Structural and Semiconductor-Metal Transition in liquid Se

近年来，人们对液态硫属元素如Se和Te进行了大量的研究。据报道，液体在高温下发生半导体到金属（S-M）转变，并伴有结构转变。人们的兴趣主要来自于S-M转变过程中明显存在的双重共价键，研究主要集中在液体硫属元素的结构与其电子性质之间的联系。对液态Te-Se（1-Te-Se）和液态As-Te（1-As-Te）混合物进行了扩展X射线吸收精细结构（EXAFS）、电导率和霍尔系数的测量。对1-Te-Se混合物的EXAFS数据分析表明，金属1-Te-Se在热搅拌作用下缩短的双折叠链由长短共价键组成 ...更多信息 长键在半导体状态下消失了。含三配位Te原子和二配位Te原子的1-As-Te混合物的网络结构转变为二配位的链状结构。电导率和霍尔系数的测量结果表明，网络链转变伴随着半导体到金属的转变。用紧束缚分子动力学模拟方法确定了1-Se在宽温、宽压范围内的径向分布函数，包括键角分布和二面角分布。结果表明，虽然平均链长减小，二面角分布变平，但在金属态下仍保持链状结构，Te的悬挂键或二次配位原子经网-链变换修饰后，使缩短链中的电荷分布发生较大波动，导致链间和链内电荷频繁转移.这是我们的情况下的源的S-M过渡的液体硫族混合物组成的共价键合链。少

In recent years, many investigations on liquid chalcogens such as Se and Te have been done. It has been reported that the liquids undergo the semiconductor to meal (S-M) transition at high temperatures, being accompanied by structural transformation. Much of the interest stems from the apparent persistence of two-fold covalent bonding across the S-M transition.The studies have been focused on the links between the structural aspects of liquid chalcogens and their electronic properties. The extended X-ray absorption fine structure (EXAFS), conductivity and Hall coefficient measurements have been carried out for liquid Te-Se (1-Te-Se) mixtures and liquid As-Te (1-As-Te) mixture. The first-principle molecular-dynamics simulation has been also performed since it provides the microscopic mechanism of the S-M transition.EXAFS data analysis for 1-Te-Se mixtures reveals that the two-fold chains in the metallic 1-Te-Se shortened by thermal agitation are composed of short and long covalent bonds … More and the long bonds vanish in the semiconducting state. The network structure of the 1-As-Te mixtures with three-fold coordinated Te atoms and two-fold coordinated Te atoms is transformed into the two-fold chain structure. The network-chain transformation is accompanied with the semiconductor to metal transition which is demonstrated by the results for conductivity and Hall coefficient. The radial distribution functions including bond-angle and dihedral-angle distribution for 1-Se are wide temperature and pressure range up to critical point have been determined by the tight-binding molecular dynamic simulation. It has been found that the chain-like structure persists even in metallic state though the average chain length decreased and the dihedral angle has a flatter distribution.The dangling bonds of Te or the two-fold coordinated as atoms modified by the network-chain transformation cause large fluctuations of the charge distribution in the shortened chains, which results in a frequent inter- and intra-charge transfer. This is our scenario for the source of the S-M transition in the liquid chalcogen mixtures composed of covalently bonded chains. Less