Preparation of perovskite powders and coatings by radio frequency suspension plasma spraying

Perovskite-type LaMnO₃ powders and coatings have been prepared by a novel technique: reactive suspension plasma spraying (SPS) using an inductively coupled plasma of approximately 40 kW plate power and an oxygen plasma sheath gas. Suitable precursor mixtures were found on the basis of solid state reactions, solubility, and the phases obtained during the spray process. Best results were achieved by spraying a suspension of fine MnO₂ powder in a saturated ethanol solution of LaCl₃ with a 1 to 1 molar ratio of lanthanum and manganese. A low reactor pressure was helpful in diminishing the amount of corrosive chlorine compounds in the reactor. As-sprayed coatings and collected powders showed perovskite contents of 70 to 90%. After a posttreatment with an 80% oxygen plasma, an almost pure LaMnO₃ deposit was achieved in the center of the incident plasma jet. This paper originally appeared in Thermal Spray: Meeting the Challenges of the 21st Century; Proceedings of the 15th International Thermal Spray Conference, C. Coddet, Ed., ASM International, Materials Park, OH, 1998. This proceedings paper has been extensively reviewed according to the editorial policy of the Journal of Thermal Spray Technology.     

二次自蔓延高温合成钙钛矿固化90Sr

采用二次自蔓延高温合成(SHS)技术制备钙钛矿固化高放废物90Sr,通过XRD, SEM和PCT粉末浸泡法,研究了钙钛矿固化体的微观组织、浸出率以及其对高放废物~(90)Sr的最大包容量.结果表明,固化体样品密度高、孔隙率小,浸出率都小于0.1 g/(m~2·d),对SrO的包容量可达36%(质量分数);表明自蔓延高温合成的钙钛矿人造岩石固化体化学稳定性好、包容量大,是固化高放废物的理想固化体.     

用程序升温脱附研究Nd_（1－x）Sr_xMnO_3体系氧的吸附、脱附特性

用氧的程序升温脱附（ＴＰＤ）技术测试了钙钛矿型复合氧化物Ｎｄ（１－ｘ）ＳｒｘＭｎＯ３（ｘ＝０．０，０．２，０．４，０．６，０．８，１．０）系列试样体相内的缺陷结构．发现随着Ｘ的变化，脱附氧量呈现出不同的变化规律。对此，用晶体化学和固体化学的基本理论进行了解释。     

钙钛矿型SmFeO3纳米材料的制备及酒敏特性研究

采用溶胶-凝胶法并经850℃热处理制备了具有单一正交钙钛矿结构、平均粒径约40nm的SmFeO3粉体,并用该粉体做成气敏元件,测试了其气敏性能.测试结果表明,SmFeO3具有较好的酒敏特性,在0.03%乙醇气氛中的灵敏度高达51.03,并具有良好的选择性及响应-恢复特性,线性检测范围较宽.     

基于逐层气相沉积制备的钙钛矿薄膜调控和器件性能优化

真空气相沉积法具有致密性好、均匀性好、膜厚可控等优点,被认为是一种制备大面积、高质量钙钛矿薄膜的关键技术,在工业化生产上有着巨大的应用潜力。但相较于溶液法,气相沉积存在薄膜晶粒尺寸小,结晶度低等缺点,导致器件光电转换效率较低。采用逐层交替气相沉积法制备钙钛矿薄膜,对碘化铅(PbI₂)含量进行调控,使用氯化甲胺和碘化甲铵混合溶液进行表面后处理,钝化了薄膜缺陷,提升了薄膜质量。PbI₂含量的优化调控了钙钛矿薄膜的化学计量比,器件光电性能得到提高。表面后处理引入的氯离子,使钙钛矿晶粒尺寸增大,结晶度提高。器件的短路电流密度明显提升,最终获得17.76%的光电转换效率以及82.1%的填充因子。     

La0.6Sr0.4Co0.8Ni0.2O3−δ hollow fiber membrane reactor: Integrated oxygen separation – CO2 reforming of methane reaction for hydrogen production

An integrated reactor system which combines oxygen permeable La_0.6Sr_0.4Co_0.8Ni_0.2O_3−δ (LSCN) perovskite ceramic hollow fiber membrane with Ni based catalyst has been successfully developed to produce hydrogen through oxy-CO₂ reforming of methane (OCRM). Dense La_0.6Sr_0.4Co_0.8Ni_0.2O_3−δ hollow fiber membrane was prepared using phase inversion-sintering method. OCRM reaction was tested from 650 °C to 800 °C with a quartz reactor packed with 0.5 g Ni/Al₂O₃ catalyst around the LSCN hollow fiber membrane. CH₄ and CO₂ were used as reactants and air as the oxygen source was fed through the bore side of the hollow fiber membrane. In order to gauge the effectiveness of this membrane reactor system, air flow was closed at 800 °C and dry reforming of methane (DRM) was tested for comparison. The results show that the oxygen fluxes of LSCN membrane swept by helium are nearly 3 times less than those swept by OCRM reactants. With increasing temperature and oxygen supply, methane conversion in the OCRM reactor reaches 100%, but CO₂ conversion decreases from 87% to 72% due to the competition reaction with POM. CO selectivity is as high as nearly 100% at reaction temperatures of 700 °C–800 °C while H₂ selectivity reaches a maximum of 88% at 700 °C. At 800 °C, when air supply was closed and DRM was conducted for comparison, CO selectivity decreased to 91%, resulting in carbon deposition which was around 4 times more than those obtained under OCRM reaction and H₂/CO ratio decreased from 0.93 to 0.74, showing better carbon resistance and higher H₂ selectivity of the Ni-based catalyst over the integrated oxygen separation-OCRM reaction across the LSCN hollow fiber membrane reactor.     

双钙钛矿氧化物Gd1.7Ce0.3NiMnO6的磁热效应

采用高温固相反应法制备了双钙钛矿氧化物Gd_(1.7)Ce_(0.3)NiMnO_6多晶样品。该样品呈现良好的单相性,空间点群为单斜晶系P2_1/n;样品在T>T_G为纯顺磁态,T_C相似文献   

Excitonic Properties of Chemically Synthesized 2D Organic–Inorganic Hybrid Perovskite Nanosheets

2D organic–inorganic hybrid perovskites (OIHPs) represent a unique class of materials with a natural quantum‐well structure and quasi‐2D electronic properties. Here, a versatile direct solution‐based synthesis of mono‐ and few‐layer OIHP nanosheets and a systematic study of their electronic structure as a function of the number of monolayers by photoluminescence and absorption spectroscopy are reported. The monolayers of various OIHPs are found to exhibit high electronic quality as evidenced by high quantum yield and negligible Stokes shift. It is shown that the ground exciton peak blueshifts by ≈40 meV when the layer thickness reduces from bulk to monolayer. It is also shown that the exciton binding energy remains effectively unchanged for (C₆H₅(CH₂)₂NH₃)₂PbI₄ with the number of layers. Similar trends are observed for (C₄H₉NH₃)₂PbI₄ in contrast to the previous report. Further, the photoluminescence lifetime is found to decrease with the number of monolayers, indicating the dominant role of surface trap states in nonradiative recombination of the electron–hole pairs.     

Deposition of nanostructured LSM perovskite thin film on dense YSZ substrate by airbrushed solution combustion (ASC) for application in SOFC cathodes

To make SOFC high efficiency energy generation devices, thin ceramic films are proposed as their main components. The rate of the oxygen reduction reaction is relevant for the overall performance of the SOFC, hence a lot of attention is given to the cathodes and their interfaces. The airbrushed solution combustion (ASC) method was used to fabricate an LSM thin film on a dense YSZ substrate. A single phase LSM perovskite was obtained with very thin and interconnected porosity, and a small average grain size (55 nm). The nanostructured LSM thin film electrode showed a low total activation energy (1.27 eV) at high temperatures, but a high area specific resistance at 850°C (55 Ω.cm²). The activation energy for the dissociative adsorption and diffusion of oxygen was significantly low (1.27 eV), while the charge transfer and oxygen ion migration activation energy at the LSM/YSZ interface (1.28 eV) was closer to those usually reported.