Studies of High-Tc and Buckminsterfullerene Superconductors under High Hydrostatic Pressure

高静压下高温和巴克明斯特富勒烯超导体的研究

• 批准号: 9803820
• 负责人: James Schilling
• 金额: $ 28.8万
• 依托单位: Washington University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-07-01 至 2001-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9803820&HistoricalAwards=false
• 关键词: Studies; Tc; Buckminsterfullerene; Superconductors; under

w:\awards\awards96\*.doc 9803820 Schilling This experimental research project is concerned with the role of defects in setting the transition temperature of two interesting types of superconductor, the cuprates and fullerides. The PI in previous work has shown that in Tl-2201 and YBCO the redistribution of oxygen defects can alter Tc by as much as 40K. The present project will make use of unique apparatus including a pressure cell incorporating a SQUID detector, to measure the time dependence of relaxational changes in transition temperature following application of hydrostatic pressure. The goals of the project are: (a) establish in which oxides and at what stoichiometries important relaxation effects occur, and in these cases to measure the T and P dependences of the relaxation times; (b) to determine through diffraction studies and NMR measurements the nature of the defects involved; (c) through correction of the measured pressure dependence of Tc for these relaxation processes, to determine at varying doping levels the intrinsic dependence of Tc on lattice parameter. This project also includes high pressure magnetization studies on several fullerene superconductors. The goal here is to clarify anomalous properties which include pressure-induced monomeric-to-polymeric transitions, orientational ordering effects, and covalency effects in the bonding. This research program is interdisciplinary in nature and involves one or more graduate students, who receive excellent training in preparation for careers in industry, government laboratories or academia. %%% This experimental research project is concerned with the role of crystalline defects in setting the transition temperature of two interesting types of superconductor, the cuprates and fullerides. The cuprates are the highest transition temperature s uperconductors known, in some cases superconducting up to 160K. The fullerides, also known as Buckminsterfullerenes, are recently discovered superconductors up to about 30K, formed by adding alkali metals such as Na or Rb to carbon-sixty molecules. The PI in previous work has shown that in certain cuprate cases the redistribution of oxygen defects can alter Tc by as much as 40K. The present project will make use of unique apparatus including a pressure cell incorporating a SQUID detector, to measure the time dependence of changes in transition temperature following application of hydrostatic pressure. The time dependence is observed in some cases even at very low temperatures, which strongly indicates that crystalline defects are involved. For example, the oxygen in the cuprate can transfer from one location to another, following the application of a change in hydrostatic pressure. Two goals of the project are: (a) establish in which oxides and at what compositions important relaxation effects occur, and in these cases to measure the temperature and pressure dependences of the relaxation times; and, (b) to determine through diffraction studies and NMR measurements the nature of the defects involved. These studies are important for applications of cuprate superconductors, because in most applications it is desirable to select compositions for which the transition temperature will be stable over time. This project also includes high pressure magnetization studies on several fullerene superconductors. The goal here is to clarify anomalous properties which include pressure-induced monomeric-to-polymeric transitions, orientational ordering effects, and covalency effects in the bonding. This research program is interdisciplinary in nature and involves one or more graduate students, who receive excellent training in preparation for careers in industry, government laboratories or academia. ***

w：\awards\awards96\*.doc 9803820 Schilling 这个实验研究项目关注的是缺陷在确定两种有趣的超导体，铜氧化物和富勒烯的转变温度中的作用。PI以前 研究表明，在Tl-2201中， 和 YBCO 氧缺陷的再分布可使Tc改变多达40 K。 本项目将利用独特的装置，包括一个压力单元，结合SQUID探测器，测量的弛豫变化的时间依赖性的转变温度后，应用静水压力。该项目的目标 （a）确定其中的氧化物和 发生了什么化学计量的重要弛豫效应，并在这些情况下测量弛豫时间的T和P依赖性;（B）通过衍射研究和NMR测量确定所涉及的缺陷的性质;（c）通过校正测量的 Tc的压力依赖性， 这些 弛豫过程，以确定在不同的掺杂水平的晶格参数的Tc的内在依赖性。该项目还包括高 压力 磁化研究几个 富勒烯超导体这里的目标是澄清异常属性， 包括 压力诱导 单体到聚合物的转变， 取向有序效应，以及 共价效应 在 的 前将芯片 这 研究 程序 是跨学科的性质，涉及一个或多个研究生，谁接受良好的培训，在工业，政府实验室或学术界的职业生涯做准备。 这个实验研究项目关注的是晶体缺陷在确定两种有趣的超导体，铜氧化物和富勒烯的转变温度中的作用。 的 铜酸 是 的 最高 过渡 已知的超导体，在某些情况下超导高达160 K。 富勒烯，也被称为巴克敏斯特富勒烯，是最近发现的温度高达30 K的超导体，通过将碱金属如Na或Rb加入到碳-60分子中形成。PI在以前的工作表明，在某些铜酸盐的情况下，氧缺陷的重新分布可以改变Tc多达40 K。 本项目将利用独特的装置，包括一个压力单元，结合SQUID探测器，以测量时间依赖性 转变温度的变化 在应用静水压力之后。 在某些情况下，甚至在非常低的温度下也观察到时间依赖性，这强烈表明涉及晶体缺陷。 例如，铜酸盐中的氧可以在施加流体静压力的变化之后从一个位置转移到另一个位置。 该项目的两个目标是：（a）确定在哪些氧化物中以及在什么成分下发生重要的弛豫效应，并且在这些情况下测量弛豫时间的温度和压力依赖性;以及（B）通过衍射研究和NMR测量来确定 缺陷 涉案 这些研究 是 重要 for applications 铜酸盐超导体，因为 在 在大多数应用中，希望选择转变温度随时间稳定的组合物。 该项目还包括对几种富勒烯超导体的高压磁化研究。这里的目标是澄清异常性质，包括压力诱导的单体到聚合物的转变， 取向有序效应，以及 共价效应 在 的 前将芯片 这 研究 程序 是跨学科的性质，涉及一个或多个研究生，谁接受良好的培训，在工业，政府实验室或学术界的职业生涯做准备。 ***