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Discrete evolution of the crystal structure during the growth of Ba-hexaferrite nanoplatelets


An understanding of the adaptation of the crystal structure of materials confined at the nanoscale, the influences of their specific structures on the evolution of their morphologies and, finally, their functional properties is essential not only for expanding fundamental knowledge, but also for facilitating the designs of novel nanostructures for diverse technological and medical applications. Here we describe how the distinct structure of barium-hexaferrite nanoplatelets evolves in a stepwise manner in parallel with the development of their size and morphology during hydrothermal synthesis. The nanoplatelets are formed by reactions between Ba- and Fe-hydroxides in an aqueous suspension at temperatures below 80 oC. Scanning-transmission electron microscopy showed that the structure of the as-synthesized, discoid nanoplatelets (2.3 nm thick, 10 nm wide) terminates at the basal surfaces with Ba-containing planes. However, after subsequent washing of the nanoplatelets with water the top two atomic layers dissolve from the surfaces. The final structure can be represented by a SRS* sequence of the barium-hexaferrite SRS*R* unit cell, where S and R represent a hexagonal (BaFe6O11)2- and a cubic (Fe6O8)2+ structural block, respectively. Due to the stable SRS* structure, the thickness of the primary nanoplatelets remains unchanged up to approximately 150 oC, when some of the primary nanoplatelets start to grow exaggeratedly and their thicknesses increase discretely with the addition of the RS segments to their structure. The SRS* structure of the primary nanoplatelets is too thin for the complete development of magnetic ordering. However, the addition of just one RS segment (SRS*R*S structure) gives the nanoplatelets hard magnetic properties.

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Publication details

The article was received on 11 May 2018, accepted on 12 Jul 2018 and first published on 13 Jul 2018

Article type: Paper
DOI: 10.1039/C8NR03815E
Citation: Nanoscale, 2018, Accepted Manuscript
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    Discrete evolution of the crystal structure during the growth of Ba-hexaferrite nanoplatelets

    D. Makovec, B. Belec, T. Goršak, D. Lisjak, M. Komelj, G. Dražič and S. Gyergyek, Nanoscale, 2018, Accepted Manuscript , DOI: 10.1039/C8NR03815E

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