CAJ | 학술논문

传统高压理论认为,高压可有效缩短金属的原子间距,导致价带和导带展宽,进而使其金属性增强.然而,目前实验可达到的压力条件已足以将物质压缩到芯电子发生重叠的状态.这一高压效应会使金属发生复杂的结构相变而具有独特的晶体结构和新奇的电子性质.曾有理论预言,简单金属锂和钠在高压下会出现原子配对而导致的绝缘相,但这一预言没有得到其它理论和实验的支持.本研究将理论模拟和高压实验测量相结合,发现金属钠在200万大气压下转变为一种新型物质状态--光学透明的宽带隙绝缘态.绝缘态钠具有简单而独特的晶体结构--c轴高度压缩的双六角密堆结构.高压钠的绝缘态不是早期理论预言的原子配对的结果,而是p和d轨道电子杂化,以及芯电子云之间高度交叠的结果.钠原子的价电子受芯电子排斥而高度局域在晶格间隙中,这些在间隙中被"冻结"的价电子完全失去了自由电子的特性,表现出绝缘体的特性.当压力足够使原子的芯电子发生强烈重叠时,这种新型绝缘状态可以在其它元素和化合物中广泛存在.
전통고압이론인위,고압가유효축단금속적원자간거,도치개대화도대전관,진이사기금속성증강.연이,목전실험가체도적압력조건이족이장물질압축도심전자발생중첩적상태.저일고압효응회사금속발생복잡적결구상변이구유독특적정체결구화신기적전자성질.증유이론예언,간단금속리화납재고압하회출현원자배대이도치적절연상,단저일예언몰유득도기타이론화실험적지지.본연구장이론모의화고압실험측량상결합,발현금속납재200만대기압하전변위일충신형물질상태--광학투명적관대극절연태.절연태납구유간단이독특적정체결구--c축고도압축적쌍륙각밀퇴결구.고압납적절연태불시조기이론예언적원자배대적결과,이시p화d궤도전자잡화,이급심전자운지간고도교첩적결과.납원자적개전자수심전자배척이고도국역재정격간극중,저사재간극중피"동결"적개전자완전실거료자유전자적특성,표현출절연체적특성.당압력족구사원자적심전자발생강렬중첩시,저충신형절연상태가이재기타원소화화합물중엄범존재.
Under pressure, metals exhibit increasingly shorter interatomic distances. Intuitively, this response is expected to be accompanied by an increase in the widths of the valence and conduction bands and hence a more pronounced free-electron-like behavior. But at the densities that can now be achieved experimentally, compression can be so substantial that core electrons overlap. This effect dramatically alters electronic properties from those typically associated with simple free-electron metals, leading in turn to structurally complex phases and electronic properties. But the most intriguing prediction--that the seemingly simple metals Li and Na will transform under pressure into insulating states, owing to pairing of alkali atoms has yet to be experimentally confirmed. Here, combining with theoretical and experimental methods, we found that the metal Na transforms into an optically transparent insulating phase at 200 GPa with wide band gap. The insulating phase of Na possesses a six-coordinated, highly distorted double-hexagonal close-packed structure. We attribute the emergence of this dense insulating state not to atom pairing, but to p-d hybridizations of valence electrons and their repulsion by core electrons into the lattice interstices. We expect that such insulating states may also form in other elements and compounds when compression is sufficiently strong that atomic cores start to overlap strongly.