Continuum theory of amorphous nanophases

Alexander Umantsev; Alexander Umantsev

doi:10.3934/matersci.2016.1.22

AIMS Materials Science

2016, Volume 3, Issue 1: 22-34. doi: 10.3934/matersci.2016.1.22

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Continuum theory of amorphous nanophases

Alexander Umantsev ^,

Department of Chemical Physics, National University of Science and Technology MISiS, 4 Leninsky Ave, 119049 Moscow, Russia and Department of Chemistry/Physics, Fayetteville State University, Fayetteville, NC 28301, USA

Received: 24 September 2015 Accepted: 13 December 2015 Published: 18 December 2015

A number of very different recent experiments with nanoparticles produced very similar results: in NPs of sizes above critical the sequence of transformations is similar to that of the bulk while in NPs of sizes below the critical a novel, amorphous (disordered) phase appears and remains stable in a significant domain of variation of the control parameters. In a series of recent publications, the author tried to analyze the origin of this phase. He has developed a field theory of the nanophase stability, which claims that the phase that appears in NPs of sizes below the critical is a transition state between the stable bulk phases in the space of the order parameter that distinguishes between the symmetries of the bulk phases. Such change of stability of the transition state from unstable to stable can occur either beyond the spinodal point on the phase diagram or in conditions of conservation—energy, matter, or volume. The theory claims that in a system of the size below the critical a two-phase mixture of the bulk phases is replaced by the homogeneous transition state because the former is energetically unfavorable due to high ‘energy cost’ of the phase separating interface.
- Phase stability,
- nanophases,
- transition state,
- interfacial energy,
- closed systems
Citation: Alexander Umantsev. Continuum theory of amorphous nanophases[J]. AIMS Materials Science, 2016, 3(1): 22-34. doi: 10.3934/matersci.2016.1.22

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Abstract

A number of very different recent experiments with nanoparticles produced very similar results: in NPs of sizes above critical the sequence of transformations is similar to that of the bulk while in NPs of sizes below the critical a novel, amorphous (disordered) phase appears and remains stable in a significant domain of variation of the control parameters. In a series of recent publications, the author tried to analyze the origin of this phase. He has developed a field theory of the nanophase stability, which claims that the phase that appears in NPs of sizes below the critical is a transition state between the stable bulk phases in the space of the order parameter that distinguishes between the symmetries of the bulk phases. Such change of stability of the transition state from unstable to stable can occur either beyond the spinodal point on the phase diagram or in conditions of conservation—energy, matter, or volume. The theory claims that in a system of the size below the critical a two-phase mixture of the bulk phases is replaced by the homogeneous transition state because the former is energetically unfavorable due to high ‘energy cost’ of the phase separating interface.

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