Modeling of Dislocations and Mismatched Layers in Pentagonal Nanorods
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1086-U08-32
Modeling of Dislocations and Mismatched Layers in Pentagonal Nanorods Anna L. Kolesnikova1, and Alexei E. Romanov2 1 Institute of Problems of Mechanical Engineering, St. Petersburg, 199178, Russian Federation 2 Ioffe Physico-technical Institute, St. Petersburg, 194021, Russian Federation ABSTRACT Pentagonal nanorods (PNRs) are crystalline objects with unique fivefold symmetry. They are often experimentally observed for materials with FCC crystal structure. In an ideal case a PNR consists of five elastically distorted but otherwise perfect crystalline regions divided by lowenergy twin boundaries. The elastic distortions in PNRs and associated stored elastic energy are effectively described in the framework of a disclination approach. As a result of mechanical stress relaxation, the stored energy can be diminished in expense of structural defect formation in PRN interior. It is demonstrated that a perfect multiple twinned PNR structure is unstable with respect to dislocation formation, i.e. prismatic dislocation loop or straight edge dislocation, for PNRs above a certain critical diameter. A new mechanism for the relaxation processes in PNRs is theoretically investigated. This mechanism assumes the formation of the shell possessing crystal lattice mismatch with respect to the PNR core region. The optimal magnitude for core/shell crystal lattice mismatch and optimal shell thickness providing maximum energy release for this mechanism of mechanical stress relaxation, are predicted. INTRODUCTION It is well-known that crystalline nanoparticles, nanowires and nanorods produced from materials with FCC crystal structure often demonstrate axes of fivefold symmetry These objects are known as pentagonal nanoparticles (PNPs) and pentagonal nanorods (PNRs), e.g. see reviews [1,2] and recent works [3-5]. During FCC crystal growth low-energy twin boundaries (TBs) can be formed in the particle or nanorod body. These TBs divide PNP or PNR into mutually misoriented crystalline regions, i.e. twins. In an ideal case, low-energy TBs are the only defects in PNPs and PNRs. Otherwise PNPs and PNRs can be defect free providing physical and mechanical properties, for example strong anisotropy, high mechanical strength and hardness, being similar to those observed for monocrystalline whiskers [1]. PNPs and PNRs demonstrate remarkable physical properties (e.g. enhanced catalytic activity [1,2], optical properties [5]) dictated by their distinct crystallography, shape morphology and intrinsic lattice distortions. The presence of elastic distortions in PNPs and PNRs leads to the emergence of various relaxation processes accompanied by the rearrangements of their structure. Present work deals with modeling of two kinds of relaxation processes in PNRs: (i) via dislocation formation in the PNR interior and (ii) via the formation of a shell possessing crystal lattice mismatch with respect to the PNR core region. BACKGROUND The structure of PNPs and PNRs and elastic distortions of their crystal lattice can be completely understood in the f
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