Structure-property relationships in oxides containing tellurium

Oxides of post-transition metals often show unique structures and properties due to the presence of lone pair electrons and the diffused s orbitals. The present work focuses on synthesis and characterizations of oxides containing Te, a heavy post transition metal. New series of pyrochlore oxides of the formula Cs(M,Te)₂O₆ (M = Al, Ga, Cr, Fe, Co, In, Ho, Lu, Yb, Er, Ge, Rh, Ti, Zn, Ni, and Mg) have been prepared. The samples were highly colored (ranging from black to dark green) indicating a possible mixed valency for Te with appreciable charge transfer between them in the octahedral sites. Electronic conductivity was observed in some phases and could be as high as 2S/cm (M=Ge). Seebeck coefficients of conducting samples show negative values which suggest that electrons are the major charge carriers. Temperature dependence of conductivity indicates that the samples are semiconductors with, in some cases, degenerate semiconducting behavior. Detailed studies on the conduction mechanism indicate the mixed valency of tellurium which leads to semiconducting behavior and the color of the compounds.Systematic studies of cesium tellurate with CsTe₂O[subscript 6-x] where x = 0, 0.15, 0.25, 1.5 have been investigated. On heating at slightly above 600ºC, CsTe₂O₆ loses oxygen resulting in cubic structure with disordered Te⁴⁺/Te⁶⁺ and oxygen vacancies. Two novel phases of CsTe₂O[subscript 6-x] were prepared with orthorhombic structure. The first phase with x value of about 0.2-0.3 crystallizes in Pnma symmetry. At higher values of x, a new compound was discovered with a structure related to Rb₄Te₈O₂₃. Optical properties of the compounds are consistent with their colors. CsTe₂O₆ belongs to class II mixed valency according to Robin and Day classification. However, structures and properties of CsTe₂O[subscript 6-x] phases indicate that they are class I mixed valence compounds. Series of compounds with formula CsTe[subscript 2-x]W[subscript x]O₆ with x=0.2-0.5 have been made which can be considered as solid solution of CsTe₂O₆ and CsTe₀.₅W₁.₅O₆. Although the two end members adopt rhombohedral and trigonal structure, these solid solution phases crystallize in cubic defect pyrochlore structure with W⁶⁺, Te⁶⁺, and Te⁴⁺ randomly occupying 16c octahedral site. The compounds show no electronic conductivity at room temperature. Novel cubic pyrochlore with the formula (CdBi)(MTe)O₇, M= Al, Cr, Ga, In, Fe, Mn, and Sc were synthesized by solid state reaction using oxides of the constituent elements. Magnetic properties analyses show paramagnetism in M=Cr and Mn but antiferromagnetism with short-range correlation in M= Fe phase. All compositions are insulating. Dielectric measurements show relatively low dielectric constants which are independent of temperature and frequency. Metallic Tl₂TeO₆ and insulating In₂TeO₆ are both known to crystallize in the Na₂SiF₆-type structure. We have now prepared a complete Tl[subscript 2-x]In[subscript x]TeO₆ series in a search for a compositionally controlled metal-insulator transition that might be expected if a complete solid solution can be obtained. Unit cell edges and volume vary monotonically with no indication of miscibility gap. The metal-insulator transition occurs at an x value of about 1.4, which can be rationalized on a percolation model. No superconductivity could be detected down to 5K. Rh₂MO₆, M = Mo, W, and Te were synthesized by solid state reaction. Electronic properties as well as thermoelectric properties were investigated and discussed. The compounds crystallize in rutile-related structure and all show relatively high electronic conductivities with Rh₂TeO₆ showing the highest electronic conductivity (~500 S/cm at room temperature) despite localized electrons in Rh³⁺ and Te⁶⁺. Measurable magnetic moments also indicate valence degeneracy between Rh and the M cation. The measured Seebeck coefficients are relatively low and positive indicating hole-type conduction

Low-Cost One-Step Fabrication of Highly Conductive ZnO:Cl Transparent Thin Films with Tunable Photocatalytic Properties via Aerosol-Assisted Chemical Vapor Deposition

Low-cost, high-efficiency, and high quality Cl-doped ZnO (ZnO:Cl) thin films that can simultaneously function as transparent conducting oxides (TCOs) and photocatalysts are described. The films have been fabricated by a facile and inexpensive solution-source aerosol-assisted chemical vapor deposition technique using NH4Cl as an effective, cheap, and abundant source of Cl. Successful ClO substitutional doping in the ZnO films was evident from powder X-ray diffraction, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry results, while scanning electron microscopy reveals the impact of Cl doping on the ZnO thin film morphology. All ZnO:Cl films deposited were transparent and uncolored; optical transmittance in the visible region (400−700 nm) exceeded 80% for depositions using 5−20 mol % Cl. Optimal electrical properties were achieved when using 5 mol % Cl with a minimum measured resistivity of (2.72 ± 0.04) × 10−3 Ω·cm, in which the charge carrier concentration and mobility were measured at (8.58 ± 0.16) × 1019 cm−3 and 26.7 ± 0.1 cm2 V−1 s −1 respectively, corresponding to a sheet resistance (Rsh) of 41.9 Ω□−1 at a thickness of 650 nm. In addition to transparent conducting properties, photocatalytic behavior of stearic acid degradation in the ZnO:Cl films was also observed with an optimal Cl concentration of 7 mol % Cl, with the highest formal quantum efficiency (ξ) measured at (1.63 ± 0.03) × 10−4 molecule/photon, while retaining a visible transparency of 80% and resistivity ρ = (9.23 ± 0.13) × 10−3 Ω·cm. The dual functionality of ZnO:Cl as both a transparent conductor and an efficient photocatalyst is a unique combination of properties making this a particularly unusual material

Refractive Index and Optical Dispersion of In2O3, InBO3 and Gahnite

Refractive indices of In₂O₃, In₂₋ₓSnₓO₃, InBO₃ and 2 different gahnite crystals (ZnAl₂O₄ and Zn.₉₅Fe.₀₅Al₂O₄) were measured at wavelengths of 435.8 to 643.8 nm and were used to calculate n at λ = 589.3 nm ( nD ) and at λ = ∞ (n∞) using the one-term Sellmeier equation 1/(n²-1) = -A/λ² + B. Total polarizabilities, αₜₒₜₐₗ, were calculated from n∞ and the Lorenz-Lorentz equation. Refractive indices, nD and dispersion values, A, were, respectively, 2.093 x 10-16 m² and 133 x 10⁻¹⁶ m² for In₂O₃; 2.0755 and 138 x 10⁻¹⁶ m² for In₂₋ₓSnₓO₃; 1.7940 and 57 x 10⁻¹⁶ m² for ZnAl₂O₄ and 1.7995 and 56 x 10⁻¹⁶ m² for Zn.₉₅Fe.₀₅Al₂O₄ and n₀ = 1.8782 and ne = 1.7756 and x 10⁻¹⁶ m² for InBO₃.Please note: Authors differ slightly in the published version

Photocatalytic and electrically conductive transparent Cl-doped ZnO thin films: Via aerosol-assisted chemical vapour deposition

A simple, economical and effective solution-based chemical vapour deposition (CVD) technique, aerosol-assisted CVD, has been successfully applied to produce inexpensive Cl-doped ZnO films using Zn acetate dihydrate and FeCl3. X-ray photoelectron spectroscopy and the increase in cell parameters from powder X-ray diffraction determined that Cl had been doped into the wurtzite ZnO lattice. The Cl-doping had a significant effect on the morphology of the thin films synthesised and resulted in an improvement in the visible light transmission and lower electrical resistance (typical resistivities of doped films ∼10−2 Ω cm). The highest transmittance (% T) of 85% was obtained when 7 mol% FeCl3 was used in the precursor solution and the lowest resistivity of 4.28 ± 0.41 × 10−2 Ω cm was obtained with 5 mol% FeCl3. The greatest photocatalytic activity of stearic acid degradation under UVA irradiation was obtained on using 10 mol% FeCl3, resulting in the highest formal quantum efficiency (FQE) of 3.0 ± 0.1 × 10−4 molecule per photon. These films, therefore, display transparent conducting oxide and photocatalytic properties, giving multifunctional characteristics and promising applications

Refractive index and optical dispersion of In_2O_3, InBO_3 and gahnite

Refractive indices of In_2O_3, In_(2−x)Sn_xO_3, InBO_3 and 2 different gahnite crystals (Zn_(0.95)Fe_(0.05)Al_2O_4 and Zn_(0.91)Mg_(0.04)Mn_(0.03)Fe_(0.03)Al_(1.99)Fe_(0.01)O_4) were measured at wavelengths of 435.8–643.8 nm and were used to calculate n (n_D) at λ = 589.3 nm and (n_∞) at λ = ∞ with the one-term Sellmeier equation 1/(n^2 − 1) = −A/λ^2 + B. Total polarizabilities, α_(total), were calculated from n_∞ and the Lorenz–Lorentz equation. Refractive indices, n_D and dispersion values, A, are, respectively, 2.093 and 133 × 10^(−16) m^2 for In_2O_3; 2.0755 and 138 × 10^(−16) m^2 for In_(2−x)Sn_xO_3; 1.7995 and 56 × 10^(−16) m^2 for Zn_(0.95)Fe_(0.05)Al_2O_4; 1.7940 and 57 × 10^(−16) m^2 for Zn_(0.91)Mg_(0.04)Mn_(0.03)Fe_(0.03)Al_(1.99)Fe_(0.01)O_4 and n_o = 1.8782 and n_e = 1.7756 and 〈63〉 × 10^(−16) m^2 for InBO_3. The lack of consistency of the polarizabilities of Zn^(2+) in ZnO and In^(3+) in In_2O_3 with the Zn_(2+) and In3+ polarizabilities in other Zn- and In-containing compounds is correlated with structural strain and very high dispersion of ZnO and In_2O_3

Photocatalytic NOₓ oxidation of BiOCl nanostructure-based films grown using aerosol-assisted chemical vapor deposition

Coating of photocatalytic nanomaterials on various surfaces enables interesting applications. This work demonstrates the ability of the aerosol-assisted chemical vapor deposition (AACVD) approach to prepare high-quality BiOCl nanostructure-based films and also to tune the nanostructure and photocatalytic properties of the films by varying the solvent and carrier gas. Solvents have a dramatic impact on the surface morphologies and crystallite size. X-ray diffraction (XRD) and grazing incidence X-ray diffraction (GIXRD) analyses indicate that BiOCl crystals displayed preferential growth in the (101) plane in most samples, while both the (101) and (102) planes were favored in films deposited using ethyl acetate and methanol. Surface energy and adsorption energy calculation reveal that the preferred growth depends on the interaction between the Bi atom and solvent molecules. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS) characterizations showed that all films did not contain any impurity elements but did contain some oxygen vacancies. The obtained nanostructured BiOCl films show good photocatalytic properties. The highest photocatalytic NOx removal efficiency is achieved in the film prepared using ethyl acetate and air, which we attribute to the large crystallite size and therefore high mobility of the carriers. Herein, we show that different crystal morphologies and sizes of BiOCl have strong impacts on the photocatalytic activity toward NO oxidation, and both factors can be effectively tuned in the AACVD process. Such knowledge may be useful for future research on coating materials for resolving environmental problems