Crystallization of Complex Metal Oxides from Ionic Liquids

9417185稳定拟议研究的长期目标是通过从离子液体中选择性沉淀制备温度低于400摄氏度的新金属氧化物。一般的策略是将反应物溶解在熔融盐中，通过调节酸度、改变电化学势、通过熔体分解使熔体过饱和或通过添加沉淀剂来沉淀氧化物产物。该方案是涉及相对较高温度(800摄氏度以上)的固相反应的更典型反应路线的替代方案，提供了两个关键优势。首先，低温处理对于氧化物的许多应用是可取的，特别是对于高温处理会破坏其他元件的器件的薄膜的形成。第二，可以制备在高温下不稳定的新材料。具体地说，拟议的研究涉及使用熔融的碱金属和碱土金属氢氧化物和硝酸盐来制备过渡金属氧化物，这些金属处于高形式的氧化态。将探索这两种熔体的化学，以努力制备：A)铜氧化物；B)Rh氧化物；以及C)早期过渡金属氧化物。人们对铜和氧化铑的兴趣源于发现新相的可能性，这些相可能表现出超导电性。对于早期的过渡金属氧化物，低温合成路线将被设计为已知的相，这些相是电子陶瓷，可能用作器件元件。金属氧化物，包括大多数陶瓷和铜酸盐超导体，通常是通过反应物混合物(例如，金属氧化物、碳酸盐、草酸盐和/或硝酸盐)的固相反应制备的。这些混合物可以通过各种方法获得，包括重复研磨、共沉淀或溅射。加热时，由于固态扩散而发生反应。然而，由于需要使用较高的活化能量、相对较高的温度(通常在800℃以上)和较长的反应时间，才能提高均质性并确保反应完全。作为这一合成方案的替代方案，拟议的研究将探索低温溶解金属氧化物的方法，涉及使用熔融的碱和碱土金属氢氧化物和硝酸盐作为溶剂。利用助熔剂进行合成已成为一项有价值的技术，特别是在制备高质量的单晶和外延薄膜方面。它们对于许多结构和物理性质的测量是必不可少的，并且是

9417185 Stacy The long-term goal of the proposed research is to prepare new metal oxides at temperatures below 400 C by selective precipitation from ionic liquids. The general strategy is to dissolve the reactants in a molten salt, and precipitate the oxide product either by adjusting the acidity, by changing the electrochemical potential, by supersaturating the melt by melt decomposition, or by adding a precipitating agent. This scheme, which is an alternative to more typical reaction routes involving solid-state reactions at relatively high temperatures (above 800 C), offers two key advantages. First, low-temperature processing is desirable for many applications of oxides, especially for the formation of thin films for devices in which high- temperature processing would destroy other components. Second, new materials that are not stable at elevated temperatures can be prepared. Specifically, the proposed research is concerned with the use of molten alkali metal and alkaline-earth metal hydroxides and nitrates for the preparation of transition metal oxides with the metals in high formal oxidation states. The chemistry of these two melts will be explored in an effort to prepare: A) copper oxides; B) rhodium oxides; and C) early transition metal oxides. Interest in the copper and rhodium oxides stems from the possibility of discovering new phases, potentially ones that exhibit superconductivity. For the early transition metal oxides, lowtemperature synthetic routes will be designed to known phases that are electronic ceramics, and potentially useful as device components. %%% Metal oxides, including most ceramics and cuprate superconductors, generally are prepared by solid-state reactions of reactant mixtures (e.g., metal oxides, carbonates, oxalates, and/or nitrates). These mixtures can be obtained by a variety of methods, including repeated grinding, co-precipitation, or sputtering . Upon heating, reactions occur due to solid-state diffusion. However, beca use of high energies of activation, relatively high temperatures (typically above 800 C) and long reaction times are required to enhance homogeneity and ensure complete reaction. As an alternative to this synthetic scheme, the proposed research will explore low-temperature solution routes to metal oxides involving the use of molten alkali and alkaline-earth metal hydroxides and nitrates as solvents. The utilization of fluxes for synthesis has become a valuable technology, especially for the preparation of high-quality single crystals and epitaxial films. These are essential for many measurements of structure and physical properties, and are