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Title: Structure and Mobility of Dissociated Vacancies at Twist Grain Boundaries and Screw Dislocations in Ionic Rocksalt Compounds

Abstract

Interfaces, grain boundaries, and dislocations are known to have significant impact on the transport properties of materials. Even so, it is still not clear how the structure of interfaces influences the mobility and concentration of carriers that are responsible for transport. Using low angle twist grain boundaries in MgO as a model system, we examine the structural and kinetic properties of vacancies. These boundaries are characterized by a network of screw dislocations. Vacancies of both types, Mg and O, are strongly attracted to the dislocation network, residing preferentially at the misfit dislocation intersections (MDIs). However, the vacancies can lower their energy by splitting into two parts, which then repel each other along the dislocation line between two MDIs, further lowering their energy. This dissociated structure has important consequences for transport, as the free energy of the dissociated vacancies decreases with decreasing twist angle, leading to an increase in the net migration barrier for diffusion as revealed by molecular dynamics simulations. Similar behavior is observed in BaO and NaCl, highlighting the generality of the behavior. Finally, we analyze the structure of the dissociated vacancies as a pair of jogs on the dislocation and construct a model containing electrostatic and elastic contributionsmore » that qualitatively describe the energetics of the dissociated vacancy. Our results represent the first validation of a mechanism for vacancy dissociation on screw dislocations in ionic materials first discussed by Thomson and Balluffi in 1962.« less

Authors:
 [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1438122
Report Number(s):
LA-UR-18-20967
Journal ID: ISSN 0897-4756
Grant/Contract Number:  
AC52-06NA25396
Resource Type:
Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 30; Journal Issue: 6; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Kolluri, Kedarnath, Martinez Saez, Enrique, and Uberuaga, Blas Pedro. Structure and Mobility of Dissociated Vacancies at Twist Grain Boundaries and Screw Dislocations in Ionic Rocksalt Compounds. United States: N. p., 2018. Web. doi:10.1021/acs.chemmater.7b05172.
Kolluri, Kedarnath, Martinez Saez, Enrique, & Uberuaga, Blas Pedro. Structure and Mobility of Dissociated Vacancies at Twist Grain Boundaries and Screw Dislocations in Ionic Rocksalt Compounds. United States. doi:10.1021/acs.chemmater.7b05172.
Kolluri, Kedarnath, Martinez Saez, Enrique, and Uberuaga, Blas Pedro. Mon . "Structure and Mobility of Dissociated Vacancies at Twist Grain Boundaries and Screw Dislocations in Ionic Rocksalt Compounds". United States. doi:10.1021/acs.chemmater.7b05172. https://www.osti.gov/servlets/purl/1438122.
@article{osti_1438122,
title = {Structure and Mobility of Dissociated Vacancies at Twist Grain Boundaries and Screw Dislocations in Ionic Rocksalt Compounds},
author = {Kolluri, Kedarnath and Martinez Saez, Enrique and Uberuaga, Blas Pedro},
abstractNote = {Interfaces, grain boundaries, and dislocations are known to have significant impact on the transport properties of materials. Even so, it is still not clear how the structure of interfaces influences the mobility and concentration of carriers that are responsible for transport. Using low angle twist grain boundaries in MgO as a model system, we examine the structural and kinetic properties of vacancies. These boundaries are characterized by a network of screw dislocations. Vacancies of both types, Mg and O, are strongly attracted to the dislocation network, residing preferentially at the misfit dislocation intersections (MDIs). However, the vacancies can lower their energy by splitting into two parts, which then repel each other along the dislocation line between two MDIs, further lowering their energy. This dissociated structure has important consequences for transport, as the free energy of the dissociated vacancies decreases with decreasing twist angle, leading to an increase in the net migration barrier for diffusion as revealed by molecular dynamics simulations. Similar behavior is observed in BaO and NaCl, highlighting the generality of the behavior. Finally, we analyze the structure of the dissociated vacancies as a pair of jogs on the dislocation and construct a model containing electrostatic and elastic contributions that qualitatively describe the energetics of the dissociated vacancy. Our results represent the first validation of a mechanism for vacancy dissociation on screw dislocations in ionic materials first discussed by Thomson and Balluffi in 1962.},
doi = {10.1021/acs.chemmater.7b05172},
journal = {Chemistry of Materials},
number = 6,
volume = 30,
place = {United States},
year = {2018},
month = {3}
}

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Figures / Tables:

Figure 1 Figure 1: Atomic structure of low angle {100} twist grain boundaries in MgO. (a−c) Structure of (a) 3.5°, (b) 5°, and (c) 10° twist grain boundaries after construction and energy minimization but before the removal of MgO formula units. As the twist angle is increased, the spacing between dislocations andmore » MDIs decreases. A 7.5° twist boundary was also considered but is not shown here. Cations are shown as larger than anions for clarity and ions are colored by their coordination number. (d) Energy of the grain boundary as a function of the number of MgO formula units removed from one MDI. The insets show the structure of the MDI as MgO formula units are removed. (e) The final structure of the 7.5° twist boundary after two formula units of MgO have been removed from each MDI.« less

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