碱金属单质的奇异高压行为

碱金属元素单质(锂、钠、钾、铷和铯)的原子最外层只有一个近自由的s电子, 在常温和常压下碱金属单质具有简单的体心立方结构. 在压力的作用下, 碱金属原子间距减小, 电子轨道重叠程度增加, 导致电荷发生重新分布(如, s→p或s→d电荷的转移), 引起一系列复杂的结构相变发生(如长程无序非公度结构的形成). 伴随结构相变的发生, 碱金属单质的电子性质也发生了很大的变化, 比如锂和铯出现了超导电性, 更令人惊奇的是锂和钠在高压下还发生了有违传统高压理论的金属到绝缘体的转变. 文中总结了5种碱金属元素单质锂、钠、钾、铷和铯在高压下的丰富结构相变行为, 介绍了各种新型高压相结构, 分析了相变产生的物理机制, 阐述了锂和铯的高压超导电性, 并重点介绍了锂和钠的金属-绝缘体相变. 最后我们还展望了碱金属元素单质的未来高压研究的重点.

The novel behaviors of alkalis metals under high pressure

At ambient pressure, alkali metals （Li, Na, K, Rb and Cs） all crystallize in the simple close-packed body-centered cubic structure with only one nearly free electron. Under high pressure, along with the decreased interatomic distance and increased electronic orbitals overlap, the electrons are redistributed （i.e. the s→p and s→d charge transfers）, inducing a series of complex phase transformations （i.e. the formation of the long range disordered incommensurate composite structures）. Such phase transformations have dramatically changed the electronic properties of the alkali metals, such as the appearance of superconductivity in Li and Cs and the surprised metal-insulator transition observed in Li and Na. The present review summarizes the abundant pressure-induced phase transitions of five alkali metals Li, Na, K, Rb and Cs, describing the new high pressure phases, the transition mechanism, analyzing the high pressure superconductivity of Li and Cs, and introducing the metal-insulator transitions in Li and Na. At last, we prospect the key points of the future high pressure researches on alkali metals.