Understanding of redox behavior of Ni–YSZ cermets

The oxidation of Ni–YSZ cermet as well the reduction of re-oxidized Ni–YSZ cermet was investigated by using temperature-programmed oxidation (TPO), temperature-programmed reduction (TPR) and scanning electron microscope (SEM). The scanning electron microscope (SEM) photographs and temperature-programmed reduction (TPR) profiles indicated that the sintering of smaller nickel oxide crystallites to larger aggregates occurred concurrently with the formation of smaller nickel oxide crystallites from the oxidation of nickel at 800 °C, and the sintering of smaller nickel oxide crystallites at 600 °C was slower than that at 800 °C. The SEM results showed that each Ni particle was separated into a lot of smaller NiO particles during oxidation. The TPO profiles showed that two kinds of nickel particles exist in the anode reduced at 800 and 600 °C, one with high activity towards oxidation for the nickel crystallites directly from reduction, and another one with low activity towards oxidation for the sintered nickel particles. The Ni–YSZ anodes reduced at higher temperature showed higher re-oxidation temperature than the one reduced at lower temperature because of the accelerated passivating and sintering of the smaller nickel particles at higher temperature. The re-oxidation profiles were almost unchanged during redox cycling at 600 °C, whereas the re-oxidation peak temperature decreased during redox cycling at 800 °C, indicating that the primary nickel grains split to smaller ones upon cyclic reduction at higher temperature.     

单晶YSZ的Xe+离子辐照效应研究

 200keV Xe⁺离子辐照使单晶YSZ由无色透明变成紫色透明，结果表明，能量为200keV，注量为1×10¹⁷cm^-22的Xe⁺离子辐照YSZ单晶产生的损伤高达350dpa，在损伤区产生高密度的缺陷，但仍然没有发生非晶化转变。吸收光谱测试结果表明，产生吸收带的注量阈值大约为10¹⁶cm^-2。注量为1×10¹⁶cm^-2和1×10¹⁷cm^-2的样品，吸收带峰值分别位于522nm和497nm。光吸收带可能与Zr阳离子最近邻的氧空位捕获电子形成的F型色心和Y阳离子近邻的氧离子捕获空穴形成的V型色心有关。     

用MOCVD法在YSZ衬底上制备YBCO膜

用低压ＭＯＣＶＤ多源法在单晶ＹＳＺ和具有双轴取向ＩＢＡＤＹＳＺ的金属基带上沉积了ＹＢＣＯ膜,它们的Ｊｃ（７７．３Ｋ,０Ｔ）分别为～２×１０６Ａ／ｃｍ２和～７×１０４Ａ／ｃｍ２．分析了本试验中的Ｊｃ差别原因．在单晶ＹＳＺ上ＹＢＣＯ高Ｊｃ数值显示了用ＭＯＣＶＤ制备涂层膜导体的潜力     

在织构Ni衬底上用电子束蒸发沉积YSZ阻挡层

用轧制及再结晶方法制备了高度立方织构的金属Ni(镍）基带。采用电子束蒸发的方法在几个厘米长的Ni基带表面上生长YSZ（钇稳定二氧化锆）阻挡层。X射线衍射分析表明，YSZ层具有纯c轴取向和良好的平面内取向及立方织要。扫描电镜观察表明，YSZ阻挡层连续致密无裂纹。     

YBCO涂层导体用YSZ缓冲层的快速制备研究

基于反应直流溅射法,采用镶嵌有钇粒的金属锆作为靶材,去离子水蒸汽为氧化反应气体,在有Y2O3种子层的双轴织构Ni-5at.%W基带上,系统地研究了温度和卷绕速度对YSZ阻挡层薄膜结构及表面形貌的影响。X射线衍射(XRD)分析表明,生长温度在700℃时制备的薄膜呈现明显的(002)取向;原子力显微镜(AFM)分析显示,该温度下制备的薄膜表面致密、无孔洞、无裂纹。在不同的卷绕速度下,虽然薄膜均为纯c轴取向,但其均方根粗糙度(RMS)和微粒大小均有较大差别。快速制备可达到抑制基片表面氧化、助于薄膜取向改善、提高薄膜制备效率的目的。     

采用EPR谱和TEM对YSZ单晶辐照损伤的研究

 利用电子顺磁共振(EPR)谱和透射电子显微镜(TEM)研究了YSZ单晶的辐照效应。200 keV的Xe和400 keV的Cs离子注入［111］取向的YSZ单晶中,注量均为5×10¹⁶ cm^-2。EPR结果表明辐照产生了共振吸收位置g‖=1.989 和 g⊥=1.869、对称轴为［111］的六配位Zr³⁺顺磁缺陷。Cs辐照产生了比Xe 离子辐照多约150倍的六配位Zr³⁺顺磁缺陷。两种样品的剖面电子显微分析表明没有发现非晶化转变,但是Cs离子辐照的样品在损伤集中区域产生了密度较高的缺陷。因此,EPR谱和电子显微观察均说明在相同离位损伤(约160 dpa)的情况下,Cs离子辐照比Xe 离子辐照产生了更多的缺陷。造成这一现象的原因是Cs离子是化学活性的而Xe 离子却是惰性的。     

IBAD技术制备涂层导体用YSZ缓冲层长带的研究

在钇钡铜氧(YBCO)高温超导涂层导体制备路线中,离子束辅助沉积技术(IBAD)是两大主流技术路线之一,取得了最为突出的研究成果.本文简要介绍了IBAD技术制备YBCO涂层导体的最新研究进展;并采用离子束辅助沉积技术在哈氏合金(Hastelloy)基底上成功制备了1米长具有钇稳定氧化锆(YSZ)缓冲层的金属基带.采用X射线衍射仪(XRD)分析YSZ缓冲层的取向;利用原子力显微镜(AFM)和扫描电镜(FESEM)观察其表面形貌.获得了可以实际应用的IBAD-YSZ/Hastelloy缓冲层长基带,可以在该基带上研制其他缓冲层以制备YBCO高温超导涂层导体带材.     

Redox stability of SOFC: Thermal analysis of Ni–YSZ composites

A re-oxidation of a Ni-based SOFC can seriously damage the cells. Important aspects of this thermomechanical instability are reduction–oxidation kinetics and the dimensional behaviour of the Ni–YSZ composites. These were investigated in the temperature range of 600–1000 °C and different combinations of reduction and oxidation temperatures. Automated temperature and gas change programmes were implemented in thermogravimetry and identically repeated using a high precision dilatometer to show the dimensional behaviour of the cermets simultaneously with the Degree of Oxidation (DoO) as a function of time during redox cycling. The activation energy for reduction was 84.4 kJ/mol and the kinetics was largely linear. Different kinetic models were fitted to the reduction data; the best agreement was found using the Avrami equation. On the re-oxidation, initially linear kinetics was observed, followed by a period of parabolic kinetics slowing down to logarithmic towards full DoO. The shifts in the kinetic shape with time depended on the temperature and DoO. The rate constants for oxidation were fitted to the data. The BET surface area of the cermets after different reduction and oxidation treatments was measured and show decrease of surface area with increasing reduction temperature and no significant differences in the surface area depending on the re-oxidation temperature in the range of 600–1000 °C.     

YSZ／Si上溅射BSCCO超导膜的生长机理分析

本研究了利用ＹＳＺ（Ｙ稳定的ＺｒＯ２）缓冲层在Ｓｉ衬底上单靶偏轴溅射Ｂｉ－Ｓｒ－Ｃａ－Ｃｕ－Ｏ高温超导薄膜的工艺条件，给出了ＹＳＺ和ＢＳＣＣＯ薄膜的性能测试结果，并根据电镜分析结果，提出了ＢＳＣＣＯ薄膜的螺旋柱状生长机理。     

单晶YSZ的Xe+辐照损伤的电子显微分析

 不同注量200keV Xe⁺ 注入YSZ单晶样品的电子显微分析结果表明，随着辐照注量的增加，缺陷簇的密度增大，在1×10¹⁵~1×10¹⁶cm^-2Xe⁺注量，缺陷簇密度迅速增大，形成间隙型位错环；当Xe⁺注量增大到1×10¹⁷cm^-2，缺陷簇密度的增加变得缓慢，并且有直径为2～4nm的Xe气泡析出。选区电子衍射花样表明YSZ样品没有产生非晶化转变。在Xe⁺辐照的离位率高达约350dpa的情况下，YSZ晶体没有非晶化，其原因主要是由于注入的Xe⁺以气泡形式析出。     

具有平面织构的超导缓冲层YSZ薄膜的离子束增强沉积研究

本文用低能离子束增强沉积技术室温下在Ｎｉ－Ｃｒ合金衬底上合成了ＹＢＣＯ超导膜缓冲层ＹＳＺ薄膜。ＸＲＤ测试表明ＹＳＺ薄膜Ｃ轴对成取向；极力产测试表明薄膜平面织构强烈。     

侧馈电H型YBCO／YSZ高温超导天线的制备与微波特性

首次采用超导化侧馈电方式和相应的匹配技术，用ＹＳＺ基片为衬底外延生长的ＹＢａ２Ｃｕ３Ｏｙ高温超导薄膜成功地制备了Ｈ型电小天线，获得了小尺寸，高效率的实验结果，在输入功率为１０ｍＷ的情况下，与同样的Ａｇ膜天线相比，其相对效率提高了１０ｄＢ左在，同时研究了两正交极化方向上相对效率的变化，给出了传输系数Ｓ２１和反射系数Ｓ１１的测试结果，为实现高温超导天线的实用化集成化提供了重要的实验资料。     

在Ni片上制备YSZ/CeO2阻挡层和YBCO超导膜

本文用平面靶射频磁控溅射在具有双轴织构的Ni片上外延生长CeO2和YSZ薄膜作为阻挡层,X-射线衍射扫描分析表明CeO2和YSZ薄膜具有强的c轴织构和较好的平面内双轴织构.用中空柱状靶直流磁控溅射在阻挡层上制备YBCO超导薄膜.在2cm波带测量了YBCO的表面电阻和谐振腔有载QL值.     

La1-xNaxMnO3/YSZ膜的化学溶液法制备及输运性能研究

本文采用化学溶液法在钇稳定的二氧化锆(Y-stabilized ZrO2,YSZ)单晶基板上制备了La1-xNaxMnO3(LNMO)膜并对其输运性能进行了研究.X-射线衍射(XRD)结果表明,所获得的LNMO膜为高度(h00)取向;输运结果表明,所制备的LNMO膜表现为外延膜的性能,且La0.7Na0.3MnO3薄膜在300K、0.5T磁场下可获得～5%磁阻值.     

Characterization of NiO–yttria stabilised zirconia (YSZ) hollow fibres for use as SOFC anodes

NiO–yttria stabilised zirconia (YSZ) hollow fibres with varying NiO content and a desired microstructure were prepared using a phase inversion technique and sintering. By controlling the fabrication parameters, microstructures with predominately finger-like pores near the inner and outer surfaces and a denser central layer with sponge-like pores were produced, for use as substrates for anode-supported hollow fibre solid oxide fuel cells (HF-SOFC). The NiO–YSZ fibres were reduced to Ni–YSZ at 250–700 °C in hydrogen flowing at 20 cm³ min^? 1 to produce Ni–YSZ hollow fibres, the mechanical and electrical properties of which were determined subsequently, reduction to Ni being verified by X-ray diffraction. The effects of NiO concentration and sintering temperature of the fibre precursors on the conductivity, strength and porosity of the reduced hollow fibres were investigated to assess their suitability for use as anode substrates. As expected, increasing Ni concentration increased electrical conductivities and decreased mechanical strength. Sintering temperature had a critical effect in producing axially conductive hollow fibres of sufficient mechanical strength for use as SOFC anodes. The hollow fibres retained their initial microstructure through the reduction process, though ca. 41% volume contraction is predicted on reduction of NiO to Ni, producing increased porosity in the reduced fibres. The mean porosity of the Ni–YSZ hollow fibres was ca. 60% and ca. 40% after sintered at 1250 °C and 1400 °C, respectively. The mean pore sizes for all the fibres after reduction varied between ca. 0.3 and 1 µm. The hollow fibres produced with 60% NiO, of length ca. 300 mm, electrical conductivities of ca. (1–2.25) × 10⁵ S m^? 1 and a porosity of ca. 43% are being used currently to construct and test the electrical behaviour of an anode-supported HF-SOFC.     

Fabrication of YBCO／YSZ and YBCO／MgO thick films using electrophoretic deposition with top-seeded melt growth process

Superconducting thick films were grown on single crystals MgO and YSZ by electrophoretic deposition with Y_2BaCuO_5(Y211) addition. YBCO thick films were then accomplished by sintering the precursor films above the peritectic temperature. Single crystals of MgO (3×3×0.5 mm^3) were used as top-seed to control crystal structure of the thick films. As shown by scanning electron microscopy, the morphologies of YBCO/YSZ and YBCO/MgO thick films are spherulitic texture and platelet type. The critical temperature is ～89 K for the YBCO/YSZ thick film; the onset transition temperature is 86.4 K and the transition width is ～3 K for YBCO/MgO thick film. The critical current densities (as determined by Bean model) are, in A/cm^2, 3870 (77 K) for YBCO/YSZ thick films and 2399 (77 K) for YBCO/MgO thick films, which are comparable to the best J_c reported of the thick films prepared by the same method.     

Deposition and characterization of YBCO/CeO2/YSZ/CeO2 multilayers on biaxially textured Ni substrates

CeO2/YSZ/CeO2 buffer layers were deposited on biaxially textured Ni substrates by pulsed laser deposition. The influence of the processing parameters on the texture development of the seed layer CeO2 was investigated. Epitaxial films of YBCO were then grown in situ on the CeO2/YSZ （yttria-stabilized ZrO2）/CeO2-buffered Ni substrates. The resulting YBCO conductors exhibited self-fleld critical current density Jc of more than 1 MA/cm^2 at 77K and superconducting transition temperature Tc of about 91K.     

Electrochemical promotion of NO reduction by C3H6 and CO on Rh/YSZ catalyst — Electrodes

The selective catalytic reduction of NO by propylene or CO in the presence of excess oxygen is a system of great technological importance. The effect of Electrochemical Promotion (or Non-faradaic Electrochemical Modification of Catalytic Activity — NEMCA) was used to promote this reaction (C₃H₆ or CO/NO/O₂) on Rh/YSZ catalyst-electrodes. It was found that both the catalytic activity and the selectivity of the Rh catalyst-electrode is affected dramatically upon varying its potential with respect to a Au pseudoreference electrode. Catalytic rate enhancements up to 15000% and 6000% were observed in the case of NO reduction by propylene, while the product selectivity to N₂ production is affected significantly (up to 200%) upon positive potential application. Remarkable promotion of the catalytic activity was also observed in the case of NO reduction by CO, since up to 20-fold increases both in catalytic rates and in NO conversion were obtained under NEMCA conditions. Paper presented at the 6th Euroconference on Solid State Ionics, Cetraro, Calabria, Italy, Sept. 12–19, 1999.