Discovery of a New Theory in the Nucleation of Substances

Contributing to Elucidation of the Phenomena of Shape and Volume Changes

2012.02.22
(2012.04.04 Update)

National Institute for Materials Science

A team headed by Dr. Masamichi Nishino, a Senior Researcher in the Computational Materials Science Unit of the National Institute for Materials Science, discovered a new process which had not been known until now in the nucleation phenomenon, and a principle explaining that process.

Abstract

  1. A team headed by Dr. Masamichi Nishino, a Senior Researcher in the Computational Materials Science Unit of the National Institute for Materials Science (President: Sukekatsu Ushioda), discovered a new process which had not been known until now in the nucleation phenomenon (trigger for changes of the states of substances), and a principle explaining that process.
  2. Nucleation is an important topic in a wide range of research fields, from electronics technology to meteorology. Traditionally, nucleation was thought to comprise a series of processes that occur at most at a microscopic nanometer scale, and in actuality, only microscopic nucleation has been known until now. However, this research revealed that nucleation can become a macroscopic process in systems characterized by long-range intermolecular interaction mediated by elastic distortions because the size of the critical nucleus is proportional to the size of the total system.
  3. Nucleation theory considers a microscopic critical nucleus having a certain size, which is determined by competition between the free energies of the critical nucleus surface (boundary) and interior (bulk). However, in this research, we analyzed a model of a spin-crossover system, in which elastic distorsions occur because each molecule in the crystal has bistable states for different sizes, and showed that, in systems with long-range interactions mediated by elastic distortions, the critical size of the nucleus does not have a specific value, but is relative to the size of the total system. The fact that nucleation can become a macroscopic process provides a new concept of “macroscopic nucleation.”
  4. The results of this research represent a new development in nucleation theory as understood to date. In the design of materials, this provides a principle that the strength of the metastable state and the width of the hysteresis loop are controlled (remarkably changed) by adjusting the size of the system. It is also considered to provide useful knowledge regarding unexplained mechanisms of structural transitions or changes such as martensitic transformation, magnetostriction, and Jahn-Teller transformation, etc.
  5. These results were published in the on-line edition of the open scientific journal Scientific Reports of the Nature Publishing Group on November 22, 2011. (A Japanese translation of the abstract was posted at the Japanese website as a “Notable Paper” on January 23, 2012.) The Scientific Reports paper can be found at: http://www.nature.com/srep/2011/111121/srep00162/full/srep00162.html#f4