Effect of dopant concentration on electrical conductivity in the Sc2O3-ZrO2 system

Electrical conductivity measurements have been made as a function of dopant concentration (4 to 8 mol% Sc₂O₃) in the scandia-zirconia system, All the compositions studied had a tetragonal structure. The hombohedral phase was present only in samples prepared from mechanical mixtures of Sc₂O₃ and ZrO₂. In specimens prepared by coprecipitation, no phase lines were observed and the monoclinic zirconia (m-ZrO₂) phase was present for only Sc₂O₃ contents 5 mol %. The conductivity of Sc₂O₃-ZrO₂ decreased continuously with time up to 300 h anneal time between 700 and 1000° C. X-ray diffraction of coprecipated specimens of 7.8 mol % Sc₂O₃-ZrO₂ composition annealed at 1000° C (28 days), 750° C (42 days) or 460° C (189 days) did not reveal any changes to account for this. However, transmission electron microscopy showed that changes associated with the formation of very fine precipitates had occurred. The activation energy for conduction in the low-temperature region decreased monotonically with decrease in the scandia content. Jumps in the conductivity curves and hysterisis effects were observed in specimens containing m-ZrO₂.     

Sc2O3-Y2O3-ZrO2陶瓷材料热物理性能

采用固相合成法制备了6.3%Sc_2O_3-1.3%Y2O3-92.4%ZrO_2(摩尔分数)陶瓷材料。分别利用X射线衍射、示差扫描量热法、高温热膨胀仪和激光导热法对陶瓷材料的物相组成、高温相稳定性、热膨胀系数和热扩散等性能进行了表征。结果表明,经1600℃烧结6h,该陶瓷材料由单一的立方相结构组成,具有良好的高温相稳定性,热导率低于传统的6~8YSZ,是一种良好的热障涂层候选材料。     

Electrical conductivity and defect structure of CeO2-ZrO2 mixed oxide

The electrical conductivity of CeO₂-ZrO₂ system was measured as functions of the temperature and oxygen partial pressure and of the composition. The ionic conduction was prevailing in the ZrO₂ rich phase due to the increase of ionic defect concentration via homovalent doping effect. The enhancement of n-type electronic conductivity was observed in intermediate and CeO₂ rich phase compared with pure CeO₂, which originated either from homovalent doping effect or increase of electronic mobility due to the change of transport mechanism.     

Structure and impedance of ZrO2 doped with Sc2O3 and CeO2

Scandia and ceria doped zirconia samples, with 10 mol% Sc₂O₃ and different content of CeO₂, were synthesized and characterized. The XRD results depict that the sintered samples have a cubic phase structure. However, Raman spectra show that besides the main cubic phase, a secondary phase is also present in the sintered samples. The addition of CeO₂ can raise the content of the cubic phase, but the minor meta-stable tetragonal phase (t′-phase) exists even at the CeO₂ content as high as 10 mol%. The near-UV Raman spectra indicate that the deformed tetragonal structure predominates at the grain boundary. The addition of CeO₂ can reduce the impurity at grain boundary, and no impurity can be found by near-UV Raman spectroscopy at the grain boundary of the samples with high CeO₂ content. The impedance measurements show that with the increase of CeO₂ content, the impedance of grain boundary decreases and the bulk impedance increases. The low impedance of grain boundary can be attributed to the formation of a clean grain boundary upon CeO₂ doping, and the increase of the bulk impedance is due to the blocking effect of the large Ce(IV) ions.     

D.c. conductivity and hopping mechanism in Bi2O3-B2O3 glasses

The physical and transport properties of semiconducting glasses are highly interesting, providing useful information regarding the structure and conduction mechanism, respectively. The physical and transport properties such as density, number of ions per unit volume, hopping distance, polaron radius, d,c. conductivity and activation energy are reported. Similarly the hopping conduction mechanism is examined. The physical property (density) is used to determine the probable structure of the glass sample. The small polaron hopping model is applied to the glass system. The methods of examining the hopping conduction mechanism are discussed in the light of the small polaron model. The methods suggested by Holstein and by Sayer and Mansingh are applied to the determination of adiabatic or non-adiabatic hopping conduction. It was observed that in this system adiabatic hopping conduction is present.     

Subsolidus,high temperature phase relations in the systems Al2O3-Cr2O3-ZrO2, MgO-Cr2O3-ZrO2 and MgO-Al2O3-ZrO2

In the temperature range 1600 to 1900° C, the system A₂O₃-Cr₂O₃-ZrO₂ is characterized by the coexistence of ZrO₂ (unstablilized) and an (Al, Cr)₂O₃ solid solution series. In the systems MgO-Cr₂O₃-ZrO₂ and MgO-Al₂O₃-ZrO₂ a nearly stoichiometric spinel coexists with both stabilized and unstabilized ZrO₂. At temperatures above 1600°C a new ternary Mg-Al-Zr oxide becomes stable in the MgO-rich part of the MgO-Al₂O₃-ZrO₂ system.     

Electrical conductivity of Cr2O3-doped Y2O3-stabilized ZrO2

The electrical conductivity of Cr₂O₃-doped Y₂O₃-stabilized ZrO₂ (YSZ) has been studied as functions of composition, temperature and oxygen pressure. The specimens have been prepared by hot preoning of co precipitated oxides to yield >99.7% density. The Cr₂O₃ added above the solubility limit ( 0.7 mol %) precipitated as a secondary phase at the grain boundaries. The conductivity of Cr₂O₃-doped YSZ was almost independent of the oxygen pressure in the range 10¹⁸ to 10⁵ Pa, indicating a dominant ionic condition. The electronic conductivity of dopant CR₂O₃ would be hindered by the higher ionic conductivity in thep _O2 ranges studied. The conductivity and the activation energy for conduction decreased slightly with the addition of Cr₂O₃. These phenomena seemed to be caused by vacancy trapping or polarization at the grain boundaries with the Cr₂O₃ precipitates. The samples with 1 mol % Cr₂O₃ addred to zirconia containing various Y₂O₃ contents showed similar conduction behaviour to those without Cr₂O₃ addition; that is, the conductivity maxima are observed at around 8 mol % Y₂O₃ addition to zirconia, and the activation energies increased with tha Y₂O₃ addition.     

Effect of annealing on d.c. conductivity of V2O5-SnO-TeO2 glasses

The d.c. conductivity (σ) of V₂O₅-SnO-TeO₂ glasses prepared by the press-quenching method was studied at temperatures from room temperature (RT) to 473 K, and the effect of annealing on σ was investigated. The conductivity of 50V₂O₅·20SnO·30TeO₂ glass was determined to be 3.98×10⁻⁴ Scm⁻¹ at 473 K and was unchanged for annealing (6–48 h) at 493 K, lower than T_g = 501 K, while its density increased with annealing time. These glasses were found to be n-type semiconductors, and the conduction was confirmed to be due to adiabatic small polaron hopping for V₂O₅ ≧ 50 mol%, and non-adiabatic for V₂O₅ < 50 mol%. The activation energy for conduction, W, decreased with annealing time. Variations in oxygen molar volume of the glasses with annealing time inferred a change in glass structure, from loosely to closely packed, resulting in a decrease in vanadium ion spacing with annealing. This caused an increase in the polaron band width, producing a decrease in polaron hopping energy and W. The effect of annealing time on the density of 50V₂O₅·20SnO·30TeO₂ glass was explained adequately by Winter's formula.     

EDTA凝胶法制备Y2O3-ZrO2纳米粉

用乙二胺四乙酸 (EDTA)强的螯合作用 ,制得钇、锆稳定的配位化合物 ,经干燥 ,煅烧研磨后得到Y2 O3-ZrO2 纳米粉。本文研究了母液浓度 (C) ,络合比 (r) ,所处介质溶液的 pH值及煅烧温度 (T)和煅烧时间 (t)对Y2 O3-ZrO2 纳米粉的粒度和结构的影响。pH =5 ,r =2 ,T=60 0℃煅烧条件下制得的Y2 O3-ZrO2 纳米粉粉末粒径约为 10～ 2 0nm     

Si3N4-ZrO2 composites with small Al2O3 and Y2O3 additions prepared by HIP

Si₃N₄-ZrO₂ composites have been prepared by hot isostatic pressing at 1550 and 1750 °C, using both unstabilized ZrO₂ and ZrO₂ stabilized with 3 mol% Y₂O₃. The composites were formed with a zirconia addition of 0, 5, 10, 15 and 20 wt%, with respect to the silicon nitride, together with 0–4 wt% Al₂O₃ and 0–6 wt% Y₂O₃. Composites prepared at 1550 °C contained substantial amounts of unreacted -Si₃N₄, and full density was achieved only when 1 wt% Al₂O₃ or 4 wt % Y₂O₃ had been added. These materials were generally harder and more brittle than those densified at the higher temperature. When the ZrO₂ starting powder was stabilized by Y₂O₃, fully dense Si₃N₄-ZrO₂ composites could be prepared at 1750 °C even without other oxide additives. Densification at 1750 °C resulted in the highest fracture toughness values. Several groups of materials densified at 1750 °C showed a good combination of Vickers hardness (HV10) and indentation fracture toughness; around 1450 kg mm^–2 and 4.5 MPam^1/2, respectively. Examples of such materials were either Si₃N₄ formed with an addition of 2–6 wt% Y₂O₃ or Si₃N₄-ZrO₂ composites with a simultaneous addition of 2–6 wt%Y₂O₃ and 2–4 wt% Al₂O₃.     

Sc2O3掺杂ZrO2电解质材料的水热合成及其电性能

采用水热法合成了SSZ(Sc2O3掺杂的ZrO2)纳米粉体,经成型、烧结得到电解质烧结体.对样品晶相组成、微观形貌、结构进行了表征,并对烧结体进行了电性能分析.研究表明:所得粉体于1500℃下烧结4 h可形成致密度达97%的立方萤石结构烧结体,比传统固相方法和Sol-gel法低200℃以上.随烧结温度升高和Sc2O3含量的增加,SSZ样品的电导率先增加后降低,经1500℃烧结的8mol%Sc2O3-ZrO2样品在900℃时电导率为0.23 S/cm,800℃为0.13 S/cm,优于采用固相法、共沉淀法、Sol-gel等方法制备的同类材料.     

Ternary eutectics in the systems FeO-UO2-ZrO2 and Fe2O3-U3O8-ZrO2

The systems FeO-UO₂-ZrO₂ (in inert atmosphere) and Fe₂O₃-U₃O₈-ZrO₂ (in air) were studied. For the FeO-UO₂-ZrO₂ system, the eutectic temperature was found to be 1310°C, with the following component concentrations (mol %): 91.8 FeO, 3.8 UO₂, and 4.4 ZrO₂. For the Fe₂O₃-U₃O₈-ZrO₂ system, the eutectic temperature was found to be 1323°C, with the following component concentrations (mol %): 67.4 FeO_1.5, 30.5 UO_2.67, and 2.1 ZrO₂. The solubility limits of iron oxides in the phases based on UO₂(ZrO₂,FeO) and UO_2.67(ZrO₂,FeO_1.5) were determined.