Phase Transformations in Rare-Earth Metals and Alloys Subjected to Ultra High Pressures and Synthetic Diamond Anvils

小行星9704428 该研究调查了稀土金属和合金在兆巴压力下的相变，并开发了通过化学气相沉积技术（CVD）制造宝石级金刚石砧所需的科学基础。 实验研究是在伯明翰亚拉巴马大学的高压和CVD实验室（UAB）以及布鲁克海文国家实验室的CHESS、康奈尔大学和NSLS的国家高压光束线进行的。 本研究的重点是建立相图选定的原型稀土金属和合金在兆巴制度（100-400 Gpa）。 重点是重稀土金属，镥和镱，其中相变和电子结构和价态的显着变化，预计在超高压。 压力也会引起f-壳层的离域，产生“塌陷-低对称性晶体结构”.“高分辨率成像板X射线衍射技术与同步辐射源结合使用，以研究低对称晶体结构以及最近在稀土金属中发现的晶粒生长现象。还检查了相关的过渡金属，钇，预计在高压下模拟稀土的行为，最近已被预测在280 Gpa转变为bcc结构。 所测得的相边界和压力-体积（P-V）关系提供了严格的测试压力下的f-离域的各种模型。 研究的第二个方向是关于CVD金刚石生长的基础研究，用于制造具有低水平氮杂质的合成金刚石，用于金刚石砧座装置中的应用。该补助金支持的高压材料研究设施用于本科生研究经验（REU）项目在夏季和本科生在亚拉巴马联盟的实里蒂参与（AMP）计划在UAB。 这项研究有可能为理解稀土材料的结构和电子特性做出重大贡献。 金刚石的研究如果成功，将具有广泛的技术应用。 ***

9704428 Vohra The research investigates phase transformations in rare- earth metals and alloys subjected to megabar pressures and develops the scientific base necessary to fabricate gem quality diamond anvils by chemical vapor deposition techniques (CVD). The experimental investigations are carried out at the High Pressure and CVD Laboratory at the University of Alabama at Birmingham (UAB) and the National High Pressure beamlines at CHESS, Cornell University and NSLS, at Brookhaven National Laboratory. The focus of this study is to establish phase diagrams for selected prototype rare-earth metals and alloys in the megabar regime (100-400 Gpa). The focus is on heavy rare-earth metals, lutetium and ytterbium, where phase transitions and dramatic changes in electronic structure and valence are expected at ultra high pressures. Pressure also causes delocalization of the f- shell giving rise to "collapsed - low symmetry crystal structures." A high resolution image plate x-ray diffraction technique is employed in conjunction with a synchrotron source to investigate low symmetry crystal structures as well as the phenomenon of crystal grain growth discovered recently in rare-earth metals. Also examined is a related transition metal, yttrium, which is expected to simulate rare-earth behavior at high pressures, and recently has been predicted to transform to the bcc structure at 280 Gpa. The measured phase boundaries and pressure-volume (P-V) relationships provide stringent tests for various models of f-delocalization under pressure. A second direction in the research is on fundamental studies on CVD diamond growth for fabrication of synthetic diamonds with low levels of nitrogen impurity for applications in diamond anvil cell devices, In addition, high pressure materials research facilities supported by this grant are employed in research experiences for undergraduates (REU) projects during the summer and for undergraduates in the Alabama Alliance for Minori ty Participation (AMP) Program at UAB. %%% This research has the potential for making significant contributions to the understanding of the structural and electronic properties of rare-earth materials. The research on diamond has broad technological applications if successful. ***