TiO2 Nb2O5 Research Articles

Photoelectric properties of CsPbBr3 perovskite solar cells based on amorphous Nb2O5 electron transport layer

Abstract The superior air and temperature stability and the cheap production costs of the inorganic CsPbBr3 solar cell (PSC) were major concerns. For inorganic CsPbBr3 devices, TiO2 crystals (c-TiO2) are frequently used as an electronic transfer layer (ETL). However, because c-TiO2 preparation necessitates temperatures over 450°C, the flexible inorganic device CsPbBr3 cannot be used. In addition, the low mobility of electrons further limits the ability to improve device performance. On this basis, a novel amorphous Nb2O5 (a-Nb2O5) was prepared. This paper introduces a simple method of preparing inorganic planar CsPbBr3 devices by room temperature sputtering. The highest efficiency of PSC prepared with a-Nb2O5 ETL was 5.74%, which was higher than that of crystalline Nb2O5 (a-Nb2O5) or crystalline TiO2 (c-TiO2) based PSC (5.12% or 4.67%). The photovoltaic properties of CsPbBr3 PSC prepared by a-Nb2O5 ETL were improved. The causes might be attributed to the following: excellent crystallization of the films made from a-Nb2O5 and CsPbBr3, low charge recombination rate of the a-Nb2O5/CsPbBr3 interface, strong optical transmission, and appropriate operating function of a-Nb2O5. In addition, PSC CsPbBr3 based on unpackaged a-Nb2O5 has good long-term stability in the atmosphere. This work offers a fresh line of inquiry for producing extremely effective inorganic PSC.

Phase equilibria in the TiO2–Nb2O5 system: New experiments and thermodynamic modeling

Phase equilibria in the TiO2–Nb2O5 system has been investigated by using the high-speed pyrometer, scanning electron microscopy and X-ray powder diffraction. The liquidus temperatures in the whole composition region are determined by cooling trace tests. Combining with the observation of solidification structure, liquidus at the TiO2-rich corner are clarified and the eutectic composition of Liquid→TiO2+TiNb2O7 is revised to be 62.3 mol % TiO2. TiNb2O7 has been measured to have some solid solubility, and the existence of Ti2Nb6O19 at high temperature is confirmed. It would probably form through the peritectic reaction of Liquid + TiNb2O7→Ti2Nb6O19. Moreover, congruent reactions of Liquid→TiNb2O7 and Liquid→TiNb5O14.5 are measured as 1491 °C and ∼1478 °C, respectively. Subsequently, thermodynamic assessment of TiO2–Nb2O5 system has been carried out by means of the CALPHAD method, and a set of self-consistent thermodynamic parameters is obtained. Calculated TiO2–Nb2O5 phase diagram can reasonably reproduce the available experimental data. The provided TiO2–Nb2O5 phase diagram and thermodynamic parameters may be useful to the development of titanium niobates and further multicomponent thermodynamic database.

Effect of co-doping Nb2O5 with equal amount of Eu2O3 or In2O3 on the electrical properties of TiO2-based varistors

In this work, TiO2 varistors with enhanced nonlinear coefficient, low breakdown voltage, high relative dielectric constant and low dielectric loss were fabricated by co-doping of Nb2O5 with equal amount of Eu2O3 or In2O3. The results indicated an appropriate proportion of dopant could improve the comprehensive performance of the varistors. For the TiO2–Nb2O5–Eu2O3 system, the breakdown voltage and relative dielectric constant of the samples decreased first and then increased, while the nonlinear coefficient increased first and then decreased with the increase of doping content, the best value appears at the doping content of 1.00 mol% (E1mA = 2.14 V/mm, α = 4.6, εr = 2.72 × 105, tanδ = 0.25). It is noted that the secondary phase formed on the grain boundary as Eu2Ti2O7, thus the growth of grain was hindered and the dielectric performances deteriorated. By contrast, for the TiO2–Nb2O5–In2O3 system, the secondary phase was not found. As a result, a low breakdown voltage, low dielectric loss and high nonlinear coefficient were obtained, reaching the best at the doping content of 5.0 mol% (E1mA = 4.6 V/mm, α = 8.4, εr = 1.85 × 105, tanδ = 0.16). The influence of this doping system on the electrical performance can be explained by Internal Barrier Layer Capacitance theory (IBLC), which is related to the potential barrier at the grain boundary.

Structure, infrared spectrum, and microwave dielectric properties of NiO–TiO2–Nb2O5 ceramics

This study reports the crystal structure and intrinsic dielectric properties of NiO–TiO2–Nb2O5 ceramics. The NiO–TiO2–Nb2O5 system is crystallized as a rutile structure based on X-ray diffraction, Rietveld refinement, and TEM analysis. The sintering temperature has a certain positive effect on the dielectric constant and Q × f value, which is attributed to the reduction of porosity and the growth of crystals. Because of the particularity of the rutile structure, ionic polarizability cannot be used to evaluate the micro-polarization mechanism. Thus, using the far-infrared reflectance spectrum and complex dielectric function analysis, the high-frequency micro-polarization mechanism of the structure has been fully explained, which is expected to be applied to other high-εr dielectric ceramic systems.

Optical properties and irradiation resistance of novel high-entropy oxide glasses La2O3–TiO2–Nb2O5–WO3–M2O3 (M=B/Ga/In)

A new class of high-entropy oxide glasses 20LaO3/2–20TiO2–20NbO5/2–20WO3–20MO3/2 (M = B/Ga/In) were designed and successfully fabricated by aerodynamic containerless processing. The results show that one can control the properties and increase the functionality of glass by changing the type of M. The Vicker's hardness reaches the highest value of 6.45 GPa for glass M = B. The best thermal stability and the glass forming ability, measured using the glass-transition temperature Tg and the temperature gap ΔT respectively, are found in glass M = In, with Tg = 740 °C and ΔT = 72 °C. The optical properties show that the as-prepared glasses exhibit good transparency and high refractive index. Especially for glass M = In, its transmittance reaches almost 78% from visible to IR region, and the value is nearly unchanged after electron beam irradiation, indicating good irradiation resistance of this high-entropy oxide glass. Furthermore, the glass M = In has the highest refractive index (nd = 2.46) and low wavelength dispersion (νd = 45.6). These results demonstrate that the conceptual design of high-entropy materials is adaptable to high performance oxide glasses, which should be promising host materials for optical applications such as smart phones with digital cameras and endoscopes.

Correlation between microstructure and mechanical properties of ZTA–TiO2–Nb2O5 ceramics sintered by SPS

Correlation between microstructure and mechanical properties of ZTA–TiO2–Nb2O5 ceramics sintered by SPS

Improving the sintering performance and dielectric properties of thermally conductive low-temperature co-fired alumina by controlling the firing atmosphere

ABSTRACT Here, we focused on the firing atmosphere to promote low-temperature sintering and enhance the dielectric properties of low-temperature co-fired alumina (LTCA) containing 5 wt.% of CuO–TiO2–Nb2O5–Ag2O as the sintering aid. Controlling the oxygen partial pressure (pO2) to form Ag–Cu–Ti–Nb–O-based complex oxides and lowering the melting temperature of the sintering aid are necessary to improve the sinterability. Moreover, controlling the pO2 such that AgNbO3 disappears is important to improve the dielectric properties of LTCA. A dense sintered body with approximately 95% relative density was obtained by firing an LTCA sample for 2 h at a firing temperature of 900°C and pO2 of 0.02 atm, and its dielectric properties were measurable. The thermal conductivity of 17 W/mK was better than that of conventional low-temperature co-fired ceramics (2–7 W/mK). These results provide important guidelines for low-temperature sintering and producing LTCA with enhanced dielectric properties.

TiO2 Nanoparticles and Nb2O5 Nanorods Immobilized rGO for Efficient Visible-Light Photocatalysis and Catalytic Reduction

TiO2 Nanoparticles and Nb2O5 Nanorods Immobilized rGO for Efficient Visible-Light Photocatalysis and Catalytic Reduction

Photocatalytic production of hydrogen and methane from glycerol reforming over Pt/TiO2–Nb2O5

In this study, platinized mixed oxides (TiO2–Nb2O5) were tested on photocatalytic hydrogen production from a glycerol solution under UV light. Different samples with different Ti:Nb ratios were prepared by using a simple method that simultaneously combined a physical mixture and a platinum photochemical reduction. This method led to improved physicochemical properties such as low band gap, better Pt nanoparticle distribution on the surface, and the formation of different Pt species. Niobia content was also found to be an important factor in determining the overall efficiency of the Pt–TiO2–Nb2O5 photocatalyst in the glycerol reforming reaction. The photocatalytic results showed that Pt on TiO2–Nb2O5 enhanced hydrogen production from the aqueous glycerol solution at a 5 wt% initial glycerol concentration. The influence of different operating conditions such as the catalyst dosage and initial glycerol concentration was also evaluated. The results indicated that the best hydrogen and methane production was equal to 6657 μmol/L and 194 μmol/L, respectively after 4 h of UV radiation using Pt/Ti:Nb (1:2) sample and with 3 g/L of catalyst dosage. Moreover, the role of water in photocatalytic hydrogen production was studied through photocatalytic activity tests in the presence of D2O. The obtained results confirmed the role of water molecules on the photocatalytic production of hydrogen in an aqueous glycerol solution.

Phase equilibria and microwave dielectric properties in the ternary La2O3–TiO2–Nb2O5 system

High-temperature phase relations in the La2O3–TiO2–Nb2O5 ternary system were investigated at 1290 °C using SEM, EDS and XRD, and a subsolidus phase equilibrium diagram was constructed. It was demonstrated that the addition of the La1/3NbO3 to the La2O3:3TiO2 mixture completely stabilizes a perovskite-La2/3TiO3 compound, which is otherwise not stable at stoichiometric composition. On the other hand, a mixture La2O3:TiO2 =1:3 dissolves in La1/3NbO3 up to 15 mol% TiO2. Moreover, a newly defined composition of compound La30Ti16Nb4O87 formed in the La2O3-rich part of the system and a solid solution La3Ti5Nb10O39.5–La2Ti2Nb8O27 were proposed. In the binary subsystem LaTiNbO6-La0.462Ti0.386Nb0.614O3, the components exhibit opposite temperature dependence of resonant frequency in the microwave frequency range. Thus, the dielectric properties of the prepared ceramics can be tailored by varying the component concentration and thermally stable dielectric properties can be achieved for a composition with a LaTiNbO6/La0.462Ti0.386Nb0.614O3 molar ratio of 0.27.

Joint metallothermic reduction of titanium and rare refractory metals of V group

The features of phase formation during the joint aluminothermic reduction of titanium, niobium, tantalum, vanadium from their oxides using methods of thermodynamic modeling, differential thermal and X-ray phase analysis were studied. Computer thermodynamic modeling made it possible to predict the optimal temperature conditions in the metallothermic process, composition and ratio of reagents in the charge, behavior of elements and sequence of phase formation. Thermodynamic calculations were supplemented by differential thermal studies using the combined scanning calorimetry method to identify the kinetic and thermochemical components of the process. An analysis of theoretical and experimental data allowed us to establish that the interaction of aluminum with titanium dioxide proceeds through the stage of titanium monoxide formation and features by the formation of TixAly intermetallic compounds of various compositions (TiAl3, TiAl, Ti2Al) depending on the Al and TiO2 ratio in the charge. When titanium dioxide is partially replaced by niobium, tantalum and vanadium oxides, the metallothermic process during interactions in the Al–TiO2–Nb2O5, Al–TiO2–Ta2O5 and Al–TiO2–V2O5 systems has a similar nature, enters the active phase once liquid aluminum appears, is accompanied by exothermic effects and features by the priority formation of titanium aluminides and binary and ternary intermetallic aluminum compounds with Group 5 rare refractory metals – AlNb3, Al3Nb, Al3Ta, Al3(Ti1–х, Taх), Al3(Ti0,8V0,2). The joint conversion of titanium dioxide and rare refractory metal pentoxides during the reduction process is carried out through sequential and parallel stages of the formation of simple and complex element oxides with low oxidation states.

Biocompatibility of strontium incorporated ceramic coated titanium oxide implant indented for orthopaedic applications

Titanium and its alloys are the most commonly used materials for manufacturing orthopaedicimplants. Various surface modifications are done in titanium alloys to improve osseointegration as well as for long term success of endosseous implants. In the present study preclinical safety evaluation of two nanoporous mixed metal oxide bone implant materials, TiO2-Nb2O5 (TN) and Sr-HAP modified TN (TNS) were assessed by in vitro and in vivo methods. The surface morphological analysis of fabricated materials was done by XRD, IR and SEM. The biocompatibility evaluations performed were In vitro cytotoxicity tests using L929 cells, Assessment of hemolytic properties of materials and Test for local effects after implantation in bone as per international standards. The results of the study conclude that the materials, TN and TNS are non-cytotoxic, non-hemolytic and biocompatible and can be used safely for orthopaedic applications.

Development of novel temperature-stable Al2O3–TiO2-based dielectric ceramics featuring superior thermal conductivity for LTCC applications

A new composition was developed using sintering to improve the dielectric properties of low-temperature co-fired alumina (LTCA) containing CuO–TiO2–Nb2O5–Ag2O. By substituting some alumina with rutile TiO2, the second-phase compound could be changed from AgNbO3 to the rutile phase. Further, low-temperature sintering at temperatures below 960 °C was possible, suppressing Al2TiO5 formation during firing. The dielectric characteristics, particularly the temperature coefficient of the resonant frequency (τf) and Q × f values, were improved without significantly reducing the sinterability and thermal conductivity. The dielectric properties of the developed 88Al2O3–12TiO2-based ceramic were εr: 14.7, τf: +0.8 ppm/K, and Q × f: 13,383 GHz (at ∼10 GHz) at a firing temperature of 940 °C. The thermal conductivity was 18.5 W/mK, which is the highest value for reported temperature-stable low-temperature co-fired ceramics (LTCCs). These results provide one of the key technologies for the practical application of LTCCs with superior thermal conductivities.

Organic dye sensitized TiO2–Nb2O5 electron collecting bilayer photoanode for efficient power conversion in solar cells

Abstract This article describes the advantage of the organic dye sensitized TiO2–Nb2O5 electron collecting bilayer photoanode for efficient power conversion in solar cell devices. The bilayer photoanodes were prepared using Nb2O5 coated TiO2 nanoparticles/nanosticks composite film. The solar cell devices were fabricated using organic dye DIAC sensitized photoanodes with different types of electrolytes and cobalt sulphide counter electrode. The power conversion efficiency of 6.64% was achieved in the solar cell device fabricated with the bilayer photoanode and quasi-solid state electrolyte. This solar cell device exhibited high power conversion efficiency as compared to bare photoanode solar cell devices. The enhanced power conversion efficiency of the cell ascribes the bilayer photoanode improved the electron transport and reduced the recombination of charge carriers at photoanode/dye/electrolyte interface.

Porous niobia spheres with large surface area: alcothermal synthesis and controlling of their composition and phase transition behaviour.

Submicron-sized niobia (Nb2O5) porous spheres with a high specific surface area (300 m2 g−1) and nano concave–convex surfaces were synthesized via a rapid one-pot single-step alcothermal reaction. Prolonged reaction time or high reaction temperatures resulted in a morphology change of Nb2O5 from amorphous sphere to rod crystals with hexagonal crystal phase. A similar alcothermal reaction yielded TiO2–Nb2O5 composite porous spheres, whose Ti : Nb molar ratio was controlled by changing the precursor solution component ratios. A simple thermal treatment of amorphous TiO2–Nb2O5 porous spheres consisting of 1 : 2 (molar ratio) Ti : Nb at 600 °C for 2 h induced crystal phase transfer from amorphous to a monoclinic crystal phase of submicron-sized TiNb2O7 porous spheres with a specific surface area of 50 m2 g−1.

Designed structure of bilayer TiO2–Nb2O5 photoanode for increasing the performance of dye-sensitized solar cells

Here, we investigate the effect of crystalline structure and design configuration of photoanode semiconductor on physical properties and electron transport parameters of dye-sensitized solar cells based on niobium pentoxide (Nb2O5) composition. At the first step, the effect of calcination on structural properties of Nb2O5 has been studied. Phase transformation from mixed monoclinic/orthorhombic to pure monoclinic phase has been observed. The performance of cells is then investigated for different designs of photoanode, including pure Nb2O5, pure TiO2 and bilayer structure composed of TiO2/calcined Nb2O5. The highest performance belonged to the cell prepared bilayer photoanode. Bilayer structure facilitated charge extraction which leads to the drastically improvement of photoconversion efficiency. Remarkable increase in JSC is reported comparing to cells without TiO2 layer, from about 0.08 to around 5.7 mA cm−2, leading to conversion efficiency as high as 1.48% in the best cell. Results of dye loading measurement and impedance spectroscopy analysis revealed that this higher photocurrent is attributed to both more injected electrons from dye to photoanode and higher electron lifetime. Furthermore, inhibition of electron back-transfer from the composite layer to the electrolyte as well as low recombination resistance plays critical roles in such dramatically photoconversion efficiency.

Pt–TiO2–Nb2O5 heterojunction as effective photocatalyst for the degradation of diclofenac and ketoprofen

Pt–TiO2–Nb2O5 heterojunction was synthetized and studied for the photocatalytic removal of diclofenac (DCF) and ketoprofen (KTF) under UV light irradiation. The physical-chemical properties of the prepared catalysts were analysed by different characterization techniques revealing that the lowest platinum nanoparticle size and the better metal distribution was observed in Pt–TiO2–Nb2O5 sample. The Pt–TiO2–Nb2O5 heterojunction possessed the best photocatalytic activity toward both the photodegradation and mineralization of the two selected pollutants. The optimal photocatalyst showed a DCF and KTF mineralization rate of 0.0555 and 0.0746 min−1, respectively, which were higher than those of Pt–TiO2 (0.0321 min−1 for DCF and 0.0597 min−1 for KTF). The experiments driven to analyse the effects of free radical capture showed that ·OH, ·O2− and h+ have a primary role in reactive during the photocatalytic reaction. The improved photocatalytic performances of the Pt–TiO2–Nb2O5 heterojunction could be argue by a direct Z-scheme mechanism in which the Pt0 nanoparticles could act as a bridge between TiO2 and Nb2O5, improving the electron-hole separation and, ultimately, enhancing the photocatalytic removal rate of both DCF and KTF.

Correlation between microstructural defects and photoelectrochemical performance of 1D Ti–Nb composite oxide photoanodes for solar water splitting

We report on the optimized fabrication of ultrathin wall nanotubes grown on Ti–Nb alloy via anodization in organic-based electrolytes. The nanotubes are vertically aligned with wall thicknesses of 5–8 nm, diameters of 180–200 nm, and lengths of 2–2.8 μm. Raman spectroscopy and glancing angle x-ray diffraction (GAXRD) measurements indicated the formation of composite oxides of anatase TiO2 and monoclinic Nb2O5. The composite oxides showed better stability at elevated temperatures up to 650 ᵒC and with much smaller induced microstrain compared to the TiO2 counterpart. X-ray photoelectron spectroscopy (XPS) analysis confirmed the composition of the fabricated nanotubes as a mixed TiO2–Nb2O5 composite. Upon their use as photoanodes to split water, the composite TiO2–Nb2O5 NTs showed almost 2-fold increase in the obtained photocurrent compared to that of bare TiO2 NTs prepared under the same conditions. Moreover, the incident photon to current efficiency (IPCE) of the mixed oxide nanotubes was higher than that of bare TiO2 with a positive shift towards longer wavelengths, indicating improved electron mobility and charge collection. Hence, the addition of Nb resulted in the formation of thermally stable and photoactive photoanodes for solar fuel production.

Ethanol sensing properties and reduced sensor resistance using porous Nb2O5-TiO2 n-n junction nanofibers

One-dimensional (1D) and porous Nb2O5-TiO2 n-n junction nanofibers with different Nb molar ratios have been synthesized by a simple electrospinning approach. A decrease in the average grain size and consequently an increase in the specific surface area were observed due to the introduction of Nb2O5 into TiO2 nanofibers. In comparison with pure TiO2 nanofibers, the Nb2O5-TiO2 nanofibers exhibited improved ethanol sensing response and a reduction in electrical resistance. The optimum operation temperature was reduced from 300 °C for pure TiO2 to 250 °C for Nb2O5-TiO2. The best sensing property was found for Nb2O5-TiO2 with 6 mol% Nb2O5, showing the highest response of 21.64–500 ppm ethanol at 250 °C, which was 2.79 times as high as that of pure TiO2 nanofibers at 300 °C. The reduction of Nb2O5-TiO2 based sensor resistance was attributed to the substitution of Ti4+ by Nb5+ ions and the formation of n-n junctions between Nb2O5 nanoparticles and TiO2 nanoparticles. The enhancement sensing mechanism of Nb2O5-TiO2 nanofibers was mainly ascribed to the enhanced resistance modulation owing to the substitution of Ti4+ by Nb5+ ions, formation of n-n junctions, and high surface area as well as small grain size of Nb2O5-TiO2 nanofibers.

The Catalytic Activity Enhancement of Commercial TiO2 and Nb2O5 Catalysts by Iron for Elemental Sulfur Production from H2S

Commercial TiO2 and Nb2O5 catalysts were used to determine catalytic activities for selective oxidation of H2S to elemental sulfur. Fe@TiO2 and Fe@Nb2O5 catalysts (containing 10% iron by weight) were also prepared by wet impregnation method to enhance the catalytic activity. TiO2 anatase phase and Nb2O5 were mainly observed in the crystalline structure of TiO2 and Nb2O5 based catalysts, respectively. Catalytic activity tests were performed in a fixed-bed flow reactor at 250 °C using stoichiometric feed ratio. 30% and 28% H2S conversions were obtained with commercial TiO2 and Nb2O5 catalysts. Complete conversion of H2S was reached with Fe@TiO2 and Fe@Nb2O5 catalysts at the same reaction conditions for 400 min. of reaction time. 100% of H2S conversion was obtained with iron-containing catalysts in the reaction tests carried out at 200 °C and 300 °C of reaction temperatures. Fe@TiO2 and Fe@Nb2O5 catalysts showed high sulfur selectivity (≥ 95%) under all reaction conditions. Iron addition enhanced the Lewis acidity and redox property of the commercial catalysts and this may be the reason for increase in catalytic activity.