Nb2CTx MXene Derived Polymorphic Nb2O5

Previously, heat treatment was the only feasible route for tuning the crystal phases of niobium pentoxide (Nb₂O₅). With the use of Nb₂CT_x MXene precursors, the first case of phase tuning of Nb₂O₅ in the low-temperature hydrothermal synthesis using sulfuric acid regulating agents is presented. By varying the amount of the agent, four pure-phase Nb₂O₅ crystals and mixed phases in-between are obtained. The required amount is found to be related to the H-covered surface energy calculated based on density functional theory. Overall, MXene-derived B-phase Nb₂O₅ is of particular interest due to its exceptionally high capacities as lithium-ion battery anodes, which are three times higher than the routine synthesized one. Oxygen vacancies induced by crystallographic shear would be responsible for the extraordinary performance. The proposed phase tuning strategy encourages the prudent synthesis of difficult-to-obtain crystal phases.     

High-pressure phase research on Nb2O5

Experimental results indicate that the direct transitions from the H form to the T form and from the H form to the B form of Nb₂O₅ are possible under high pressures. Both highly pure and less pure reagents were used. The distinct TT form was obtained only when less pure reagents were used so that the TT form seems to be stabilised by means of trace impurities. Previously the TT form was indexed as having a pseudohexagonal unit cell. However, the present distinct TT form has a monoclinic unit cell,a=7.23₈Å,b=15.7₉Å,c=7.18₈Å,=119°5₉,V=711_.7(Å)³. Eight molecules are contained per cell. Probably only B, T and H have stable regions; the other polymorphs of Nb₂O₅ may be metastable forms or forms stabilised by impurities.     

球形Ta2O5/Nb2O5制备方法的研究

研究了用氨沉淀氟钽(或铌)酸溶液制备球形Ta2O5/Na2O5工艺.通过实验探讨了沉淀条件、溶液浓度、沉淀时间、焙烧温度等工艺参数的最佳组合.结果表明,用氨沉淀氟钽(或铌)酸溶液制备球形的Ta2O5/Nb2O5,必须首先得到不规则的Ta(OH)5/Nb(OH)5.要得到不规则Ta(OH)5/Nb(OH)5,反应时搅拌强度要大,搅拌速率应控制在800～1 200 r/min,反应结束后继续搅拌10～20 min,终点pH值控制为8.5;氟钽(或铌)酸溶液浓度为60～80 g/L沉淀10 min,浓度为120～140 g/L沉淀15 min,之后可得到不规则Ta(OH)5/Nb(OH)5.再在800～850℃,焙烧6 h可得到球形Ta2O5/Nb2O5.     

Nb_2O_5对碲铅铋铌系玻璃结构和性能的影响

采用熔融法制备不同Nb2O5含量的TeO2-PbO-Bi2O3-Nb2O5系玻璃粉,研究了Nb2O5的加入量对TeO2-PbO-Bi2O3-Nb2O5系玻璃热膨胀系数、软化温度和热稳定性的影响。利用傅里叶变换红外光谱仪检测玻璃粉的结构,通过热机械分析仪和综合热分析分别测试玻璃的膨胀系数和析晶温度,采用场发射扫描电镜观察太阳能电池Ag/Si接触界面。结果表明,随着Nb2O5含量的增加,玻璃的热膨胀系数和软化温度逐渐降低,玻璃化温度和析晶温度逐渐升高,玻璃的热稳定性逐渐增强。添加Nb2O5的玻璃粉所对应的太阳能电池正面电极中,Ag/Si接触界面存在大量的纳米银粒子,这将更有利于晶硅太阳能电池的光电子传导。     

Sintering behaviour of lithium ferrites containing Nb2O5 and V2O5

Lithium ferrite toroids with various compositions and with various amounts of Nb₂O₅ or V₂O₅, have been prepared by a powder compacting method, and their sintering behaviours, microstructures and weight-loss characteristics have been investigated. The rate of sintering is higher in an Fe₂O₃-deficient lithium ferrite than in an Fe₂O₃-excess lithium ferrite due to the presence of excess oxygen vacancy in the Fe₂O₃-deficient lithium ferrite during sintering. The presence Of LiNbO₃ or LiVO₃, which is formed by Nb₂O₅ or V₂O₅, on the surface of lithium ferrite grains causes an increase in oxygen activity of the lithium ferrite and a decrease in the rate Of lithium evaporation during sintering, resulting in a strong enhancement in the sintering rate. The enhancing effect of V₂O₅ in the sintering Of lithium ferrite is stronger than that of Nb₂O₅ due to the possible formation of liquid V₂O, before the formation of LiVO₃.     

Nb2O5掺杂对TiO2陶瓷性能的影响

在Nb2O5含量x为0.1～1.5%的范围内,研究了Nb2O5掺杂对TiO2压敏陶瓷电性能的影响.发现x＝0.7%的样品显示出最低的压敏电压(Eb=8.57V/mm )以及最高的相对介电常数2.385×104.分析认为Nb2O5掺杂的实质是Nb5 固溶于 TiO2中取代Ti4 使晶粒半导化,但掺杂量受晶格畸变作用有一定限制.     

Oxides formed between ZrO2 and Nb2O5

High-purity monoclinic ZrO₂ and monoclinic Nb₂O₅ powder samples were mixed in varying ratios, and heated at 1300°C for 24 h before furnace cooling. X-ray diffraction analysis showed that two compounds, Nb₂O₅-6ZrO₂ and Nb₂O₅·8ZrO₂ (or (Zr, Nb)₈O₁₇ and (Zr, Nb)₁₀O₂₁), were formed. Some of the reflections from the two compounds were overlapped and interfered with those from the zirconium oxide, especially the tetragonal ZrO₂. A thermodynamic analysis was used to demonstrate that it is possible to have ZrO₂ as well as Nb₂O₅ formed on Zr-Nb alloys in an oxidizing environment. The relevance of these results (experimental and calculated) to the corrosion of a Zr-Nb alloy in high temperature aqueous environments is discussed. It is suggested that the incorporation of niobium into the oxide during the corrosion of Zr-Nb alloys could be by the formation of compounds such as (Zr, Nb)₈O₁₇ and (Zr, Nb)₁₀O₂₁. Also, the tetragonal ZrO₂, which has been found to be a barrier layer oxide, could, in fact, be either of the ternary compounds Nb₂O₅·6ZrO₂ and Nb₂O₅·8ZrO₂ both of which are orthorhombic with lattice parameters very close to those of the tetragonal ZrO₂.     

Mechanical properties of Nb2O5 and Ta2O5 prepared by different procedures

We have studied the mechanical properties of niobium pentoxide and tantalum pentoxide ceramics prepared by a conventional ceramic processing technique and by exposure to high-intensity light (HIL). The results demonstrate that, after HIL exposure in an optical furnace, the niobium pentoxide and tantalum pentoxide ceramics possess enhanced microhardness and improved mechanical properties (strength, fracture toughness, and brittle microstrength) owing to the formation of fractal micro- and nanostructures. With increasing exposure intensity, the strength of the Nb₂O₅ and Ta₂O₅ ceramics increases.     

Nb2O5纳米纤维的物相对光催化性能的影响

采用静电纺丝技术在不同退火条件下制备不同物相的Nb2O5纳米纤维,研究了产物的物相对光催化染料降解性能的影响。光吸收结果表明,伪六方相Nb2O5纳米纤维的光学带隙为2.77eV,单斜相为主的混合相Nb2O5纳米纤维带隙为2.51eV。在混合相材料中,光学带隙随着单斜相成分的增加而改变。光催化结果表明,伪六方相Nb2O5纳米纤维具有最高的光催化活性,其效率k值可达-0.025min-1。混合相纳米纤维中,单斜相的增加会引起催化活性的变化,其变化趋势与带隙相符。物相对Nb2O5纳米纤维光催化活性的影响可归结于带隙变化引起的入射光吸收效率和电子空穴对氧化能力的变化。     

去除Ta2O5/Nb2O5中杂质S的工艺研究

从理论和实际应用方面,研究了去除Ta2O5/Nb2O5中杂质S的方法.通过对制取高纯Ta2O5和Nb2O5的中间产品高纯Ta(OH)5/Nb(OH)3进行过氧化处理,改变Ta,Nb,S等元素在物料中的存在方式,增大了含S杂质的溶解性,降低了物料对含S离子的吸附能力及硫酸盐的分解温度,通过洗涤、焙烧达到有效去除产品中杂质元素S的目的.该方法可在不影响Ta2O5/Nb2O5产品质量的情况下,使杂质S降低到0.0001%以下.     

TiO2- and Nb2O5-based photocatalytic composites

We have studied the influence of Nb content (0.35–60 wt %) and heat treatment on the phase composition, texture, and photocatalytic activity (PCA) of composites based on titanium(IV) and niobium(V) oxides and obtained materials that possess PCA under illumination at λ ≥ 900 nm.     

Nb2O5-CoO-La2O3复合掺杂的BaTiO3基粉体改性研究

采用铌、钴、镧的金属有机盐(柠檬酸-EDTA复合螯合前驱液)掺杂法实现对氧化硅掺杂的纳米晶BaTiO3粉体的掺杂改性.实验结果表明:随着Nb、Co、La掺量的增加以及Nb/C0比的增大,陶瓷烧结体的烧成收缩以及密度增加,晶粒尺寸减小.随着Nb/Co比的增大,材料的铁电弛豫特性增加.当Nb/Co=2时,随着La掺量的增加,材料的铁电弛豫特性增加.当Nb/Co＞2时,La掺量对材料的介电温度特性影响不大.当La掺量一定时随着Nb、Co复合掺量的增加,材料的铁电弛豫特性明显增强.烧结温度的升高,使杂质容易固溶进入BT中,固溶量的增大,使材料的铁电弛豫性能增加.     

Bi2O3掺杂对Nb2O5-TiO2电容-压敏双功能陶瓷的影响

研究了Bi2O3掺杂对Nb2O5-TiO2电容压敏双功能陶瓷材料的烧结温度,相对介电常数,非线性,压敏电压的影响.实验发现,烧结温度为1200℃,Bi2O3掺杂量为0.2%时,非线性系数α高达6.6148;Bi2O3掺杂量为1.0%时,相对介电常数εr高达1.3733×104.烧结温度在1450℃时,压敏电压最低,Eb=1.979 V·mm-1.     

Nonlinear high-field conductivity in Nb2O5 thin films

The conduction mechanism in thin amorphous films of Nb₂O₅ with Nb counterelectrodes has been investigated for undoped films and for films doped with Nb by a low energy implantation-diffusion process occurring during sputtering of the Nb counterelectrodes. For films with evaporated electrodes, the conductance G versus the applied voltage V showed three regions: (a) an ohmic region at low fields up to a field E₁ = 1.33 × 10⁵ V/cm; (b) a nonlinear dependence of the form I∝V^m, where m = 3.8, at intermediate fields; and (c) for fields E>1.2×10⁶ V/cm an exponential dependence of G on V corresponding to the Poole-Frenkel field-assisted emission mechanism. Films with sputtered Nb electrodes exhibited ohmic regions up to a field E₁ = 4×10⁴ V/cm (where E₁ decreases with increasing sputtering voltage), a relation G ∞ V⁴ at intermediate fields up to E = 8.3 × 10⁴ V/cm, and then an exponential dependence of G and V corresponding to the Poole-type emission mechanism. The conductance and capacitance increased in films with sputtered Nb electrodes and were found to increase, while the thermal activation energy decreased, with increasing sputtering voltage. The above results indicate an increase of coulombic donor sites in Nb₂O₅ films as a consequence of the Nb implantation-diffusion process.