei I die Gitterkonstantena ₀undc ₀geringfügig zu und die drei Hauptabsorptionsbanden verschieben sich ein wenig in Richtung IR. In II liegt keine lückenlose Mischkristallreihe vor. Sowohl röntgenographisch als auch spektralphotometrisch wurde für die an CoTiO₃ gesättigte CdTiO₃-Phase die Zusammensetzung Co_0,3Cd_0,7TiO₃ (II a) und für die an CdTiO₃ gesättigte CoTiO₃-Phase die Zusammensetzung Co_0,8Cd_0,2TiO₃ (II b) gefunden.Beim Übergang III (x=0,1) wird eine beträchtliche IR-Verschiebung beobachtet. Die IR-Verschiebung ist die Folge der Gitteraufweitung bei der Substitution von Mg²⁺ durch Cd²⁺. Hierbei nimmt derRacah-Parameter geringfügig zu infolge Verminderung der covalenten Anteile der Bindung Co-O.

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The systems Co _x Mg _1-x TiO₃ (I) and Co _x Cd _1-x TiO₃ (II) had been investigated spectrophotometrically and by X-ray diffraction. I represents mixed crystals without any miscibility gap. An increase ofx causes a small enhancement of the lattice unitsa ₀andc ₀of I and the three main absorption bands will be shifted slightly towards IR. II are mixed crystals with a broad miscibility gap. Spectrophotometrically and by X-ray diffraction it could be found that the CdTiO₃-phase saturated with CoTiO₃ and the CoTiO₃-phase saturated with CdTiO₃ have the compositions Co_0,3Cd_0,7TiO₃ (II a) and Co_0,8Cd_0,2TiO₃ (II b), respectively. The transition III (x=0,1) produces a considerable shift of the main absorption bands towards IR as a consequence of the expansion of the lattice caused by the substitution of Cd²⁺ for Mg²⁺. This shift is accompanied by a small increase of theRacah-Parameter owing to a decrease of covalency of the bonding Co-O.

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Mit 4 Abbildungen

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11. Mitt.:D. Reinen, Mh. Chem.96, 730 (1965).     

Einkristalle von CoNbO4 mit AlNbO4-Struktur

Single Crystals of CoNbO₄ with AlNbO₄ Structure The hitherto unknown single crystals of CoNbO₄ were prepared. CoNbO₄ has AlNbO₄ structure with monoclinic symmetry (space group C?C2/m; a = 1212.9; b = 374.9; c = 651.2 pm; β = 107.6°). X-ray investigations shows on ordered arrangement of Co³⁺ and Nb⁵⁺ with well defined differences in respect to oxocobaltates with Columbite type (CoNb₂O₆ = Co_0.33Nb_O.66O₂) and Rutil type (CoNbO₄ = Co_0.5-xNb_0.5+xO₂; 0 ? × ? 0.166) structure.     

Metallkomplexe der Phosphinsäuren. XVIII. Ansa- und Oligokomplexe bifunktioneller Dithiophosphinsäuren

Metal Complexes of Phosphinic Acids. XVIII. Ansa- and Oligo-Complexes of Bifunctional Dithiophosphinic Acids The influence of R′ in the bifunctionell chelate ligands ^?S(S)P(R)? R′? (R)P(S)S^? on the association of their planar Ni^II and tetrahedral Co^II complexes is investigated by vapour pressure osmometry and in the case of diamagnetic Ni^II compounds also by ³¹P-NMR spectroscopy. While insoluble coordination polymers [S₂P(R)? R′? (R)PS₂M]_x (M = Ni^II, Co^II) are formed with R′ = p-(C₂H₄)₂C₆H₄ it can be shown, that in solutions of the complexes with R′ = o-(C₂H₄)₂C₆H₄ and R′ = o-(C₃H₆)₂C₆H₄ there exists an association equilibrium comprehending oligomers with n ? x. Above all in the latter case steric conditions seem to favour intramolecular chelating and thus formation of ansa-type complexes. Synthesis of the ligands and the complexes is described.     

Farbe und Konstitution bei anorganischen Feststoffen, 11. Mitt.: Die Lichtabsorption des oktaedrisch koordinierten Co2+-Ions in der Mischkristallreihe Mg1−x Co x O und anderen oxidischen Wirtsgittern

Zusammenfassung Für das oktaedrisch koordinierte Co²⁺-Ion werden ein Termschema und Energiegleichungen für zwei charakteristischeDq/B-Werte angegeben und mit deren Hilfe aus den Spektren der Co²⁺-haltigen Ilmenite MgTiO₃ und CdTiO₃ ¹ die Zuordnung des intensitätsstärksten Quartett-Dublett-Überganges ( _a ⁴ T_{1g b} ² T_1g) auf eindeutige Weise ermöglicht.Weiter wird das spektrale Verhalten der Mg_1–x CO _x O-Mischkristalle (0,05x1,0) in Abhängigkeit von der Co²⁺-Konzentration untersucht. Die Änderungen der Bandenintensitäten und desRacah-ParametersB werden wie in der analogen MgO-NiO-Mischkristallreihe² auf Spin-Spin-Wechselwirkungen der über Sauerstoff benachbarten Co²⁺-Ionen zurückgeführt.

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The energy levels of the octahedrally coordinated Co²⁺-ion and energy equations for two characteristicB-values are given, which allow to identify the quartet-doublet-transition ( _a ⁴ T_{1g b} ² T_1g) of the highest intensity from the spectrum of the Co²⁺ containing ilmenites MgTiO₃ and CdTiO₃ ¹.In addition, the variation of the spectra of the Mg_1–x Co _x O-mixed crystals (0.05x1.0) with the Co²⁺ concentration is investigated. The changes in the intensities of the absorption bands and of theRacah-parameterB are (as for the corresponding MgO-NiO-mixed crystals² interpreted as being caused by spin-spin-interactions between Co²⁺ ions bonded to the same oxygen.

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Mit 3 Abbildungen     

Farbeffekte in oxidischen and anderen Mn2+-Verbindungen – die Ligandenfeldspektren von MgO/MnO- und CaO/MnO-Mischkristallen sowie von MnAl2O4

Colour Effects in Oxidic and Other Mn²⁺ Compounds – the Ligand Field Spectra of Mixed Crystals MgO/MnO, CaO/MnO, and of MnAl₂O₄ The colour intensity and the shift of the hue is examined for mixed crystals Mg_1?xMn_x^IIO and Mn_1?y^IICa_yO in dependence of the Mn²⁺-concentration and interpreted in terms of Mn²⁺? Mn²⁺ pair interactions and variations of the Mn? O bond length, respectively. The experimental band positions (sextet-quartet transitions) could be fitted quantitatively – also in case of Mn²⁺ in tetrahedral (MnAl₂O₄) and dodecahedral oxygen coordination (Mn₃Al₂Ge₃O₁₂, MnY₂Mg₂Ge₃O₁₂) – by means of crystal field calculations. The obtained ligand field parameters are discussed in comparison with data for octahedral Mn²⁺ ions with H₂O, F^? and Cl^? as ligands.     

High-temperature defect structure and electrical conduction in Ni1−xMgxO

The ionic transference number, the electrical conductivity, and Seebeck coefficient of Ni_1?xMg_xO (0.1 ≤ x ≤ 0.9) were measured as functions of temperature (900–1400°C) and oxygen partial pressure (10²–10⁵ Pa). The contribution of ionic conduction to the total conductivity of Ni_0.9Mg_0.1O was of the order of 10^?3?10^?2 at 900–1300°C, which led us to assume that the electronic conduction was predominating in Ni_1?xMg_xO (x ≤ 0.9). The electrical conductivities of both undoped and Al-doped Ni_1?xMg_xO depended on the $\text{1}\text{4}$ power of P_O2, which indicated a significant impurity effect on the defect equilibria and was interpreted as showing that doubly ionized cation vacancies were the dominant point defects at high temperatures. Analyses of the difference in the temperature dependences of conductivity and Seebeck coefficient showed that band-like conduction took place in the NiO-rich composition range (x ≤ 0.1), while thermally activated hopping of small polarons occurred in Ni_1?xMg_xO with x ≥ 0.3. The calculated drift mobility abruptly decreased in the composition region where the conduction mechanism changed.     

Activity—composition relations of solid solutions and stabilities of manganese and nickel titanates at 1250°C as derived from equilibria in the systems MnOCoOTiO2 and MnONiOTiO2

Equilibria between a metal phase (either cobalt or nickel), a gas phase of known oxygen pressures, and pairs of solid-solution phases in the systems MnOCoOTiO₂ and MnONiO₂ are used to calculate activity—composition relations in the solid-solution series Mn₂TiO₄Co₂TiO₄, MnTiO₃CoTiO₃, MnTi₂O₅CoTi₂O₅, Mn₂TiO₄Ni₂TiO₄ and MnTiO₃NiTiO₃, and free energies of formation of the manganese titanates Mn₂TiO₄, MnTiO₃ and MnTi₂O₅ and of nickel orthotitanate, Ni₂TiO₄.     

Chemischer Transport fester Lösungen. 8 [1] Zum Chemischen Transport von ternären und quaternären Cobalt(II)‐ und Nickel(II)‐germanaten

Chemical Vapor Transport of Solid Solutions. 8 The Chemical Vapor Transport of Ternary and Quarternary Cobalt and Nickel Germanates By means of chemical vapor transport methods using HCl as transport agent CoGeO₃, Co₂GeO₄, and Ni₂GeO₄ have been prepared (1000 → 900 °C and 900 → 700 °C). In this system the formation of a continuous crystalline solid solution of Co₂GeO₄ and Ni₂GeO₄ was found as well as the deposition of the compound NiGeO₃ which — although unknown as a pure solid — can be stabilized as a mixed crystal Ni_xCo_1—xGeO₃ (0 < x < 0, 6).     

Tailoring Transition‐Metal Hydroxides and Oxides by Photon‐Induced Reactions

Controlled synthesis of transition‐metal hydroxides and oxides with earth‐abundant elements have attracted significant interest because of their wide applications, for example as battery electrode materials or electrocatalysts for fuel generation. Here, we report the tuning of the structure of transition‐metal hydroxides and oxides by controlling chemical reactions using an unfocused laser to irradiate the precursor solution. A Nd:YAG laser with wavelengths of 532 nm or 1064 nm was used. The Ni²⁺, Mn²⁺, and Co²⁺ ion‐containing aqueous solution undergoes photo‐induced reactions and produces hollow metal‐oxide nanospheres (Ni_0.18Mn_0.45Co_0.37O_x) or core–shell metal hydroxide nanoflowers ([Ni_0.15Mn_0.15Co_0.7(OH)₂](NO₃)_0.2?H₂O), depending on the laser wavelengths. We propose two reaction pathways, either by photo‐induced redox reaction or hydrolysis reaction, which are responsible for the formation of distinct nanostructures. The study of photon‐induced materials growth shines light on the rational design of complex nanostructures with advanced functionalities.     

Sn-doped Li<Subscript>1.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>O<Subscript>2</Subscript> cathode materials for lithium-ion batteries with enhanced electrochemical performance

Sn-doped Li-rich layered oxides of Li_1.2Mn_0.54-x Ni_0.13Co_0.13Sn _x O₂ have been synthesized via a sol-gel method, and their microstructure and electrochemical performance have been studied. The addition of Sn⁴⁺ ions has no distinct influence on the crystal structure of the materials. After doped with an appropriate amount of Sn⁴⁺, the electrochemical performance of Li_1.2Mn_0.54-x Ni_0.13Co_0.13Sn _x O₂ cathode materials is significantly enhanced. The optimal electrochemical performance is obtained at x = 0.01. The Li_1.2Mn_0.53Ni_0.13Co_0.13Sn_0.01O₂ electrode delivers a high initial discharge capacity of 268.9 mAh g^?1 with an initial coulombic efficiency of 76.5% and a reversible capacity of 199.8 mAh g^?1 at 0.1 C with capacity retention of 75.2% after 100 cycles. In addition, the Li_1.2Mn_0.53Ni_0.13Co_0.13Sn_0.01O₂ electrode exhibits the superior rate capability with discharge capacities of 239.8, 198.6, 164.4, 133.4, and 88.8 mAh g^?1 at 0.2, 0.5, 1, 2, and 5 C, respectively, which are much higher than those of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (196.2, 153.5, 117.5, 92.7, and 43.8 mAh g^?1 at 0.2, 0.5, 1, 2, and 5 C, respectively). The substitution of Sn⁴⁺ for Mn⁴⁺ enlarges the Li⁺ diffusion channels due to its larger ionic radius compared to Mn⁴⁺ and enhances the structural stability of Li-rich oxides, leading to the improved electrochemical performance in the Sn-doped Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode materials.