Synthesis and Properties of Narrow-Band Materials

本研究的目的是合成和测量高温超导体的性能。总的来说，有人建议将之前的铜氧化物研究扩展到更复杂的系统，并研究降低的马德隆能量是否允许在n型超导体的超导相中从更多的离子键到共价键的交叉。具体地，讨论了与固体中的窄带现象有关的八个问题：1)从超导体到常规金属的转变；2)n型超导体中高温超导的临界特性；3)150K以下体系中电荷波动频率的测量；4)用低温合成方法制造具有不寻常价态的金属氧化物；5)钒氧化物中窄带现象的研究；6)钴化合物中低自旋和高自旋组态的研究；7)固体中重叠氧化还原电势的检测；以及8)由于氧化还原对相对于价键边缘的放置而引起的单醇类化合物和杂多酸的性质变化的探索。最终目的是找出使高温现象成为可能的本质属性的汇合是什么。即使在发现高温超导现象六年后，对于铜氧化物高温超导的机制也没有达成共识。这一建议通过将化学和物理的实验技术和概念思维结合在一起，在相对广泛的战线上解决了这个问题。总的来说，有人建议将以前的氧化铜研究扩展到更复杂的系统。对具有窄带现象的材料进行了制备和表征，并提出了八个主题，以明确什么是使高温现象成为可能的本质性质的汇合。

The goal of this research is synthesize and measure properties of high temperature superconductors. In general, it is proposed to extend previous copper-oxide studies to more complex systems and investigate whether a reduced Madelung energy allows for a cross- over from more ionic to covalent bonding in the superconducting phase of the n-type superconductors. Specifically, eight topics associated with narrow-band phenomena in solids are addressed: 1) the transition from a superconductor to a conventional metal; 2) the critical feature of high temperature superconductivity in n- type superconductors; 3) measurements of frequency of charge fluctuation in systems below 150 K; 4) use of low-temperature synthetic procedures to make metal oxides with unusual valence states; 5) study of narrow-band phenomena in vanadium oxides; 6) investigation of low-spin vs. high-spin configurations in cobalt compounds; 7) examination of overlapping redox potentials in solids; and 8) exploration of variation of properties of monochalcogenides and pnictides due to the placement of redox couples with respect to the valence-bond edge. The ultimate aim is to pin point what is the essential confluence of properties that makes possible the high temperature phenomenon. There is no consensus as to the mechanism responsible for high- temperature superconductivity in copper oxides, even six years after the discovery of the phenomenon. This proposal addresses this issue on a relatively broad front by bringing together experimental techniques and conceptual thinking from both chemistry and physics. In general, it is proposed to extend previous copper- oxide studies to more complex systems. Materials exhibiting narrow-band phenomena are prepared and characterized, and eight topics are addressed to pin point what is the essential confluence of properties that makes possible the high temperature phenomenon.