Characterization and activity of visible-light-driven TiO2 photocatalyst codoped with nitrogen and cerium

Nitrogen and cerium codoped TiO₂ photocatalysts were prepared by a modified sol-gel process with doping precursors of cerium nitrate and urea, and characterized by X-ray diffraction (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC), X-ray photoelectron spectra (XPS) and ultraviolet-visible light diffuse reflectance spectra (UV-vis DRS). Results indicate that anatase TiO₂ is the dominant crystalline type in as-prepared samples, and CeO₂ crystallites appear as the doping ratio of Ce/Ti reaches to 3.0 at%. The TiO₂ starts to transform from amorphous phase to anatase at 987.1 K during calcination, according to the TG-DSC curves. The XPS show that three major metal ions of Ce³⁺, Ce⁴⁺, Ti⁴⁺ and one minor metal ion of Ti³⁺ coexist on the surface. The codoped TiO₂ exhibits significant absorption within the range of 400-500 nm compared to the non-doped and only nitrogen-doped TiO₂. The enhanced photocatalytic activity of the codoped TiO₂ is demonstrated through degradation of methyl orange under visible light irradiation.     

Synthesis, crystal and band structures, and optical properties of a new lanthanide-alkaline earth tellurium(IV) oxide: La2Ba(Te3O8)(TeO3)2

A new quaternary lanthanide alkaline-earth tellurium(IV) oxide, La₂Ba(Te₃O₈)(TeO₃)₂, has been prepared by the solid-state reaction and structurally characterized. The compound crystallizes in monoclinic space group C2/c with a=19.119(3), b=5.9923(5), c=13.2970(19) Å, β=107.646(8)°, V=1451.7(3) Å³ and Z=4. La₂Ba(Te₃O₈)(TeO₃)₂ features a 3D network structure in which the cationic [La₂Ba(TeO₃)₂]⁴⁺ layers are cross-linked by Te₃O₈⁴⁻ anions. Both band structure calculation by the DFT method and optical diffuse reflectance spectrum measurements indicate that La₂Ba(Te₃O₈)(TeO₃)₂ is a wide band-gap semiconductor.     

Temporal evolution study of the plasma induced by CO2 pulsed laser on targets of titanium oxides

This paper reports studies on time-resolved laser induced breakdown spectroscopy (LIBS) of plasmas induced by IR nanosecond laser pulses on the titanium oxides TiO and TiO₂ (anatase). LIBS excitation was performed using a CO₂ laser. The laser-induced plasma was found strongly ionized yielding Ti⁺, O⁺, Ti^2 +, O^2 +, Ti^3 +, and Ti^4 + species and rich in neutral titanium and oxygen atoms. The temporal behavior of specific emission lines of Ti, Ti⁺, Ti^2 + and Ti^3 + was characterized. The results show a faster decay of Ti^3 + and Ti^2 + ionic species than that of Ti⁺ and neutral Ti atoms. Spectroscopic diagnostics were used to determine the time-resolved electron density and excitation temperatures. Laser irradiation of TiO₂-anatase induces on the surface sample the polymorphic transformation to TiO₂-rutile. The dependence on fluence and number of irradiation pulses of this transformation was studied by micro-Raman spectroscopy.     

In situ study of electrochromic properties of self-assembled TiO2 nanotubes

Electrochromical properties of anodic self-assembled nanotubes were investigated. It was found that amorphous titania nanotubes were able to insert H⁺ ions in a highly reversible manner. Coloration of the TiO₂ nanotubes occurred at potentials below ?0.5 V vs. Ag/AgCl in 1M (NH₄)₂SO₄ aqueous solution. The proton insertion reaction probably leads to the formation of a Ti³⁺/Ti⁴⁺ solid solution in the amorphous titania electrode, as was shown by the analysis of the derivative curve. The nanotubular titania electrode shows reasonable color efficiency when compared with other electrochromic materials and it is a promising candidate for the fabrication of low-cost interdigitated electrochromic devices.     

Preparation and Crystal Structures of the Hydrous Mercury Tellurates,HgII(H4TeVIO6) and HgI2(H4TeVIO6)(H6TeVIO6)·2H2O

Single crystals of Hg^II(H₄Te^VIO₆) (colourless to light‐yellow, rectangular plates) and Hg^I₂(H₄Te^VIO₆)(H₆Te^VIO₆)·2H₂O (colourless, irregular) were grown from concentrated solutions of orthotelluric acid, H₆TeO₆, and respective solutions of Hg(NO₃)₂ and Hg₂(NO₃)₂. The crystal structures were solved and refined from single crystal diffractometer data sets (Hg^II(H₄Te^VIO₆): space group Pna2₁, Z = 4, a =10.5491(17), b = 6.0706(9), c = 8.0654(13)Å, 1430 structure factors, 87 parameters, R[F² > 2σ(F²)] = 0.0180; Hg^I₂(H₄Te^VIO₆)(H₆Te^VIO₆)·2H₂O: space group P1¯, Z = 1, a = 5.7522(6), b = 6.8941(10), c = 8.5785(10)Å, α = 90.394(8), β = 103.532(11), γ = 93.289(8)°, 2875 structure factors, 108 parameters, R[F² > 2σ(F²)] = 0.0184). The structure of Hg^II(H₄Te^VIO₆) is composed of ribbons parallel to the b axis which are built of [H₄TeO₆]^2— anions and Hg²⁺ cations held together by two short Hg—O bonds with a mean distance of 2.037Å. Interpolyhedral hydrogen bonding between neighbouring [H₄TeO₆]^2— groups, as well as longer Hg—O bonds between Hg atoms of one ribbon to O atoms of adjacent ribbons lead, to an additional stabilization of the framework structure. Hg^I₂(H₄Te^VIO₆)(H₆Te^VIO₆)·2H₂O is characterized by a distorted hexagonal array made up of [H₄TeO₆]^2— and [H₆TeO₆] octahedra which spread parallel to the bc plane. Interpolyhedral hydrogen bonding between both building units stabilizes this arrangement. Adjacent planes are stacked along the a axis and are connected by Hg₂²⁺ dumbbells (d(Hg—Hg) = 2.5043(4)Å) situated in‐between the planes. Additional stabilization of the three‐dimensional network is provided by extensive hydrogen bonding between interstitial water molecules and O and OH‐groups of the [H₄TeO₆]^2— and [H₆TeO₆] octahedra. Upon heating Hg^I₂(H₄Te^VIO₆)(H₆Te^VIO₆)·2H₂O decomposes into TeO₂ under formation of the intermediate phases Hg^II₃Te^VIO₆ and the mixed‐valent Hg^IITe^IV/VI₂O₆.     

Fluoroalkylsilane Modification of Sol–Gel SiO2-TiO2 Coatings

Sol–gel chemistry of SiO_{2(1 – x)}TiO_2(x) involving the partial pre-hydrolysis of tetraethoxysilane (TEOS) and subsequent reaction with titanium isopropoxide has been used to produce materials of high area and variable absorption edge in the UV-visible spectrum. As x increases so the total surface area of these phases unexpectedly passed through a maximum, but the UV-vis cut off moved to greater wavelength. On the other hand, X-ray photoelectron spectroscopy (XPS) measured O_1s binding energies and temperatures of maximum rates of reduction (T_max) that were intermediate between those of pure SiO₂ and TiO₂. Both suggested that SiO_{2(1 – x)}TiO_2(x) samples were an intimate mixture of Si^{4 +} and Ti^{4 +} in the sol–gel matrix. Perfluoroalkylsilane (PFAS) was strongly adsorbed on this sol–gel coating making it strongly hydrophobic. This mode of modification was better than PFAS incorporation at the start of the sol–gel synthesis. Such sol–gel chemistry might in the future be optimised for water-repelling surfaces.     

Sol–gel preparation and photocatalytic performance of TiO2/SrAl2O4: Eu2+, Dy3+ toward the oxidation of gaseous benzene

It has been found that the photocatalytic activity of TiO₂ toward the decomposition of gaseous benzene can be greatly enhanced by loading TiO₂ on the surface of SrAl₂O₄: Eu²⁺, Dy³⁺ using sol–gel technology. The prepared photocatalyst was characterized by BET, XRD, and XPS analyses. XRD results reveal that the peaks of titania in either rutile or anatase form are not detected by XRD in the 2θ region from 20° to 50°. The binding energy values of Ti 2p of pure TiO₂ are 458.90 and 464.60 eV, while for TiO₂/SrAl₂O₄: Eu²⁺, Dy³⁺, the binding energy values of Ti 2p are 458.50 and 464.20 eV. The results indicate that the optimum loading of TiO₂ is 1 wt% and TiO₂/SrAl₂O₄: Eu²⁺, Dy³⁺ (1 wt%) demonstrates 1.4 times the photocatalytic activity of that of pure TiO₂, but the underlying mechanism of SrAl₂O₄: Eu²⁺, Dy³⁺ in the photocatalytic reaction remains to be unraveled.     

钛、铝和玻璃上TiO2光催化膜的失活研究

采用浸渍提拉法，在平行条件下制备了钛、铝和玻璃载体上的TiO₂膜TiO₂ / Ti、TiO₂ / Al和TiO₂ / G，利用X射线光电子能谱(XPS)、原子力显微镜(AFM)和光催化降解实验等手段对膜样品进行了表征和活性评价。实验结果表明，在铝和玻璃基材上制膜时发生了显著的基材元素溢出，使各膜样品的化学组成不同，同时TiO₂粒子和膜表面形貌也因前驱物烧结行为不同而差异较大。TiO_{2相似文献}   

Surface properties and photoactivity of TiO2 treated with electron beam

The improvement of the TiO₂-photoactivitiy by electron beam treatment (1 MeV) as a function of the absorbed radiation dose (MGy) is reported. The radiation-induced effects in the TiO₂ crystal structure, e.g. change of the Ti³⁺/Ti⁴⁺ ratio, increase of the photoactivity, etc. were investigated. Three methods were implemented in this respect: for the change of the TiO₂ crystal structure X-ray photoelectron spectroscopy and photoluminescence spectroscopy were applied. The photocatalytic activity of the EB-treated TiO₂ was tested by taking the degree of methylene blue photodegradation as a measure of the achieved effect. The obtained experimental data of all testing methods showed that in TiO₂ at an absorbed dose of 0.5 MGy optimum changes in crystal structure of the catalyst occur, resulting in the highest photocatalytic efficiencies.     

Two new layered oxohalides in the system Cu–Yb–Te–O–Cl

Two complex lanthanide(III) transition metal(II) tellurium(IV) oxyhalides, Cu₃Yb₂(TeO₃)₄Cl₄ and Cu₃Yb₃(TeO₃)₄Cl₆ have been synthesized and the crystal structures were determined by single-crystal X-ray diffraction. Both compounds are layered with only weak connections in between the layers. The layers are made up of [YbO₈], [TeO₃] and [CuO_xCl_y] polyhedra. In both compounds the strong Lewis acid cations Yb³⁺ and Te⁴⁺ only form bonds to oxygen while Cu²⁺ form bonds to both oxygen and chlorine. This leads the Cl^? ions to be expelled from the bonding volumes of the crystal structures and protrude from the layers. Magnetic susceptibility measurements were performed on a powder sample of Cu₃Yb₂(TeO₃)₄Cl₄. The Curie–Weiss law found at low temperatures indicates a Curie–Weiss temperature of ca. ?5(1) K. However, indication for long-range magnetic ordering could not be observed down to 1.87 K. The two new phases are to the best of our knowledge the first containing all three of Cu, Yb and Te.     

Time-of-flight mass spectroscopy of femtosecond and nanosecond laser ablated TeO2 crystals

Single-pulse femtosecond (fs) (pulse duration ～200 fs, wavelength 398 nm) and nanosecond (ns) (pulse duration 4 ns, wavelength 355 nm) laser ablation have been applied in combination with time-of-flight mass spectrometer (TOFMS) to analyze the elemental composition of the plasma plume of single-crystalline telluria (c-TeO₂, grown by the balance controlled Czochralski growth method). Due to the three-order difference of the peak intensities of the ns and fs-laser pulses, significant differences were observed regarding the laser-induced species in the plasma plume. Positive singly, doubly and triply charged Te ions (Te⁺, Te₂⁺, Te₃⁺) in the form of their isotopes were observed in case of both irradiations. In case of the ns-laser ablation the TeO⁺ formation was negligible compared to the fs case and there was no Te trimer (Te₃⁺) formation observed. It was found that the amplitude of Te ion signals strongly depended on the applied laser pulse energy. Singly charged oxygen ions (O⁺) are always present as a byproduct in both kinds of laser ablation.     

Synthesis, characterization and dielectric properties of new unidimensional quaternary tellurites: LaTeNbO6, La4Te6Nb2O23, and La4Te6Ta2O23

Three new tellurites, LaTeNbO₆ and La₄Te₆M₂O₂₃ (M=Nb or Ta) have been synthesized, as bulk phase powders and crystals, by using La₂O₃, Nb₂O₅ (or Ta₂O₅), and TeO₂ as reagents. The structures of LaTeNbO₆ and La₄Te₆Ta₂O₂₃ were determined by single crystal X-ray diffraction. LaTeNbO₆ consists of one-dimensional corner-linked chains of NbO₆ octahedra that are connected by TeO₃ polyhedra. La₄Te₆M₂O₂₃ (M=Nb or Ta) is composed of corner-linked chains of MO₆ octahedra that are also connected by TeO₄ and two TeO₃ polyhedra. In all of the reported materials, Te⁴⁺ is in an asymmetric coordination environment attributable to its stereo-active lone-pair. Infrared, thermogravimetric, and dielectric analyses are also presented. Crystallographic information: LaTeNbO₆, triclinic, space group P−1, a=6.7842(6) Å, b=7.4473(6) Å, c=10.7519(9) Å, α=79.6490(10)°, β=76.920(2)°, γ=89.923(2)°, Z=4; La₄Te₆Ta₂O₂₃, monoclinic, space group C2/c, a=23.4676(17) Å, b=12.1291(9) Å, c=7.6416(6) Å, β=101.2580(10)°, Z=4.     

Opposite effect of Li<Superscript>+</Superscript> codoping on the upconversion emissions of Er<Superscript>3+</Superscript>-doped TiO<Subscript>2</Subscript> powders

The Er³⁺-Li⁺ codoped TiO₂ powders have been prepared by the non-aqueous sol–gel method. The green and red upconversion emissions centered at about 526, 550 and 663 nm were observed by the ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺, respectively. Li⁺ codoping has opposite effect on the upconversion emissions intensities for Er³⁺-doped TiO₂ at sintering temperatures of 1,073 and 1,273 K. At 1,073 K, the Er³⁺-doped TiO₂ phase transition from anatase to rutile was accelerated with increasing Li⁺ codoping concentration, leading to the increase of crystal field symmetry of Er³⁺, thus the upconversion emissions intensities decreased. At 1,273 K, Li⁺ codoping had no effect on the phase structure of Er³⁺-doped TiO₂ and only increased the Er–O bond length, it indicated that the upconversion emissions intensities greatly enhanced because of the decrease of crystal field symmetry of Er³⁺.     

Thermally stimulated crystallization of (20−x)LiO2-80TeO2-xWO3 glass system

Tellurite glasses of the (20−x)LiO₂-80TeO₂-xWO₃ system were synthesized (x=0, 5, and 10) and annealed at different temperatures, and the crystallization kinetics was studied using XRD, FTIR spectroscopy, and DSC techniques. XRD data evidenced the amorphous state of as-quenched samples, while thermally treated samples showed the growth of crystalline phases. FTIR spectroscopy was used to observe the evolution of the vibrational mode assigned to the TeO₂ phases. The presence of γ-TeO₂, α-TeO₂, and α-Li₂Te₂O₅ crystalline phases was observed for the sample TL, x=0, while only the first and second phases were observed for TLW5 and TLW10 samples, x=5 and 10, respectively, suggesting that WO₃ enters the structure preferentially as glass former, inhibiting the growth of the phase α-Li₂Te₂O₅.     

Exploration of New Birefringent Crystals in Bismuth d0 Transition Metal Selenites

The first examples of bismuth fluoride selenites with d⁰-TM/Te^VI polyhedrons, namely, Bi₄TiO₂F₄(SeO₃)₄ ( 1 ), Bi₄NbO₃F₃(SeO₃)₄ ( 2 ), Bi₄TeO₄F₂(TeO₃)₂(SeO₃)₂ ( 3 ), Bi₂F₂(MoO₄)(SeO₃) ( 4 ) and Bi₂ZrO₂F₂(SeO₃)₂ ( 5 ) have been successfully synthesized under hydrothermal reactions by aliovalent substitution. The five new compounds feature three different types of structures. Compounds 1 – 3 , containing Ti^IV, Nb^V and Te^VI respectively, are isostructural, exhibiting a new 3D framework composed of a 3D bismuth oxyfluoride architecture, with intersecting tunnels occupied by d⁰-TM/Te^VI octahedrons and selenite/tellurite groups. Interestingly, compound Bi₄TeO₄F₂(TeO₃)₂(SeO₃)₂ ( 3 ) is the first structure containing Se^IV and mixed-valent Te^IV/Te^VI cations simultaneously. Compound 4 features a new 3D structure formed by a 3D bismuth oxyfluoride network with MoO₄ tetrahedrons and selenites groups imbedded in the 1D tunnels. Compound 5 displays a novel pillar-layered 3D open framework, consisting of 2D bismuth oxide layers bridged by the [ZrO₂F₂(SeO₃)₂]⁶⁻ polyanions. Theoretical calculations revealed that the five compounds displayed very strong birefringence. The birefringence values of compounds 1 – 3 , especially, are above 0.19 at 1064 nm, which are larger than the mineral calcite. Based on the structure and property analysis, it was found that the asymmetric SeO₃ groups (and TeO₃ in compound 3 ) displayed the largest anisotropy, compared with the bismuth cations and the d⁰-TM/Te polyhedra, which is beneficial to the birefringence.     

Topotaxial formation of titanium-rich barium titanates during solid state reactions on (110) TiO2 (rutile) and (001) BaTiO3 single crystals

The orientation relationships of Ti-rich barium titanate phases formed by solid state reactions at high temperatures were studied using (110) TiO₂ (rutile) and (001) BaTiO₃ single-crystal substrates. Well-oriented Ba₆Ti₁₇O₄₀ islands were observed after a vapor–solid reaction of a BaO quantity equivalent to a nominal BaO film thickness of 1 nm with the TiO₂ substrate, whereas a thin film consisting of well-oriented BaTiO₃ and Ba₆Ti₁₇O₄₀ grains was formed after vapor–solid reaction of a BaO quantity equivalent to a nominal BaO film thickness of 50 nm with the rutile substrate. A topotaxial orientation relationship between Ba₆Ti₁₇O₄₀ and TiO₂ was found. Topotaxy is facilitated by a certain similarity in the oxygen sublattices of TiO₂ and Ba₆Ti₁₇O₄₀. The mechanism of the reaction occurring between BaO vapor and the TiO₂ surface at high temperature is discussed. On the other hand, several well-oriented Ba₄Ti₁₃O₃₀, Ba₆Ti₁₇O₄₀ and Ba₂Ti₅O₁₂ phases were observed to be embedded in the mainly forming Ba₂TiSi₂O₈ phase after a solid–solid reaction of amorphous SiO₂ thin films with (001) BaTiO₃ substrates at temperatures above 1000 °C. They were formed by a topotaxial reaction involving the transformation of (111) planes of BaTiO₃ into (001) planes of the Ti-rich phases by removal of BaO and insertion of TiO₂. Cross-sections of the interfaces between the substrates and the various reaction products are studied by (high-resolution) transmission electron microscopy.     

Preparation and Structure of Cerium Titanates Ce2TiO5, Ce2TiO7, and Ce4Ti9O24

Compounds Ce₂TiO₅, Ce₂Ti₂O₇, and Ce₄Ti₉O₂₄ were prepared by heating appropriate mixtures of solids containing Ce⁴⁺ and Ti³⁺ or Ti which were placed in a platinum-silica-ampoule combination at T = 1250°C (3d) under vacuum. The new compounds were characterized by powder patterns. We obtained Ce₂TiO₅ which is isotypic to La₂TiO₅ and crystallizes in the Y₂TiO₅-type (space group Pnma) with a = 10.877(6) Å, b = 3.893(1) Å, c = 11.389(8) Å, Z = 4. Ce₂Ti₂O₇ is isotypic to La₂Ti₂O₇ and crystallizes in the monoclinic Ca₂Nb₂O₇ type (space group P 2₁) with a = 7.776(6) Å, b = 5.515(4) Å, c = 12.999(6) Å, β = 98.36(5), Z = 4. The compound Ce₄Ti₉O₂₄ crystallizes orthorhombic with a = 14.082(4) Å, b = 35.419(8) Å, c = 14.516(4) Å, Z = 16. The new cerium titanate Ce₄Ti₉O₂₄ is isotypic to Nd₄Ti₉O₂₄ (space group Fddd (No. 70)) which represents a novel type of structure.     

Fractional precipitation synthesis and photoluminescence of La2Ti2O7:xEu3+ phosphors

Eu³⁺ ions activated La₂Ti₂O₇ (La₂Ti₂O₇:xEu³⁺) phosphors have been successfully synthesized by a fractional precipitation method from commercially available La₂O₃, Eu₂O₃, HNO₃, Ti(SO₄)₂·9H₂O and NH₃·H₂O as the starting materials. Detailed characterizations of the synthetic products were obtained by fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), differential thermal analysis, thermogravimetry and derivative thermogravimetry (DTA-TG-DTG), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy. The results show that the precursor is composed of amorphous particles with quasi-spherical in shape and about 50 nm in size. Moreover, the precursor could be converted into pure La₂Ti₂O₇ phase by calcining at 1000 °C for 2 h in air. The as-synthesized La₂Ti₂O₇ particles are approximate polyhedron in shape and about 100–200 nm in size. PL spectroscopy of La₂Ti₂O₇:xEu³⁺ phosphors reveals that the strongest emission peak is located at 616 nm under 275 nm ultraviolet (UV) light excitation, which corresponds to the ⁵D₀→⁷F₂ transition of Eu³⁺ ions. The quenching concentration of Eu³⁺ ions is 10.0 mol%, and its corresponding fluorescence lifetime was 1.82 ms according to the linear fitting result. Decay study reveals that the ⁵D₀→⁷F₂ transition of Eu³⁺ ions has a single exponential decay behavior.     

HoClTe2O5: Ein tellurdioxidreiches Holmium(III)‐Chlorid‐Oxotellurat(IV)

HoClTe₂O₅: A Telluriumdioxide‐rich Holmium(III) Chloride Oxotellurate(IV) While attempting to synthesize anionically derivatized holmium oxotellurates by reacting holmium chloride (HoCl₃) with tellurium oxide (TeO₃; molar ratio 1 : 3, 800°C 10 d) in evacuated silica ampoules, transparent, greenish yellow and coarse single crystals of holmium(III) chloride oxotellurate(IV) HoClTe₂O₅ (triclinic, P1; a = 762.07(6), b = 796.79(6), c = 1010.36(8) pm, α = 100.987(4), ß = 99.358(4), γ = 91.719(4)°; Z = 4) were obtained. The crystal structure contains eightfold coordinated (Ho1)³⁺ (only surrounded by oxygen atoms) and sevenfold coordinated (Ho2)³⁺ cations (surrounded by one chloride and six oxide anions). Each sort of holmium polyhedra convenes independently to chains along [100] by edge‐sharing which again combine alternately via O6 and O9 to form ²{[Ho₂O₁₀(Cl1)]^15—} layers parallel (001). Each of the four crystallographically different Te⁴⁺ cations are surrounded by three close oxygen atoms (d(Te—O) = 188 — 195 pm) and always one more situated further away. The stereochemical activity of the non‐bonding electron pairs (“lone pairs”) leads to ψ¹‐trigonal bipyramidal coordination figures. The ψ¹‐tetrahedral [TeO₃]^2— basic units form discrete [Te₂O₅]^2— doubles with ecliptic conformation which are arranged in a fish‐bone pattern parallel to (001) on both sides of the ²{[Ho₂O₁₀Cl]^15—} layers. The coherence of the ²{[Ho₂(Cl1)Te₄O₁₀]⁺} layers is exclusively maintained via Cl2—Te1 contacts with an extraordinary long distance of 335 pm. As (Cl1)^— belongs to the coordination sphere of (Ho2)³⁺ and (Cl2)^— is only surrounded by Te⁴⁺, the compound should be correctly named holmium(III) chloride oxochlorotellurate(IV) Ho₂Cl[Te₄O₁₀Cl] (Z = 2).     

The mixed valent tellurate SrTe3O8: Electronic lone pair effect of Te

A novel mixed valent tellurium oxide, SrTe₃O₈, has been synthesized and its crystal structure was determined ab initio from powder X-ray diffraction data. This oxide, which crystallizes in a tetragonal unit-cell, P4₂/m space group, with very close a and c cell parameters (6.8257(1) and 6.7603(1) Å, respectively), exhibits a very original structure built up of corner-sharing TeO₆ (Te⁶⁺) octahedra and Te₂O₈ (Te⁴⁺) twin-pyramidal units. The latter ones form [Te₃O₈]_∞ chains running along the [001] and the [110] directions. Besides the four sided tunnels where the Sr²⁺ cations are located, there are very large four sided tunnels running along the c-axis which are obstructed by the electronic lone pairs of the Te⁴⁺ cations.