Structural Arrangement in Close-Packed Cobalt Polytypes

Abstract

In this paper, we present a comprehensive study on how stacking faults, crystallite size, crystallite size distribution as well as shape and strain dictate the nature of the X-ray powder diffraction patterns of small (<20 nm) and large (>20 nm) cobalt (Co) nanoparticles. We provide a unique library of simulated diffractograms which can be used for fingerprint analysis. Likewise, the simulated data are used as a basis for structural refinements of experimentally obtained Xray powder diffractograms. We provide examples of using the library for fingerprint analysis and for full structural analysis of synthesized Co nanoparticles. Structural refinements presented in this study allow to reveal fine structural details that directly correlate to different behavior upon heating in a CO atmosphere relative to a H 2 or He atmosphere. All calculations were performed using the Discus package and the Debye scattering equation.

A real-space approach to the analysis of stacking faults in close-packed metals: G(r) modelling and Q-space feedback

“…and hexagonal closepacked (h.c.p.) signatures: these constitute clear evidence of the occurrence of complex patterns of stacking faults in this metal, as observed by several authors (more recently, Sokalski et al, 2011;Longo et al, 2014;Sławiń ski et al, 2018;Li et al, 2018). More generally, stacking fault disorder is recognized in several close-packed metals, even if in a less evident way than in cobalt (Yu et al, 2016;Bertolotti et al, 2016;Dupraz et al, 2015;Longo & Martorana, 2008).…”

There's no place like real-space: elucidating size-dependent atomic structure of nanomaterials using pair distribution function analysis

“…Since then, several PDF and total scattering studies have focused on the structures of non-fcc and hcp structures in metallic nanoparticles. 117,123,124 Vargas et al used PDF and TEM to characterize the atomic structure in long and ultrathin Au nanowires. In this study, many possible structural models in 2 nm by 12 nm nanowires were generated and energetically optimized using Molecular Dynamics simulations.…”

Atomic Structure of 2 nm Size Metallic Cobalt Prepared by Electrochemical Conversion: An in Situ Pair Distribution Function Study

“…The level of stacking faults can be quantified by a probability of stacking faults. For example, a 50% probability of stacking faults implies that there is an equal proportion of hcp and fcc sequences, a situation referring to randomly stacked layers …”