Amorphous Nb2O5 Research Articles

Characterization of thin oxide layers formed by Ti-Nb Alloy anodization

Ti-Nb alloys are gaining more prominence in the industrial and scientific environment due to their high biocompatibility, mechanical strength/weight ratio, and exceptional corrosion resistance compared to other metallic materials. Metals exhibiting this passivation characteristic are known as metal valves and may exhibit semiconductive or insulating oxides. Controlling the growth of distinct thickness layer films is possible through tunning anodization conditions. In this work, a Ti-Nb binary system is anodized, and the grown oxide layer is comprehensively characterized using ellipsometry based on its optical properties and thickness at different applied potentials. Confocal Microscopy assessed their surface roughness, and SEM/EDS probed the surface material's elemental composition. CF-LIBS successfully confirmed the 70/30 composition of the Ti-Nb alloy. Raman spectra have detected the presence of amorphous TiO2 and Nb2O5 at potentials higher than 80V, 100V, and 120V. Finally, a linear dependence of the oxide thickness with the applied potential was observed.

High Broadband Optical Absorption and Bandstop Filter Characteristics of Pb/Nb2O5 Interfaces

AbstractIn this study, semitransparent lead films serve as substrates for depositing niobium pentoxide thin films, forming versatile electro‐optical devices. Using vacuum evaporation and ion sputtering techniques at ≈10−5 mbar, stacked layers of crystalline Pb and amorphous Nb2O5 are created. This process reduces free carrier absorption in Nb2O5 and forms Urbach tail states with a width of 0.91 eV. Pb/Nb2O5 thin films exhibit remarkable broadband absorption, exceeding 440% in the visible and 98% in the infrared. Moreover, Pb substrates induce a redshift in Nb2O5’s energy bandgap. Electrical analysis using impedance spectroscopy on Pb/Nb2O5/Ag structures reveals their series/parallel resonance and bandstop filter properties. Notably, the bandstop filters exhibit reflection coefficient minima at a notch frequency of 1.66 GHz, with a bandwidth of 280 MHz, return loss of 26 dB, and voltage standing wave ratio of 1.13. These findings underscore the device's potential for wide‐ranging electro‐optical applications across the electromagnetic spectrum.

Spontaneous Electrochemical Reconstruction of NiNb2O6@C for High-Rate Lithium-Ion Batteries

Niobium oxides are widely active in the arena of lithium-ion batteries due to their distinctive structure and rapid charging capability, nevertheless facing the serious challenge from their inherently low electrical conductivity. Herein, a molten salt method is proposed to prepare nickel niobate (NiNb2O6) anode materials for lithium-ion batteries, and a carbon coating derived from mesophase pitch is fabricated to construct NiNb2O6@C composites. Importantly, NiNb2O6@C undergoes spontaneous electrochemical reconstruction to generate metallic Ni and amorphous Nb2O5 during the initial charge/discharge cycle. The presence of the outer carbon layer not only serves as a uniform conductive coating to improve the conductivity and thereby deliver superior rate performance, but also effectively inhibits the stripping of Ni0 to guarantee a great cycling stability. The synergistic effects of the dual conductive interfaces, consisting of the carbon layer and the Mott-Schottky heterojunction between amorphous Nb2O5 and metallic Ni, culminate in exceptional electrochemical performance. Specifically, NiNb2O6@C-10% delivers impressive specific capacity of 436.3 mAh g−1 at 0.5C and conspicuous cycling stability, maintaining 86.3% capacity retention after 800 cycles at 10C. This work underscores the substantial potential of nickel niobate anode materials in advancing the development of next-generation lithium-ion batteries.

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.

Inhibition of Phase Transition in Amorphous Niobium Oxide by Covalent Carbon Reinforcement Enables Fast‐Charge and Long‐Duration Lithium Storage

AbstractNiobium oxides are potential anode materials for ultrafast and safe lithium‐ion batteries due to their high ionic conductivity and relatively high operation voltage. However, the electrochemically induced phase transformations that involve multi‐electron redox reactions in a wide voltage window cause rapid capacity degradation and poor rate capability. Here, a novel carbon‐covalent amorphous niobium oxide anode is reported to greatly suppress the phase transition during cycling via formation of strong Nb─O─C bonds, achieving high‐capacity, fast‐charge and long‐duration lithium storage. This amorphous structure and forming covalent carbon contribute to good volume accommodation and high electron conductivity. The carbon‐covalent amorphous Nb2O5 displays a high reversible capacity of 361.5 mAh g−1 at 0.1 A g−1 and excellent cycling stability with a capacity of 189.8 mAh g−1 at a high rate of 10 A g−1 after 9000 cycles. Structure characterizations reveal that the well‐preserved amorphous structure without phase transition during repeated Li+ insertion/desertion is responsible for the superior performance. This work opens a new avenue on rational design of high‐performance amorphous electrode materials for next‐generation batteries.

Radiation-enhanced crystallization of amorphous Nb2O5 films according to TEM with in situ video recording

Amorphous films are formed on substrates at room temperature in the process of anodic oxidation of niobium foil. The studies were carried out using methods of electron diffraction and “in situ” transmission electron microscopy (TEM) with video recording of structural changes. It was found that electron beam irradiation of the film with a dose rate (4–7)·104 e−/Å2·s inside the column of the electron microscope causes its layer polymorphous crystallization (LPC) with the formation of Nb2O5 crystals with hexagonal lattice. The dimensionless parameter of the relative crystallization length δ0≈ 5000 − 7000. The dependence on time of the crystal diameter is described by a power function with exponents of 1.55, 1.1 and 1.3. According to this the dependence of the fraction of the crystalline phase on time is described by a power function with exponents of 3.1, 2.2 and 2.6. This non-quadratic nature is explained with the formation of a domain superstructure in the low-temperature modification of α-Nb2O5 and phenomenon of polyamorphism in amorphous films.

Metastable 2D amorphous Nb2O5 for aqueous supercapacitor energy storage

Nb2O5 is a promising electrode material of energy storage due to its high specific capacity and phase transition resistance. However, the facile generation of niobic acid poses a challenge, hindering controlled growth and impeding improvements in electrical conductivity and structural stability, especially in realizing two-dimensional (2D) Nb2O5. Herein, we have discerned that the addition of hexamethylenetetramine (HMTA) in ethanol solvent facilitates the controlled and restricted growth of metastable 2D amorphous Nb2O5 (a-Nb2O5) within graphene domains. Nitrogen atoms within HMTA, rich in lone pair electrons, strongly interact with niobium ions, promoting 2D amorphous growth on graphene interface. This unique 2D amorphous interface offers high surface area, enhanced electron mobility, rapid ion transport, and superior structural stability compared to crystalline counterparts. The prepared metastable 2D a-Nb2O5/rGO electrode exhibits unprecedented cycle life in aqueous asymmetric supercapacitor. This confined growth strategy offers a novel approach for the innovative design of metastable 2D materials.

Silver Containing Antimicrobial Coatings on Innovative Ti-30Nb-5Mo β-Alloy Prepared by Micro-Arc Oxidation for Biomedical Implant Applications

Micro-arc oxidation (MAO) is a versatile surface-modification method that promotes higher wear and corrosion resistance, osseointegration, and biological activity to titanium alloys’ surfaces. This study aimed to modify the surface of a recently developed metastable β Ti alloy, which exhibits more favorable mechanical properties for implant applications compared to some commercial Ti alloys, by incorporating Ag into the coatings to introduce a bactericidal function to the surface. The Ti-30Nb-5Mo alloy, with lower elastic modulus, was treated by the MAO method using electrolyte solutions containing calcium acetate, magnesium acetate, β-glycerol phosphate, and varied concentrations of silver nitrate (1.5 mM, 2.5 mM, and 3.5 mM). With an increase in the concentration of silver ions in the electrolyte, the galvanostatic period during the MAO process decreased from 1.7 s to 0.5 s. The Ca/P ratio increased from 0.72 up to 1.36. X-ray diffraction showed that the MAO coatings were formed by rutile and anatase TiO2 main phases and calcium phosphates. X-ray photoelectron spectroscopy analysis detected the presence of amorphous Nb2O5, CaCO3, and MgCO3, and metallic and oxide forms of Ag. The increase in Ag in the electrolyte decreased the coating thickness (from 14.2 μm down to 10.0 μm), increased the contact angle (from 37.6° up to 57.4°), and slightly increased roughness (from 0.64 μm up to 0.79 μm). The maximum inhibition of Enterococcus faecalis, Pseudomonas aeruginosa, and Candida albicans strains growth was of 43%, 43%, and 61%, respectively. The Ag did not negatively affect the differentiation of adipose-tissue-derived mesenchymal stem cells. Therefore, the treatment of the surface of the innovative Ti-30Nb-5Mo alloy by the MAO method was effective in producing a noncytotoxic porous coating with bactericidal properties and improved osseointegration capabilities.

Nb2O5 deposited by ion-assisted reactive magnetron sputtering for near-infrared optical coating: Power modulation and performance degradation

Nb2O5 exhibits outstanding optical properties within the near-infrared spectra, suggesting considerable potential for application in optical coatings. In this work, Nb2O5 was deposited by ion-assisted reactive magnetron sputtering. The potential of sputtering power modulated various properties of Nb2O5 was revealed. The results showed that the deposition rate rose up to 2.05 Å/s with increasing power. Optimal deposition of amorphous Nb2O5 was achieved at 450–600 W, exhibiting a defect-free surface and cross-section, accompanied by a minimal roughness of 0.36 nm and a consistent refractive index range of 2.10 to 2.35. These Nb2O5 demonstrated excellent optical performance in the near-infrared band. The reflectance of high-reflective coatings achieved 99.8 %, and the reflectance of antireflective coatings achieved 0.06 %. NbO2 was successfully deposited at 900 W, presenting a promising method for large-scale NbO2 deposition, independent of precise oxygen control. The high-temperature performance of Nb2O5 was evaluated, and the results showed significant crystallization at 750 °C, inducing a substantial rise in defects and surface roughness, exceeding 6 nm. The optical properties of Nb2O5 were affected, resulting in high-temperature performance degradation in optical coatings. Specifically, the reflection spectra of anti-reflective coatings experienced a 48 nm shift. The reflectance of high-reflective coatings decreased from 99.8 % to 41.2 %, and was accompanied by a blue shift exceeding 80 nm in the near-infrared band. The critical temperature of this dramatic change was identified to be within 450–550 °C. Typical catastrophic optical damage on the laser facet was observed. These findings provide valuable insights for the application of Nb2O5 optical coatings in near-infrared lasers.

Investigation of the dynamic interaction between dopants and oxygen vacancies in amorphous Nb2O5: Simulation and experimental study

Resistive random-access memory can potentially be used to construct high-speed, low-power, and high-density data-storage drives. Managing oxygen flow at the electrode-oxide interface is vital for improving endurance. Dopant-oxygen interactions govern ion diffusion and vacancy creation. The interactions between multivalent dopants and oxygen vacancies in Nb2O5 have been investigated in previous studies. In this study, we simulated the relationship between a multivalent dopant Mn and oxygen vacancies in amorphous Nb2O5. We introduced oxygen vacancies and Mn ions with different oxidation states to determine the effects of spin densities and band gaps. Experimental results obtained from deposited amorphous thin films validated the simulation results, demonstrating a close agreement between the experimentally obtained (1.11 eV) and predicted bandgaps (0.93 eV). The results of study illuminate the amorphous structure of Nb2O5, the interactions between multivalent Mn dopants and oxygen vacancies, and the resulting electronic properties, offering the potential for designing and optimizing functional materials.

In-situ Raman unveiled Nb-O-bond-dependency selectivity for methanol electro-oxidation at high current density

Selective methanol oxidation reaction (MOR) to value-added formate can maximize the energy utilization by replacing the high onset-potential and sluggish oxygen evolution reaction. However, to date, only first-row 3d transition metal oxides exhibit the capacity of selective MOR, motivating the design of new kinds of electrocatalysts to further enhance the performance. Here we develop amorphous Nb2O5 as an efficient electrocatalyst, for the first time, for selective MOR to formate, with a low operating potential of 1.47 V vs. RHE to achieve the industry-relevant current densities (>100 mA cm−2) with a formate Faradaic efficiency of ∼100 %. We demonstrate, via operando Raman measurements, that this superior electrochemical MOR capacity originates from the in-situ induced short Nb-O bonds from the amorphous structure. Besides, the interface between amorphous Nb2O5 and nickel foam could also faciltate the MOR. This work may provide insights for designing novel transition metal oxides as efficient catalysts for selective MOR.

Application of a flexible memristor in self-color electronics and its depth mechanism analysis

Memristor has a high-density information storage capability and can manipulate a large amount of data computing in parallel, so it can be applied in neuromorphic computing. The advanced intelligent applications are one of the major breakthroughs made in the past decade based on the memristor's research. In this work, amorphous Nb2O5 film as functional layers on flexible niobium (Nb) foil were fabricated by anodic oxidation in oxalic acid aqueous solution. A broad spectrum of well-defined color was acquired by varying the anodic voltage during oxidation of the Nb foil. The results of spectroscopic ellipsometry (SE) tests show that the Nb2O5 layers with various colors have different thickness. The willow yellow Nb2O5 film with a thickness of ∼85 nm based memristor show an excellent memristive memory behavior. Finally, it was proposed that the potential well of the ionization center tilts under the external electric field, which causes the probability of charge to escape along and against the direction of the external electric field to explain the memristive effect of the device. This work opens up a new method for fabricating the flexible memristor, which provides the potential applications for next generation self-color electronics.

Ultralow Operating Voltage Nb2O5-Based Multilevel Resistive Memory with Direct Observation of Cu Conductive Filament

Amorphous Nb2O5 is proposed as the resistive switching layer for conductive bridge random access memory. The Nb2O5 device is fabricated with the top Cu and bottom Au electrodes, which is fabricated at a fully room temperature process, exhibiting excellent resistive switching performance with an on/off ratio of up to 105 and ultralow operating voltage. The multilevel resistive switching characteristic can be rationally demonstrated by changing the compliance current in the Nb2O5 device. Each level of the resistance state is uniform with distinguishable read windows. The reset voltage reduces significantly as the compliance current decreases, which is merely 0.002 V when the compliance current is 10–5 A. An approach of the broken-down device is elaborately developed to firmly identify the migration of Cu and the existence of a Cu conductive filament and to explain the ultralow operating voltage. Amorphous Nb2O5 devices exhibit excellent resistive switching performance, proving it is a promising material for memory applications.

Anomalous thermal conductivity in amorphous niobium pentoxide thin films: A correlation study between structure and thermal properties

Niobium pentoxide (Nb2O5) based thin films are predominantly used in optical filters, solar cells, electrochromic devices, sensors and microelectronic devices. The temperature-dependent thermophysical properties of Nb2O5 films are crucial for the performance and reliability of such devices. Within this work, for the first time, the thermal properties of sputter deposited Nb2O5 films are correlated with their structural properties at different length scales. Thermal measurements were carried out by time-domain thermoreflectance, yielding a thermal conductivity of 3.0±0.3 W/mK at 25 °C for crystalline Nb2O5 films, which decreases to 2.6±0.2 W/mK at 450 °C. In contrast, amorphous Nb2O5 films had a thermal conductivity of 2.2±0.2 W/mK below 275 °C. Above 275 °C, an abrupt increase in thermal conductivity up to a maximum value of 2.8±0.2 W/mK at 325 °C was recorded. The average and local structure are determined by in-situ high-temperature X-ray diffraction and in-situ high-temperature Raman spectroscopy, respectively. These characterization techniques together enable to cross-correlate structural and thermal properties of Nb2O5 thin films highlighting the observed peculiarity of the thermal conductivity. This substantial increase in thermal conductivity cannot be linked to any macroscopic phase change but rather to a local phase rearrangement near the crystallization temperature, evidenced by temperature-dependent Raman spectra analysis. This study serves as a guide to engineering future Nb2O5 based thin film devices and for their reliability optimization.

Enhancing the electrochemical performance of LiNi0.8Co0.1Mn0.1O2 cathodes through amorphous coatings

LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes have attracted the attention of the automotive industry due to their higher capacity and operating voltage. Despite their promising electrochemical behavior, these materials do not have a stable cycling performance, as parasitic reactions take place when they come in contact with the electrolyte. Herein, amorphous Nb2O5 is applied as a multifunctional protective layer to stabilize the NCM811 interface, resulting in reduced surface contamination (Li2CO3), alleviation of transition metal (TM) ion dissolution, and suppression of surface corrosion and phase transformations during cycling. As a result, after 200 cycles, the coated NCM811 had a capacity of 180 mAh g−1 displaying an excellent capacity retention of 85.7%, which is 30% higher than that of the uncoated samples. Similarly, the Nb2O5 coating allows for an enhanced rate capacity of 139 mAh g−1 at 5 C, compared to 117.6 mAh g−1 for the pure NCM811. In addition, the Nb2O5 coating effectively suppresses the voltage decay with cycling, resulting in a voltage decay of 70 mV after 200 cycles, while a reduction of 190 mV takes place without the coating.

Resistive switching properties of Mn-doped amorphous Nb2O5 thin films for resistive RAM application

In this work, based on the calculation of the band gap of amorphous Nb2O5, we proposed that the amorphization in Nb2O5 thin films could narrow the band gap. As a proof of concept, amorphous Nb2O5 based resistive random-access memory devices were fabricated. In addition to the amorphization effect, the influence of Mn dopants and temperature on the conduction mechanism of the Nb2O5-based devices were investigated. Furthermore, oxygen vacancies were demonstrated to dominate the conduction mechanism of the Mn-doped Nb2O5-based devices. The oxidation states of O, Nb, and Mn analyzed by X-ray photoelectron spectroscopy signifying that the Mn addition was conducive to the oxidation of Nb during the conduction formation process, consequently offering immense benefits for the improvement of RRAM memory performance.

Effect of crystallization degree on optical characteristics of NB2O5 by sol–gel process

In this study, Nb2O5 was prepared by the sol–gel method. Crystallization process was investigated by thermal analysis (TG–DSC), X-ray diffraction (XRD), UV–vis spectra and Raman spectra. TG–DSC results indicated that amorphous Nb2O5 appeared at 460[Formula: see text]C. XRD results indicated that amorphous Nb2O5 transformed into pseudo-hexagonal phase and crystallization degree has an increasing trend with an increase of temperature. UV–vis and Raman spectra results reflected the significant variations of optical property and atomic structure in this process. Nb2O5 atomic arrangement transforms from short-range order to medium-range order, then to long-range order. Atoms transform into long-range ordered structure through connection of structural units with increasing temperature. Additionally, crystallization degree, optical property and atomic arrangement all are mutually connected in the crystallization process.

Achieving highly stable Sn-based anode by a stiff encapsulation heterostructure

Rationally designed heterostructures provide attractive prospects for energy storage electrodes by combining different active materials with distinct electrochemical properties. Herein, through a phase separation strategy, a heterostructure of SnO2 encapsulated by amorphous Nb2O5 is spontaneously synthesized. Insertion-type anode Nb2O5 outer shell, playing as reaction containers and fast ionic pathways, physically inhibits the Sn atoms’ migration and enhances the reaction kinetics. Moreover, strong chemical interactions are found at the SnO2/Nb2O5 interfaces, which ensure the solid encapsulation of the SnO2 cores even after 500 cycles. When used for lithium-ion batteries, this heterostructured anode exhibits high cycling stability with a capacity of 626 mA h g−1 after 1000 cycles at 2 A g−1 (85% capacity retention) and good rate performance with the capacity of 340 mA h g−1 at 8 A g−1.

Thermally grown Nb-oxide for GaN-based MOS-diodes

We have grown 10 nm of amorphous Nb2O5 on AlGaN/GaN heterostructure by a combination of sputtering of a thin film of niobium (Nb) followed by rapid thermal annealing in oxygen (O2) ambience. X-ray photoelectron spectroscopy (XPS) analysis shows an ideal stoichiometry of Nb2O5 at annealing temperature 500 °C. The band gap (Eg) and valence band offset with AlGaN (ΔEv) for Nb2O5 are estimated to be 4.15 eV and 0.15 eV, respectively. The root mean square (RMS) roughness of the oxide as measured by atomic force microscopy (AFM) is 1.32 nm. The thickness and crystallinity of the oxide are confirmed by transmission electron microscopy (TEM). The reverse leakage current is observed to reduce by three orders of magnitude for Nb2O5/AlGaN/GaN metal–oxide–semiconductor (MOS) diode as compared to the schottky diode. The dielectric constant of Nb2O5 (εox) and interface density of states (Dit) with AlGaN are estimated to be 58 and 7.0 × 1013 cm−2 eV−1 by capacitance voltage (CV) characteristics, respectively.

3D ordered macroporous amorphous Nb2O5 as anode material for high-performance sodium-ion batteries

The development of society has an increasing demand for clean energy. Sodium ion batteries (SIB) have emerged because of their abundant sodium reserves and low cost. However, there is still a gap in performance between sodium-ion batteries and lithium-ion batteries. Orthogonal Nb2O5 (T-Nb2O5) is a promising sodium carrier due to its good intercalation/deintercalation characteristics and surface capacitance reaction. However, T-Nb2O5 as electrode material suffers from the low conductivity, and the crystalline phase will change to amorphous during the charge and discharge process, resulting in poor electrochemical performance of SIB. Therefore, this work has carefully designed a 3D ordered macroporous amorphous Nb2O5 (3DOM A-Nb2O5) with rich mesoporosity as anode material for superior sodium storage. Unsaturation defects in A-Nb2O5 alter the electronic structure, thereby improving electrical conductivity. Meanwhile, the hierarchical porous structure facilitates the insertion and extraction of sodium ions, with the structural integrity can be well maintained upon long cycles at high current density. As a result, the 3DOM A-Nb2O5 electrode exhibits excellent cycle performance with high capacity retention of 131 mAh g−1 after 500 cycles at 5 A g−1.