Synthesis of Nb2O5 nanosheets and its electrochemical measurements

In this study, Nb₂O₅ nanosheets were first synthesized using NbO₂ particles as the precursor via a simple hydrothermal route. The synthesized Nb₂O₅ nanosheets are highly crystalline and their thicknesses are found to be ca. 3–5 nm. Based on the experimental results of XRD, SEM and TEM measurements, a possible mechanism for the formation of nanosheets was discussed. An electrode materials made of the product containing Nb₂O₅ nanosheets shows a larger capacity of 355 mAh g⁻¹ at a current density of 0.1 A g⁻¹. Cyclic measurements indicate that such an electrode exhibits a high reversible charge/discharge capacity and cycling stability. This might be attributed to the intrinsic characteristics of Nb₂O₅ nanosheets.     

Large third-order optical nonlinearity of SrBi2Nb2O9 thin films fabricated by pulsed laser deposition

SrBi₂Nb₂O₉ (SBN) thin films with a single phase of layered perovskite structure have been fabricated on fused quartz substrates at room temperature by pulsed laser deposition. The XRD and AFM analysis indicated that the films had better crystallinity, less rough surface morphology, and larger grain size with increasing oxygen pressure. The nonlinear optical properties of the samples were determined using a single beam Z-scan technique at a laser wavelength of 532 nm with laser duration of 25 ps. The real and imaginary parts of the third-order nonlinear optical susceptibility χ⁽³⁾ of the films were measured to be 3.18 × 10^− 8 esu and 5.94 × 10^− 9 esu, respectively.     

Studies on switching mechanisms in Pd-nanodot embedded Nb2O5 memristors using scanning tunneling microscopy

Current imaging tunneling spectrum obtained from scanning tunneling microscopy has been used to probe the formation and/or rupture of conductive filaments responsible for bipolar switching in Pd nano-dots embedded Nb₂O₅ memristors. Filamentary conduction mechanism has been confirmed by scanning tunneling microscopy study using a Pt-Ir tip that enabled performing electroforming and reset operations at the nanoscale. The back and forth transition between the fully oxidized and metallic sub-oxide states of niobium under applied bias, as observed from X-ray photoelectron spectroscopy, is believed to be the source of bipolar switching in Nb₂O₅ memristors. The incorporation of Pd nanodots in Nb₂O₅ matrix plays a critical role by acting as an oxygen ion reservoir and/or by polarizing a large volume of oxygen vacancies. The formation and/or rupture of the conducting filaments through trapping-detrapping phenomena are found to boost the memristive switching performance.     

Fabrication of KTa0.65Nb0.35O3 film by pulsed laser deposition on glass substrate with various buffer layers

KTa_0.65Nb_0.35O₃ (KTN) thin films were deposited on amorphous glass substrates using a range of single buffer layers such as indium tin oxide (ITO), zinc oxide (ZnO), 3 at% Al-doped ZnO (AZO), and 3 at% Ga-doped ZnO (GZO), as well as a variety of multi-buffer layers such as SrTiO₃ (STO)/ITO, STO/ZnO, STO/AZO, and STO/GZO using a pulsed laser deposition system. All films showed a polycrystalline perovskite phase with the exception of all single buffer layers and STO/ITO multi-buffer layers. The STO buffer layer is important for crystallizing KTN films due to the similar lattice constant and same crystal structure. The optical transmittance of all films exhibited a transmittance ?90% in the wavelength range.     

Preparation and characterization of Ti/SnO(2)-Sb(2)O(3)-Nb(2)O(5)/PbO(2) thin film as electrode material for the degradation of phenol

In this work, a novel electrode of titanium substrate coated with mixed metal oxides of SnO(2), Sb(2)O(3), Nb(2)O(5) and PbO(2) was successfully prepared using thermal decomposition and electrodeposition. The surface morphology and the structure of the prepared thin film were characterized by scanning electronic microscopy (SEM) and X-ray diffraction (XRD), respectively. Experimental results showed that the structure of the prepared electrode might be described as a Ti/SnO(2)-Sb(2)O(3)-Nb(2)O(5)/PbO(2) thin film and its surface was mainly comprised pyramidal-shape beta-PbO(2) crystals. The modified electrode had higher oxygen evolution potential than that of other PbO(2) modified electrodes. Electrocatalytic oxidation of phenol in aqueous solution was studied to evaluate the potential applications of this electrode in environmental science. The phenol removal efficiency in an artificial wastewater containing 0.50g/L phenol could reach 78.6% at 20 degrees C and pH 7.0 with an applied electricity density of 20mA/cm(2) and treatment time of 120min. When 21.3g/L chloride was added to this wastewater, the removal efficiency could reach to 97.2%.     

Overview about the optical properties and mechanical stress of different dielectric thin films produced by reactive-low-voltage-ion-plating

Thin films of Ta₂O₅, Nb₂O₅, and HfO₂ were deposited by reactive-low-voltage-ion-plating (RLVIP) on unheated glass and silicon substrates. The film thickness was about 200 nm. Optical properties as well as mechanical film stress of these layers were investigated in dependence of various deposition parameters, i.e. arc current and oxygen partial pressure. For an arc current in the range between 40 and 50 A and an oxygen partial pressure of at least 11 · 10^− 4 mbar good results were obtained. The refractive index and film thickness were calculated from spectrophotometric transmission data using the Swanepoel theory. For example at 550 nm wavelength the refractive index for thin RLVIP-Nb₂O₅-films was found to be n₅₅₀ = 2.40. The optical absorption was obtained by photo-thermal deflection spectrometry. For the investigated materials absorption coefficients in the range of k = 5 · 10^− 4 at 515 nm wavelength were measured. The mechanical film stress was determined by measuring the difference in bending of silicon substrates before and after the deposition process. For dense films, i.e. no water vapour sorption on atmosphere, the mechanical film stress was always compressive with values of some hundred MPa. In case of films deposited with higher arc currents (I_arc > 60A) and lower oxygen pressure (< 15 · 10^− 4 mbar) the influence of a post deposition heat treatment at 350 °C for 4 h on air was also investigated. For these films the properties could clearly be improved by such treatment. However, by using lower arc currents and higher oxygen partial pressure during the ion plating process, immediately dense and environmental stable films with good optical as well as mechanical properties could be achieved without post deposition heat treatment. All the results obtained will be presented in graphs and diagrams.     

In2O3-ZnO transparent conductive oxide film deposition on polycarbonate substrates

Amorphous transparent conductive oxide films in the In-Zn-O system were deposited on polycarbonate (PC) substrates by simultaneous DC sputtering of an In₂O₃ target and a ZnO target with either 4 wt% Al₂O₃ or 7.5 wt% Ga₂O₃ impurities. Although the resistivity of the amorphous, non-doped In-Zn-O film on PC was about one order of magnitude higher than that on the glass substrate, the resistivity of the In-Zn-O films with Ga₂O₃ impurities on PC substrates was reduced to the level of the non-doped In-Zn-O films on glass substrates. The addition of Al₂O₃ or Ga₂O₃ to the In-Zn-O films also induced the widening of the optical band gap, which would improve transparency at blue wavelengths.     

Speciation of Cr(III) and Cr(VI) in environmental samples determined by selective separation and preconcentration on silica gel chemically modified with niobium(V) oxide

In this study a new method for chromium speciation in water using solid phase extraction coupled to a flow injection system and flame atomic absorption spectrometry was developed. The adsorption behavior of Cr(III) and Cr(VI) on Nb2O5-SiO2 allowed the selective separation of Cr(III) from Cr(VI) in the pH range of 6-9. Thus, a method for Cr(III) preconcentration and extraction using Nb2O5-SiO2 was developed. Total chromium was determined after the reduction of Cr(VI) to Cr(III) using sodium sulfite in acidic medium. The operational variables of the preconcentration and reduction procedures were optimized through full factorial and Doehlert designs. The limit of detection for Cr(III) was 0.34microgL(-1) and the precision was below 4.6%. Results for recovery tests using different environmental samples were between 90 and 105%. Certified reference materials (NIST 1640 and NIST 1643e) were analyzed in order to check the accuracy of the proposed method, and the results were in agreement with the certified values.     

The effect of Sb2O5 additions on the dielectric properties of Ag(Nb0.8Ta0.2)O3 ceramics

The sintering behavior and dielectric properties for perovskite Ag(Nb_0.8Ta_0.2)O₃ ceramic with Sb₂O₅ doping was explored. A small amount of Sb₂O₅ (2.5 wt.%) led to high densification at temperatures < 1060 °C. The dielectric constant increased and the temperature coefficient decreased with increasing concentration of Sb₂O₅, and the dielectric constant reached 673, combined with a low temperature coefficient of 147 ppm/°C, and dielectric loss of 0.0044 (at 1 MHz) for the sample with 3.5 wt.% Sb₂O₅ sintered at 1080 °C.     

Molten salt synthesis of acicular sodium strontium niobate particles

Acicular particles of Na_0.5Sr_0.25NbO₃ and NaSr₂Nb₅O₁₅ were successfully synthesized in the KSr₂Nb₅O₁₅ + NaCl system and SrCO₃ + Nb₂O₅ + NaCl + KCl system, respectively. It was found that the anisometric particles could not be obtained in the SrCO₃ + Nb₂O₅ + NaCl system. A facile ion-exchange approach was utilized to prepare acicular Na_0.5Sr_0.25NbO₃ particles. Acicular NaSr₂Nb₅O₁₅ particles with large aspect ratio could be obtained at the weight ratio of salt-to-mixture of 5:1, which were ideal template for fabricating textured ceramics. The growth process was researched and the synthesis method was suggested to be a self-precursor templating route. The results will be propitious to guide the fabrication of other templates with anisotropic morphology which were hard to prepare directly.     

A citrate complex process to prepare nanocrystalline PbBi2Nb2O9 at a low temperature

PbBi₂Nb₂O₉ nanocrystals with a perovskite-type structure were successfully synthesized at a relative low temperature via a citrate complex method. Metal ions were dispersed by citric acid in ethanol and ethylene glycol solvent, and then reacted with NH₄H₂[NbO(C₂O₄)₃·3H₂O] to form the gel. XRD results showed that pure PbBi₂Nb₂O₉ nanocrystals could be obtained after calcined treatment of xerogel at 800 °C. The average particles size was 57 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the sintering process led to the agglomeration of the nanoparticles. The photocatalytic test showed that the sample prepared by the citrate complex method exhibited a higher photocatalytic activity than that of the sample prepared by the solid-state reaction.     

Effects of TiO2 doping on microstructure and properties of directed laser deposition alumina/aluminum titanate composites

ABSTRACT

Al₂O₃-based composite ceramics have excellent high temperature performance and are ideal materials for preparing hot end components. However, poor fracture toughness and thermal shock resistance limit its applications. Based on the excellent low thermal expansion characteristics and thermal shock resistance of Al₂TiO₅ ceramic, different composition ratios of Al₂O₃/Al₂TiO₅ composite ceramics were prepared by directed laser deposition (DLD) technology. Effects of TiO₂ doping amount on microstructure and properties of the composite ceramics were investigated. Results show that α-Al₂O₃ phase is discretely distributed in the continuous aluminum titanate matrix when TiO₂ doping amount between 2 and 30?mol%. With the increase of TiO₂ doping amount, content of Al₂O₃ gradually decreases and its morphology changes from cellular to dendritic. When TiO₂ doping amount reaches 43.9?mol%, the microstructure transforms into fine Al₂TiO₅/Al₆Ti₂O₁₃ eutectic structure. Property test results show that Al₂O₃/Al₂TiO₅ composite ceramics have good comprehensive mechanical properties when TiO₂ doping amount between 2 and 6?mol%.     

Ion sensing properties of vanadium/tungsten mixed oxides

Vanadium/tungsten mixed oxide (V₂O₅/WO₃) sensing membranes were deposited on glassy carbon substrates and used as the H⁺ sensor of the extended gate field effect transistor (EGFET) device. X-ray diffractograms indicated a decrease of the interplanar spacing of V₂O₅ after the insertion of WO₃ revealing that the lamellar structure is under compressive stress. The crystallinity increases with increasing WO₃ molar ratio. The film is not homogeneous, with more WO₃ material sitting at the surface. This influences the response of pH sensors using the EGFET configuration. The maximum sensitivity of 68 mV pH⁻¹ was obtained for the sample with 5% WO₃ molar ratio. For higher WO₃ molar ratios, the behavior is not linear. It can be concluded that V₂O₅ dominates for acidic solutions while WO₃ dominates for basic solutions. Therefore, the mixed oxide with low amount of WO₃ is the main candidate for further use as biosensor.     

New heat generation material in AC magnetic field for Y3Fe5O12-based powder material synthesized by reverse coprecipitation method

We found the most promising powder material for the application of the thermal coagulation therapy for the treatment of cancerous tissues. The maximum heat generation ability (ΔT = 40-77 °C, 370 kHz, 1.77 kA·m^− 1) was obtained for the powder materials by the calcination at 1100 °C for the Y_3 − XGd_XFe₅O₁₂ system. This ΔT value is higher than ca. ΔT = 30 °C in same magnetic field for fine FeFe₂O₄ particles as the candidate material for this type of therapy. The particle growth with the formation of the cubic single phase might influence to the high heat generation. As an unexpected result, the Gd₃Fe₅O₁₂ (X = 3) has no heat generation ability in an AC magnetic field.     

Influence of Ga2O3 addition on transparent conductive oxide films of In2O3-ZnO

Influence of incorporation of Ga in amorphous In-Zn-O transparent conductive oxide films was investigated as a function of Zn/(Zn + In). For In-Zn-O films with no Ga₂O₃, the range of Zn/(Zn + In) ratio where the amorphous phase appears became narrow at a substrate temperature of 250 °C. With increasing Ga₂O₃ quantity, amorphous films were obtained even at a high substrate temperature of 250 °C in a wider range of Zn/(Zn + In) than that of In-Zn-O films with no Ga₂O₃. This means that the trend of crystallization at higher substrate temperature was disturbed with additional Ga incorporation. For the film deposited from ZnO:Ga (Ga₂O₃: 4.5-7.5 wt%) and In₂O₃ targets, we obtained a resistivity of 2.8 × 10⁻⁴ Ω cm, nearly the same value as that for an In-Zn-O film with no Ga₂O₃. The addition of more than 7.5 wt% Ga₂O₃ induced a widening of the optical band gap.     

Material properties and growth control of undoped and Sn-doped In2O3 thin films prepared by using ion beam technologies

Undoped (IO) and Sn-doped In₂O₃ (ITO) films have been deposited on glass and polymer substrates by an advanced ion beam technologies including ion-assisted deposition (IAD), hybrid ion beam, ion beam sputter deposition (IBSD), and ion-assisted reaction (IAR). Physical and chemical properties of the oxide films and adhesion between films and substrates were improved significantly by these technologies. By using the IAD method, non-stoichiometry and microstructure of the films were controlled by changing assisted oxygen ion energy and arrival ratio of assisted oxygen ion to evaporated atoms. Relationships between structural and electrical properties in ITO films on glass substrates were intensively investigated by using the IBSD method with changing ion energy, reactive gas environment, and substrate temperature. Smooth-surface ITO films (R_rms ≤ 1 nm and R_p-v ≤ 10 nm) for organic light-emitting diodes were developed with a combination of deposition conditions with controlling microstructure of a seed layer on glass. IAR surface treatment enormously enhanced the adhesion of oxide films to polymer substrate. The different dependence of IO and ITO films' properties on the experimental parameters, such as ion energy and oxygen gas environment, will be intensively discussed.     

Nb2O5对透辉石基矿渣微晶玻璃显微结构和力学性能的影响

为研究Nb_2O_5对透辉石基矿渣微晶玻璃显微结构和力学性能的影响机理,以富铁白云鄂博西尾矿、粉煤灰为主要原料,采用熔融工艺制备了添加质量分数0%~4%Nb_2O_5的透辉石基矿渣微晶玻璃。DTA、XRD、SEM和力学测试结果表明,Nb_2O_5主要以Ca2Nb2O7第二相的形式存在于辉石相界,其含量随Nb_2O_5添加量升高而增大。同时辉石主晶相从类菊花状枝晶组织转变成平均尺寸逐渐减小的圆角岛状组织。微晶玻璃的抗折强度平均为207 MPa,当Nb_2O_5质量分数为2%时最高,达236 MPa。     

Synthesis of a novel langanite-type compound La3Al5.5Nb0.5O14 by the sol-gel process

Langanite (La₃Ga_5.5Nb_0.5O₁₄, LGN) and its isomorphs are a few piezoelectric materials which have the unique temperature compensation and piezoelectric properties. But the high Ga₂O₃ content makes them very expensive and limits their applications. We reported a new langanite-type compound La₃Al_5.5Nb_0.5O₁₄ (LAN) which has the advantage of no Ga₂O₃ content. Chemically homogeneous La₃Al_5.5Nb_0.5O₁₄ sol was synthesized using La (NO₃)₃·6H₂O, Al (NO₃)₃·9H₂O and niobium citrate as starting materials. Single-phased LAN powder was prepared by decomposition of a citrate polymer precursor and subsequent reactions at high temperatures. TG-DTA, XRD and FTIR were employed to investigate the transformation process of gel to LAN powder. The results showed that, after calcination at 900 °C, pure La₃Al_5.5Nb_0.5O₁₄ polycrystalline powder with a narrow particle size distribution was obtained, which has the same structure with La₃Ga_5.5Nb_0.5O₁₄.     

Preparation and characterization of Nb2O5-Al2O3 composite oxide formed by cathodic electroplating and anodizing

Al foil was coated with niobium oxide by cathodic electroplating and anodized in a neutral boric acid solution to achieve high capacitance in a thin film capacitor. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) revealed the niobium oxide layer on Al to be a hydroxide-rich amorphous phase. The film was crystalline and had stoichiometric stability after annealing at temperatures up to 600 °C followed by anodizing at 500 V, and the specific capacitance of the Nb₂O₅-Al₂O₃ composite oxide was approximately 27% higher than that of Al₂O₃ without a Nb₂O₅ layer. The capacitance was quite stable to the resonance frequency. Overall, the Nb₂O₅-Al₂O₃ composite oxide film is a suitable material for thin film capacitors.     

Nb2O5对ZTM-Al2O3性能及ZrO2增韧机制的影响

探讨了Ｎｂ２Ｏ５对ＺＴＭ－Ａｌ２Ｏ３的性能和ＺｒＯ２在瓷体中增韧机制的影响。发现Ｎｂ２Ｏ５的引入可明显提高瓷体中ｍ－ＺｒＯ２含量而降低ｔ－ＺｒＯ２含量,材料的机械性能也随Ｎｂ２Ｏ５添加量的增大出现了显著的改善,并且有韧性的平方正比于ｍ－ＺｒＯ２含量的关系,ｍ－ＺｒＯ２含量的增加强化了微裂纹增韧是材料性能改善的原因。