Phase Transitions in Magnetite and Nickel Sulphide-Selenide Systems

本研究主要围绕两个项目展开。第一部分涉及对磁铁矿和锌铁氧体的持续研究。本研究的主要目的是研究硫化镍-硒化物体系。当x值分别为0、2和0.5时，这种材料表现出良好的绝缘体、良好的金属或金属绝缘体的特性。这一性质可能是由电子关联效应驱动的。可以通过改变硫化物/硒的比例而保持阳离子亚晶格不变来研究该体系。计划进行以下研究：单晶生长，随后调整化学计量比、电学测量、磁化研究、比热研究、结构研究和光学测量。数据采集不仅具有内在的意义，而且将被用来识别从绝缘态、通过窄带关联态、到金属绝缘过渡区的转变，以及进入良好的金属行为区域，在此期间晶格基本保持不变。因此，这些数据是对当前各种制度下电子传输理论的一种检验。

This research is focussed on two projects. The first part involves continued studies on magnetites and zinc-ferrites. The main thrust of this research is directed to the investigation of nickel sulphide-selenide systems. This material exhibits properties of a good insulator, a good metal, or a metal-insulator for x values of 0, 2, and 0.5, respectively. This property presumably is driven by electron correlation effects. The systems can be studied by varying the sulphide/selenide ratio while leaving the cation sublattice intact. The following studies are planned: growth of single crystals, followed by adjustments of stoichiometry, electrical measurements, magnetization investigations, specific heat studies, structural research, and optical measurements. The data acquisition is not just of intrinsic interest but is to be used to identify the changeover from the insulating state, through a narrow band correlated state, to the metal-insulated transition regime, and into the region of good metallic behavior, during which the lattice remains basically unaltered. The data thus serve as a test for current theories of electron transport in the various regimes.