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In this work, the photovoltaic outputs of the lead‐free FASnI3‐based perovskite solar cells are discussed by using Solar Cell Capacitance Simulator in One Dimension. The device outputs estimated theoretically in this study are almost equal to the experimental results, thereby verifying accuracy of this simulation. To find the decent electron transport layer (ETL), herein, various ETLs are presented instead of C60/BCP in the experimental FASnI3‐based perovskite solar cell (PSC). The designed FASnI3 PSC utilizing niobium pentoxide (Nb2O5) as an ETL with an appropriate band alignment and a low lattice mismatch at FASnI3/ETL interface provides better efficiency by decreasing recombination at front side. The performances of the proposed PSC are also measured by altering the thickness and doping of ETL and absorber, interface defects, and series and shunt resistances. Furthermore, this paper reports the calculation of recombination coefficients at absorber/ETL interface, depletion region, and quasi‐neutral region. An improved efficiency of 22.24% is evaluated at optimized thicknesses of 100 nm for HTL, 500 nm for absorber, 50 nm for ETL, and 50 nm for ITO for the proposed inverted PSC of ITO/PEDOT:PSS/FASnI3/Nb2O5/Ag. These results suggest that chemically stable and less‐toxic Nb2O5 can be applied as a useful ETL in inverted PSCs for further improving the performances. [ABSTRACT FROM AUTHOR]

Silicon carbide based composites with 30, 40 and 50 wt % of Ti and NbC as sintering additives were prepared by hot-press method. Molar ratio of Ti:NbC was kept at 1:1.8. The two step sintering was performed in order to avoid the squeezing out the melted titanium above 1668 °C. Composite powders were sintered at 1650 °C for 3 h and subsequently at 1850 °C for 1 h under mechanical pressure of 30 MPa in Ar atmosphere. XRD pattern confirmed the formation of (Ti, Nb)C ss in the SiC matrix. Composite with 50% of Ti–NbC phase showed the extraordinary electrical conductivity of 2.4 × 105 S/m which was achieved by homogeneous distribution of Ti and NbC in SiC matrix and forming a continuous conductive network. Prepared composites show complex magnetic properties, diamagnetism originated from SiC matrix, paramagnetism caused by Ti and NbC admixing, as well as weak ferromagnetism probably coming from impurities contained in the initial powders. Samples with 30 and 40 wt % of Ti and NbC exhibit superconducting state below 2 K. [ABSTRACT FROM AUTHOR]

In recent times, much attention has been given to the study of the interaction between biomimetic assemblies with graphene oxide (GO), as the outcome of these interactions has a substantial impact on the biological and physicochemical properties of both the biomimetic assemblies and GO. Several applications of GO have been established over the years, and GO has the potential to be used as a biomedical material. In this article, we report the interaction of a red-emitting molecule, Nile blue A (NB), in the presence of four different bile salt aggregates as well as in the presence and absence of GO using various spectroscopic techniques. In the presence of different bile salts in water and varying concentrations of GO, NB undergoes a transition from the monomeric form to a J-dimer involving NB–bile salt interactions. The equilibrium between the H-dimer and J-dimer form of NB is also perturbed in the presence of GO and varying the concentration of bile salts. Raman spectroscopy establishes the fact that NB does indeed interact with the various functional groups present on the GO surface. [ABSTRACT FROM AUTHOR]

Synthesis of high-entropy carbides (HEC) requires high temperatures that can be provided by electric arc plasma method. However, the formation temperature of a single-phase sample remains unknown. Moreover, under some temperatures multi-phase structures can emerge. In this work, we developed an approach for a controllable synthesis of HEC TiZrNbHfTaC5 based on theoretical and experimental techniques. We used Canonical Monte Carlo (CMC) simulations with the machine learning interatomic potentials to determine the temperature conditions for the formation of single-phase and multi-phase samples. In full agreement with the theory, the single-phase sample, produced with electric arc discharge, was observed at 2000 K. Below 1200 K, the sample decomposed into (Ti-Nb-Ta)C, and a mixture of (Zr-Hf-Ta)C, (Zr-Nb-Hf)C, (Zr-Nb)C, and (Zr-Ta)C. Our results demonstrate the conditions for the formation of HEC and we anticipate that our approach can pave the way towards targeted synthesis of multicomponent materials. [ABSTRACT FROM AUTHOR]

In this presented work, pure and holmium, niobium, and holmium–niobium co-doped titanium dioxide nanopowders were synthesized by the sol–gel method. Their morphological, structural, optical, and photocatalytic properties were analyzed by scanning electron microscopy, X-ray diffraction, and UV–visible spectrophotometer. The photocatalytic activities of the synthesized nanopowders were examined using ultraviolet light. The results have shown that doping both with a single (holmium, niobium) or two types of elements (holmium–niobium) have significantly changed the properties of titanium dioxide. It was concluded that, compared with others, the holmium–niobium co-doped sample has the smallest crystal size. Other values, such as forbidden band gap and kinetic constants, are in the range of the data obtained for single-element doping. [ABSTRACT FROM AUTHOR]

The oxidation characteristics of Fe‐25Cr‐35Ni‐2.5Al‐XNb (0, 0.6, and 1.2 wt%) alumina‐forming austenitic alloys at 1000°C and 1100°C in air were investigated. Results show that Nb has an important effect on the high‐temperature oxidation resistance. A bilayer oxide scale with a Cr2O3‐rich outer layer and Al2O3‐rich internal layer forms on the surface of the Nb‐free alloy and exhibits a poor oxidation resistance at 1000°C and 1100°C. With Nb addition, both the 0.6Nb‐addition and 1.2Nb‐addition alloys exhibit better oxidation resistance at 1000°C. Because of the third element effect, Nb addition reduces the critical Al content and forms a single external protective Al2O3 scale, which greatly improves the oxidation resistance. After oxidation at 1100°C, niobium oxides (mainly Nb2O5) are formed on the surface of the 1.2Nb‐addition alloy and destroy the integrity of the Al2O3 scale, which causes the formation of Cr‐rich oxide nodules and eventually develops to be a loose bilayer oxide scale with NiCr2O4, Cr2O3, and Fe2O3 outer layers and Al2O3 inner layer. [ABSTRACT FROM AUTHOR]

Niobium aluminide Nb3Al, a typical A15 conventional superconductor, has been believed to adopt the cubic β-W type structure with a space group of Pm 3 ¯ n at ambient pressure since its discovery. Herein, we report a new crystal structure with a space group of C2/c, as predicted from the ab initio evolutionary algorithm, is energetically more favorable than the A15 phase at ambient pressure and low temperature. Phonon calculations indicate this phase is dynamically stable. The application of the Allen-Dynes modified McMillan equation to the C2/c phase yields a superconducting transition temperature Tc in the range of 17.44 – 19.48 K, which is in good agreement with experiments (18.8 K). A key difference between the A15 and C2/c crystal structures is the distortion of the Nb atomic chains, which are believed to be closely related to the superconducting behavior. Based on ab initio molecular dynamics simulations, we find that Nb3Al transforms from the newly discovered C2/c phase to the standard A15 phase as temperature increases. Furthermore, another new phase with a space group of Cmcm is found to become stable as a hydrostatic pressure is applied. [ABSTRACT FROM AUTHOR]

Potassium sodium niobate (KNN) is a lead free ceramic that can potentially replace PZT (Pb(ZrTi)O3). However, KNN suffers from a few major disadvantages. These include the presence of highly volatile alkaline elements and stoichiometry sensitive properties coupled with severe difficulties in controlling the composition. In this work, La doped sodium potassium niobate based perovskite (ABO3) ceramics, more specifically [{(1-x)(K0.5Na0.5)xLa}Nb(1–2x/5)O3] (0 < x < 0.1), have been developed. Among these, the material at 5 mol. % La doping appears with an unusually high density up to 99% of its theoretical value, while densities of the parent K0.5N0.5NbO3 (KNN) ceramics typically only reach ∼70% to 89% of the theoretical limit. The developed ceramics in their circular and rectangular disk form with thickness 0.8 mm show transparency and most importantly, this transparency is electrically tunable up to 52%. Additionally, the material shows sensitivity of its magnetic and optical properties to ultraviolet (UV) irradiation, i.e., these materials transform to a metastable and reversible state that exhibits graded color change from clear to deep blue and shows a considerable increase in magnetization under UV exposure. This feature makes the developed ceramics attractive for the fabrication of new generation devices; e.g., powerless UV detectors as well as protectors, since it absorbs UV completely. Based on first-principles calculations, we developed a model that attributes these observations to the occupancy of La fxyz orbitals induced by UV excitations. The model also indicates that UV induced absorption in the visible range and magnetism are related. [ABSTRACT FROM AUTHOR]

Topological semimetals represent one of the most interesting classes of materials that continue to attract worldwide interest. Here, we report magnetotransport properties of MPn2-type (M=Nb, Ta; Pn=P, As, Sb) NbSb2 single-crystal semimetals with a centrosymmetric C12/m1 space group, paramagnetic ground state, and non-saturation parabolic-like magnetoresistance. The NbSb2 crystals show metallic conductivity down to 2K and undergo a metal-to-insulator-like transition under a magnetic field B (B ≥ 4 T) and exhibit a resistivity plateau in the lowtemperature region (T ≤ 10K), where the value of resistivity strongly depends on the magnitude and direction of the magnetic field. Upon sweeping the magnetic field from 0 to 14.5 T in the transverse configuration at T=1.5K, the NbSb2 crystal shows a large positive magnetoresistance (4.2 x 10³% at B=14.5 T) with Shubnikov-de Haas (SdH) oscillation. Hall measurements reveal that both the carrier compensation between electrons and holes and the high mobility and large mean free path of carriers contribute to the large magnetoresistance. Fast Fourier transform analyses of angle-resolved SdH oscillation indicate that the Fermi surface of the NbSb2 crystal is quasi-two-dimensional with three-dimensional components. These findings, together with the theoretically calculated electronic band structure obtained within the framework of density functional theory, suggest that NbSb2 is a good candidate compensated semimetal for further theoretical and experimental investigation of this family of materials. [ABSTRACT FROM AUTHOR]

The production of conjugated C4–C5 dienes from biomass can enable the sustainable synthesis of many important polymers and liquid fuels. Here, we report the first example of bimetallic (Nb, Al)‐atomically doped mesoporous silica, denoted as AlNb‐MCM‐41, which affords quantitative conversion of 2‐methyltetrahydrofuran (2‐MTHF) to pentadienes with a high selectivity of 91 %. The incorporation of AlIII and NbV sites into the framework of AlNb‐MCM‐41 has effectively tuned the nature and distribution of Lewis and Brønsted acid sites within the structure. Operando X‐ray absorption, diffuse reflectance infrared and solid‐state NMR spectroscopy collectively reveal the molecular mechanism of the conversion of adsorbed 2‐MTHF over AlNb‐MCM‐41. Specifically, the atomically‐dispersed NbV sites play an important role in binding 2‐MTHF to drive the conversion. Overall, this study highlights the potential of hetero‐atomic mesoporous solids for the manufacture of renewable materials. [ABSTRACT FROM AUTHOR]

The development of sustainable chemical processes for dehydrogenative transformations yields promising results for the selective synthesis of nitrogen-containing compounds. We report the synthesis of Nb2O5/Co3O4 catalyst using co-precipitation, followed by the hydrothermal method. FESEM, NH3-TPD, PXRD, FT-IR pyridine adsorption studies, and XPS were used to characterize the chemical and structural properties of the synthesized material. The FESEM analysis revealed that Nb was distributed uniformly on the surface of the Co3O4. The 3.3 wt% Nb showed (2 5 0) and (0 0 1) facet on Co3O4, and these results are confirmed further by PXRD d-spacing. Whereas cobalt oxide exists in (2 2 2), (3 1 1), and (1 1 1) facet, which confirms the crystal cubic spinel structure of Co3O4. The TPD ammonia desorption Nb2O5/Co3O4 result confirms the presence of 0.441 mmol/g acidic sites. The synthesized Nb2O5/Co3O4 catalyst effectively transformed aromatic amines and benzyl alcohols to imines through a dehydrogenative coupling reaction. The 3.3 wt% Nb2O5/Co3O4 exhibited excellent catalytic activity, with the conversions reached as high as > 99% at 140 °C. The Nb5+ played a vital role by generating the Lewis acid species, oxygen vacancy, and defects on the Co3O4 could be responsible for excellent selective activation of alcohol in the presence of a reactive amine. Oxidant-free, easy product separation, and significant reusability makes our catalyst versatile for the synthesis of imine derivatives. [ABSTRACT FROM AUTHOR]

The pore structure of powders prepared via magnesium vapor reduction of Nb2O5 and Mg4Nb2O9 in the range 540–680°C has been studied in detail. The results demonstrate that lowering the reduction temperature slows down diffusion processes, which allows coarsening of the primary structure of the reduced oxide particles to be prevented, thereby increasing the volume and surface of pores less than 5 nm in diameter. Reducing Nb2O5 at a temperature of 680°C, we have obtained niobium powder with a specific surface area of 83.4 m2/g. As the reduction temperature is lowered further, the pore size decreases to the extent that most pores become filled with native Nb2O5 oxide and the specific surface area decreases. In the case of Mg4Nb2O9 reduction under such conditions, the pore size is such that the powder obtained upon leaching of magnesium oxide is in effect an amorphous Nb2O5 oxide. [ABSTRACT FROM AUTHOR]

Using the solid-state process, the new compound Ba0.54Na0.46Nb1.29W0.37O5 was effectively produced in a single crystalline phase. The material's characteristics were determined by X-ray diffraction and Raman techniques. The Rietveld method was applied to refine the structural properties of this sample using X-ray diffraction data and derive the diffraction line profile. The cell parameters a = b = 12.37843 ± 0.02 and c = 3.93526 ± 0.02 were accustomed to crystallizing this compound in the tetragonal tungsten bronze (TTB) structure of the space group P4bm. Thanks to Raman measurements, we were able to detect numerous vibration modes in this crystalline phase. The adsorption of methylene blue (MB) on crystalline phase was studied by UV–visible spectroscopy. On account of methylene blue adsorption on Ba0.54Na0.46Nb1.29W0.37O5, it was discovered that this material can be used to remove organic pollutants and thus be used for water treatment. [ABSTRACT FROM AUTHOR]

Cu3MX4 (M = V, Nb, and Ta; X = S, Se, and Te) compounds have recently emerged as greatly promising solar energy conversion materials due to their tailorable band gaps, high optical absorption coefficients, environmentally benign nature and comparatively abundant elements. However, solution synthesis of Cu3NbSe4 nanocrystals as a photoactive material for investigating their optoelectronic properties has not yet been reported. Herein, we present a facile synthesis of cube-shaped Cu3NbSe4 nanocrystals with high crystallinity, high uniformity and monodispersity. Studies of the formation process disclose that the reaction temperature, time and surface ligand play significant roles in determining the crystalline phase, size and morphology evolution of the Cu3NbSe4 nanocrystals. Excitingly, a Cu3NbSe4-based photodetector exhibits a high Ilight/Idark ratio of 35, fast response speeds of 0.3/0.1 s for rise/fall times and excellent stability, indicating its robust potential for application in electronics and optoelectronics. [ABSTRACT FROM AUTHOR]

BACKGROUND: It is difficult to accurately determine the content of Ag in soil and sediment due to the mass spectrum interference of niobium, zirconium oxide and hydroxide during inductively coupled plasma - mass spectrometry (ICP-MS) analysis. OBJECTIVES: To develop methods for the determination of trace Ag in soil and sediment samples by four collision/ reaction modes. METHODS: The changes of mass spectrum signals of 93Nb16O+, 91Zr16OH+2, 92Zr16OH+ and 109Ag+ in helium, oxygen and ammonia were determined using inductively coupled plasma-tandem mass spectrometry (ICP -MS/ MS). The interference elimination ability and elimination mechanism of different collision/ reaction modes were investigated. The samples were digested by HCl -HNO3 -HF -HClO4. The content of Ag in soil and stream sediments was determined by helium MS/ MS mode, oxygen MS/ MS mode, ammonia MS/ MS mode and ammonia Mass-Shift mode. RESULTS: With the optimal gas flow rate in the tank of the four collision/ reaction modes, the interference degree of niobium and zirconium on Ag were decreased more than 20, 1500, 1500 and 2000 times, respectively. The detection limits of the method were 0. 005mg/ kg, 0. 002mg/ kg, 0. 003mg/ kg and 0. 003mg/ kg, respectively. The accuracy and precision were verified by national reference materials of soil and sediment, while the relative errors of measured values and certified values were -1. 4%-84. 3%, -7. 6%-7. 2%, -15. 0%-10. 0% and -12. 5%-8. 6%, respectively. The relative standard deviations were 1. 5%-6. 3%, 1. 4%-8. 3%, 1. 4%-5. 9% and 0. 7%-8. 2%, respectively. CONCLUSIONS: Helium MS/ MS mode has a low capacity to eliminate mass spectrometry interference, and is suitable for the determination of samples with little interference of niobium and zirconium. Oxygen MS/ MS, ammonia MS/ MS and ammonia Mass-Shift modes have a strong ability to eliminate mass spectrometry interference, which can be used for the determination of trace Ag in soil and stream sediments; and have the advantages of lower detection limit, wider linear range, and simultaneous determination of multiple elements, when compared with the industry standard DZ/ T 0279. 11—2016. [ABSTRACT FROM AUTHOR]

Bulk glasses of the series (100−x)[0.4Na2O-0.2Nb2O5-0.4P2O5]-xB2O3 with x = 0–48 mol% B2O3 were prepared by slow cooling in air. Their glass transition temperature increases within the range of 0–16 mol% B2O3, but further additions of B2O3 result in its decrease. Their structure was investigated by Raman, 11B, and 31P MAS NMR spectroscopy. The relative number of BO4 units decreases with increasing B2O3 content, while the number of BO3 units increases up to 59 % at x = 48. The upfield shift of a broad resonance peak in the 31P MAS NMR spectra is ascribed to an increasing connectedness of the structural network with increasing B2O3 content. Strong Raman band at 916–929 cm−1 shows on the presence of NbO6 octahedra in the structural network of these glasses. With the B2O3 addition, a decrease in DC conductivity is observed, which is attributed to the decrease in the concentration of Na+ ions. [ABSTRACT FROM AUTHOR]

Four new compounds were synthesized which belong to the so far very small group of hexanuclear niobium cluster alcoholates. These are [Mg(HOCH3)6]3[Nb6Cl12(OCH3)6]2 ⋅ 6CH3OH (1), (Ph4P)2[Nb6(OC2H5)12Cl6] (2), (Ph4P)2[Nb6(OC3H7)i4Cli8Cla6] (3) and (NC5H6)2[Nb6(OC3H7)12Cl6] (4). The last two compounds represent the first examples with isopropanolato ligands on the inner coordination sites of the octahedral metal atom cores. The X‐ray structures of 1–3 have been determined. All cluster units with alcoholato ligands on the inner sites carry 14 cluster‐based electrons (CBEs), as do all other so far known cluster alcoholates. The cluster unit in Compound 1, which carries chloride ligands on the inner coordination sites, is a 15 CBE unit. The cluster anion in 3 has four inner ligand sites occupied by isopropanolate anions, which are arranged trans to each other and define a common plane. Because of the smaller size of the alcoholato O donor atom compared to halogenido ligands matrix effects are not much or not at all present in the cluster anions of 2 and 3 (and 4) and thereby the Nb−Nb distances are much smaller than found in cluster units with halogenido ligands. [ABSTRACT FROM AUTHOR]

The doping influence of niobium pentoxide (Nb2O5) on the structure, physical, FTIR, and optical properties of new synthesized glass systems of the calcium zinc borate glasses with chemical formula 60B2O3·25CaO·15ZnO·xNb2O5: 0 ≤ x ≤ 1 mol% has been investigated. The BCZNbx samples were synthesized using the melt quenching technique. XRD measurements were used to confirm the noncrystalline structure of the prepared glasses. The density (ρ) gradually increased from 3.261 to 3.312 g/cm3 and molar volume (Vm) from 20.849 to 21.335 cm3/mol for BCZNb0.0 to BCZNb1.0 glasses, respectively. The oxygen molar volume (OMV) reduced nonlinearly from 9.81 to 9.68 cm3/mol as the Nb2O5 mol% increasing followed a reverse trend of (ρ) and (Vm). The oxygen packing density (OPD) increased from 101.91 to 103.26 g.atom/l. The estimated optical band gap (E g) values were 3.66 (± 0.01), 3.61 (± 0.01), 3.57 (± 0.01), and 3.55 (± 0.01) eV for the 0 mol%, 0.2 mol%, 0.6 mol%, and 0.8 mol% of Nb2O5 contents, respectively. Values of linear refractive index (n0) showed a very slight increment from 2.26 to 2.29 with further additions Nb2O5, while nonlinear one (n2) showed an increase from 2.26 × 10–11 (at 0 mol% of Nb2O5 content) to 2.53 × 10–11 (at 0.8 mol% of Nb2O5 content). FTIR measurements reflected that relative fraction of BO4 (P4) decreases while relative fraction of BO3 (P3) increases by Nb2O5 doping. Such a result confirmed that the Nb ions cause a variation in borate structural coordination and partially back conversion from [BO4] to [BO3] units in the glass network. [ABSTRACT FROM AUTHOR]

The Bayan Obo deposit is the largest REE resource in the world. Although many isotopic dating methods have been applied, ages based on petrography and closure temperatures still lack discussion. In this study, three digital petrographic images were created based on full-scanning microscopy, BSE, and TESCAN integrated mineral analysis (TIMA), providing a more scientific method for analyzing the mineral types, distributions, and content of the Bayan Obo deposit. By combining the full-scan images, monazites were selected in thin sections and dated in situ. The monazite in the body ores sample yields three 207Pb intercept ages of 657 ± 25 Ma (MSWD = 1.06), 763 ± 16 Ma (MSWD = 1.3), and 689 ± 22 Ma (MSWD = 8.1), and the monazite in one section yields maximum and minimum ages of 1393 ± 142 Ma and 429 ± 24 Ma, respectively. Combined with previous studies, the earliest and major stages of carbonatites, REE, and dikes in the Bayan Obo deposit area were dated at ~1.4 Ga and ~1.3 Ga, respectively. Due to the multiple subduction and accretion events related to the Paleo-Asian Ocean and North China Craton, the Bayan Obo deposit is intensely overprinted, with a tectonic-thermal event recorded at ~1.0–0.2 Ga. The multiple or protracted isotopic ~1.4–0.4 Ga ages in the Bayan Obo deposit account for five reasons. First, the separate thermal events and the partial recrystallization of monazite. Second, the diffusion of daughter products from the host mineral over time. Third, differences in the closure temperatures of different minerals and isotopic chronologies. Four, resetting of the closure system due to high temperature and hydrothermal alteration. Five, the minerals and transformed ores that formed in the Paleozoic. The in situ monazite U–Pb ages in thin sections provide insight into formation sequences from the giant Bayan Obo Fe–REE–Nb deposit. [ABSTRACT FROM AUTHOR]

Radical polymerization reactions were employed to synthesize thermo‐responsive poly(N‐isopropylacrylamide‐co‐1‐vinylimidazole), p (NIPAM‐co‐VIm), hydrogels at room temperature. A postquaternized cross‐linking strategy was reported to fabricate thermo‐sensitive quaternized‐p (NIPAM‐co‐VIm) ionic hydrogels, Q‐p (NIPAm‐co‐VIm). Combination of methods (high‐resolution X‐ray photoelectron spectroscopy, dynamic light scattering, and atomic absorption spectroscopy) was employed to characterize the composite material. Following the concept of a "green chemistry," the oxidation of alcohols/olefins was carried out in aqueous solution by using nanocomposites, p (NIPAM‐co‐VIm) and Q‐p (NIPAM‐co‐VIm). It was found that the catalytic activity of the metal nanocomposite can be modulated by the lower critical solution temperature (LCST) of particles. The catalyst showed improved catalytic activity above LCST. Quaternized composites showed higher catalytic activity than unquaternized counterparts, due to their high hydrophobicity, effective interactions between substrates and catalyst, and high flexibility. In addition, we demonstrated that the catalytic activity of the nanocomposites can be tuned by the volume phase transition within the hydrogel by using the catalytic reduction of 4‐nitrophenol/nitrobenzene, NP/NB, as the hydrophilic/hydrophobic substrates model. For 4‐NP, with an increase in temperature from 25°C to 35°C (

For potential applications in electronic components and sensor elements, lithium-niobium-titanium oxide ceramics are prepared by a solid-state reaction method. Two different weight percentages (2 and 5 %) of ZnO as a functional additive are added before the mechanical milling step in two separate procedures and changes in microstructure, and electrical properties are investigated. Analysis of microstructure by scanning electron microscopy showed the morphology of the synthesized particles in the form of plates and rods, which corresponds to the desired microstructure of the M-phase class of lithium-niobium-titanium oxide ceramic materials. The addition of ZnO creates a trend of increasing the total bulk density. X-ray diffraction analysis by Rietveld refinement and deconvolution of the Raman spectra by Lorentzian line shape fitting enabled the characterization of the crystal structure and vibration properties. In the frequency range from 100 Hz to 10 MHz, the analysis of the obtained impedance spectra at room temperature shows that the tested samples have non-Debye dielectric relaxation. Furthermore, the appearance of one semicircle on the Cole-Cole plots indicates the dominant influence of grain boundary effects on the electrical behavior of the studied ceramics in the measurement frequency range. Finally, a room temperature study of the humidity sensing properties showed that the 2% ZnO sample had a better linear impedance change response over a wide range of relative humidity from 15% to 85% at a frequency of 15 kHz. [ABSTRACT FROM AUTHOR]

The crystal structure of the NbO compound can be described as a vacancy-ordered derivative of the NaCl (B1) structure type with a concentration of structural vacancies of 25 at.% simultaneously in two sublattices. It was previously supposed that as the pressure increased, the vacancy-free NbO crystal with the B1 structure stabilized. In this work, effects of the pressure and the concentration of vacancies on the NbO structure are investigated by density functional theory methods. A new vacancy-free NbO phase with the rhombohedral crystal structure is found, its thermodynamic stability is evaluated, and the electronic structure is analyzed. It is demonstrated that with an increase in the pressure, rhombohedral NbO must be enthalpically stabilized rather than the vacancy-free NbO phase with the B1 structure. [ABSTRACT FROM AUTHOR]

Fused alumina is a material used in the manufacturing of abrasive tools, due to its high fusion point, great hardness, and mechanical toughness. In this context, this study addressed the influence of niobium addition on the properties of fused alumina for abrasive applications. A comparison was also made between this oxide and the brown fused alumina and the white fused alumina traditionally applied in this market, using different characterization techniques, such as particle size characterization, scanning electron microscopy, real and bulk density, chemical analysis, fracture resistance, and abrasiveness indexes. Among the main findings of this study, it was possible to observe that the addition of niobium to fused alumina significantly increased the fracture resistance and abrasiveness indexes compared to the brown and white fused alumina. [ABSTRACT FROM AUTHOR]

The π–η5:σ–η1 coordination mode of early transition metal pentafulvene ligands yields a strongly nucleophilic exocyclic carbon atom (Cexo). The substitution of the chlorido ligand of bis(η5:η1-(di-p-tolyl)pentafulvene)niobium chloride (1) by reaction with ethyl magnesium bromide is subsequently followed by a β-C–H activation employing this Cexo, forming the pentafulvene niobium ethylene complex 2. The intermediately formed ethyl complex can be intercepted with water, protonating both pentafulvene moieties and thereby retaining the ethyl moiety to give the terminal oxo complex 3. Complex 2 shows cooperative reactions of the remaining pentafulvene and the ethylene ligand. While the pentafulvene functions as a proton acceptor, the ethylene can be liberated to provide a NbIII metal center, available for E–H bond addition. Thereby, the imido hydride complex 4 and niobaaziridine hydride 5 are obtained. These hydride complex formations are investigated by deuterium labeling, concluding the redox mechanism. An alternative β-hydride elimination pathway is further disproven by purposely synthesizing a proposed intermediate and thermally treating it, to show that it does not undergo the β-hydride elimination under reaction conditions. [ABSTRACT FROM AUTHOR]

This study describes the application of Ag/Nb2O5 catalysts, suspension and spheres alginate immobilized for the degradation of 17α-Ethinylestradiol (EE2). The techniques used to characterize the photocatalysts were as follows: X-ray diffraction (XRD), N2 adsorption–desorption analysis (BET), point charge zero charge (PZC), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Different catalyst calcination temperatures were studied by keeping the silver metal loading at 5%. Among the operational conditions analyzed were pH, catalyst concentration, the emitting source of radiation and the inlet flow rate (in continuous operation). The results of the experiments performed initially with the catalyst in suspension revealed that the highest catalytic activity in the degradation of EE2 was the 5%Ag/Nb2O5 catalyst calcined at 973 K, which removed 77.7% of the initial pollutant concentration in 120 min of reaction. The immobilization of the catalyst in alginate spheres resulted in a degradation reduction, being able to degrade 69.2% of the initial EE2 in a batch system. In the continuous system, the immobilized catalyst obtained a total degraded of 37.3%, with a flow rate of 10 L·h−1. Catalyst reuse was promising, even dropping the removal, degrading around 27% of the initial EE2 concentration in the third cycle of use. [ABSTRACT FROM AUTHOR]

Cationic doping has been recommended as one of the most effective methods of reducing the number of trivalent manganese (Mn3+) ions that undergo a disproportionation reaction in lithium manganese oxide-based (LiMn2O4) lithium-ion batteries. However, the effect of surface doping on the major LiMn2O4 surfaces and their interactions with the electrolyte components is not yet fully understood. In this work, spin-polarised density functional theory-based calculations [DFT + U-D3 (BJ)] were employed to study the adsorption of the electrolyte components ethylene carbonate (EC) and hydrogen fluoride (HF) onto the Nb-doped major LiMn2O4 (001), (011), and (111) surfaces. During the substitution of niobium for manganese ions in the second surface layers (Nbsecond), it was found that the (111) surface stability improves, resulting in an enhanced (111) plane on the morphology. However, replacing the first (Nbfirst) as well as both top and sub-surface (Nbboth) layers of Mn atoms in the slabs maintains the same stability trend as in the pure pristine surfaces. Moreover, both adsorbates greatly preferred binding to the surfaces through the Nb instead of Mn atoms, and the largest adsorption energy was calculated for EC on the LiMn2O4 (011) surface doped on the Nbsecond site and for HF on the LiMn2O4 (111) surface doped on the Nbboth site. Furthermore, the EC/HF adsorptions further enhance the stability of the Nbsecond (111) surface plane. However, minimal charge transfer was calculated for both HF and EC interacting with the pure and Nb-doped surfaces. Our findings are interesting, since exposing the (111) surface promotes the formation of a stable solid electrolyte interface (SEI), significantly reducing Mn dissolution and enhancing the adsorption of EC and HF. [ABSTRACT FROM AUTHOR]

Ba(Mg1/3Nb2/3)O3–MgO composite ceramics were prepared by solid-phase method. The ceramic exhibited the 1:2 ordered structure. By adding a proper amount of MgO, the permittivity decreased rapidly compared with other Ba(Mg1/3Nb2/3)O3-based ceramics. The Q × f values of the samples were greatly improved by nano-silica. Raman spectra showed that the permittivity and Q × f value showed a strong correlation with Raman shift and full width at half maximum of the A1g(O) phonon mode, respectively. The Raman shift of A1g(O) was consistent with the variation trend of permittivity. And the full width at half maximum of the A1g(O) phonon mode had a negative correlation with the Q × f value. The results showed that upon adding 1.5 wt% nano-silica to the ceramics, the ceramics sintered at 1550 °C for 5 h had the lowest Raman shift and the narrowest full width at half maximum, achieving the best microwave dielectric properties: εr = 22.22, Q × f = 80,436 GHz, τf = – 5.89 ppm/°C. [ABSTRACT FROM AUTHOR]

In most beam steering applications such as 3D printing and in vivo imaging, one of the essential challenges has been high-resolution high-speed multi-dimensional optical beam scanning. Although the pre-injected space charge controlled potassium tantalate niobate (KTN) deflectors can achieve speeds in the nanosecond regime, they deflect in only one dimension. In order to develop a high-resolution high-speed multi-dimensional KTN deflector, we studied the deflection behavior of KTN deflectors in the case of coexisting pre-injected space charge and composition gradient. We find that such coexistence can enable new functionalities of KTN crystal based electro-optic deflectors. When the direction of the composition gradient is parallel to the direction of the external electric field, the zero-deflection position can be shifted, which can reduce the internal electric field induced beam distortion, and thus enhance the resolution. When the direction of the composition gradient is perpendicular to the direction of the external electric field, two-dimensional beam scanning can be achieved by harnessing only one single piece of KTN crystal, which can result in a compact, high-speed two-dimensional deflector. Both theoretical analyses and experiments are conducted, which are consistent with each other. These new functionalities can expedite the usage of KTN deflection in many applications such as high-speed 3D printing, high-speed, high-resolution imaging, and free space broadband optical communication. [ABSTRACT FROM AUTHOR]

Vanadium and niobium cation-water complexes, V+(H2O) and Nb+(H2O), are produced by laser vaporization in a pulsed supersonic expansion, mass selected in a time-of-flight spectrometer, and studied with infrared photodissociation spectroscopy using rare gas atom (Ar, Ne) complex predissociation. The vibrational bands measured in the O--H stretching region contain K-type rotational sub-band structure, which provides insight into the structures of these complexes. However, rotational sub-bands do not exhibit the simple patterns seen previously for other metal ion-water complexes. The A rotational constants are smaller than expected and the normal 3:1 intensity ratios for K = odd:even levels for independent ortho:para nuclear spin states are missing for some complexes. We relied on highly correlated internally contracted multi-reference configuration interaction and Coupled Cluster [CCSD(T)] electronic structure calculations of those complexes with and without the rare gas atoms to investigate these anomalies. Rare gas atoms were found to bind via asymmetric motifs to the hydrated complexes undergoing large amplitude motions that vibrationally average to the quasi-C2v symmetry with a significant probability off the C2 axis, thus explaining the reduced A values. Both vanadium and niobium cations exhibit unusually strong nuclear spin coupling to the hydrogen atoms of water, the values of which vary with their electronic state. This catalyzes ortho-para interconversion in some complexes and explains the rotational patterns. The rate of ortho-para relaxation in the equilibrated complexes must therefore be greater than the collisional cooling rate in the supersonic expansion (about 106 s-1). [ABSTRACT FROM AUTHOR]

[Display omitted] • Preparation of graphene (G) nanosheets up to the kg scale from waste electronic. • Preparation of binary Nb 2 O 5 @G and Ag@G nanocomposite-based photocatalysts. • The as-synthesized photocatalysts were used for degradation of doxycycline antibiotics. • Nb 2 O 5 @G photocatalyst showed high degradation (98.5%) for doxycycline in 120 min under visible light. • In addition, these nanocomposites showed good potential against E. coli bacterial strains. Herein, we report the successful preparation of high-quality graphene (G) nanosheets up to the kg scale using an electrochemical technique using graphite rods from scrap dry cell batteries. The as-prepared graphene was then decorated in-stiu with niobium oxide (Nb 2 O 5) and silver (Ag) nanoparticles to prepare Nb 2 O 5 @G and Ag@G nanocomposites. Powdered X-ray diffraction (p-XRD), Fourier-transform (FT-IR) infrared spectroscopy, UV–visible (UV–vis) spectroscopy, Raman spectroscopy, and scanning electron microscopy (SEM) were used to characterize the as-prepared nanocomposite material. This binary Nb 2 O 5 @G nanocomposite was subsequently used to degrade doxycycline antibiotic with an efficiency of 98.5 % in 120 min under visible light conditions. To determine the optimal scope of the as-prepared composite catalyst, degradation studies were performed at different pH values, photocatalyst doses and temperatures. Kinetics studies revealed that the processes followed pseudo-first-order kinetics. In addition, the as-synthesized graphene , Nb 2 O 5 @G and Ag@G nanocomposites were used for selective application against E. coli bacterial strains. Overall, Ag@G has shown good potential application prospects in the development of antibacterial materials in comparison with Nb 2 O 5 @G and pristine graphene. This study highlights the potential of as-prepared graphene-based nanocomposites for use in waste treatment and environmental bioremediation. [ABSTRACT FROM AUTHOR]

Reaction of benzilic acid, Ph2C(OH)(CO2H), L1H2, with equimolar amounts of M(OR)5 (M = Nb, Ta) led, following work-up, to the tetranuclear complexes [Nb4(OEt)8(L1)4(μ-O)2] (1) or [Ta4(OEt)8(L1)4(μ-O)2]·0.5MeCN (2·0.5MeCN), respectively. Similar use of 2,2′-diphenylglycine, Ph2C(NH2)(CO2H), L2H3, led to the isolation of the dinuclear complexes [Nb2(OEt)4(L2H2)4(μ-O)]·2MeCN (3·2MeCN) or [Ta2(OEt)4(L2H2)4(μ-O)]·2.25MeCN (4·2.25MeCN). The molecular structures of 1–4 are reported. Complexes 1–4 have been screened for their potential to act as catalysts for the ring opening polymerization (ROP) of ε-caprolactone (ε-CL) and rac-lactide (r-LA), with or without benzyl alcohol (BnOH) present. In the case of ε-CL, complex 1 displayed best activity with >99% conversion at 100 °C, whilst 3 and 4 were virtually inactive under the same conditions. All complexes show moderate activities towards the ROP of r-LA at 160 °C, with 1–3 producing heterotactic enriched PLA while 4 afforded isotactic enriched PLA. Copolymerization studies revealed the most efficient system involved the initial addition of r-LA (for 6 h) followed by ε-CL (for 42 h), which led to 99% conversion for each of the monomers. Block copolymers of PLA-b-CL and PCL-b-LA and random copolymers PLA-co-CL were successfully synthesized by adjusting the feed sequence. [ABSTRACT FROM AUTHOR]

Aggregates of niobium–alumina refractory composites are characterized, which are produced by a castable technology followed by a crushing process. Phase separation between niobium and corundum is found for the obtained aggregate classes and the impurity phases NbO and β–Nb2C are present according to X‐ray diffraction measurements. Among the studied aggregate classes, niobium shows differences in chemistry expressed by the corresponding lattice parameters. The determined morphology and roughness parameters show that the synthesized aggregates are not substantial different independent of their density and porosity. [ABSTRACT FROM AUTHOR]

Niobium‐alumina composite aggregates with 60 vol% metal content and with particle sizes up to 3150 μm are produced using castable technology followed by sintering, and a crushing and sieving process. X‐Ray diffraction (XRD) analysis reveals phase separation during crushing as the niobium:corundum volume ratios is between 37:57 and 64:31 among the 4 produced aggregate classes 0–45, 45–500, 500–1000, and 1000–3150 μm. The synthesized aggregates are used to produce coarse‐grained refractory composites in a second casting and sintering step. The fine‐ and coarse‐grained material shows porosities between 32% and 36% with a determined cold modulus of rupture of 20 and 12 MPa, and E‐moduli of 37 and 46 GPa, respectively. The synthesized fine‐grained composites reached true strain values between 0.08 at 1100 °C and 0.18 at 1500 °C and the coarse‐grained ones values between 0.02 and 0.09. The electrical conductivity for the fine‐grained and the coarse‐grained material is 448±66 and 111±25 S cm−1, respectively. [ABSTRACT FROM AUTHOR]

We report on the catalytic activity of Nb4C3Tx based composites towards the catalytic reduction of nitro compounds and organic dyes for the first time. Nb4C3Tx-PdNP composites have been synthesized by in situ reduction of Pd nanoparticles (PdNPs) on Nb4C3Tx MXenes with different ratios of Pd. Catalytic reduction experiments showed that the Nb4C3Tx-Pd5% composite was able to facilitate the reduction of 4-nitrophenol (4-NP) and organic dyes; it was found that the reduction of 4-NP occurred completely within 3 min. The optimum concentration of the PdNPs in the composite has been evaluated by varying the ratio of PdNPs in the composite and it was found that Nb4C3Tx-Pd5% is the best catalyst. The reusability test of the Nb4C3Tx-Pd5% catalyst showed that the catalyst could be reused up to 5 times with 86% activity remaining at the 5th cycle. In addition, the Nb4C3Tx-Pd5% catalyst can also be used as the catalyst for the reduction of methylene blue and methyl orange. This work explores the possibility of application of the Nb4C3Tx based composite for the first time as the catalyst for the reduction of nitro compounds and organic dyes. [ABSTRACT FROM AUTHOR]

In this paper, the energy band structure and properties of Nb doped ZnO with different concentration were calculated based on the first-principle of density functional theory, and the simulation results of intrinsic ZnO, Al doped ZnO (AZO) and Nb doped ZnO (NZO) were compared and analyzed. The results show that: (1) the band gap values of NZO and AZO are lower than that of intrinsic ZnO, and the band gap values of NZO with the same concentration of 6.25% are lower than that of AZO. With the increase of Nb doping concentration, the conduction band bottom and the peak density of states of NZO decrease obviously, and Nb-4d electrons occupy the main quantum states of Fermi level. (2) With the increase of doping concentration, the absorption peaks and dielectric function peaks of NZO and AZO decrease, and move to the low energy region. Among them, the absorption peaks of NZO move more obviously to the low energy region, and the imaginary part of dielectric function has new peaks at 0.42 eV and 34.29 eV respectively, which is mainly due to the transition of Nb-4d and Nb-5p electronic energy levels in the valence band. The static dielectric constant of NZO with the same concentration of 6.25% is greater than that of AZO, which indicates that NZO has stronger polarization ability, and NZO can improve the photoelectric properties of ZnO more effectively. With the increase of Nb doping concentration, the absorption coefficient and the imaginary part strength of dielectric function of NZO increase and move to the high energy region. The theoretical simulation results of NZO provide a theoretical reference for the experimental research and practical application of high valence element Nb doped ZnO. [ABSTRACT FROM AUTHOR]

The requirement for environmentally friendly catalysts for the isomerization of alkanes has prompted research on the tungstate-zirconia (WZ) system. The present work examines the activity and selectivity of lanthanum (La) promoted tungstate-zirconia (LWZ) and niobium (Nb) promoted tungstate-zirconia (NWZ) catalysts. In this study, 1 % La promoted WZ (1 % LWZ) and 1 % Nb promoted WZ (1 % NWZ) catalysts were investigated in isomerization of n-butane in the presence of hydrogen. The studied catalysts were characterized by different methods: nitrogen physisorption, temperature programmed desorption of NH3, thermogravimetric analysis, and X-ray diffraction. The catalytic activity and selectivity were significantly improved by the addition of 1 % Nb. The redox process in the Nb-containing catalyst (1 % NWZ) played a central role by providing the highest acidic sites (283.53 µmol g−1) with appropriate activation energies for the skeletal rearrangement of the reactant (n-butane). Furthermore, this study highlights the determining role of the transfer process of adsorbed species from ZrO2 to W as well as to the Nb environment. The conversion of n-butane (27.34 %) and the selectivity to i-butane (92.34 %) for NWZ were significantly higher than WZ and LWZ catalysts. The experimental results revealed that Nb was a more effective promoter than La. [ABSTRACT FROM AUTHOR]

Carbonatites and associated rocks are commonly known to host precious commodities, including rare earth elements (REE), niobium, and phosphates. They form ring-shaped complexes frequently found as small occurrences in hard-to-reach areas, making their exploration a challenging task using conventional methods. Remote sensing has been increasingly regarded as a time- and cost-saving method to map and identify new potential zones, meeting the growing need for mineral resources. In this study, we use multispectral data by combining information from ASTER and Sentinel 2A sources to delineate and map carbonatite-associated REE- and Nb-enriched iron oxide deposits. The Moroccan Oulad Dlim massif, at the NW margin of the west African craton, where carbonatite occurrences are reported, was selected as a study area. A fuzzy gamma approach was adopted to combine information from several image processing techniques, including mineral indices, principal component analysis (PCA) and minimum noise fraction (MNF). A concentration-area (C-A) fractal model is applied together with the prediction-area (P-A) plot for objective anomalies classification and prediction ability assessment for each fuzzy integrated map. Subsequently, a prospective map that predicts and defines potential areas was produced through the integration of Sentinel- and ASTER-derived evidential maps. Validation was carried out via field surveys coupled with in-situ portable X-Ray Fluorescence analysis and laboratory mineralogical characterization. The Results were consistent with field data, reaching a prediction rate of 90%. They reveal the importance of the investigated structures as potential sites for REE, Nb, and phosphates. These outcomes are encouraging and provide evidence that data fusion (ASTER-Sentinel 2A) is an effective and helpful approach for geological exploration programmes. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) MXenes have attracted extensive attentions for their excellent energy storage ability. In the current study, our main goal is to report on the delamination of the Nb2C MXene using a chlorophyll-a derivative (zinc methyl 3-devinyl-3-hydroxymethyl-pyropheophorbide a (Chl)) to produce Chl@Nb2C composites as the anode materials in the lithium-ion batteries. The electrochemical behaviors of the delaminated Chl@Nb2C composite electrodes were superior to the multilayered pristine Nb2C. The specific capacity of 1%(wt/wt) Chl@Nb2C achieved 384 mA h g−1 at the current density of 100 mA g−1, while the capacity of Nb2C was 295 mA h g−1. Furthermore, the specific capacity of the Chl@Nb2C composite increased along with the increasing number of cycles at the current density of 500 mA g−1. This work provides a novel delaminated strategy by intercalating organic dye aggregates between the MXenes layers to improve the energy storage performance of 2D MXene materials. [ABSTRACT FROM AUTHOR]

Lead zirconate PbZrO3 has been the subject of research interest for several dozen years. Recently, even its antiferroelectric properties have started to be questioned, and many researchers still deal with the so-called intermediate phase below Curie temperature (TC), whose existence is not fully understood. It turns out that PbZrO3 doped with Nb exhibits below TC phases with complex domain structures. One of them undergoes self-organization taking place at a constant temperature, and transforms, after several minutes, into a lower phase. This isothermal transition was investigated through dielectric, pyroelectric current and Raman scattering measurements. Discontinuities accompanied it in the permittivity and pyroelectric current. The obtained Raman spectra proved that those discontinuities are strictly linked with the isothermal transition between two intermediate phases. The ordering process in lead sublattice stimulated by thermal fluctuations is discussed as a driving force for this peculiar phenomenon. [ABSTRACT FROM AUTHOR]

Three isostructural porous ionic crystals (PICs) based on Keggin-type POMs with different compositions but equal negative charge ([BW12O40]5− (BW12), [SiW11NbO40]5− (SiW11Nb), and [SiW11TaO40]5− (SiW11Ta)) are synthesized. Experimental and theoretical characterizations of the three PICs (1_BW12, 1_SiW11Nb, and 1_SiW11Ta) show that the substitution of Nb/Ta for W in the POMs enhances the basicity of PICs, which increases in the order of 1_BW12 < 1_SiW11Nb < 1_SiW11Ta. These findings clearly show that the increase in basicity is due not only to the increase in negative charge of the POM molecule as is often explained, but also to the character of the substituted element itself. [ABSTRACT FROM AUTHOR]

We investigated the AC electrical response of MgFe2O4–Nb2O5 nanocomposite. A simple auto-combustion approach was used to synthesize MgFe2O4. The nanocomposite made of MgFe2O4–Nb2O5 was effectively made by using a basic mechanical alloying-technique. The FTIR, XRD, SEM, and EDX methods were used for the structural characterization of elaborated nanocomposites. The dielectric studies indicate that the Nb2O5 reduces the grain resistance when doped in Mg ferrite. As compared to MgFe2O4–Nb2O5 nanocomposites, the AC conductivity for the nanocomposite MgFe2O4 and Nb2O5 increased. The polarization mechanism of conductivity is explained by permittivity and impedance spectroscopy. The increase in conductivity of nanocomposite is due to the effect of Nb2O5 on relaxation time and grain boundaries found in cole–cole plot. [ABSTRACT FROM AUTHOR]

This paper presents the analysis of some quench tests addressed to study the dynamic effects in the 1-m-long 120-mm-aperture Nb3Sn quadrupole magnet, i.e., HQ02b, designed, fabricated, and tested by the LHC Accelerator Research Program. The magnet has a short sample gradient of 205 T/m at 1.9 K and a peak field of 14.2 T. The test campaign has been performed at CERN in April 2014. In the specific tests, which were dedicated to the measurements of the dynamic inductance of the magnet during the rapid current discharge for a quench, the protection heaters were activated only in some windings, in order to obtain the measure of the resistive and inductive voltages separately. The analysis of the results confirms a very low value of the dynamic inductance at the beginning of the discharge, which later approaches the nominal value. Indications of dynamic inductance variation were already found from the analysis of current decay during quenches in the previous magnets HQ02a and HQ02a2; however, with this dedicated test of HQ02b, a quantitative measurement and assessment has been possible. An analytical model using interfilament coupling current influence for the inductance lowering has been implemented in the quench calculation code QLASA, and the comparison with experimental data is given. The agreement of the model with the experimental results is very good and allows predicting more accurately the critical parameters in quench analysis (MIITs, hot spot temperature) for the MQXF Nb3Sn quadrupoles, which will be installed in the High Luminosity LHC.

Structural phase transition is always accompanied by measurable property changes in the material, which provides us more opportunities for material modification. Herein, a new niobium oxyfluoride, [HIm][NbOF4] (HIm = imidazole cation, compound 1), was obtained, and its structural phase transition behavior was investigated. The compound features a one-dimensional chain of anionic [NbOF4]n− connected by corner-sharing oxygen. It undergoes an obvious structural phase transition at 284 K, as confirmed by variable-temperature structural analyses, differential scanning calorimetry (DSC), and dielectric measurements. In particular, the reversibility of dielectric switching properties of 1 was identified around the phase transition point. This discovery will enrich the potential applications of niobium oxyfluoride in dielectric switching. [ABSTRACT FROM AUTHOR]

Two series of Sc3+- and Nb5+-doped TiO2 (rutile) samples were synthesized and characterized by SEM, ICPE spectroscopy, XPS, and BET methods. Photocatalytic activity of the doped TiO2 samples was tested in photocatalytic degradation of phenol. Dependences of the photocatalytic activities of the doped TiO2 samples demonstrate a volcano-like behavior, indicating the existence of the optimal dopant concentrations to achieve the highest activity of photocatalysts. Remarkably, the optimal dopant concentrations correspond to the extrema observed in work function dependences on the dopant concentrations, that indicates a significant energy redistribution of the defect states within the bandgap of TiO2. Such a redistribution of the defect states is also proven by the alterations of the optical and EPR spectra of the intrinsic Ti3+ defect states in TiO2. Based on the analysis of the experimental results, we conclude that both Sc3+ and Nb5+ doping of TiO2 results in redistribution of the defect states and the optimal dopant concentrations correspond to the defect structures, which are ineffective in charge carrier recombination, that ultimately leads to the higher photocatalytic activity of doped TiO2. [ABSTRACT FROM AUTHOR]

β-Nb2ZnO6 nanoparticles were synthesized by a hydrothermal process and calcined at two temperatures, 500 °C and 700 °C, and assigned as A and B, respectively. X-ray diffraction, together with transmission electron microscopy, revealed that the β-Nb2ZnO6 nanoparticles calcined at 700 °C (B) were more crystalline than the β-Nb2ZnO6 calcined at 500 °C (A) with both types of nanoparticles having an average size of approximately 100 nm. The physiochemical, photocatalytic, and cytotoxic activities of both types of β-Nb2ZnO6 nanoparticles (A and B) were examined. Interestingly, the photodegradation of methyl orange, used as a standard for environmental pollutants, was faster in the presence of the β-Nb2ZnO6 nanoparticles calcined at 500 °C (A) than in the presence of those calcined at 700 °C (B). Moreover, the cytotoxicity was evaluated against different types of cancer cells and the results indicated that both types of β-Nb2ZnO6 nanoparticles (A and B) exhibited high cytotoxicity against MCF-7 and HCT116 cells but low cytotoxicity against HeLa cells after 24 and 48 h of treatment. Overall, both products expressed similar EC50 values on tested cell lines and high cytotoxicity after 72 h of treatment. As a photocatalyst, β-Nb2ZnO6 nanoparticles (A) could be utilized in different applications including the purification of the environment and water from specific pollutants. Further biological studies are required to determine the other potential impacts of utilizing β-Nb2ZnO6 nanoparticles in the biomedical application field. [ABSTRACT FROM AUTHOR]

The foliated low-grade metamorphic rocks of the Triassic Bagolyhegy Metarhyolite Formation, mainly of pyroclastic origin, host post-metamorphic quartz-albite veins containing abundant tourmaline and occasionally rutile/ilmenite. The study of the Ti-oxide-mineralized veins with SEM-EDX revealed an unusual mineral assemblage comprising fine-grained Nb–Ta-bearing oxides (columbite-tantalite series, fluorcalciomicrolite and other Nb–Ti–Y–Fe-REE-oxide minerals) intergrown with Nb-rich polymorphs of TiO2 (anatase, rutile), ilmenite and zircon enriched with hafnium. This high field strength elements (HFSE)-bearing paragenesis is unexpected in this lithology, and was not described from any formation in the Paleozoic-Mesozoic rock suite of the Bükk Mountains (NE Hungary) before. The host metavolcanics are significantly depleted in all HFSE compared to the typical concentrations in felsic volcanics and the mineralized quartz-albite veins have even lower Ti–Nb–Ta concentration than the host rock, so the mineralization does not mean any enrichment. From proximal outcrops of the Triassic Szentistvánhegy Metavolcanics, potassic metasomatized lenses with albite-quartz vein fillings containing rutile/ilmenite are known. We studied them for comparison, but they only contain REE mineralization (allanite-monazite-xenotime); the Nb–Ta-content of Ti-oxide minerals is undetectably low. LA-ICP-MS measurements for U–Pb dating of Hf-rich zircon of the Nb–Ta-rich mineral assemblage gave 71.5 ± 5.9 Ma as lower intercept age while dating of allanite of the REE mineralized quartz-albite veins gave 113 ± 11 Ma as lower intercept age. The REE-bearing vein fillings formed during a separate mineralization phase in the Early Cretaceous, while the Nb–Ta mineralization was formed by post-metamorphic alkaline fluids in the Late Cretaceous., controlled by fault zones and fractures. [ABSTRACT FROM AUTHOR]

We report experimental vibrational spectra of small neutral niobium carbide clusters in the 350-850 cm-1 spectral range. Clusters were first irradiated by IR light and subsequently probed using UV light with photon energies just below the ionization threshold. Upon resonance with an IR vibrational mode, the number of cluster ions increases, allowing to record a vibrational spectrum. In complementary density functional theory calculations, we have simulated the IR spectra for several low-energy isomers. We were able to assign the spectra experimentally obtained for each cluster size to a specific geometric structure based on the match with the computed spectra. The number of the cluster sizes investigated here allows to follow the evolution of the geometric structure of the niobium and carbon components of clusters separately. For Nb6Cm (m = 4, 5, 6), we observe the emergence of the cubic crystal structures similar to the bulk. [ABSTRACT FROM AUTHOR]