Broadband spectroscopy of the complex conductivity of polycrystalline yttria-stabilized zirconia

Broadband conductivity spectra from 100 to 10¹⁴ Hz (100 THz) were acquired for yttria-stabilized zirconia (10 mol% Y₂O₃-doped ZrO₂, 10YSZ) to quantify contributions from conduction due to the electrolyte-electrode interface, grain boundaries, universal dielectric response (UDR), and optical phonons. The UDR contribution governed the intrinsic conductivity at all frequencies except specific frequencies in the terahertz range, where phonon contributions governed conductivity for both ceramics and single crystals. UDR parameters σ₀ and σ_dc increased with increasing temperature, resulting in increased microwave conductivity. The complex conductivity converged at frequencies of hundreds of gigahertz due to a decrease in the power-law constant, s, with increasing temperature. The optical phonon contribution to the total conductivity, due to an increase in the damping factor γ_1TO with increasing temperature, was small, while the phonon-mode frequency ω_1TO affected the microwave conductivity of 10YSZ.     

Hollow fibers of yttria-stabilized zirconia (8YSZ) prepared by calcination of electrospun composite fibers

8YSZ fibers were synthesized by calcination of PVP/zirconium oxychloride/yttrium nitrate composite fibers (PVP-Precursor) obtained by electrospinning. Scanning electron microscopy (SEM) indicated that the 8YSZ fibers are hollow and the gas released during organic binder decomposition resulted in the formation of hollow center in fibers. Proper controlling heating rate is necessary to the formation of hollow structure. Both X-ray diffraction (XRD) and Raman spectroscopy analysis indicated that the 8YSZ fibers have crystal structure of tetragonal phase. The hollow structure should make the fibers to have a higher resistance to sintering than solid fibers at elevated temperature. This result has important applications in catalytic combustion.     

Preparation and characterization of yttria-stabilized zirconia nanotubes

Yttria-stabilized zirconia (YSZ) nanotubes were synthesized by the sol–gel method using porous anodic alumina oxide (AAO) as the templates. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersion X-ray (EDX) spectrum and selected area electron diffraction (SAED) techniques were used to characterize the morphology and crystalline structure of the prepared YSZ nanotubes. The length and the diameter of the YSZ nanotubes are 50 μm and 200 nm, respectively, which are in good agreement with the dimensions of the template pores, while the wall thickness of the nanotubes depends on the impregnation time. XRD and SAED measurements indicate that the obtained YSZ nanotubes after sintering at 1073 K possess a polycrystalline structure and a cubic crystal phase. Brunauer–Emmett–Teller (BET) measurement shows that the YSZ nanotubes have a surface specific area of around 40.5 m² g⁻¹ that is higher than that corresponding to the YSZ nanopowders.     

Enhancement of the crystalline quality of reactively sputtered yttria-stabilized zirconia by oxidation of the metallic target surface

Yttria-stabilized zirconia (YSZ) thin films were fabricated on glass substrates by direct current magnetron reactive sputtering. We found out that the crystalline quality of the YSZ film was improved by an oxidation process of the metallic target surface prior to the sputtering deposition process. It is speculated that, at the initial stage of the sputtering, the sputtered particles from the oxidized target surface form a layer with higher degree of crystallization on the substrate, compared with those particles from the metallic target surface. This crystallized layer can enhance the crystallization of the film deposited subsequently. Other sputtering conditions such as sputtering pressure, oxygen flow rate, substrate temperature, and Y₂O₃ content in the film were investigated, for optimization of the crystalline quality of the deposited YSZ film.     

The effect of deposition parameters on the properties of yttria-stabilized zirconia thin films

Yttria-stabilized zirconia (YSZ) films were deposited by RF magnetron sputtering in order to examine the effects of sputtering conditions on the properties of the resulting thin-films. X-ray diffraction (XRD), Rutherford backscattering spectroscopy (RBS) and scanning electron microscopy (SEM) were used to characterize the films. Additionally, films were deposited on alumina bars to examine the effect of the coatings on the strength of a brittle substrate. RBS analysis indicated that the ratio of oxygen to zirconium in the films varied from 1.84 to 2.10. XRD showed that there was a wide variation in the amount of monoclinic and tetragonal phases that appeared to be related to the O:Zr ratio. Despite these variations, there was no significant difference found in flexural strength found among the groups of alumina bars that were coated with YSZ. The likely cause is the columnar grain morphology of the deposited thin-films, which does not allow strengthening mechanisms to become operative.     

Microstructural evolution and magnetic properties of pressureless-sintered nanosized iron prepared by a facile combustion-based route

High-activity iron nanopowders were prepared through a facile combustion-based route, combining solution combustion synthesis and hydrogen reduction. The as-synthesized iron nanopowders were densified by pressureless sintering. The densification behavior, microstructure, mechanical properties and magnetic properties of the iron bulk sintered at different temperatures were studied in detail. At a low sintering temperature of 700 °C, the relative density of the sintered iron reaches 97.3%, because the iron nanopowders exhibit a low sintering activation energy of 123 KJ/mol. The iron bulk sintered at 700 °C exhibits relatively regular equiaxed grains with an average grain size of 0.45 μm, and has a maximum tensile strength of 510.1 MPa, a high microhardness of 201.9 HV, and a saturation induction of 1.75 T. As the sintering temperature increases, the grain size and magnetic properties of the sintered iron enhance, while the mechanical strength decreases. For the sintered iron prepared at 1300 °C with the average grain size ~ 80.9 μm, the saturation induction value reaches 1.78 T and the tensile strength is 334.9 MPa.     

Distribution and structures of nanopores in YSZ-TBC deposited by EB-PVD

Distribution and arrangement of nanopores in an YSZ (7 wt% Y₂O₃–ZrO₂)-thermal barrier coating (TBC) deposited by an electron beam-physical vapor deposition (EB-PVD) have been investigated by means of transmission electron microscopy. The YSZ-TBC deposited by the EB-PVD showed a typical columnar structure normal to the bond coat surface on the substrate. It has been generally believed that one column is a single crystal and grows continuously from the substrate. In the present study, however, it was found that each column consisted of a number of subcolumns with different misorientations and contained nanopores at the subcolumn boundaries. In addition to the nanopores at the subcolumn boundaries, nanopores with smaller size were observed within subcolumns, and were arranged periodically perpendicular to the growth direction of the subcolumns. Such arrangement and distribution of nanopores may be due to the misorientation of YSZ plate-like grains in the formation and coalescence processes of the YSZ subcolumns.     

The microstructure and mechanical properties of yttria-stabilized zirconia prepared by arc-melting

The microstructure of ZrO₂-Y₂O₃ alloys prepared by arc-melting was examined mainly by electron microscopy. It was found that the microstructure changed markedly with yttria content between 0 and 8·7 mol%. Pure zirconia was a single monoclinic phase, while ZrO₂-8·7 mol% Y₂O₃ alloy was single cubic phase as expected from ZrO₂-Y₂O₃ phase diagram. Tetragonal phase was found in alloys with 1 to 6 mol% Y₂O₃ together with monoclinic or cubic phase. The tetragonal phase found in present alloys normally had a lenticular shape with a length 1 to 5m and a width 0.1 to 0.3m, which is much larger than that formed by annealing. The phase with a herring-bone appearance was found in alloys with Y₂O₃ between 2 and 3 mol%, which was recognized to be a metastable rhombohedral phase. The structure of the present alloys is likely to be formed by martensitic or bainitic transformation during fairly rapid cooling from the melt temperature. The change in hardness and toughness with yttria content of the alloys is discussed on the basis of microstructural observations.     

Distribution and structures of nanopores in YSZ-TBC deposited by EB-PVD

Distribution and arrangement of nanopores in an YSZ (7 wt% Y₂O₃–ZrO₂)-thermal barrier coating (TBC) deposited by an electron beam-physical vapor deposition (EB-PVD) have been investigated by means of transmission electron microscopy. The YSZ-TBC deposited by the EB-PVD showed a typical columnar structure normal to the bond coat surface on the substrate. It has been generally believed that one column is a single crystal and grows continuously from the substrate. In the present study, however, it was found that each column consisted of a number of subcolumns with different misorientations and contained nanopores at the subcolumn boundaries. In addition to the nanopores at the subcolumn boundaries, nanopores with smaller size were observed within subcolumns, and were arranged periodically perpendicular to the growth direction of the subcolumns. Such arrangement and distribution of nanopores may be due to the misorientation of YSZ plate-like grains in the formation and coalescence processes of the YSZ subcolumns.     

电泳沉积制备氧化钇稳定的二氧化锆薄膜

采用恒压电泳沉积方法在Ni-YSZ(氧化钇稳定的氧化锆)阳极基体上制备YSZ电解质膜,研究了悬浮体系YSZ含量、外加电压、沉积时间对电泳过程及YSZ膜层质量的影响,结果表明,YSZ含量为20 g/L,沉积电压为10 V,沉积时间5 min时,恒压电泳一次即可得到均匀致密的YSZ膜:膜层与基体结合紧密,厚度约为10 μm.     

Photocatalytic studies of antimonate compounds prepared by a self-combustion route

Antimonates compounds with 1Ca:1Sb and 2Ca:1Sb:1Al compositions were synthesized by a self-combustion method. For the 1Ca:1Sb composition, a calcination at 1573 K led to a pure Ca₂Sb₂O₇ weberite phase, whose structure was determined using the Rietveld method. In the case of the 2Ca:1Sb:1Al composition, a pure phase was achieved at 1073 K, and the use of higher calcination temperatures led to a mixture of phases. Some of the products (1Ca:1Sb (873 K), 2Ca:1Sb:1Al (1073 K) and Ca₂Sb₂O₇ (1573 K)) were tested as photocatalysts for the methyl orange degradation. The results clearly demonstrated that Ca₂Sb₂O₇ is the catalyst exhibiting the best results for the MO photocatalytic degradation. This fact was interpreted as due to a predominant role of structural features on the photocatalytic activity of the prepared compounds.     

CuS nanoflowers prepared by a polyol route and their photocatalytic property

CuS nanoflowers with a specific surface area of 18.8 m²/g were prepared through a rapid polyol route at 140 °C for 90 min, and characterized by XRD, SEM, UV-vis spectrum and BET surface area. The formation of CuS nanoflowers is proposed to experience an aggregation and growth process. The photocatalytic activity of CuS nanoflowers was investigated by decomposing Rhodamine B at atmosphere and the result shows that the photocatalytic activity under halogen lamp irradiation is comparable to that of Degussa P25 TiO₂.     

Gas sensing performance of nanocrystalline ZnO prepared by a simple route

The nanocrystalline powders of pure and Al³⁺-doped ZnO with hexagonal structure were prepared by a simple hydrothermal decomposition route. The structure and crystal phase of the powders were characterized by X-ray diffraction (XRD) and the microstructure by transmission electron microscopy (TEM). All the compositions exhibited a single phase, suggesting a formation of solid solution between Al₂O₃ and ZnO. DC electrical properties of the prepared nanoparticles were studied by DC conductivity measurements. The indirect heating structure sensors based on pure and doped ZnO as sensitive materials were fabricated on an alumna tube with Au electrodes. Gas-sensing properties of the sensor elements were measured as a function of concentration of dopant, operating temperature and concentrations of the test gases. The pure ZnO exhibited high response to NH₃ gas at an operating temperature of 200 °C. Doping of ZnO with Al³⁺ increased its response towards NH₃ and the Al³⁺-doped ZnO (3.0 wt% Al₂O₃) showed the maximum response at 175 °C. The selectivity of the sensor elements for NH₃ against different reducing gases like LPG, H₂S and H₂ was studied. The results on response and recovery time were also discussed.     

Morphology and conductivity of polyaniline sub-micron fibers prepared by electrospinning

Sub-micron fibers of pure polyaniline (PANI) doped with sulfuric acid or hydrochloric acid were prepared by electrospinning PANI with suitable molecular weight dissolved in hot sulfuric acid. A modified electrospinning setup was employed with a coagulation bath as a collector, where dilute sulfuric acid was used as coagulation bath. The factors influencing the morphology and conductivity of the synthesized PANI fibers were investigated, including the concentration of dilute H₂SO₄ solution in the coagulation bath, the doped PANI concentration in H₂SO₄ solution, the type of doping acid and the voltage applied to the solution. The morphologies of doped PANI fibers were characterized by scanning electron microscope (SEM). The structure of the resulting fibers was analyzed by Fourier transform infrared spectroscopy and UV–vis spectrometer. The conductivity of PANI fibers were characterized by I–V characteristics. Homogeneous PANI fibers with a diameter of 370 nm and a high conductivity of 52.9 S/cm were prepared. The possible mechanisms of different morphology formation and conductivity of PANI fibers were also discussed.     

水热合成法制备杯状氧化锌微晶及其光学性质研究

以Zn(CH3COO)2·2H2O为源反应物,采用水热合成反应法成功地制备了杯状的氧化锌微晶粉体材料.X射线衍射(XRD)谱的结果表明获得了典型的六方结构晶体.扫描电子显微镜(SEM)照片观测到杯状的氧化锌微晶,并且单个微晶互相结合形成对称结构.实验发现,水热时间影响着晶体的形貌,对其结构变化机制进行了探讨.同时,通过...     

Incorporation of cobalt and nickel metal nano-particles in nano-grain zirconia film matrix by solution route

Precursor solutions of cobalt/nickel incorporated nano-grain zirconia films were prepared from aquo-organic solutions of zirconium oxychloride octahydrate and corresponding transition metal nitrate. The films were deposited onto silica glass substrate by the dipping technique. Annealing was made at different temperatures from 450°C to 1200°C ± 5°C in air atmosphere. The range of thickness of the films baked at 450°C was 1800–1870 å. For cobalt system Co₃O₄ was formed initially at 450°C which gradually transformed to alpha cobalt and next to cubic cobalt along with a non-stoichiometric compound (Zr_0.71Co_0.23O_0.06) with increasing annealing temperature. On the other hand, for nickel system nickel metal of nano-size was observed in the nano-grain zirconia film matrix at 450°C. By increasing annealing temperature to 1200°C, a compound, ZrNi₄O, was formed which was found to be stable for ～ 30 days.     

Tubular-shaped nanocarbons prepared from polyaniline synthesized by a self-assembly process and their electrical conductivity

A tubular-shaped polyaniline less than 5 microm in length and 170 nm in outer diameter was synthesized by a self-assembly process using D-camphorsulfonic acid as a dopant. A tubular-shaped nanocarbon was prepared from the tubular-shaped polyaniline by means of pyrolysis at 1000 degrees C in argon gas. The structural and electrical properties of the resultant tubular-shaped nanocarbons were investigated using Raman scattering spectrum, X-ray diffraction measurements, scanning and transmission electron microscopes, and a low resistivity meter. The tubular-shaped nanocarbons are very short in length and are an amorphous state. The short length and amorphous tubular-shaped nanocarbon were crystallized to some extent by heat-treatment at 2600 degrees C. The tubular-shaped nanocarbons mentioned in this work are appropriate for mass production, compared to the well-known multi-walled carbon nanotubes. The electrical conductively of the tubular-shaped polyaniline was remarkably improved by the carbonization and was enhanced by the heat-treatment.     

Photoluminescence of nanocrystalline SrMgF4 prepared by a solution chemical route

SrMgF₄ was prepared by precipitation in aqueous solution. Alkaline earth metal acetates and ammonium fluoride were used as precursors. After drying and annealing the samples at different temperatures and times, single phase SrMgF₄ was obtained. By varying the annealing conditions, the mean crystallite size could be adjusted. Furthermore, the thermally treated samples displayed UV-excited intensive broad band luminescence in the visible region. The emissions colour and intensity can be adjusted by the tempering conditions. X-Ray diffraction, TEM-microscopy, fluorescence and IR-spectroscopy were used for analysis.     

Microstructures of in situ Al/TiB2 MMCs prepared by a casting route

In situ Al/TiB₂ metal matrix composites (MMCs) have been successfully produced by Salt-Metal reactions. This is a novel low-cost reactive approach, which involves adding Ti and B bearing salts to molten Al. The reactions between the salts lead to the formation of the reinforcing TiB₂ particles in the Al matrix. The in situ formed TiB₂ particles are very fine (below 1 m in size). Strings and clusters of particle agglomerates are distinct microstructural features of all the composites with pure Al as the matrix. The effects of processing parameters on the kinetics of TiB₂ formation and on the final microstructures are studied in detail. Besides, efforts are made to improve the distribution of TiB₂ particles in the Al matrix by means of chemical additions; it is found that a homogeneous distribution is obtained by using a eutectic Al-Si alloy as the matrix material.