The Network-Chain Trasnformation in the Liquid As-Te Mixtures near the Semiconductor-Metal Transition

摘要

The results of neutron diffraction and EXAFS measurements for 1-Te and 1-As-Te mixtures (10,20,30 and 40 at.% As) are discussed. The g(r) patterns of 1-Te show a substantial overlap between the first and second peaks. The first minimum after the first peak of g(r) around 3.2A is filled up at high temperature. Upon the addition of As to 1-Te the first peak of g(r) becomes sharp, implying that As atoms bridge between Te chains and suppress the thermal fluctuations of the inter-chain distances. The filling of the first minimum around 3.2A observed for 1-As-Te mixtures at high temeprature is associated with the inter-chain correlation in a densely packed configuration. From the EXAFS analysis of 1-As-Te mixtures we conclude that the network structure composed of threefold coordinate As atoms and twofold coordinated Te atoms is transformed into a twofold coordianted chain structure. The network-chain transformation is accompanied by a gradual semiconductor to metal transition. The first sharp diffraction peak observed for 1-As_(20)Te_(80) and 1-As_(40)Te_(60) is related to the Te-Te intermediate range order in-Te-As-Te-or -Te-As-As-Te-chain molecules.