Magneli Phases Research Articles

Surface pecularities of vanadium oxides grown in the field of laser light

Peculiarities of O/V atomic and weight ratios of vanadium oxides grown on the surface of metallic vanadium plates under influence of CW YAG laser radiation have been investigated. The dependence of the normalized weight ratio on the oxygen content showed that the area of the surface to be illuminated consists of nonstoichiometric oxides (oxygen content of 30%–35%). otherwise in the vicinity of the laser spot almost stoichiometric vanadium pentoxide polycrystals have grown: the oxygen content varied between 35% and 50%. Far from the laser spot the oxygen content decreased drastically to 4%–8%. There were some very specific zones with sizes of a few micronmeters showing particularly high or low vanadium contents (saturated V 2O 5 and /or VO 4 with x ≤ 2 or some Magneli phases V n O 2 n−1 ) randomly distributed on the surface. Special microhardness measurements have been carried out in order to follow the surface structures among the commonly used SEM, BSE and EDS methods.

Electron microscope study of non-stoichiometric titania

The distribution and coexistence of Magneli phases (TinO2n−1) withn=4, 5 and 6 in hydrogen-reduced TiO2 has been investigated using transmission electron microscopy. The major phase was Ti5O9. Ti6O11 was found in Ti5O9 grains in the form of narrow lamellae (<10 nm wide) epitaxially intergrown on (001) planes. The Ti4O7 phase, however, was never observed as a second phase in Ti5O9 grains but formed single-phase grains. The Ti5O9 phase was twinned on the (011)r planes of the rutile subcell structure and the Ti6O11 lamellae were pinned to these twins. This pinning may be responsible for the hysteresis that occurs during the oxidation-reduction of non-stoichiometric TiO2. We also report observations onin situ oxidation of the line phases.

Hydrothermal phase relations in V 2O 2-H 2O system

Hydrothermal phase relations in the vanacium oxide-water system have been studied and the phase diagram for V 2O 5-H 2O is given. The Magneli phases found in between the two stable fields of V 2O 5 and V 3O 5 were invariably found with good euhedral morphology. This suggests that oxides of vanadium with a wide range of oxygen stoichiometry can be grown as single crystals using water as a mineralizer.

Band electronic structure study of the structural modulation in the Magneli phase molybdenum oxides, Mo8O23

We examined the cause for the 0.5b{sup *} superlattice modulation in the Magneli phase Mo{sub 8}O{sub 23} by performing tight-binding band electronic structure calculations on Mo{sub 8}O{sub 23}, which consists of perovskite Mo{sub 4}O{sub 15} layers linked by Mo{sub 4}O{sub 14} chains. Our study shows that Mo{sub 8}O{sub 23} is a semimetal and does not possess a half-filled band dispersive along the b{sup *} direction. Thus, the superlattice modulation is not caused by an electronic instability associated with Fermi surface nesting. The most likely cause for the superlattice modulation is a concerted pairwise rotation of MoO{sub 6} octahedra in the perovskite Mo{sub 4}O{sub 15} layers. 18 refs., 5 figs.

ESR, XRD, and DRS studies of paramagnetic titanium(3+) ions in a colloidal solid of titanium oxide prepared by the hydrolysis of titanium trichloride

By the hydrolysis of TiCl{sub 3} in aqueous solution with urea, several differently blue colored solids of colloidal titanium oxide have been synthesized, colloidal solids which show commonly a broad absorption in the visible to the near-infrared wavelength region by means of diffuse reflection spectroscopy (DRS). The intensity of this band is proportional to that of the integrated Ti{sup 3+} ESR signal, which indicates the origin of the blue coloration to be unoxidized Ti{sup 3+} ions in the solids. With the aid of X-ray diffraction (XRD), it is clear that Ti{sup 3+} ions exist in the Magneli phases. Stability of Ti{sup 3+} ions is discussed.

ChemInform Abstract: Band Electronic Structure Study of the Electronic Instability in the Magneli Phase Mo4O11.

ChemInformVolume 20, Issue 30 Physical Inorganic Chemistry ChemInform Abstract: Band Electronic Structure Study of the Electronic Instability in the Magneli Phase Mo4O11. E. CANADELL, E. CANADELL Lab. Chim. Theor., CNRS, Inst. Chim. Mol. Orsay, Univ. Paris-Sud, F-91405 Orsay, Fr.Search for more papers by this authorM.-H. WHANGBO, M.-H. WHANGBO Lab. Chim. Theor., CNRS, Inst. Chim. Mol. Orsay, Univ. Paris-Sud, F-91405 Orsay, Fr.Search for more papers by this authorC. SCHLENKER, C. SCHLENKER Lab. Chim. Theor., CNRS, Inst. Chim. Mol. Orsay, Univ. Paris-Sud, F-91405 Orsay, Fr.Search for more papers by this authorC. ESCRIBE-FILIPPINI, C. ESCRIBE-FILIPPINI Lab. Chim. Theor., CNRS, Inst. Chim. Mol. Orsay, Univ. Paris-Sud, F-91405 Orsay, Fr.Search for more papers by this author E. CANADELL, E. CANADELL Lab. Chim. Theor., CNRS, Inst. Chim. Mol. Orsay, Univ. Paris-Sud, F-91405 Orsay, Fr.Search for more papers by this authorM.-H. WHANGBO, M.-H. WHANGBO Lab. Chim. Theor., CNRS, Inst. Chim. Mol. Orsay, Univ. Paris-Sud, F-91405 Orsay, Fr.Search for more papers by this authorC. SCHLENKER, C. SCHLENKER Lab. Chim. Theor., CNRS, Inst. Chim. Mol. Orsay, Univ. Paris-Sud, F-91405 Orsay, Fr.Search for more papers by this authorC. ESCRIBE-FILIPPINI, C. ESCRIBE-FILIPPINI Lab. Chim. Theor., CNRS, Inst. Chim. Mol. Orsay, Univ. Paris-Sud, F-91405 Orsay, Fr.Search for more papers by this author First published: July 25, 1989 https://doi.org/10.1002/chin.198930014Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume20, Issue30July 25, 1989 RelatedInformation

Band electronic structure study of the electronic instability in the Magneli phase molybdenum oxide [Mo4O11

To probe the origin of the resistivity anomaly in the Magneli phases {gamma}- and {eta}-Mo{sub 4}O{sub 11}, we carried out tight-binding band electronic structure calculations on their common building block, the Mo{sub 6}O{sub 22} layer made up of MoO{sub 6} octahedra. With two d electrons per formula unit Mo{sub 4}O{sub 11}, the bottom three bands of the Mo{sub 6}O{sub 22} layer are partially filled. The Fermi surfaces of those partially filled bands are all closed, in agreement with the observation that Mo{sub 4}O{sub 11} is a two-dimensional metal. Nevertheless, the Fermi surfaces have a partial nesting consistent with the superlattice spots at (0, 0.23b*, 0) observed for {eta}-Mo{sub 4}O{sub 11}. A charge density wave associated with this partial nesting is most likely to cause the resistivity anomaly in {gamma}- and {eta}-Mo{sub 4}O{sub 11}. 16 refs., 5 figs., 1 tab.

Investigations of chromium doped ceramic rutile electrodes

The chromium content of rutile electrodes prepared using the ceramic method at 1400°C varied from 0.4% to 20%. Some of these electrodes showed n-type conductivity when treated additionally with hydrogen at 900°C. Dopand concentration was shown to influence significantly the bulk (SEM and x-ray analysis) and surface properties (photoelectrochemical investigations) of TiO 2 electrodes. The doping of TiO 2 with Cr 2O 3 near the solubility limit (the formation of solid solutions) was established as between 0.4% and 1%. This concentration produces optimum photoresponse and a shift in the flat-band potential toward more negative values. However, a negative effect of doping due to the decreased hole diffusion length was observed The formation of Andersson (Magneli) phases with the general formula Ti n−2Cr 2O 2n−1, where n is more than 5, associated with high levels of chromium content well above the solubility limit, leads to reduced activity of these electrodes when used as photoanodes or preparative anodes in heterogenous redox catalysis. Important factors affecting the properties of these electrodes as preparative anodes in redox catalysis are the process of thermal pretreatment and the atmosphere in which they are heated.

Transient homologous structures in nonstoichiometric YBa2Cu

We propose that a homologous series of transient ordered structures may form during the spinodal decomposition of the nonstoichiometric superconducting oxide $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$. These transient phases provide the best kinetic accommodation of the local vacancy concentration. Their structures should be similar to those of the ${\mathrm{Ti}}_{m}{\mathrm{O}}_{2m\ensuremath{-}1}$ and ${\mathrm{Mo}}_{m}{\mathrm{O}}_{2m\ensuremath{-}1}$ series of Magneli phases. The transient phases in the oxide have the stoichiometry $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{\frac{7\ensuremath{-}n}{(2n+1)}}$, where $n$ is an integer. The structure of the $n$ phase has a diffraction maximum at the point ($\frac{n}{(2n+1) 00}$). Examples have been experimentally observed.

Oxygen deficient Ti oxides (natural magn�li phases) from mudstone xenoliths with native iron from Disko, central West Greenland

Mudstone xenoliths in a strongly reduced andesitic subaquatic breccia with native iron from the Asuk Member on Disko contain Ti oxides which are oxygen deficient relative to rutile. Ore microscopy reveals that the mudstone xenoliths contain former clastic oxide grains which have equilibrated to blue Ti oxides and grey aluminous Ti oxides. They also contain still immature coal fragments in a glassy matrix with native iron. The blue oxides are compositionally similar to magneli phases TinO2n−1 within the range n=4 to 7, and several grains contain more than one natural magneli phase. Two other phases found are 1) pale orange blebs in magneli phases with a composition approaching Al1Ti 1 3+ Ti 2 4+ O7 (AlTi phase B) and 2) grey oxide rims on magneli phases or independent grains of the compositional series Al2−x(Ti 0.5 4+ (Mg,Fe)0.5)xTi n−2 4+ O2n−1 with n mostly between 7 and 10 (AlTi phase A). The natural magneli phases equilibrated at oxygen fugacities 4 to 5 log units below the Fe-W oxygen buffer at igneous temperatures and represent the most reduced high-temperature environment yet recorded among native iron bearing rocks from Disko. The extremely reducing conditions were met in rocks where coal fragments were still in a state of degassing hydrocarbon components at the time of quenching. Field geology and carbon barometry indicate equilibration at pressures of less than 10 bars.

X-ray diffraction study on oxidized titanium iron alloys as semiconducting photoelectrodes for the production of hydrogen

The bulk and surface phase composition of oxidized titanium alloys containing 0.1 to 10 at% of iron was investigated by means of different X-ray diffraction techniques. On samples exposed to oxygen of 1 bar at 873 K for 30 minutes isotropically segregated TiO 2 (rutile) was observed. Oxygen diffusion into the bulk material led to the formation of TiO x (alpha titanium oxide) and TiFe. Alloys treated at 1173 K for 1 hour under oxygen of 1 bar followed by a high vacuum annealing showed an inhomogenous structure of free iron, rutile and Magneli phases.

Concentration wave approach to the pairwise interaction model for predicting the atomic structure of ceramics, II

The concentration wave approach is applied to Ti and V oxides with noninteger variable valences. This approach enables both the composition and the structure of the homologous series of Magneli phases Ti n O 2 n−1 and V n O 2 n−1 to be predicted in the composition range between Ti 2O 3 and TiO 2.

Ti n O2n?1 Magn�li phase formation in SrTiO3 dielectrics

Electron diffraction, high-resolution transmission electron microscopy and scanning transmission electron microscopy reveal that TinO2n−1 Magneli phases, Ti4O7, Ti5O9 and others, exist at the multiple grain junctions in strontium titanate dielectrics. A new type of ledge structure detected at coherent grain boundaries in the Ti4O7 phase is characterized in detail. The SrTiO3 grain and the second phase maintains a particular orientation relationship. Epitaxial growth of Ti4O7 from the silica-rich liquid phase occurs during cooling; the crystal growth geometry of Ti4O7 is related to the directly observed atomically rough interface and atomically smooth interface.

Intergrowth structures in inorganic solids: A new class of materials

An increasing number of inorganic solids forming long-period structures due to recurrent intergrowth of two chemically distinct but structurally related units are getting to be known in recent years. These novel structures have given rise to new chemistry at solid-solid interfaces. Besides intergrowth structures with long-range order, many solids with random intergrowth (similar to stacking faults in polytypes) are known. Ordered integrowth gives rise to homologous series of structures in many systems. Barium ferrites, the Aurivillius family of oxides and other perovskite-related oxides, siliconiobates, and tungsten oxide bronzes are some of the systems exhibiting ordered intergrowth structures. Both ordered and disordered intergrowths are fruitfully investigated by high resolution electron microscopy. The main emphasis in this article is on intergrowth structures where the component units are compositionally different. These systems are obviously most fascinating since compositional change occurs across each interface (intergrowth plane), unlike in polytypic materials where the composition remains constant. Even in ordered intergrowth structures, there is always some disorder. If order in an intergrowth structure does not prevail over large distances, but occurs only over shorter stretches (say, a few repeats of the sequence), it becomes difficult to describe the solid except in terms of the gross composition and where possible, the unit cell dimensions. Structures with occasional intergrowths are found in a variety of materials such asβ-alumina, Magneli phases, silicates, ferrites and several other oxide systems. In addition to examining the structural features of various intergrowths, the origin of the intergrowth phenomenon is discussed.

Microstructures of SrTiO3 Internal Boundary Layer Capacitors During and After Processing and Resultant Electrical Properties

The microstructure of strontium titanate internal boundary layer capacitors at various stages in their processing was studied by transmission electron microscopy of rapidly quenched and normally cooled samples. Compositions containing excess TiO2, Al2O3, and SiO2 have a completely wetting liquid phase at the sintering temperature; during cooling TinO2n−1, Magneli phases precipitate at multiple grain junctions. Diffused metal oxides and flux (Bi2O3, PbO, CuO, and B2O3) rapidly penetrate as a liquid phase along boundaries in postsintering heat treatment. This liquid phase disappears during slow cooling.

X-ray diffraction of polycrystalline Ti 4O 7

X-ray powder diffraction of powder and sintered EBONEX (nominally Ti 4O 7) is reported. The patterns show clearly the existance of another Magneli phase (Ti 5O 9) in both forms of the material. Its concentration was determined from the integrated intensity ratios of the (101) vs. (101) the (121) vs. (121) and the (206) vs. (208) lines of Ti 4O 7 vs. Ti 5O 9, respectively. For samples taken from one batch, the powder form of EBONEX contains ca. 25±5 a% of Ti 5O 9 while the sintered form contains about twice as much. Samples from another batch, prepared under improved process control, showed ca. 10a% of Ti 5O 9 in the powder form of the material. Both forms contain small traces of other phases as well, e.g., Ti 3O 5 in the powder and Ti 6O 11 in the sintered material. These results agree with recently reported ESR line-broadening measurements. We also observed aging effects such as gradual oxidation in the sintered material.

Electrochemical properties of a new electrode material, Ti 4O 7

Cyclic voltamograms of Ti 4O 7 (Ebonex) together with its overpotentials for the production of H 2 and O 2 in acidic and basic aqueous solutions are reported. Ti 4O 7 electrode properties are compared to other electrodes: TiO 2, Pt, carbon, and vitreous carbon. Strong adsorption of ruthenium and platinum to the surface of Ti 4O 7 reduces the overpotentials for H 2 and O 2 production and modifies its electrode behavior. ESR results indicate small amounts of higher oxide phases (Magneli phases) may be present in the Ebonex material.

On the theory of phase transitions in vanadium oxides V nO 2n-1 (magneli phases)

The phenomenological theory of the phase transitions in Magneli's vanadium-oxide series is proposed. The phase diagram is derived with allowance for the pecularities of these compounds. The sequence of the phase transitions and their basic features (i.e. dependence of critical temperatures of the metal-dielectric and antiferromagnetic transitions upon the index of n in formula V n O 2 n-1 ) are explained.

Ｎｉ‐Ｔｉ‐Ｏ系におけるＮｉ側等温状態図

In order to study fundamentally the influences of oxygen on the properties of TiC-base cermets, the phase relationships of the Ni-Ti-O system, which is a part of the four ternary systems constituting the Ni-Ti-C-O quaternary system, were determined at 1000°C (in a solid state) and at about 2000°C (in a liquid state) mainly in the region of less than 50 at % Ti.Even in the molten state at 2000°C or above, the oxide-metal phase separation was observed over a wide composition range, and the mutual solubility scarcely changed with temperature. At 1000°C, a nickel solid solution (γ-phase) was in equilibrium with Ti2O3, Ti3O5, Magneli phases, TiO2, NiTiO3 and NiO in turn as the titanium content decreased. The solubility of oxygen in the γ-phase was minimum at about 4 at% Ti.

Growth and characterization of titanium suboxide crystals

The titanium and vanadium suboxides MO x (where 1.5 < x < 2 and M is Ti or V) are particularly interesting compounds because many show metal-insulator transitions which result in interesting electrical, magnetic and spectroscopic phenomena. We have grown high purity crystals of the congruently melting compounds Ti 2O 3, Ti 3O 5 and V 2O 3 and mixed compounds using the tri-arc melting technique. Crystals were grown at speeds of 1-1.5 cm/h. The Magneli phases M n O 2 n-1 ( n⩾4) do not melt congruently and therefore we have grown a number of these compounds using chemical vapor transport with TeC1 4 or NH 4C1. Twinned needles typically larger than 1 cm long are grown by pulling transport in 3–5 days. The crystals have been characterized by X-ray diffraction, atomic absorption and gamma-ray activation analysis. In addition, the use of a scanning microcalorimeter made it possible to determine phase transitions on needles weighing as little as 2–10 mg. The stoichiometry was determined using X-ray diffraction, pycnometric density measurements and thermogravimetry.