Die Kristallstruktur von [Cl3PNPCl3][VOCl4]

Investigations on Electronically Conducting Oxide Systems. XIV. Solid Solutions and Conductivity in the System MgTiO₃? Ti₂O₃ Solid solution formation and conductivity is reported for the system Mg_1?xTiTiO₃ (0 < x < 1). Ti^III atoms are predominantly substituted in pairs for Mg^II and Ti^IV. In the range of low x values Ti^III? Ti^III bonds typical for Ti₂O₃ in the semiconducting state are very weakened because of the distances preserved in the host lattice of MgTiO₃. Up to x = 0,5 EPR measurements at 77 K indicate magnetic “dimers” with S = 1 at a distance of 550 pm resulting from antiparallel spin orientation of the Ti^III pairs and transfer of the magnetic interaction by super exchange to a next-neighboured Ti^III pair. Electrical conductivity is caused by polaron hopping. The steep increase in the range of small Ti^III concentration is interpreted by a screening field approximation.     

Weitere magnetische Untersuchungen an Ti3−xMxO5-Phasen (M = Al3+, Fe2+, Mn2+, Mg2+) mit einem Beitrag über CrTi2O5

Additional Magnetic Examinations of Ti_3?xM_xO₅-Phases (M = Al³⁺, Fe²⁺, Mn²⁺, Mg²⁺) with a Contribution about CrTi₂O₅ Ti_3?xM_xO₅ was prepared with M = Al³⁺, Fe²⁺, Mn²⁺, and Mg²⁺. Die magnetic properties of this phases were examinated by the Faraday method in respect to the temperature. The well known magnetic effect of Ti₃O₅ near 450 K is shifted to lower degrees if Ti is replaced by Al, Fe, Mn, or Mg. Compared to Ti_3?xV_xO₅ and Ti_3?xCr_xO₅ the stability of the low temperature-form of Ti₃O₅ is much more reduced in Ti_3?xM_xO₅ (M = Al, Fe, Mn, Mg). The crystal structure investigation of CrTi₂O₅ explained the anomalous behaviour of the Cr³⁺ and V³⁺ doped Ti₃O₅.     

Single-crystal synthesis, structure analysis, and physical properties of the calcium ferrite-type NaxTi2O4 with 0.558<x<1

Single crystals of calcium ferrite CaFe₂O₄-type NaTi₂O₄ having millimeter-sized needle shapes were synthesized by a reaction of Na metal and TiO₂ in a sealed iron vessel at 1473 K. Sodium-deficient Na_xTi₂O₄ single crystals with 0.558<x<1 were successfully synthesized by a topotactic oxidation reaction using NaTi₂O₄ single crystals as parent materials. The crystal structures of Na_xTi₂O₄ with x=0.970, 0.912, 0.799, 0.751, 0.717, 0.686, 0.611, and 0.558 were determined by the single-crystal X-ray diffraction method. The basic framework constructed by the Ti1O₆ and Ti2O₆ double rutile chains was maintained in these Na_xTi₂O₄ compounds. Based on the results of bond valence analysis, we speculated that the Ti1 sites are preferentially occupied by Ti³⁺ cations over the compositional range of 0.8<x<1, while both the Ti1 and Ti2 sites are randomly occupied by Ti³⁺ and Ti⁴⁺ cations at x=0.558. Magnetic susceptibility data indicated that the broad maximum around 40 K observed in as-grown NaTi₂O₄ is suppressed by an Na deficiency and vanishes in Na_0.717Ti₂O₄. The electrical resistivity increased with the Na deficiency; however, it was still semiconductive in Na_0.799Ti₂O₄.     

Titanates de cuivre substitués à structure bixbyite: Les composés Cu1−xTi1−xFe2xO3 (0.15 ≤ x ≤ 0.33)

A new bixbyite family, Cu_1?xTi_1?xFe_2xO₃ (0.15 ≤ x ≤ 0.33) has been synthesized and characterized. The unit cell is cubic: a ～ 9.40Å. The X-ray powder diffraction study shows up an isotypism with the (Fe, Mn)₂O₃ compounds. There is a disordered distribution of Cu^II, Ti^IV, and Fe^III over the two cyrstallographic sites: P_I and P_II. P_II is highly distorted (two long MO distances) by the Jahn-Teller effect of Cu^II. The bixbyite structure is described in terms of polyhedra arrangement, as a particular case of the CM₂O₃ family. The cation packing is discussed in relation with the existence of the bixbyite structure for the Cu_1?xTi_1?xFe_2xO₃ compounds. The electrical properties (σ ～ 10^?5(Ω cm)^?1 for x = 0.286 at room temperature) show an electron conduction with probably a hopping mechanism.     

Structural Study of Li1+x−yNb1−x−3yTix+4yO3 Solid Solutions

The structures of Li_1+x−yNb_1−x−3yTi_x+4yO₃ solid solutions within the so-called M-phase field in the Li₂O-Nb₂O₅-TiO₂ system were investigated using high-resolution transmission electron, microscope (HRTEM) and single-crystal X-ray diffraction. The results demonstrated that the phase field is not a solid solution but rather a homologous series of commensurate intergrowth structures with LiNbO₃-type (LN) slabs separated by single [Ti₂O₃]²⁺ corundum-type layers. The thickness of the LN slab decreases with increasing Ti-content from ∼55 to 3 atomic layers in the metastable H-Li₂Ti₃O₇ end-member. The LN slabs accommodate a wide range of Ti⁴⁺/Nb⁵⁺ substitution, and for a given homolog the distribution of Ti and Nb is not uniform across the slab. A single-crystal X-ray diffraction study of a structure composed of nine-layer LN slabs revealed preferential segregation of Ti to the slab surfaces which apparently provides partial compensation for the charge on the adjacent [Ti₂O₃]²⁺ corundum layers. The extra cations in phases with x>0 are accommodated through the formation of Li-rich Li₂MO₃-type layers in the middle of the LN slabs. The fraction of layers with extra cations increases with increasing Ti-content in the structure.     

Structure and electrical properties of Y,Fe-based perovskite mixed conducting composites fabricated by a modified polymer precursor method

In this work, samples of Y_0.07Sr_0.93Ti_1-xFe_xO_3-δ with 20, 40, 60 and 80 mol% of iron amount were prepared by a low-temperature polymer precursor method. The SEM-EDS analysis proved that analyzed Y_0.07Sr_0.93Ti_1-xFe_xO_3-δ samples were composites of two Ti- and Fe-rich perovskite samples. This kind of composite consists of two phases in which one has a good ionic and the other electronic conductivity, which makes such a composite a potential mixed ionic and electronic conductors (MIECs) material. The total electrical conductivities of analyzed samples were measured in air atmosphere (cathode conditions in Solid Oxide Fuel Cell). The values changed from ∼10⁻³ to 10⁻¹ S cm⁻¹ and depended on the ratio between two observed perovskite phases. The 0.12 S cm⁻¹ conductivity value at 800 °C for sample with the highest amount of Fe-rich perovskite in the structure makes this composite material a candidate for air electrode in electrochemical devices.     

Phase equilibria in the system V2O3Ti2O3TiO2 at 1473°K

The phase equilibria in the V₂O₃Ti₂O₃TiO₂ system have been determined at 1473°K by the quench method, using both sealed tubes and controlled gaseous buffers. For the latter, $\text{CO}{}_2\text{H}{}_2$ mixtures were used to vary the oxygen fugacity between 10^?10.50 and 10^?16.73 atm. Under these conditions the equilibrium phases are: a sesquioxide solid solution between V₂O₃ and Ti₂O₃ with complete solid solubility and an upper stoichiometry limit of (V, Ti)₂O_3.02; an M₃O₅ series which has the V₃O₅ type structure between V₂TiO₅ and V_0.69Ti_2.31O₅ and the monoclinic pseudobrookite structure between V_0.42Ti_2.58O₅ and Ti₃O₅; series of Magneli phases, V₂Ti_n?2O_2n?1Ti_nO_2n?1, n = 4–8; and reduced rutile phases (V, Ti)O_2?x, where the lower limit for x is a function of the $\text{V}\text{(V + Ti)}$ ratio. The extent of the different solid solution areas and the location of the oxygen isobars have been determined.     

Activation of Water-Splitting Photocatalysts by Loading with Ultrafine Rh–Cr Mixed-Oxide Cocatalyst Nanoparticles

The activity of many water-splitting photocatalysts could be improved by the use of Rh^III–Cr^III mixed oxide (Rh_2−xCr_xO₃) particles as cocatalysts. Although further improvement of water-splitting activity could be achieved if the size of the Rh_2−xCr_xO₃ particles was decreased further, it is difficult to load ultrafine (<2 nm) Rh_2−xCr_xO₃ particles onto a photocatalyst by using conventional loading methods. In this study, a new loading method was successfully established and was used to load Rh_2−xCr_xO₃ particles with a size of approximately 1.3 nm and a narrow size distribution onto a BaLa₄Ti₄O₁₅ photocatalyst. The obtained photocatalyst exhibited an apparent quantum yield of 16 %, which is the highest achieved for BaLa₄Ti₄O₁₅ to date. Thus, the developed loading technique of Rh_2−xCr_xO₃ particles is extremely effective at improving the activity of the water-splitting photocatalyst BaLa₄Ti₄O₁₅. This method is expected to be extended to other advanced water-splitting photocatalysts to achieve higher quantum yields.     

An Extensive Family of Heterometallic Titanium(IV)–Metal(III) Rings with Structure Control through Templates

A family of heterometallic [Cat][Ti_xMO_(x+1)(O₂C^tBu)_2x+2] rings is reported where Cat=a secondary or tertiary alkyl ammonium ion, x=7, 8 or 9, and M=Fe^III, Ga^III, Cr^III, In^III and Al^III. The structures are regular polygons with eight, nine or ten vertices with each edge bridged by an oxide and two pivalates. The size of the ring formed is controlled by the alkylammonium cation present. In each case a homometallic by‐product is found [Cat][Ti_xO_(x+1)(O₂C^tBu)_2x−1].     

Tunnel and intergrowth structures in the gallia-rich gallium titanate system

Phase analysis studies of the homologous series Ga₄Ti_m?4O_2m?2 by electron microscopy and diffraction reveals that m = 5 and 7 may occur but they are metastable, appearing only in incompletely reacted specimens. Thus m = 9 is the lowest stable member of the series. The observation of and structure determination of a new tetragonal tunnel structure, containing hollandite-type tunnels separated by elements of the β-gallia and rutile structure types, are also reported. The stoichiometry range M_xGa_10+2xTi_6?2xO₂₇ (M = Al₂O²⁺; 0.80 < x < 1.20) is suggested for this phase, since Al³⁺ is necessary to stabilize this phase. Lattice image studies of Ga₂TiO₅ reveal that it does not have the pseudobrookite structure, as assumed by previous authors, but instead adopts the “low-temperature” Ti₃O₅ structure type.     

Activation of Water‐Splitting Photocatalysts by Loading with Ultrafine Rh–Cr Mixed‐Oxide Cocatalyst Nanoparticles

The activity of many water‐splitting photocatalysts could be improved by the use of Rh^III–Cr^III mixed oxide (Rh_2?xCr_xO₃) particles as cocatalysts. Although further improvement of water‐splitting activity could be achieved if the size of the Rh_2?xCr_xO₃ particles was decreased further, it is difficult to load ultrafine (<2 nm) Rh_2?xCr_xO₃ particles onto a photocatalyst by using conventional loading methods. In this study, a new loading method was successfully established and was used to load Rh_2?xCr_xO₃ particles with a size of approximately 1.3 nm and a narrow size distribution onto a BaLa₄Ti₄O₁₅ photocatalyst. The obtained photocatalyst exhibited an apparent quantum yield of 16 %, which is the highest achieved for BaLa₄Ti₄O₁₅ to date. Thus, the developed loading technique of Rh_2?xCr_xO₃ particles is extremely effective at improving the activity of the water‐splitting photocatalyst BaLa₄Ti₄O₁₅. This method is expected to be extended to other advanced water‐splitting photocatalysts to achieve higher quantum yields.     

Semiconductor-metal transition in Ti3O5

Ti₃O₅ shows a first-order phase transition from the monoclinic structure to the pseudobrookite structure at 448°K, at which temperature a magnetic susceptibility anomaly has been reported earlier in the literature. There is an electrical conductivity discontinuity accompanying the phase transition. Incorporation of Fe stabilizes the high-temperature phase of Ti₃O₅; while with 2% Fe the transition temperature and enthalpy change are lowered, with 5% Fe there is no transition. Mössbauer spectra of 2% Fe-doped Ti₃O₅ are similar below and above the transition temperature and show no evidence for magnetic ordering in the low-temperature phase. These results are compared to the VO₂ transition.     

Ti3C2: An Ideal Co‐catalyst?

How 2D Ti₃C₂ enhances photocatalytic efficiency remains unclear. Now, it is shown that it is graphene quantum dots (GQDs) derived from Ti₃C₂, rather than 2D Ti₃C₂ itself, that play the role of co‐catalyst for La₂Ti₂O₇/Ti₃C₂ (LTC) composites during the photocatalytic reaction. After modification of Ti₃C₂ derivatives, the photocatalytic efficiency of La₂Ti₂O₇ is enhanced 16 times over pure La₂Ti₂O₇. Solid‐state NMR, Raman, and HRTEM results confirm the existence of GQDs in Ti₃C₂ and LTC composites. The GQDs are formed during the chemical change from Ti₃AlC₂ to Ti₃C₂ via HF etching, as Ti atoms are removed and unsaturated carbon bonds are left, which react with each other to form sp² π‐conjugation GQDs. 2D Ti₃C₂ is completely oxidized to CO_x modified TiO_x species, causing Ti₃C₂ to lose its electrical conductivity and the role as co‐catalyst. GQDs largely suppress the photogenerated charge recombination of La₂Ti₂O₇, as revealed by the photoluminescence (PL) and transient photocurrent.     

Crystal structure and electrical conductivity of lanthanum-calcium chromites-titanates La1−xCaxCr1−yTiyO3−δ (x=0-1, y=0-1)

Five series of perovskite-type compounds in the system La_1−xCa_xCr_1−yTi_yO₃ with the nominal compositions y=0, x=0-0.5; y=0.2, x=0.2-0.8; y=0.5, x=0.5-1.0; y=0.8, x=0.6-1.0 and y=1, x=0.8-1 were synthesized by a ceramic technique in air (final heating 1350 °C). On the basis of the X-ray analysis of the samples with (Ca/Ti)?1, the phase diagram of the CaTiO₃-LaCr^IIIO₃-CaCr^IVO₃ quasi-ternary system was constructed. Extended solid solution with a wide homogeneity range is formed in the quasi-ternary system CaCr^IVO₃-CaTiO₃-LaCr^IIIO₃. The solid solution La_{(1−x′−y)}Ca_(x′+y)Cr^IV_x′Cr^III_{(1−x′−y)}Ti_yO₃ exists by up to 0.6-0.7 mol fractions of CaCr^IVO₃ (x^′<0.6-0.7) at the experimental conditions. The crystal structure of the compounds is orthorhombic in the space group Pbnm at room temperature. The lattice parameters and the average interatomic distances of the samples within the solid solution ranges decrease uniformly with increasing Ca content. Outside the quasi-ternary system, the nominal compositions La_0.1Ca_0.9TiO₃, La_0.2Ca_0.8TiO₃, La_0.4Ca_0.6Cr_0.2Ti_0.8O₃ and La_0.3Ca_0.7Cr_0.2Ti_0.8O₃ in the system La_1−xCa_xCr_1−yTi_yO₃ were found as single phases with an orthorhombic structure. In the temperature range between 850 and 1000 °C, the synthesized single-phase compositions are stable at pO₂=6×10⁻¹⁶-0.21×10⁵ Pa. Oxygen stoichiometry and electrical conductivity of the separate compounds were investigated as functions of temperature and oxygen partial pressure. The chemical stability of these oxides with respect to oxygen release during thermal dissociation decreases with increasing Ca-content. At 900 °C and oxygen partial pressure 1×10⁻¹⁵-0.21×10⁵ Pa, the compounds with x>y (acceptor doped) are p-type semiconductors and those with x<y (donor doped) and x=y are n-type semiconductors. The type and level of electrical conductivity are functions of the concentration ratios of cations occupying the B-sites of the perovskite structures: [Cr³⁺]/[Cr⁴⁺] and [Ti⁴⁺]/[Ti³⁺]. The maximum electrical conductivity at 900 °C and pO₂=10⁻¹⁵ Pa was found for the composition La_0.1Ca_0.9TiO₃ (near 50 S/cm) and in air at 900 °C for La_0.5Ca_0.5CrO₃ (close to 100 S/cm).     

Magnetic phase transformation induced by electrochemical lithium intercalation in Li1 + x EuTiO4 and Li2 + 2x Eu2Ti3O10 (0 ≤ x ≤ 1) compounds

Ion exchange of Li for Na in the layered compounds NaEuTiO₄ and Na₂Eu₂Ti₃O₁₀ transforms the (NaO)₂ rock-salt layers into Li₂O₂ antifluorite layers. Li can be inserted reversibly into the Li₂O₂ layers to reduce the Eu³⁺ to Eu²⁺, not the Ti(IV) to Ti(III). An internal electric field perpendicular to the layers is reduced by Li insertion; this field induces a ferroic displacement of the Ti(IV) toward the alkali-ion layers that is eliminated as the internal electric field vanishes in Li_2?+?2x Eu₂Ti₃O₁₀ with x?≈?1. The spins of the (EuO)₂ and the (EuTiO₃)₂ bilayers of Li_1?+?x EuTiO₄ and Li_2?+?2x Eu₂Ti₃O₁₀ with x?≈?1 order at low temperature into ferromagnetic Eu–Eu chains that form a 2D ferromagnetic spiral spin configuration in zero magnetic field. The M-H curve shows zero coercivity and zero remanence, but the M of a polycrystalline sample rises to 4 μ_B/Eu in an H?=?1 T and approaches saturation above 5 μ_B/Eu in 5 T.     

The influence of substituting metals (Ti, V, Cr, Mn, Co and Ni) on the thermal stability of magnetite

In this paper, a systematic study on the influence of substituting metals on the thermal stability of magnetite was carried out. Six series of substituted magnetite (Fe_3?x M _x O₄, M = Ti, V, Cr, Mn, Co and Ni) and Ti–V co-doped magnetite were prepared by a precipitation-oxidation method, followed by the characterization of X-ray diffraction (XRD), X-ray absorption near-edge structure (XANES) spectroscopy and thermogravimetry and differential scanning calorimetry (TG-DSC) analyses. XRD patterns confirmed the formation of samples with spinel structure and XANES probed the valence and site occupancy of the substituting ions. From the TG-DSC analysis results, the substitution of Ti⁴⁺, Mn²⁺, Co²⁺ and Ni²⁺ stabilizes the magnetite structure, while V³⁺ and Cr³⁺ do not show such an effect. For the thermal stability of maghemite, V³⁺ has a negative effect while the other studied ions show a positive effect. In Ti–V co-doped magnetites, the influence of Ti⁴⁺ and V³⁺ on the thermal stability of magnetite is similar to the case of their single-metal-substituted magnetites. The mechanism about the thermal stability change of magnetite by metal substitution was also discussed. The obtained results will be of high importance for the industrial applications of magnetite.     

Structural Aspects of Lithium Transfer in Solid Electrolytes Li2x Zn2-3xTi1+xO4 (0.33≤ x≤ 0.67)

Solid solutions Li_{2x Zn2-3x}Ti_1+xO₄, where x =1/3, 1/2, 3/5, 2/3, were studied by powder X-ray diffractometry and differential thermal analysis. Conductivity measurements have been performed in the gas phase at different temperatures and oxygen pressures. Distribution of cations over the sites of the spinel structure has been determined. Conductivity increases substantially with lithium concentration. The high lithium conductivity of Li₃Zn_0.5Ti₄O₁₀ (x=3/5) and Li₄Ti₅O₁₂ (x=2/3) is the result of two sequential phase transitions associated with different lithium distributions in high-temperature phases with defective NaCl type structures. Possible routes of lithium ion transport are discussed and rationalized based on the conductivity and crystal data.     

A Non-Hydrolytic Sol-Gel Approach for the Preparation of Mg x Al2(1−x)Ti(1+x)O5 Powders

The study of non-hydrolytic reactions for the synthesis of Mg _x Al_2(1?x)Ti_(1+x)O₅ solid solution with x = 0.6 is reported. The reagents chosen were Al(OsBu)₃, Ti(OiPr)₄, TiCl₄ and Mg(NO₃)₂·6H₂O in toluene. The reactions were followed using ¹³C Nuclear Magnetic Resonance (NMR) spectroscopy. Sol-gel synthesized powders were calcined in air at 300, 500, 1000, and 1200°C for 1 h. The powders were analysed by X-Ray Diffraction (XRD) demonstrating the formation of a Mg_0.6Al_0.8Ti_1.6O₅ phase in samples treated at the higher calcination temperature.     

Ba3MIIITiMVO9 (MIII = Fe,Ga, Y,Lu; MV = Nb,Ta, Sb) perovskite oxides: Synthesis,structure and dielectric properties

We describe the synthesis, structures and dielectric properties of new perovskite oxides of the formula, Ba₃M^IIITiM^VO₉, for M^III = Fe, Ga, Y, Lu and M^V = Nb, Ta, Sb. While M^V = Nb and Ta oxides adopt disordered/partially ordered 3C perovskite structures where M^III/Ti/M^V metal-oxygen octahedra are corner-connected, the M^V = Sb oxides show a distinct preference for the 6H structure, where Sb^V/Ti^IV metal-oxygen octahedra share a common face forming (Sb,Ti)O₉ dimers that are corner-connected to the M^IIIO₆ octahedra. The preference of antimony oxides (Sb^V:4d¹⁰) for the 6H structure – which arises from a special Sb^V–O chemical bonding that tends to avoid linear Sb–O–Sb linkages unlike Nb^V/Ta^V:d⁰ atoms which prefer ～180° Nb/Ta–O–Nb/Ta linkages – is consistent with the crystal chemistry of M^V–O oxides in general. The dielectric properties reveal a significant difference among M^III members. All the oxides with the 3C structure excepting those with M^III = Fe show a normal low loss dielectric behaviour with ε = 20–60 in the temperature range 50–400 °C; the M^III = Fe members with this structure (M^V = Nb, Ta) display a relaxor-like ferroelectric behaviour with large ε values at frequencies ≤1 MHz (50–500 °C).     

Significantly Improved Colossal Dielectric Properties and Maxwell—Wagner Relaxation of TiO2—Rich Na1/2Y1/2Cu3Ti4+xO12 Ceramics

In this work, the colossal dielectric properties and Maxwell—Wagner relaxation of TiO₂–rich Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ (x = 0–0.2) ceramics prepared by a solid-state reaction method are investigated. A single phase of Na_1/2Y_1/2Cu₃Ti₄O₁₂ is achieved without the detection of any impurity phase. The highly dense microstructure is obtained, and the mean grain size is significantly reduced by a factor of 10 by increasing Ti molar ratio, resulting in an increased grain boundary density and hence grain boundary resistance (R_gb). The colossal permittivities of ε′ ~ 0.7–1.4 × 10⁴ with slightly dependent on frequency in the frequency range of 10²–10⁶ Hz are obtained in the TiO₂–rich Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ ceramics, while the dielectric loss tangent is reduced to tanδ ~ 0.016–0.020 at 1 kHz due to the increased R_gb. The semiconducting grain resistance (R_g) of the Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ ceramics increases with increasing x, corresponding to the decrease in Cu⁺/Cu²⁺ ratio. The nonlinear electrical properties of the TiO₂–rich Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ ceramics can also be improved. The colossal dielectric and nonlinear electrical properties of the TiO₂–rich Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ ceramics are explained by the Maxwell–Wagner relaxation model based on the formation of the Schottky barrier at the grain boundary.