非晶硫熔化过程中的链环转变

Chain-ring transition during exothermic “melting” in amorphous sulfur

熔化通常表现为吸热和体积膨胀,对放热或体积收缩的反常熔化现象的研究在凝聚态物理中具有重要的科学意义.本文研究了非晶硫反常放热熔化的机理,进行了加热过程中特别是放热熔化前后非晶硫的拉曼光谱分析,表明熔化前的非晶硫中含有大量聚合链结构的团簇,熔化后的液态硫则主要为S8环团簇结构,非晶硫放热熔化过程中应该伴随着链环转变.分子动力学模拟的结果表明链环转变过程是放热的.文中提出非晶硫的反常放热熔化过程是链环转变和熔化过程的耦合,还进一步讨论了非晶硫反常熔化过程中的链环转变与非晶硫晶化过程中链环转变的不同.

A normal melting process is endothermic and causes volume expansion. Exothermic melting or volume contraction is therefore abnormal, and has important effects in condensed-matter physics. In the present study, we investigated the mechanism of abnormal exothermic ＂melting＂ of amorphous sulfur. Analysis of Raman spectra obtained before and after exothermic melting showed that before melting the amorphous sulfur contains clusters in the form of polymeric chains. After melting, sulfur clusters in the form of S8 predominate, i.e., the polymeric chains are converted to S8 rings during melting, which affects the overall internal energy of the system. Density functional method calculations confirmed that the net effect in the chain–ring transition is exothermic. This abnormal exothermic melting in amorphous sulfur can be described as chain–ring transitions coupled with melting. The difference between the chain–ring transition reported in this work and that reported in crystallization relaxation of amorphous sulfur is also discussed.