| 摘要: | 研究期間：10201~10207;In this three-year project, we propose to study the structural, electronic, magnetic, elastic, and thermodynamic properties of correlated materials under pressure or epitaxial strains using state of the art first-principles computation techniques. Our research will be focused on two categories of materials for their geophysical importance, scientific interests, and technological potentials. One category of materials in this project is iron alloys. So far, all geophysical and geochemistry evidences have suggested that the Earth’s solid inner core consists of iron (Fe) and lighter elements, possibly hydrogen (H), sulfur (S), silicon (Si), carbon (C), and oxygen (O). To decipher the mysterious properties of the Earth’s inner core, including its seismic anisotropy and heterogeneity, and to shed light on how the inner core affects the evolution the Earth, solid knowledge for materials in this region is essential. We plan to study Fe-H, Fe-S, Fe-Si, and Fe-C alloys under high pressure, and to search for the most likely crystal structure in the inner-core conditions, so we can better understand this innermost and the least known region of the Earth’s interior. We also plan to investigate thin-film martensite Fe-N alloys for their possible (and yet controversial) extraordinarily high magnetization ( > 3.0/Fe) suggested by experiments. The other category of materials in this project is epitaxially-strained complex oxides, in particular, perovskite cobaltite thin films. Compared to their manganite counter parts, thin-film cobaltites have just started attracting attention, mainly due to their extra degree of freedom in cobalt spin state and the potential novel properties induced by epitaxial strains. A few examples include lanthanum cobaltite (LaCoO3), which is a diamagnetic insulator in bulk and a ferromagnetic insulator in tensile-strained thin film, and (Nd,Sr)CoO3, whose coercivity can be enhanced by strain by two orders of magnitude. Detailed mechanisms of these phenomena are still unclear, and plenty of thin-film cobaltites remain unexplored. We therefore plan to use first-principles calculations to understand and perhaps even predict strain-induced novel properties in this class of materials. |
