skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Preferential nucleation during polymorphic transformations

Abstract

Polymorphism is the ability of a solid material to exist in more than one phase or crystal structure. Polymorphism may occur in metals, alloys, ceramics, minerals, polymers, and pharmaceutical substances. Unresolved are the conditions for preferential nucleation during polymorphic transformations in which structural relationships or special crystallographic orientation relationships (OR’s) form between the nucleus and surrounding matrix grains. We measured in-situ and simultaneously the nucleation rates of grains that have zero, one, two, three and four special OR’s with the surrounding parent grains. These experiments show a trend in which the activation energy for nucleation becomes smaller – and therefore nucleation more probable - with increasing number of special OR’s. As a result, these insights contribute to steering the processing of polymorphic materials with tailored properties, since preferential nucleation affects which crystal structure forms, the average grain size and texture of the material, and thereby - to a large extent - the final properties of the material.

Authors:
 [1];  [2];  [2]
  1. Delft Univ. of Technology, Mekelweg (Netherlands); Argonne National Lab. (ANL), Argonne, IL (United States)
  2. Delft Univ. of Technology, Mekelweg (Netherlands)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
Netherlands Organisation for Scientific Research (NWO); USDOE
OSTI Identifier:
1340284
Grant/Contract Number:
AC02-06CH11357
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 6; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; metals and alloys; pharmaceutics; solid-state chemistry; structural geology

Citation Formats

Sharma, H., Sietsma, J., and Offerman, S. E. Preferential nucleation during polymorphic transformations. United States: N. p., 2016. Web. doi:10.1038/srep30860.
Sharma, H., Sietsma, J., & Offerman, S. E. Preferential nucleation during polymorphic transformations. United States. doi:10.1038/srep30860.
Sharma, H., Sietsma, J., and Offerman, S. E. 2016. "Preferential nucleation during polymorphic transformations". United States. doi:10.1038/srep30860. https://www.osti.gov/servlets/purl/1340284.
@article{osti_1340284,
title = {Preferential nucleation during polymorphic transformations},
author = {Sharma, H. and Sietsma, J. and Offerman, S. E.},
abstractNote = {Polymorphism is the ability of a solid material to exist in more than one phase or crystal structure. Polymorphism may occur in metals, alloys, ceramics, minerals, polymers, and pharmaceutical substances. Unresolved are the conditions for preferential nucleation during polymorphic transformations in which structural relationships or special crystallographic orientation relationships (OR’s) form between the nucleus and surrounding matrix grains. We measured in-situ and simultaneously the nucleation rates of grains that have zero, one, two, three and four special OR’s with the surrounding parent grains. These experiments show a trend in which the activation energy for nucleation becomes smaller – and therefore nucleation more probable - with increasing number of special OR’s. As a result, these insights contribute to steering the processing of polymorphic materials with tailored properties, since preferential nucleation affects which crystal structure forms, the average grain size and texture of the material, and thereby - to a large extent - the final properties of the material.},
doi = {10.1038/srep30860},
journal = {Scientific Reports},
number = ,
volume = 6,
place = {United States},
year = 2016,
month = 8
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record

Save / Share:
  • Kinetics and mechanism of polymorphic transformation in TiSi[sub 2] thin films from a base-centered orthorhombic structure ([ital C]49-TiSi[sub 2]) to a face-centered orthorhombic structure ([ital C]54-TiSi[sub 2]) were investigated with emphasis on effect of film thickness scaling on phase transition using [ital in] [ital situ] resistance measurements, XRD, and TEM. [ital C]49 disilicide films of different thicknesses were prepared by annealing Ti/polycrystalline Si thin film couples of varying Ti thicknesses (250, 550, and 1000 A). Transformation rate was found to be a strong function of film thickness and temperature, and can be described by [tau][proportional to]exp([ital E][sub [ital a]]/[ital kT])more » with an activation energy of 3.73, 4.44, and 5.08 [+-]0.07 eV for 1000, 550, and 250 A Ti, respectively. An unusual transition between nucleation sites was observed as a result of the scaling: for samples with 250 A Ti, the transformation proceeded by nucleating the [ital C]54 polymorph at grain edges (three-grain junctions) of the [ital C]49-TiSi[sub 2] films while the [ital C]54 nuclei were predominantly formed at the grain boundaries (two-grain junctions) in thicker films, which are in good agreement with predictions of the nucleation mode from kinetics analyses. It has been suggested that the nucleation of the [ital C]54-TiSi[sub 2] is likely to be the rate-limiting step in the overall transformation. Based on microstructural evidences provided by TEM, the significance of these observations due to reduction in film thickness was discussed by considering energetics of nucleation at different geometrical sites, nucleation site density, and effects of surface and stress. It was demonstrated that the surface contribution and nucleation site density become important for nucleation in thinner films with largely increased surface-to-volume ratio...« less