EAGER: Is Na-NH3 a High Temperature Superconductor?

EAGER：Na-NH3 是高温超导体吗？

• 批准号: 1431408
• 负责人: Moses Chan
• 金额: $ 22万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-07-15 至 2018-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1431408&HistoricalAwards=false
• 关键词: EAGER; Na; NH3; Temperature; Superconductor

Non-technical AbstractBelow a specific temperature, electricity can flow in some materials with zero resistance and hence without any input of energy. These materials are known as superconductors and are currently in use, for example, to provide strong and stable magnetic fields for magnetic resonance imaging (MRI) machines. In order for superconductors to have an even larger impact in technology and in the reduction of energy consumption, the temperature where superconductivity is found needs to be raised significantly from the current record of -135C ( or -211F) found in some ceramic materials known as high temperature superconductors. Interestingly, experiments carried out in 1946 and 1973 reported evidence of superconductivity in rapidly frozen solutions of sodium in ammonia below -93C (or -135F), more than forty degrees Celsius higher than the high temperature superconductors. A number of other experimental groups however were not able to confirm the existence of superconductivity in this system. This project, with greatly improved experimental conditions is a systematic attempt in clarifying this important unresolved issue. Graduate students and post-doctoral scholars working on this project will receive unique experience in carrying research in an unique exploratory mode.Technical AbstraactThe 1946 report of superconductivity by Ogg was based on the observations of a dramatic drop in resistance from 10,000 down to 10 ohms in a fraction of the rapidly frozen samples of sodium-ammonia solution confined in glass capillary. Persistent current, deduced from the observation of a small magnetic field in 7 out of the 100 quenched cooled samples were also seen when the samples were removed from a permanent magnet. The failure of observing such signatures in the majority of the samples were attributed to the cracking the samples in the cooling process. While six other experimental groups had attempted to replicate the results of Ogg, only two were successful. The research team uses today's improved experimental conditions to directly clarify this important unresolved scientific puzzle. Ogg interpreted the superconductivity in his samples is the consequence of fast cooling rate so that the miscible sodium-ammonia solution bypasses the liquid-liquid phase separation region when it freezes. The sodium-ammonia solutions of the research team are prepared in high purity glove box instead of ambient laboratory environment to eliminate any contamination. Sample cells are made from thin stainless steel capillary to speed up the cooling rate to 0.01 s, ~two orders of magnitude faster than Ogg's samples. With a metallic cell, a superconducting transition cannot be masked by a cracked solid sample. In the second set of experiments, the research team infiltrates the sodium-ammonia solutions into hollow glass fibers of 150 nm inner diameter and into porous Vycor glass cylinders with pore diameter of 7 nm. Liquid metal and binary fluid mixtures inside these hosts show no evidence of phase separation. It is possible that phase separation of the sodium-ammonia solutions are similarly suppressed thus providing an ideal condition for the onset of superconductivity without quench-cooling.

非技术摘要在特定温度以下，电流可以在某些材料中以零电阻流动，因此不需要任何能量输入。这些材料被称为超导体，目前正在使用，例如为磁共振成像（MRI）机器提供强大而稳定的磁场。为了使超导体在技术和减少能源消耗方面产生更大的影响，超导性的温度需要从目前某些陶瓷材料中的-135°C（或-211°F）记录大幅提高。高温超导体。有趣的是，1946年和1973年进行的实验报告了在低于-93°C（或-135°F）的快速冷冻的氨钠溶液中存在超导性的证据，比高温超导体高出四十多摄氏度。然而，许多其他实验小组无法证实该系统中超导性的存在。该项目大大改善了实验条件，是澄清这一重要未解决问题的系统尝试。从事该项目的研究生和博士后学者将获得以独特的探索模式进行研究的独特经验。 技术摘要 Ogg 1946 年的超导性报告基于对电阻从 10,000 欧姆急剧下降到 10 欧姆的观察一部分快速冷冻的钠氨溶液样品被限制在玻璃毛细管中。当样品从永磁体上取下时，在 100 个淬火冷却样品中的 7 个样品中观察到小磁场，由此推断出持续电流。在大多数样品中未能观察到此类特征的原因是样品在冷却过程中破裂。虽然其他六个实验组试图复制奥格的结果，但只有两个成功。研究小组利用当今改进的实验条件直接阐明了这一重要的未解决的科学难题。奥格解释说，他的样品中的超导性是快速冷却速率的结果，因此可混溶的钠-氨溶液在冻结时绕过了液-液相分离区域。研究团队的钠氨溶液是在高纯度手套箱中制备的，而不是在实验室环境中制备的，以消除任何污染。样品池由薄不锈钢毛细管制成，可将冷却速率加快至 0.01 秒，比 Ogg 的样品快两个数量级。对于金属电池，超导转变不能被破裂的固体样品所掩盖。在第二组实验中，研究团队将钠氨溶液渗透到内径150纳米的中空玻璃纤维和孔径为7纳米的多孔Vycor玻璃圆柱体中。这些主体内的液态金属和二元流体混合物没有显示出相分离的证据。钠-氨溶液的相分离也可能受到类似的抑制，从而为超导的开始提供理想的条件，而无需骤冷。