Electrical properties of modified TZP(+TiO2,FeOx)

1 to 24 mol% TiO₂ and FeO_X were added to 3.2 mol% Y₂O₃ doped ZrO₂ (Z3Y) to obtain tetragonal zirconia polycrystals (TZP) with modified electronic properties. The materials were prepared by coprecipitation which allows to obtain fine, homogeneous and sinteractive powders. The solubility of TiO₂ in Z3Y can reach 24 mol%, while the maximum solubility of FeO_x is about 8 mol%. The impedance results show a decrease of the bulk and total conductivity of titania doped TZP with increasing titania concentration, while those of FeO_x doped TZP show only minor changes. The Hebb-Wagner polarization method was applied to evaluate the partial hole and electron conductivities. Three models are presented to interpret the polarization curves. 1.6 mol% FeO_x doped TZP has higher hole conductivity in air, while titania doped TZP has higher electronic conductivity at low oxygen partial pressures as compared to pure Z3Y. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11–18 Sept.1994     

High oxide ion conductivity in non-stoichiometric pyrochlores and fluorites in the ternary system ZrO2 - Gd2O3 - TiO2

The extents of the cubic fluorite and pyrochlore regions in the ternary oxide system ZrO₂-Gd₂O₃-TiO₂ have been determined experimentally. AC impedance measurements of single phase fluorite and pyrochlore compositions show high oxide ion conduction in compositions containing 20 mol% TiO₂. Resolution of the bulk and grain boundary contributions to the total conductivity show that the bulk ionic conductivity increases with Gd₂O₃ content up to the stoichiometric composition containing 33.33 mol% Gd₂O₃ and then decreases upon further addition of the aliovalent dopant. Trends in conductivity as a function of temperature and dopant density are discussed. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997.     

Horizontally networked carbon nanotubes grown on Au–Fe catalyst nanoparticles

Undoped and doped indium tin oxide (ITO) with different concentrations (2, 4, and 6 mol%) of different dopants (CuO, Cr₂O₃, and ZrO₂) were prepared in the nano-size scale (19–33 nm) using Pechini method. The thermal decomposition of the precursors was studied. The electrical properties of all the prepared samples were investigated. All the investigated systems have higher conductivity than that of ITO. For ITO doped with CuO, as the concentration of CuO increases, the conductivity increases. The highest conductivity was obtained for ITO doped with 6 mol% of CuO. For ITO doped with Cr₂O₃, as the concentration of Cr₂O₃ increases the conductivity increases and above 4 mol% Cr₂O₃ the conductivity decreases. For ITO doped with ZrO₂, as the ZrO₂ concentration increases, the conductivity increases up to 4 mol% of ZrO₂ and then decreases. The band gap was detected for all the investigated systems.     

Development of ceria-doped zirconia electrolytes with high toughness and ionic conductivity

Development of Y₂O₃ stabilized ZrO₂ electrolytes for solid oxide fuel cell with better mechanical properties was attempted. 3 mol% Y₂O₃ stabilized ZrO₂ doped with 3–15 mol% CeO₂ was investigated in the present work. The results reveal that the toughness and the bending strength of 3–6 mol% CeO₂ doped 3 mol% Y₂O₃–ZrO₂ are much higher than that of 8 mol% Y₂O₃–ZrO₂. The best ionic conductivity observed in 6 mol% ceria-doped 3 mol% Y₂O₃–ZrO₂ electrolyte is better than that of 8 mol% Y₂O₃–ZrO₂ at 800 °C, which indicates the possibility of developing ZrO₂-based electrolyte with enhanced toughness.     

The effect of alumina addition on the conductivity, microstructure and mechanical strength of zirconia — yttria electrolytes

The effect of alumina additions on the ionic conductivity and mechanical properties of 3 and 8 mol% Y₂O₃ - ZrO₂ compositions has been investigated. Such materials are of interest for use in fuel cells and other similar applications. Sintered specimens were characterised by XRD, SEM, impedance spectroscopy, four — probe DC conductivity and mechanical strength measurements. Alumina additions had no affect on the conductivity degradation behaviour at 1000 °C and the activation energy but resulted in an increase in the strength of 8 mol% Y₂O₃ - ZrO₂ composition by about 25%. However, a significant drop in the ionic conductivity well above what could be accounted for by the decrease in the volume fraction of the conducting phase, was observed.     

Impedance spectroscopy analysis of percolation in (yttria-stabilized zirconia)-yttria ceramic composites

(ZrO₂:8 mol% Y₂O₃)+m mol% Y₂O₃ ceramic composites with nominal yttria concentration varying from 0 to70 mol% (0–82.9 vol.%) were prepared by evaporation of a suspension of ZrO₂:8 mol% Y₂O₃ and Y₂O₃ in ethanol followed by pressing and sintering. The samples were analyzed by X-ray diffractometry and scanning electron microscopy for microstructural characterization. The electrical properties were studied by impedance spectroscopy (IS) allowing for the separation of the inter- and intragranular components of the electrical conductivity. The percolative behavior of these components was analyzed using the general effective media (GEM) equation and the percolation thresholds found were ∼28 vol.%. The results indicate that impedance spectroscopy provides useful information in addition to the dc techniques concerning the electrical characterization of composite materials.     

The optimisation of mixed conduction in potential S.O.F.C. anode materials

The success of the SOFC rests heavily on materials selection. In this work we address the optimisation of mixed conductivity in fluorite compounds in the search for new improved SOFC anodes based upon oxides. The mobility of electronic carriers is considered to be much higher than that of ionic defects, therefore, doping a good ionic conductor with a small concentration of reducible transition metal ions can form promising mixed conductors. Zirconia based mixed conductors were studied for two reasons. Firstly, zirconia, stabilised in the defect fluorite structure, exhibits a high level of ionic conductivity. Secondly it is the most common electrolyte material for a S.O.F.C. An anode based on zirconia would therefore be expected to offer a good physical compatibility with the electrolyte material and to exhibit a high ionic contribution to total conductivity. Work on the system ZrO₂-Nb₂O₅-Y₂O₃ showed that the influence of composition on conduction could be determined. This enabled the optimisation of both the electronic and ionic contributions to conduction by compositional selection. These factors were extended to explain conductivity behaviour observed in the comparable system ZrO₂-TiO₂-Y₂O₃. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Electrical characterization of nylon-6 composite nanofibers

The electrical characteristics of nylon-6 nanofibers incorporated with TiO₂ and Fe₃O₄ nanoparticles were investigated. The resultant nanofibers exhibited good incorporation of nanoparticles. The impregnated TiO₂ and Fe₃O₄ nanoparticles into the nylon-6 nanofibers were confirmed by high resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray (EDX) spectroscopy studies. The electrical conductivity of the nylon-6 incorporated with TiO₂ and Fe₃O₄ composite nanofibers were higher than that of the pristine nylon-6 nanofibers. The impregnation of TiO₂ and Fe₃O₄ nanoparticles significantly enhanced the electrical property of the composite nanofibers. These polymeric/nanoparticles composite nanofibers structure may open a new direction for future organic electronics.     

Bi2O3-Y2O3系高氧离子导体的离子电导和电子电导的研究

用交流电桥法研究了Bi₂O₃-Y₂O₃体系含22.5—30mol％Y₂O₃烧结试样在po₂值由1至10^-21atm范围内氧离子的电导率,实验证明该种材料的氧离子电导率比同温度下ZrO₂基固体电解质高若干倍;用这种材料作为固体电解质组成氧浓差电池,电池电动势和理论电动势的比值E/E₀等于1或接近1,说明这种材料几乎为纯氧离子导体,p型电子空穴导电性很小;用库伦滴定抽氧法测定了含Y₂O₃ 27.5mol％样品的电子导电特征氧分压,其值为lgp_e＇=(-767000/T)+655,电子导电性极小。可期望为一种新型氧离子导体材料。 关键词：     

Correlation between microstructure and degradation in conductivity for cubic Y2O3-doped ZrO2

The application of Yttria-stabilized Zirconia (YSZ) as solid electrolyte in high-temperature solid oxide fuel cells (SOFC) is well established. However, the strong decrease of the ionic conductivity in 8.5 mol% Y₂O₃-doped ZrO₂ at high temperature has not yet been clarified completely. To contribute to the understanding of the degradation process, transmission electron microscopy (TEM) was applied to analyze the microstructure in YSZ electrolyte substrates in as-sintered and aged material. Selected area electron diffraction and conventional TEM imaging were performed to investigate the evolution of different phases and phase transitions in YSZ. Grain boundary charging and the possible formation of a glassy phase at grain boundaries after aging were investigated using transmission electron holography and high-resolution TEM. The ionic conductivity was characterized by dc-conductivity measurements and impedance spectroscopy.     

Influence of sintering conditions on the electrical properties of 10% ZrO2–10% Y2O3–CeO2 (mol%)

Yttria–zirconia doped ceria, 10% ZrO₂–10% Y₂O₃–CeO₂ (mol%) (CZY) and 0.5 mol% alumina-doped CZY (CZYA), prepared through oxide mixture process, were sintered by isothermal sintering (IS) and two-step sintering (TSS) having as variable the temperature and soaking time. The electrical conductivity of sintered samples was investigated in the 250 to 600 °C temperature range by impedance spectroscopy in air atmosphere. The microstructure was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Alumina, as additive, improves the grain boundary conductivity of samples sintered at temperatures lower than 1500 °C. Concerning the sintering mode, two-step sintering (TSS) proved to be a good procedure to obtain CZYA samples with high electrical conductivity and density (> 95%) at relatively low sintering temperature and long soaking time.     

A Mössbauer study of the binary system LiNbO3-Fe2O3 in a broad concentration range

The binary system LiNbO₃-Fe₂O₃ has been studied by Mössbauer spectroscopy in the concentration range up to 24 mol% Fe₂O₃. For Fe₂O₃ concentrations up to 6 mol% iron is incorporated into the matrix of LiNbO₃ as Fe²⁺ and Fe³⁺, whereby the Fe²⁺ content decreases with increasing Fe₂O₃ concentration. Samples containing 9 and 11 mol% Fe₂O₃ showed only the Fe³⁺ valence state. There were no indications of any considerable formation of superparamagnetic Fe₂O₃ clusters up to 11 mol% Fe₂O₃. This is in agreement with the X-ray and DTA investigations of Takei and Katsumata (1982) who found that a solid solution exists between 0 and 11 mol% Fe₂O₃. Above 11 mol% the appearance of magnetically split sextets in the Mössbauer spectra indicated the formation of a second α-Fe₂O₃ phase. The isomer shift, which reflects the electron density at the Fe nucleus, measured as a function of the Fe₂O₃ concentration showed two steps, one at 6 mol% Fe₂O₃ (the turning point of the C_H axis parameter (Takei et al. 1982) and one at 11 mol% Fe₂O₃ (phase boundary). These steps were tentatively related to abrupt changes in the spontaneous polarization.     

Study on the mechanisms of photoinduced carriers separation and recombination for Fe-TiO2 photocatalysts

The iron(III)-ion doped TiO₂ (Fe³⁺-TiO₂) with different doping Fe³⁺ content were prepared via a sol-gel method. The as-prepared Fe³⁺-TiO₂ nanoparticles were investigated by means of surface photovoltage spectroscopy (SPS), field-induced surface photovoltage spectroscopy (FISPS), and the photoelectrochemical properties of Fe³⁺-TiO₂ catalysts with different Fe³⁺ content are performed by electrical impedance spectroscopy (EIS) as well as photocatalytic degradation of RhB are studied under illuminating. Based on the experiment results, the mechanism of photoinduced carriers separation and recombination of Fe³⁺-TiO₂ was revealed: that is, the Fe³⁺ captures the photoinduced electrons, inhibiting the recombination of photoinduced electron-hole pairs, this favors to the photocatalytic reaction at low doping concentration (Fe/Ti ≤ 0.03 mol%); while Fe³⁺ dopant content exceeds 0.03 mol%, Fe₂O₃ became the recombination centers of photoinduced electrons and holes because of that the interaction of Fe₂O₃ with TiO₂ leads to that the photoinduced electrons and holes of TiO₂ transfer to Fe₂O₃ and recombine quickly, which is unfavorable to the photocatalytic reaction.     

The role of iron ions on the structure and certain physical properties of PbO-As2O3 glasses

Various studies have been carried out viz optical absorption, infrared spectra, magnetic susceptibility, dielectric parameters (dielectric constant, loss and a.c. conductivity over a range of frequency and temperature; and breakdown strength) and differential thermal analysis of PbO-As₂O₃ glasses containing 0-1 mol% of Fe₂O₃. An anomaly has been observed in all the properties of these glasses when Fe₂O₃ concentration is about 0.25 mol%. The reasons for such anomaly have been identified and found that PbO-As₂O₃ glasses are more stable when Fe₂O₃ concentration is about 0.25 mol%.     

Enhanced optical activation of Er in Er-doped Al2O3 powders by Y codoping in a sol-gel method

Enhanced photoluminescence (PL) mechanism of Er³⁺-doped Al₂O₃ powders by Y³⁺ codoping at wavelength 1.53 μm has been investigated through PL measurements of 0.1 mol% Er³⁺- and 0-20 mol% Y³⁺-codoped Al₂O₃ powders prepared at a sintering temperature of 900 °C in a non-aqueous sol-gel method. PL intensity and lifetime of Er³⁺-Y³⁺-codoped Al₂O₃ powders composed of γ-(Al,Er,Y)₂O₃ and θ-(Al,Er,Y)₂O₃ phases increased with increasing Y³⁺-codoping concentration. The 10-20 mol% Y³⁺ codoping in 0.1 mol% Er³⁺-doped Al₂O₃ powders intensified the PL intensity by about 20 times, with a PL lifetime prolonged from 3.5 to 5.8 ms. A maximal increase of the optical activity of Er³⁺ in 0.1 mol% Er³⁺-Y³⁺-codoped Al₂O₃ powders about one order was achieved by 10-20 mol% Y³⁺ codoping. It is found that the improved PL properties for Er³⁺-Y³⁺-codoped Al₂O₃ powders are mainly attributed to enhanced optical activation of Er³⁺ in the Al₂O₃ by Y³⁺ codoping, and to the slightly increased radiative quantum efficiency of Er³⁺ in the Al₂O₃.     

Comparative in vitro cytotoxicity assessment of some manufacturednanoparticulate materials characterized by transmissionelectron microscopy

A range of manufactured nanoparticulate materials, including Ag, TiO₂, Fe₂O₃, Al₂O₃, ZrO₂, Si₃N₄, and a range of carbonaceous nanoparticulate materials: single-wall and multi-wall carbon nanotube aggregates and aggregated nanoparticles of black carbon, as well as commercial (mineral grade) chrysotile asbestos nanotube aggregates, have been rigorously characterized by transmission electron microscopy. These nanoparticulate materials ranged in primary particle sizes from roughly 3 to 150 nm (except for the nanotube materials with lengths in excess of 15 μm). Aggregate sizes ranged from 25 nm to 20 μm. Comparative cytotoxicological assessment of these nanomaterials was performed utilizing a murine (lung) macrophage cell line. Considering the chrysotile asbestos to be a positive control, and assigning it a relative cytotoxicity index of unity (1.0), relative cytotoxicity indexes were observed as follows at concentrations of 5 μg/ml: 1.6 and ∼ 0.4 for Ag and TiO₂, respectively; 0.7–0.9 for the Fe₂O₃, Al₂O₃ and ZrO₂, 0.4 for the Si₃N₄, 0.8 for the black carbon, and 0.9 to 1.1 for the carbon nanotube aggregate samples. Observations of a cytotoxic response, nearly identical to that for chrysotile asbestos, for multi-wall carbon nanotube aggregates which very closely resemble anthropogenic multi-wall carbon nanotubes in the environment, raise some concern for potential health effects, especially for long-term exposure.     

IR investigation of amorphous BaO-Fe2O3-B2O3 glasses prepared using 1 mol% TiO2

An infrared (IR) investigation of 35BaO-25Fe₂O₃-40B₂O₃glasses prepared by rapidly quenching the melts containing 1 mol% of TiO₂ at room temperature (25°C) is reported. The system is composed of BO₃ and BO₄ groups in the form of boroxol ring with tetraborate and diborate units forming the network structure. The iron oxide (Fe³⁺) possesses the positions in the network to occupying tetrahedral coordination sites. The TiO₂ (Ti⁴⁺) added by 1 mol% in the system probably maintain a tetrahedral (TiO₄) structure in the quenched glass, and thus induces growth of FeO₄ and BO₄ structural groups in the network. The network with latter groupings enhances the thermal stability as long as the sample does not crystallise significantly by given thermal treatments at temperatures upto 1000°C. A correlation with IR data has been made to account for the factors inhibiting the crystallisation of a system on addition of TiO₂.     

Effect of titanium ion substitution in the barium hexaferrite studied by M?ssbauer spectroscopy and X-ray diffraction

A series of M-type barium hexaferrite has been synthesized in a glass melt by partially substituting the Fe₂O₃ with TiO₂ for investigation of their structure. The glass melt has the basic composition (mol%): 40 BaO + 33 B₂O₃ + (27-x) Fe₂O₃ + x TiO₂ with x =?0, 3.6, 5.4 and 7.2 mol% TiO₂. The substituted ferrites were studied by means of X-ray diffraction, Mössbauer spectroscopy and vibration sample magnetometer. X-ray diffraction studies revealed that not all samples have a single ferritic phase, a small second phase corresponding to BaTi₆O₁₃ was also observed to form. The Mössbauer spectra changed from magnetically ordered (x =?0) to magnetically ordered with strong line broadening. Moreover, the broadening increases with TiO₂ content. The Mössbauer parameters suggested that Ti^4?+? occupies the 2a and 12k crystal sites, and the Ti^4?+? substitution on the 2b and 4f₂ site also occurs at high melt dopings. Therefore, coercivity and saturation magnetization decreased.     

Electrochemical transient investigations on the diffusion of minority charge carriers in YSZ doped by transition metal oxides

The voltage relaxation of galvanic cells with zirconia based electrolytes polarised between an inert Pt electrode and a Pt/air electrode is analysed to obtain the diffusion coefficients of holes and electrons. The hole diffusion coefficient can be reduced by replacing zirconium with guest ions of different size, e.g. Nb⁵⁺ and Ti⁴⁺. The TZP phase with 3 mol% Y₂O₃ of dopant has a higher hole diffusion coefficient than the CYZ phase doped with 8 mol% Y₂O₃. 1 and 3 mol% p-type MnO_1.5 doping increases the conductivity of holes in CYZ to a large extend, but does not influence the diffusivity. This indicates that the doping increases the hole conductivity through an increased concentration of holes. In the case of 10 and 15 mol% MnO_1.5 doped Z3Y, the electronic conductivity is dominant. The chemical diffusion coefficients which are related to the oxygen vacancies were determined by GITT. The results show that the chemical diffusion coefficient of oxygen vacancies is much larger than that for holes in zirconia.     

Comparative <Emphasis Type="Italic">in vitro</Emphasis> cytotoxicity assessment of some manufacturednanoparticulate materials characterized by transmissionelectron microscopy

A range of manufactured nanoparticulate materials, including Ag, TiO₂, Fe₂O₃, Al₂O₃, ZrO₂, Si₃N₄, and a range of carbonaceous nanoparticulate materials: single-wall and multi-wall carbon nanotube aggregates and aggregated nanoparticles of black carbon, as well as commercial (mineral grade) chrysotile asbestos nanotube aggregates, have been rigorously characterized by transmission electron microscopy. These nanoparticulate materials ranged in primary particle sizes from roughly 3 to 150 nm (except for the nanotube materials with lengths in excess of 15 μm). Aggregate sizes ranged from 25 nm to 20 μm. Comparative cytotoxicological assessment of these nanomaterials was performed utilizing a murine (lung) macrophage cell line. Considering the chrysotile asbestos to be a positive control, and assigning it a relative cytotoxicity index of unity (1.0), relative cytotoxicity indexes were observed as follows at concentrations of 5 μg/ml: 1.6 and ∼ 0.4 for Ag and TiO₂, respectively; 0.7–0.9 for the Fe₂O₃, Al₂O₃ and ZrO₂, 0.4 for the Si₃N₄, 0.8 for the black carbon, and 0.9 to 1.1 for the carbon nanotube aggregate samples. Observations of a cytotoxic response, nearly identical to that for chrysotile asbestos, for multi-wall carbon nanotube aggregates which very closely resemble anthropogenic multi-wall carbon nanotubes in the environment, raise some concern for potential health effects, especially for long-term exposure.This revised version was published online in August 2005 with a corrected issue number.