Nanocrystalline orthoferrite powders: Synthesis and magnetic properties

Nanocrystalline orthoferrite powders were synthesised at low temperatures by employing an aqueous sol–gel process. Colloidal sols and water re-dispersible gels of orthoferrite precursors were prepared by room-temperature processing of inexpensive metal salts. The average diameter (Z_av) of the precursor particles was in the size range from 4 to 7 nm; the diameters had a narrow size distribution. Water re-dispersible translucent gel monoliths were obtained by concentrating the aqueous sols followed by drying them under reduced pressure (10⁻² Torr) at room temperature. The sol–gel transition was found to be completely reversible. Nanocrystalline fine powders of orthoferrites of general formula, LnFeO₃ (Ln = La, Sm, Gd, Dy, Er, Yb and Y) having a crystallite size of about 25 nm were prepared by heating the gel precursors at 650–700 °C in air. Powder X-ray diffraction and thermogravimetry, respectively, were employed to identify perovskite phase formation and delineate thermal events that lead to gel to crystallite conversion. Magnetic measurements were carried out on the resultant powders at room temperature and down to 40 K. Nanocrystalline orthoferrite powders exhibited weak ferromagnetic behaviour, and reduced magnetic moments.     

低温熔盐法合成铁酸镧纳米粉体

文章首次以低温熔盐法在合成LaFeO3纳米粉体,用X射线衍射仪(XRD)和透射电子显微镜(TEM)等测试手段对材料的结构、粒径进行了分析和表征;并探讨了不同煅烧温度、不同硝酸锂添加量条件下对铁酸镧粉体结晶情况等的影响。     

金属离子掺杂对LaFeO3光催化性能的影响

采用溶胶-凝胶法制La1-xLixFeO3（x=0,0.03,0.05.0.07,0.10）纳米晶体粉末,用XRD,TEM,UV-Vis,IR,SPS对合成产物进行表征.结果显示,L1掺杂的LaFeO3晶体粉末比纯LaFeO3具有更强的光催化性,x=0.03的掺杂效果比较好.La0.97Li0.03FeO3复合氧化物是甲基蓝光催化降解和工业污水处理的高效光催化剂.     

铁酸镧粉体的合成及其光催化性能研究

采用低温熔盐法制备了LaFeO3光催化剂,用X射线衍射仪(XRD)和透射电子显微镜(TEM)等测试手段对材料的结构、粒径进行了分析和表征,研究了其对罗丹明B溶液的光催化降解性能.试验表明:煅烧温度对LaFeO3粉体的结晶发育等具有重要的影响;光催化降解试验数据表明低温熔盐法制备的LaFeO3粉体具有较高的催化活性.     

Accelerated Ionic Motion in Amorphous Memristor Oxides for Nonvolatile Memories and Neuromorphic Computing

Memristive devices based on mixed ionic–electronic resistive switches have an enormous potential to replace today's transistor‐based memories and Von Neumann computing architectures thanks to their ability for nonvolatile information storage and neuromorphic computing. It still remains unclear however how ionic carriers are propagated in amorphous oxide films at high local electric fields. By using memristive model devices based on LaFeO₃ with either amorphous or epitaxial nanostructures, we engineer the structural local bonding units and increase the oxygen‐ionic diffusion coefficient by one order of magnitude for the amorphous oxide, affecting the resistive switching operation. We show that only devices based on amorphous LaFeO₃ films reveal memristive behavior due to their increased oxygen vacancy concentration. We achieved stable resistive switching with switching times down to microseconds and confirm that it is predominantly the oxygen‐ionic diffusion character and not electronic defect state changes that modulate the resistive switching device response. Ultimately, these results show that the local arrangement of structural bonding units in amorphous perovskite films at room temperature can be used to largely tune the oxygen vacancy (defect) kinetics for resistive switches (memristors) that are both theoretically challenging to predict and promising for future memory and neuromorphic computing applications.     

Stabilisation of active nickel catalysts in partial oxidation of methane to synthesis gas by iron addition

Mixed LaNi_xFe_(1−x)O₃ perovskite oxides (0≤x≤1) have been prepared by a sol–gel related method, characterised by X-ray diffraction (XRD), specific surface area measurements, transmission electron microscopy (TEM) coupled to an energy dispersive X-ray spectrometer (EDS). These systems are the precursors of highly efficient catalysts in partial oxidation of methane to synthesis gas. Studies on the state of these systems after test show the stabilisation of active nickel by increasing the amount of iron. These systems permit to control the reversible migration of nickel from the structure to the surface. The best mixed perovskite for the partial oxidation of methane is LaNi_0.3Fe_0.7O₃.     

LaFeO3甲烷氧化催化剂的表征及反应性能评价

采用高温熔融法制备出LaFeO3系列催化剂,利用XRD,BET,XPS等分析手段对催化剂样品进行了表征,并通过CH4/O2切换反应考察了催化剂的反应性能.结果表明,纯LaFeO3催化剂具有2个O1s峰,低结合能的氧归属为晶格氧,高结合能的氧归属为吸附氧;负载型的催化剂除了含有晶格氧和吸附氧外,还含有大量与Al2O3结合的表面氧;加入助剂会降低各种结合状态氧的结合能;高温熔融致使催化剂中晶格氧的结合能降低.采用挤条法制备的活性组分质量分数为40％的Al基新鲜LaFeO3催化剂反应性能最佳,其CH4转化率、CO选择性分别为87.9％,97.1％,且产物H2/CO（摩尔比）为2.     

钙钛矿复合氧化物的介孔化及用于CH4催化燃烧

利用有序介孔立方相(Ia3d)乙烯基三乙氧基硅烷(TEVS)为模扳,通过纳米组装法在硅基硬模板的介孔中填入La - Fe -柠檬酸络合物,经焙烧和碱洗去除硅基模板,制备具有有序介孔结构且高比表面积的LaFeO3钙钛矿(ABO3),并与软模板法和自燃烧法制备的LaFeO3钙钛矿催化荆作对比,运用XRD、TEM和BET对合...     

碳纳米管修饰银改性铁酸镧甲醛气敏传感器的制备和性能

银改性铁酸镧(Ag-LaFeO3)具有优良的甲醛敏感性能,但尚存在工作温度偏高、灵敏度不够理想等不足。在前期研究的基础上,采用碳纳米管(CNTs)对其进一步修饰,用溶胶-凝胶法(sol-gel)结合微波化学法制备了CNTs-Ag-LaFeO3粉末,研究了其结构和气敏性能,结果表明,CNTs-Ag-LaFeO3粉末均为单一钙钛矿结构,0.75%CNTs-Ag-LaFeO3在86℃下,对1.0×10-6甲醛气体的灵敏度为13,响应恢复时间分别为110和60s,而且在58℃下对1.0×10-6的甲醛气体也有明显的响应。