Abstract
The evolution of the short range order (SRO) as a function of temperature in a Lennard-Jones model liquid with Ar parameters was determined and juxtaposed with thermodynamic and kinetic properties obtained as the liquid was cooled (heated) and transformed between crystalline solid or glassy states and an undercooled liquid. The Lennard-Jones system was studied by non-equilibrium molecular dynamics simulations of large supercells (approximately 20000 atoms) rapidly cooled or heated at selected quenching rates and at constant pressure. The liquid to solid transition was identified by discontinuities in the atomic volume and molar enthalpy; the glass transition temperature range was identified from the temperature dependence of the self-diffusion. The SRO was studied within the quasi-crystalline model (QCM) framework and compared with the Steinhardt bond order parameters. Within the QCM it was found that the SRO evolves from a bcc-like order in the liquid through a bct-like short range order (c/a=1.2) in the supercooled liquid which persists into the glass and finally to a fcc-like ordering in the crystalline solid. The variation of the SRO that results from the QCM compares well with that obtained with Steinhardt’s bond order parameters. The hypothesis of icosahedral order in liquids and glasses is not supported by our results.
Highlights
The short range order (SRO) in amorphous systems, even in simple liquids, is the subject of ongoing study, centered on both the nature of the short range order and the methods of its determination.[1,2,3,4,5,6] It is well known that as a liquid is cooled it can enter the supercooled liquid state and transform to the glass or solid states depending on the cooling rate
In the present contribution we study the evolution of the short range order in a Lennard-Jones liquid with Ar-like parameters by varying the cooling rate of non-equilibrium molecular dynamics calculations in large supercells
This pressure was chosen so that the system would be well above the critical point of the liquid-gas transition in this system and the choice of temperature range ensures that the process will begin with the system in the liquid state, well below the Widom line[40] and terminate in the solid state
Summary
The short range order (SRO) in amorphous systems, even in simple liquids, is the subject of ongoing study, centered on both the nature of the short range order and the methods of its determination.[1,2,3,4,5,6] It is well known that as a liquid is cooled it can enter the supercooled liquid state and transform to the glass or solid states depending on the cooling rate. Thermophysical equilibrium properties change with temperature continuously between the liquid, supercooled and glassy states and discontinuously at crystallization. Short range order of supercooled and glassy monatomic liquids is of increased relevance due to the development of experimental techniques that access the required high cooling rates to form these systems and their subsequent characterization. The vitrification of monatomic metallic liquids has been achieved by creating an unprecedented high liquid-quenching rate of 1014 K/s. Under such a high cooling rate, even melts of pure metals were successfully vitrified to form metallic glasses.[17] In addition, similar conditions have been found to occur in novel technologically important processes [e.g., Ref. 18]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
