Spinel-related Structure Research Articles

LiCoO2: formation, structure, lithium and oxygen nonstoichiometry, electrochemical behaviour and transport properties

The formation, structure and transport properties of LiCoO2 are described. LiCoO2 exhibits two crystal structures, depending on both the preparation method and synthesis temperature. High temperature lithium cobalt oxide (HT-LiCoO2) has a hexagonal layered structure, while the low temperature oxide (LT-LiCoO2) has a cubic spinel-related structure. The dependence of the morphological characteristics (grain size, size distribution, crystallinity) of LiCoO2 on synthesis method as well as their effect on the electrochemical properties are extensively reviewed. As the electrochemical properties and the electrical conductivity strongly depend on the structure of the oxide, primary attention is given to lithium cobalt oxide with defect structure and lithium and oxygen nonstoichiometry.

Characterization of the spinel-related oxides NixCo3−xO4 (x=0.3,1.3,1.8) prepared by spray pyrolysis at 350 °C

Films of nominal composition NixCo3−xO4 (x=0.3,1.3,1.8) prepared by spray pyrolysis have been characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that the film with x=0.3 is monophasic, presents a spinel-related structure and contains Ni2+, Ni3+, Co2+ and Co3+. In the films with x=1.3 and 1.8 the preparation leads to the formation of significant amounts of NiO and CoO which are segregated to the surface of the sprayed films. The effect on the reducibility of the different materials under Ar+ sputtering has also been investigated. The film with x=0.3 was found to be the most difficult to reduce, whilst the films with x=1.3 and 1.8 were reduced to metallic Ni, metallic Co, and CoO.

Characterization of the Mn–Li ferrite system Li1–0.5xFe1.5x+1Mn1–xO4 (0.2 ≤ x ≤ 1)

The Mn–Li ferrite system Li1−0.5xFe1.5x+1Mn1−xO4 (x = 1, 0.8, 0.6, 0.4, 0.2) has been studied by means of X-ray diffraction, Mossbauer spectroscopy and Mn K- and Fe K-edge XANES/EXAFS. All the samples show the spinel-related structure with the lattice constant a gradually decreasing between a = 0.8310 nm (x = 1) and a = 0.8301 nm (x = 0.2). Mossbauer and Fe K-edge XANES/EXAFS results have shown that the oxidation state of Fe is +3 and that the fractions of Fe3+ ions occupying the octahedral and tetrahedral sublattices do not change significantly along the series. Mossbauer data recorded under applied magnetic field indicate the existence in the Mn-containing samples of canted spin structures for the Fe3+ ions on both the tetrahedral and octahedral sites, the canting angle being larger for the octahedral sublattice. Mn K-edge XANES and EXAFS have shown Mn to be present as Mn3+ and Mn4+ and to occupy only octahedral sites. The XANES/EXAFS results have also shown that the Mn4+/Mn3+ ratio increases with increasing Li/Mn content. The results indicate that as the extent of Li/Mn insertion increases the new inserted Li+ ions occupy tetrahedral sites and that some of the Li+ ions initially occupying octahedral sites are also driven into tetrahedral positions.

Tin-, titanium-, and magnesium-doped α-Cr 2O 3: characterisation and rationalisation of the structures

Tin- and titanium-doped α-Cr 2O 3 have been prepared by the calcination of precipitates. Rietveld structure refinement of the X-ray powder diffraction patterns shows that the dopant metals occupy interstitial sites and partially substitute on octahedral chromium sites in the corundum-related α-Cr 2O 3 structure. Interatomic potential calculations show that such defects are energetically more favourable than the exclusive substitution of chromium or the occupation by the dopant of interstitial sites in α-Cr 2O 3 with charge balance being achieved by an appropriate number of cation vacancies. However, the attempted incorporation of magnesium within α-Cr 2O 3 results in the formation of spinel-related MgCr 2O 4. The observation is rationalised in terms of the greater thermodynamic stability of the spinel-related structure.

Disordering and Electronic State of Cobalt Ions in Mechanochemically Synthesized LiCoO2

Mechanical activation (MA) combined with heat treatment at moderate temperatures was used to prepare disordered and highly dispersed LiCoO2 starting from the mixtures of various cobalt precursors (CoOOH, Co(OH)2, and Co) and LiOH. X-ray powder diffraction and IR spectroscopy were used to investigate the phase composition and the crystal structure of as-prepared samples, while the electronic state of cobalt ions was characterized by diffuse reflectance electron spectroscopy. MA of the LiOH+CoOOH mixture led to the formation of LT-LiCoO2 with a cubic spinel-related structure. Heat treatment at 600°C of the latter resulted in the formation of HT-LiCoO2 with a hexagonal layered structure similar to ceramic LiCoO2. However, as-prepared HT-LiCoO2 is characterized by Co3+O6 octahedra less perfect than those of ceramic LiCoO2. All MA-LiCoO2 samples are exclusively described by localized d electrons.

Cation distribution and magnetic structure of the ferrimagnetic spinel NiCo2O4

The compound NiCo2O4, with spinel-related structure, has been prepared by thermal decomposition of metal nitrates and its bulk structural properties examined by means of magnetic measurements, neutron diffraction, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The results suggest a delocalised electron distribution on the octahedral sites with average oxidation states of +3.5 and +2.5 for nickel and cobalt, respectively, and lead to a cation distribution for NiCo2O4 of {Ni3+0.1Co2+0.9}tet[Ni3.5+0.9Co2.5+1.1]octO4. This electronic configuration is consistent with magnetisation measurements if applied magnetic fields cause a charge redistribution on the octahedral sites to favour Co3+ and Ni3+. The surface of NiCo2O4 was examined by X-ray photoelectron spectroscopy (XPS) and found to have a different composition containing Co2+, Co3+, Ni2+, Ni3+ and, probably, Ni4+.

Synthesis and characterisation of tin-doped iron oxides

Rietveld structure refinement of the X-ray powder diffraction data recorded from tin-doped Fe 3 O 4 prepared by heating metallic iron, α-iron(III) oxide and tin(IV) oxide in sealed evacuated quartz ampoules shows the tin to substitute on the octahedral sites of the inverse spinel-related structure. Tin-doped γ-Fe 2 O 3 , prepared by boiling a precipitate derived from iron(III), iron(II) and tin(II) under reflux, also adopts an inverse spinel-related structure containing tin on the octahedral sites and, compared to pure γ-Fe 2 O 3 , is stabilised with respect to conversion to α-Fe 2 O 3 . 57 Fe Mossbauer spectroscopy shows the Neel temperature for γ-Fe 1.9 Sn 0.1 O 3 to be between 750 and 820 K. Tin-doped α-Fe 2 O 3 prepared by hydrothermal methods is shown by Rietveld structure refinement of the X-ray powder diffraction data to contain tin in both the substitutional and interstitial octahedral sites of the corundum-related structure.

Mössbauer spectroscopic examination of a single crystal of

Mössbauer spectra have been recorded in fields of up to 13 T from a single crystal of cut perpendicular to the [111] axis. The spectra were best fitted with five magnetic components complementing studies on a crystal cut normal to a [100] axis. One component corresponds to situated on the tetrahedral A sites of the inverse spinel-related structure whilst the other four correspond to and on two non-equivalent octahedral sites.

Electrochemical lithium insertion in a cation deficient thiospinel Cu3.31GeFe4Sn12S32

We present the characterization and the electrochemical study of the cation deficient thiospinel Cu3.31GeFe4Sn12S32 as a cathodic material in lithium cells. The pristine compound has a spinel-related structure, where the copper defect in the tetrahedral site induces a partial oxidation of FeII to FeIII. The discharge curve shows the presence of several insertion steps. The reduction of FeIII to FeII and a copper extraction takes place during the first and second steps, respectively. Moreover, the lithium insertion originates a first-order spinel to rocksalt transition, indicated by the third step of the discharge curve. Finally, at low voltages (<1.65 V) a SnIV to SnII reduction takes place.

Effects of Aluminum Doping on The Phase Stability and Electrochemical Properties of LiCoO2 and LiMnO2

ABSTRACTAluminum is of interest as a constituent for Li battery electrodes due to its low cost and low mass, and because ab initio calculations indicate that solid solution of LiAlO2 with LiMO2 (M = transition metal) in the α-NaFeO2 structure can increase intercalation voltage [1]. In this study, we investigated the effect of Al doping on LiCoO2 and LiMnO2. Single phase LiAlyCo1-yO2 has been synthesized up to y = 0.5 by firing homogenous hydroxide precursors. A systematic increase in the open circuit voltage is observed with Al content. In LiAlyMn1-yO2, the addition of LiAlO2 stabilizes LiMnO2 in the α-NaFeO2 structure under conditions where neither endmember is stable in the structure. High reversible capacity was obtained over both a 4 V and 3 V plateau, indicating that the compound transforms to a spinel-related structure during cycling, but that the cooperative Jahn-Teller distortion is suppressed.

Powder neutron diffraction study of LiMnVO4

Powder neutron diffraction data have been recorded for LiMnVO4. The crystal structure was determined by Rietveld analysis. The Rietveld refinement confirmed that the compound adopts an orthorhombic spinel-related structure. The framework structure of the compound is comprised of nearly regular, edge-sharing octahedra of MnO6. The lithium and vanadium atoms in LiMnVO4 occupy, as partially mixed species, the two kinds of tetrahedral interstitial sites constructed by cubic close-packed oxygen atom arrays; this structural feature is quite similar to those of CrVO4 and LiCuVO4. The magnetic susceptibility and the metal–oxygen bond distances estimated from the refined structure of LiMnVO4 clearly indicate that the valence states for the transition-metal ions are divalent for manganese ions and pentavalent for vanadium ions.

Structural Characterization of LiMnVO4 with a Spinel-Related Structure

Abstract A new compound of LiMnVO4 has been synthesized. The crystal structure was determined by the Rietveld analysis. The framework structure is comprised of nearly regular octahedra of MnO6 with edge-sharing. The lithium and vanadium ions occupy alternatively the tetrahedral interstitial sites constructed by close-packing arrays of oxide ions. The structure is discussed in relation to a normal spinel structure.

Lithium manganese oxides from Li 2MnO 3 for rechargeable lithium battery applications

Electrochemically active lithium-manganese-oxide phases have been synthesized by chemical leaching of Li 2O from the rock salt phase Li 2MnO 3 (Li 2O.MnO 2) with acid at 25°C. Preliminary electrochemical tests have shown that capacities of approximately 200 mAh/g based on the mass of the lithium-manganese oxide electrode can be obtained in room-temperature lithium cells, and that capacities in excess of 140 mAh/g can be achieved on cycling. Although a detailed structure analysis of an extensively delithiated sample has not yet been undertaken, it is believed that it may be a novel layered lithium-manganese oxide compound Li 2− x MnO 3− x 2 (0< x<2 ) with a cubic-close-packed oxygen anion array in which some of the Li + ions are ionexchanged with H + ions. Heat-treatment of an extensively delithiated Li 2MnO 3 sample at 300°C in air transforms the product to a γ β − MnO 2 type phase, whereas delithiated samples that still contain an appreciable amount of lithium transform on heating to a two-phase product of Li 2MnO 3 and a compound with a spinel-related structure.

Structural modifications induced by proton exchange in γ-LiFeO 2

The tetragonal crystalline modification of LiFeO 2 was subjected to partial proton exchange reactions by hydrothermal treatment at 160°C in distilled water. The product after 1 day treatment had a Li/Fe ratio of ca. 0.15. A partial displacement of octahedrally coordinated Fe(III) ions to A sites of a spinel-related structure was observed. The presence of hydrogen in the structure was shown by water release reactions between 300 and 500°C. The product treated at 800°C was a mixture of LiFe 5O 8 and α-Fe 2O 3.

Cation-deficient Mn, Co spinel oxides obtained by thermal decomposition of carbonate precursors

Co, Mn mixed oxides with spinel-related structure are prepared by the thermal decomposition of mixed carbonates under air atmosphere at 400 and 600°C. These oxides are cation-deficient phases with stoichiometries ranging from MO 1.333 to MO 1.6 that depend on Mn content and temperature of preparation and show tetragonal to cubic spinel structure as the Co content increases. Additionally, the X-ray diffractograms and electron microscopy data reveal the occurrence of vacancy ordering in a tetragonal superstructure, which is similar to γ-Fe 2O 3 in cubic phases and implies a′ = a and c′ = 3 c for tetragonally distorted spinels.

The system NiAl 2O 4Ni 2SiO 4 at high pressures and temperatures: Spinelloids with spinel-related structures

Phase relations in the system NiAl 2O 4Ni 2SiO 4 were studied in the pressure range 1.5 ∼ 13.0 GPa and in the temperature range 800 ∼ 1450°C. Two new phases, IV and V, were found in regions of pressure higher than 4 GPa. Phase V disproportionates into a mixture of Ni 2SiO 4-spinel, NiO, and Al 2O 3 at approximately 9.5 GPa and 1100°C. Phases III, IV, and V form a solid solution in some compositional range: phases IV and V have a composition around NiAl 2O 4·Ni 2SiO 4, whereas phase III spreads from NiAl 2O 4·Ni 2SiO 4 to the NiAl 2O 4-rich side. All the phases I ∼ V are structurally considered to be spinel derivatives, “spinelloids,” with three kinds of tetrahedral groups; isolated tetrahedra TO 4, linked ones T 2O 7, and triply linked ones T 3O 10. The ratios of isolated tetrahedra to linked ones are large in the higher-pressure phases and small in the lower-pressure phases. The difference of compositional range of phase III from that of phases IV and V is possibly explained by the avoidance of linked tetrahedra such as O 3AlOAlO 3.

準スピネル:AB&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;4&lt;/SUB&gt; 型化合物の高圧下相転移で見られるスピネル類縁構造

常圧でオリビンやフェナサイト型構造をとる AB2O4 型の化合物が高圧下で変形スピネルを経てスピネルや,他の高圧相に転移する例は広く研究されてきたが,この相転移は常圧相→ 準スピネル→ 高圧相とするのがより一般的であることが, NiAl2O4-Ni2SiO4 系高圧相の研究の結果明らかである。この系の高圧相には構造上スピネルおよび変形スピネルと密接な類縁関係にある5種の相が見い出されている。変形スピネルも準スピネルの一員として含まれる。準スピネルの構造はスピネルに見られる陽イオン四面体・八面体から成る構造単位をもってすべて記述出来るものであり,その構造単位の配列は合成時の温度圧力条件や組成によって変化する。準スピネルには NiAl2O4-Ni22SiO4系各相の他に,変形スピネル, Li2WO4II,鉱物のマンガノスチバイト:Mn7SbAsO12等も含まれる。