Pore formation during the breakdown process in anodic Ta2O5 films

The breakdown damage during the anodic oxidation of tantalum has been studied through reanodization experiments. The results have been interpreted assuming the formation of non-shorting pores produced as a consequence of the breakdown process. On the basis of this model, the extent of the damaged area and the pore depth has been assessed.     

Thermal and optical properties of La2O3–Ga2O3– (Nb2O5 or Ta2O5) ternary glasses

La₂O₃–Ga₂O₃–M₂O₅ (M = Nb or Ta) ternary glasses were fabricated using an aerodynamic levitation technique, and their glass‐forming regions and thermal and optical properties were investigated. Incorporation of adequate amounts of Nb₂O₅ and Ta₂O₅ drastically improved the thermal stabilities of the glasses against crystallization. Optical transmittance measurements revealed that all the glasses were transparent over a wide wavelength range from the ultraviolet to the mid‐infrared. The refractive indices of the glasses increased and the Abbe number decreased upon substituting Ga₂O₃ with Nb₂O₅, and the decrease in the Abbe number was significantly suppressed when Ta₂O₅ was incorporated into the glass. As a result, excellent compatibility between high refractive index and lower wavelength dispersion was realized in La₂O₃–Ga₂O₃–Ta₂O₅ glasses. Analysis based on the single‐oscillator Drude–Voigt model provided more systematical information and revealed that this compatibility was due to an increase in the electron density of the glass.     

Effects of Ta2O5 content on mechanical properties and high-temperature performance of Zr6Ta2O17 thermal barrier coatings

Zr₆Ta₂O₁₇/YSZ double ceramic top coat thermal barrier coatings (TBCs) with different Ta₂O₅ content are prepared by atmospheric plasma spraying (APS). The effects of Ta₂O₅ content on mechanical properties and high-temperature performance of Zr₆Ta₂O₁₇ TBCs are investigated. With the decrease in Ta₂O₅ content, the hardness and fracture toughness of the Zr₆Ta₂O₁₇ coating increases from 12.833 to 15.117 GPa and from 3.3592 to 3.7753 MPa m^1/2, respectively. The Zr₆Ta₂O₁₇ coating specimens with different Ta₂O₅ content do not delaminate from the substrate except the edge peeling after 180 h of oxidation or 2000 thermal cycles at 1150°C. The Zr-12Ta specimen (the molar ratio of ZrO₂/Ta₂O₅ of 0.88:0.12) presents the more excellent mechanical properties and high-temperature performance. The reduction in Ta₂O₅ content will improve the mechanical properties, high-temperature oxidation, and thermal cycle performance of Zr₆Ta₂O₁₇/YSZ double ceramic top coat TBCs.     

Microwave dielectric properties of BaO–Ta2O5–TiO2 system

Microwave dielectric properties of the BaO–Ta₂O₅–TiO₂ system were investigated by the solid-state reaction method. It was recognized that the Ba₁₀Ta_7.04(Ti_1.2 − xSn_x)O₃₀ solid solutions have the higher Q · f value in comparison with the Ba₈(Ta_4 − xNb_x)Ti₃O₂₄ solid solutions. The limit of the Ba₁₀Ta_7.04(Ti_1.2 − xSn_x)O₃₀ solid solutions was approximately x = 0.75; the lattice parameter c of the solid solutions, which is related to the change in the B(1)O₆ octahedron, was significantly increased in the composition range from 0 to 0.75. The Q · f values of the Ba₁₀Ta_7.04(Ti_1.2 − xSn_x)O₃₀ solid solutions are remarkably improved by the Sn substitution for Ti; the highest Q · f value of 59,100 GHz is obtained at x = 0.75. Moreover, the ɛ_r and τ_f values of the Ba₁₀Ta_7.04(Ti_1.2 − xSn_x)O₃₀ solid solutions at x = 0.75 were 25.6 and 30.3 ppm/°C, respectively.     

Physico-chemical and antimicrobial properties of Ag/Ta2O5 nanocomposite coatings

Surface modification of surgical instruments is carried out in order to improve the antibacterial performance against the surgical site infections. Healthcare acquired infections (HAI) and Nosocomial infections are one of the leading causes of complications/deaths after surgery. There is an increasing trend of antibiotic resistance in bacteria such as, vancomycin-resistant Enterococcus (VRE), carbapenem-resistant Enterobacteriaceae (CRE), multi-drug-resistant Mycobacterium tuberculosis (MDR-TB), methicillin-resistant Staphylococcus aureus (MRSA), and Neisseria gonorrhoeae. Thus, surfaces that counteract the adherence and growth of bacteria are employed to avoid the infections. In present study, stainless steel 316 L (SS 316 L) was coated with Silver/Tantalum oxide (Ag/Ta₂O₅) nanocomposite using reactive magnetron sputtering. The as-sputtered Ag/Ta₂O₅ nanocomposite (a-Ag/Ta₂O₅) film was crystallized via thermal treatment at 400 °C. Due to the annealing, the AgNPs migrated to the surface through the columnar paths of the a-Ag/Ta₂O₅. Thus, the crystallized layer (c-Ag/Ta₂O₅) exhibited 302% improvement in adhesion strength and enhanced hydrophopibicity. The c-Ag/Ta₂O₅ also demonstrated excellent antibacterial performance against Staphylococcus aureus (NCTC 6571) (gram-positive bacteria) and Escherichia coli (ATCC 15597) (gram-negative bacteria) according to the inhibition zone measurements. These results suggest that c-Ag/Ta₂O₅ deposition on SS 316 L substrate has a high potential to serve as an adherent, antibacterial layer on the surgical tools, in order to resist surgical site infections.     

Comprehensive properties and thermal stability of Ta2O5-doped PIN-PHT ceramics

Herein, high-performance 0.11 Pb(In_1/2Nb_1/2)O₃-0.89 Pb(Hf_0.47Ti_0.53)O₃-0.8Ta₂O₅ (PIN-PHT-0.8Ta) ceramics are successfully synthesized. In addition, performance improvement is comprehensively analyzed from viewpoints of microstructure, phase structure and electrical properties. Experimental results reveal that the addition of Ta₂O₅ changes phase structure of PIN-PHT ceramics from ferroelectric tetragonal phase to rhombohedral phase. This leads to the appearance of morphotropic phase boundaries (MPBs). At the same time, the addition of Ta₂O₅ reduces grain size and enhances grain uniformity. Also, Ta₂O₅ doping improves internal and external contribution of piezoelectric response, which greatly improves dielectric, piezoelectric and ferroelectric properties of PIN-PHT. Key performance parameters include d₃₃, k_p, T_C, ε_r and tanδ, which are found to be 630 pC/N, 0.73, 322.6 °C, 1917 and 1.55%, respectively. In particular, thermal stability of PIN-PHT-0.8Ta ceramics is found to be higher than PZT-based ceramics, as well as d₃₃ value and performance retention rate of PIN-PHT-0.8Ta are found to be 560 pC/N and 89% at 300 °C, respectively, which are far superior to commercial PZT-5 and PZT-8 ceramics. These properties indicate potential of PIN-PHT-0.8Ta ceramics in high-temperature applications.     

Study on properties of Hf6Ta2O17/Ta2O5 system: A potential candidate for environmental barrier coating (EBC)

Ta₂O₅ doped Hf₆Ta₂O₁₇ system (Hf₆Ta₂O₁₇/Ta₂O₅) is considered to have potential application prospect in the field of aero-engine. We herein focus on the thermo-physical, mechanical properties and CMAS corrosion resistance of Hf₆Ta₂O₁₇/Ta₂O₅ to systematically evaluate the possibility for the application of environmental barrier coating (EBC). By changing the content of Ta₂O₅, the gradient adjustment of thermal expansion coefficient can be realized while maintaining low thermal conductivity (1.5–2.2 W/(m·K)). The introduction of Ta₂O₅ significantly reduces the modulus and improves the fracture toughness. Single-phase Hf₆Ta₂O₁₇ shows excellent corrosion resistance against molten calcium-magnesium-alumina-silicate (CMAS). The crystallization of CaTa₂O₆ and HfSiO₄ is the important factor to prevent further corrosion. The introduction of Ta₂O₅ weakens the ability to prevent Si penetration and greatly increases the thickness of the corrosion layer. The results highlight the merit of Hf₆Ta₂O₁₇/Ta₂O₅ system as potential candidate for multi-layer gradient coating on the surface of ceramic matrix composites.     

Effect of TiO2 and Ta2O5 additions on the electrical properties of Li2CaAl4Si4O16 glass-ceramic

Influence of TiO₂ and Ta₂O₅ on crystallisation for ceramic based on Li–Ca–Al–Si was studied. Sintering of glass-ceramics leads to the formation of β-eucryptite, anorthite and Ca-olivine. These phases are developed only on samples containing TiO₂ and Ta₂O₅. Incorporation of either TiO₂ or Ta₂O₅ gives clear crystals of low pores than in the base sample. Addition of Ta₂O₅ or TiO₂ improves densification properties and reduces sintering temperature. Electrical measurements were done in audio frequency range and lower (90?Hz–100?kHz). Composition changes on electrical properties were examined. Experimental electrical data show that the response of specimens was not simple (not a linear relation). The increase of TiO₂ and Ta₂O₅ generally decreases the electrical properties of the ceramic specimens used in this case. Electrical properties were able to follow and interpret the change in composition. This information was correlated to the internal structure of the samples.     

BNT-based ferroelectric ceramics: Electrical properties modification by Ta2O5 oxide addition

Due to their superior piezo-responses (strain S > 0.3%), bismuth sodium titanate (BNT)-based relaxor ferroelectrics have received much attention. Compared to other chemical elements, tantalum (Ta) doping provides superior electro-strain for these ferroelectrics, while the effect of Ta₂O₅ as oxide additive has been rarely reported. Herein, lead-free piezoceramics of Bi_0.5(Na_0.72K_0.22Li_0.06)_0.5TiO₃-xTa₂O₅ (BNKLT-xTa₂O₅, x = 0-0.015) are synthesized. We study the effects of Ta₂O₅ addition on the crystal structure, piezoelectric responses, dielectric properties, and ferroelectric properties of BNKLT ceramics. All of the ceramics exhibit a typical perovskite structure, and Ta₂O₅ diffuses into the BNKLT lattice to form a uniform solid solution. The addition of Ta₂O₅ can make the grains more regular and uniform, while excess Ta₂O₅ result in finer grains. The undoped BNKLT ceramics show good ferroelectric and piezoelectric properties (remnant polarization P_r = 22.5 μC/cm² and piezoelectric coefficient d₃₃ = 250 pC/N); however, the addition of Ta₂O₅ leads to an clear degradation in d₃₃ and P_r. Meanwhile, the addition of an appropriate Ta₂O₅ amount leads to an increase in the electro-strain, and the unipolar strain reaches 0.385% under 60 kV/cm for x = 0.003, together with a higher normalized strain (d₃₃^*=S_max/E_max) of 633 pm/V (x = 0.003). The enhanced strain behaviors can be attributed to the coexistence of the ferroelectric and relaxor states, and an excellent electrostriction coefficient Q₃₃ (Q₃₃ = S/P²) value of 0.038 m⁴C⁻² is obtained under 60 kV/cm for x = 0.003.     

Influence of Ta2O5 Interfacial Oxide Layer Thickness on Electronic Parameters of Al/Ta2O5/p-Si/Al Heterostructure

Silicon - We describe the impact of Ta2O5 interfacial oxide layer thickness (ranging from 100-350 nm) on electrical and structural properties of Al/Ta2O5/p-Si/Al Metal-Insulator-Semiconductor (MIS)...     

Hf6Ta2O17/Ta2O5 composite ceramic: A new eutectic system

Eutectic oxides are considered as the most promising candidates applied in extreme environment for long periods, and the pace of exploring new eutectic systems has never stopped. In the present work, Hf₆Ta₂O₁₇/Ta₂O₅ eutectic system is firstly prepared by the joint process of solvothermal method and spark plasma sintering (SPS). Eutectic liquid phase produced during the process of SPS fills the closed-pores and promotes the sintering process. Orthorhombic-Hf₆Ta₂O₁₇ and tetragonal-Ta₂O₅ of both eutectic and hypereutectic systems show single crystal characteristics and are combined by coherent interface instead of grain boundaries. The clean and flat interface also shows the characteristics of single crystal diffraction without impurities and amorphous phase. Based on the analysis of microstructure, the sintering mechanism is proposed, and the potential application of Hf₆Ta₂O₁₇/Ta₂O₅ eutectic system is analyzed.     

Evolution of Hot Corrosion Behavior of YSZ‐Ta2O5 Composites with Different YSZ/Ta2O5 Ratios

This study compares the hot corrosion performance of yttria‐stabilized zirconia (YSZ)‐Ta₂O₅ composite mixtures (TaYSZ) in the presence of molten mixture of Na₂SO₄ + V₂O₅ at 1100°C. The tested compositions vary from pure YSZ (0TaYSZ) to a Ta₂O₅‐dominating (70 wt% Ta₂O₅+ balance YSZ, 70TaYSZ) composite mixture with a gradual increase of Ta₂O₅. 50TaYSZ (50 wt% Ta₂O₅ + balance YSZ) sample forms a highly stable zirconium tantalum oxide. 50TaYSZ is more stable, both thermally and chemically in Na₂SO₄+V₂O₅ media at 1100°C, than other tested YSZ‐Ta₂O₅ (TaYSZ) composites, and shows a good hot corrosion resistance.     

The ability of Nb2O5 and Ta2O5 to generate active oxygen in contact with hydrogen peroxide

Amorphous and crystalline niobium(V) and tantalum(V) oxides were treated with hydrogen peroxide and studied by XRD, UV–vis, FTIR and ESR techniques to identify changes on their surface upon interaction with hydrogen peroxide. Differences between amorphous and crystalline materials in the interaction with H₂O₂ depending on the hydroxylation of the surface and the nature of OH groups were evident. The type of radical species formed on hydroxylated amorphous materials treated with H₂O₂ depended on the nature of metal oxide. It was proved that peroxo radical species formed in the interaction of H₂O₂ with amorphous Nb₂O₅ were the active intermediates in the oxidation of glycerol to glycolic acid with hydrogen peroxide. The radicals formed on amorphous Ta₂O₅ surface treated with hydrogen peroxide were poorly active in the oxidation of glycerol. Detailed study of the above mentioned radicals is in progress and will be a subject of a separate paper.     

Synthesis of Nb2O5 and Ta2O5 nanopowders by means of an endo-templating method

Finding efficient templates for the nanostructuring of materials is a key point. Here, the niobium (V) - and tantalum (V) oxide ceramics nanopowders have been synthesized by a hard-templating approach by using the tricalcium phosphate biomaterial (Ca₃(PO₄)₂.xH₂O) as template agent. The oxide ceramics were investigated by X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, nitrogen physisorption and Scanning Electron Microscopy (SEM). It was observed that the surface properties (specific surface areas, pore volumes) of the Nb₂O₅ and Ta₂O₅ powders were strongly dependent of the amount of the Ca₃(PO₄)₂.xH₂O template previously used in the preparation of the [oxide ceramics/template] composites. For instance, with a Ca₃(PO₄)₂.xH₂O/ceramic salt weight ratio ranging from 0 to 1, the specific surface areas of Nb₂O₅ and Ta₂O₅ were gradually enhanced of 48–166 m²/g and 5–84 m²/g, respectively. The pore volumes were increased as well. The use of the eco-friendly tricalcium phosphate material (Ca₃(PO₄)₂.xH₂O) as template in the hard-templating approach may be suitable and efficient in the aim of synthesizing materials with enhanced surface properties.     

Ta_2O_5掺杂Bi_2O_3–ZnO–Nb_2O_5陶瓷的晶体结构、结晶化学及介电性能

采用固相反应法制备Bi1.5ZnNb1.5–xTaxO7陶瓷,研究了不同掺杂量Ta2O5对Bi2O3–ZnO–Nb2O5陶瓷相结构、晶体化学特性和介电性能的影响。结果表明:当x≤0.1时,样品均保持单一的立方焦绿石结构(α–BZN)。通过对样品结晶化学计算发现,随着Ta2O5掺杂量的增加,晶格常数a逐渐减小,结晶化学参数键价和AV(O')[A4]增大,AV(O)[A2B2]减小,48f(O)坐标ξ增加。在组成样品晶体结构的多面体中,由6个48f(O)组成的八面体结构(BO6)逐渐变得扭曲,而6个48f(O)和2个8b(O')组成的六面体结构逐渐变得规则,向正立方体结构变化。室温下样品的介电常数和损耗随Ta2O5掺杂量的增加而减小,弛豫度逐渐减小。     

助剂和制备方法对V2O5/Al2O3催化性能的影响

用浸渍法制备了负载型MxOy-V2O5/Al2O3催化剂,同时考察了不同的制备方法对MoO3-V2O5/Al2O3催化剂的性能影响。用BET、H2-TPR、TPD平衡法等考察了催化剂的比表面积、氧化还原性能、表面氧脱附性能,结果表明,添加变价助剂Mo、Fe和Cr氧化物会增加供氧数目,提高α-蒎烯转化率。MoO3-V2O5/Al2O3催化剂表面O 2-和O-物种较多,活性也较好,桃金娘烯醛收率较高。MoO3-V2O5/Al2O3催化剂的制备方法影响其催化性能,表面化学改性法制备的催化剂表面具有较多O2-和O-物种,有利于催化剂的活性提高,α-蒎烯的转化率达88.9%,桃金娘烯醛的收率为79.1%。     

Sintering and properties of molybdenum-doped SrBi2Ta2O9 ceramics

The effects of molybdenum doping on the sintering, microstructure, dielectric properties, and ferroelectric properties of SrBi₂(Ta_1−xMo_x)O_9+y ceramics were investigated. The densification process of the molybdenum doped ceramics with x=0.025–0.1 can be shifted to a lower temperature range. When the degree of densification is nearly the same, the doped ceramics showed reduced dielectric constant as compared with the undoped ceramics. For the ceramics with relative density ⩾90%, the dielectric constant is 120–125 and 80–120 for the undoped and doped ceramics, and the dielectric loss tangent is below 2%. For nearly the same relative density, all the molybdenum-doped ceramics have significantly increased P_r and decreased E_C as compared with the undoped ceramics. There are optimum molybdenum content (x=0.025–0.05) and optimum sintering temperature (1100 °C) for maximum P_r and minimum E_C.     

Which phase of Ta2O5 being of the largest dielectric constant

As a promising dielectric material, tantalum pentoxide (Ta₂O₅) exhibits multi-phase co-existing under common fabrication conditions, so it is highly desired to predict theoretically which phase is of the largest dielectric constant. Considering that the specific operations and parameters employed in ab initio calculations may lead to considerably different lattice structure, we set the experimental lattice constants as the criteria to select the functional and parameters in density of functional theory and calculated the dielectric tensors of crystalline δ-, β-, L_SR-, B-, and Z-Ta₂O₅, showing that the dielectric constant is very sensitive to the lattice constants and δ-Ta₂O₅ possesses the largest dielectric constant, 375.1, which is about 10 times larger than those of the other four phases and the experimental measurement of common Ta₂O₅ samples with several phases co-existed, and furthermore, the dielectric constant of δ- and β-Ta₂O₅ could be enhanced to 1175.2 and 939.5, respectively, with the Ta atom replaced by Ti atom at a molar ratio of 7.14%, which is in qualitative agreement with the experimental observations of Ti-doped β-, L_SR-, and H-Ta₂O₅.