组分简单环境友好的铜基高温超导材料:“铜系”

Composition simple and environmental friendly high temperature cuprate superconductors:Cu12(n-1)n

铜基高温超导材料是目前唯一能在常压环境实现液氮温区超导的物质,对其深入认识入选Science发布的125个重大科学问题之一,具有重要的科学价值和巨大的应用开发前景.为了合成铜基超导材料,通常需要引入重金属元素如稀土、Bi、Tl和Hg等昂贵、易挥发或有毒元素以稳定基本结构,这些体系相应称为"钇系"、"铋系"、"铊(汞)系"铜基超导材料.探索组分简单环境友好且在液氮温区超导性能优良的新体系,是超导新材料研发的前沿和重大挑战.本文基于铜基超导材料结构特点,通过介绍运用高压高温合成技术研制钙钛矿型功能材料的优势,重点讨论作者参与设计发现的Cu12(n–1)n(简称"铜系")铜基超导材料体系."铜系"只含铜和碱土氧化物,这是构成铜基超导材料最简单的成分,组分经济环境友好.如同人造金刚石一样,"铜系"块体材料虽然需高压高温合成,但在常压条件能够保持结构稳定,本文讨论的性能都是常压条件测量."铜系"具有独特的全钙钛矿型构型,呈现强的层间耦合,常压超导特性优良:(1)起始超导转变温度(T_c )可达120 K以上,高于"铋系"超导材料,仅次于常压T_c 最高的铜基Hg1223超导体;(2)在液氮温区临界电流密度特性优于"铋系"铜基超导材料,可媲美综合性能最好的"钇系"铜基超导材料,(3)成分只有碱土和铜氧化物,环境友好不含有毒元素,且在空气环境中可保持性能长期稳定.

High temperature cuprate superconductors are the only materials that have a Tc higher than liquid nitrogen temperature at ambient condition so far. The comprehensive study of cuprate superconductors was selected as one of the 125 unsolved most challenging scientific issues published on Science. It triggers huge innovative scientific inquiry as well as of important application prospects. Heavy metal elements such as Rare-Earth, Bi, Tl and Hg etc are usually induced to stabilize the basic cystal structure in synthesis of the cuprate superconductors, which are classified as Y based system, Bi based sytem, Tl based system, respectively. As these heavy metal elements are usually expensive, volatile, or toxic, to develop new superconducting materials with simple and environmental friendly compositions but with Tc above liquid nitrogen temperature, is a great challenge in superconductor material research. In this paper, we primarily focus on the author＇s research to briefly introduce the Cu12（n-1）n（i. e., Cu homologous series） cuprate superconductors that are synthesized using high pressure method. The ＂Cu homologous series＂ superconductors comprise only copper and alkaline oxides, which are the simplest reagents that are necessary to form high Tc cuprates as well as envioramental friendly compositions. The compounds can be synthesized only at high pressure high temperature and can be very stable at ambient pressure like artificial diamond. The properties measured in this paper are all measured at ambient pressure.＂Cu homologous series＂ superconductors own a special crystal structure of a perovskite type charge reservoir layer,which presents a strong interlayer coupling, and exhibit excellent superconductivity properties at high temperature region. The advantages of the ＂Cu homologous series＂ superconductors include：（1） high Tc above 120 K at ambient pressure, near Hg1223 that has the highest Tc in cuprates;（2） excellent critical current densities at liquid nitrogen temperature, which are superior to Bi cuprate homologous superconductors and are comparable to the classical Y123 based system that are the best in terms of comprehensive properties;（3） containing alkaline earth copper oxides only but stable in air condition.