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Martin Bremholm

Towards atomistic understanding of polymorphism in the solvothermal synthesis of ZrO2 nanoparticles

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Varying atomic short-range order is correlated with the ratio of the monoclinic (m) to tetragonal (t) phase in ZrO2 nanoparticle formation by solvothermal methods. Reactions from Zr oxynitrate in supercritical methanol and Zr acetate in water (hydrothermal route) were studied in situ by X-ray total scattering. Irrespective of the Zr source and solvent, the structure of the precursor in solution consists of edge-shared tetramer chains. Upon heating, the nearest-neighbor Zr - O and Zr - Zr distances shorten initially while the medium-range connectivity is broken. Depending on the reaction conditions, the disordered intermediate transforms either rapidly into m-ZrO2, or more gradually into mixed m- and t-ZrO2 with a concurrent increase of the shortest Zr - Zr distance. In the hydrothermal case, the structural similarity of the amorphous intermediate and m-ZrO2 favors the formation of almost phase-pure m-ZrO2 nanoparticles with a size of 5nm, considerably smaller than the often-cited critical size below which the tetragonal is assumed to be favoured. Pair distribution function analysis thus unravels ZrO2 phase formation on the atomic scale and in this way provides a major step towards understanding polymorphism of ZrO2 beyond empirical approaches.The chemical path towards different polymorphs in the solvothermal synthesis of zirconia nanoparticles is decided by a complex interplay among reactants and applied conditions: at low temperature the structural similarity between the amorphous intermediate phase and monoclinic ZrO2 results in almost phase-purenm monoclinic ZrO2. Atomic scale pair distribution function analysis over the entire course of the reaction provides an understanding, and thereby control, of nanoparticle polymorphism.

Original languageEnglish
JournalActa Crystallographica Section A: Foundations and Advances
Pages (from-to)645-650
Number of pages6
Publication statusPublished - 2016

    Research areas

  • nanoparticles, pair distribution function, polymorphism, solvothermal synthesis, zirconia

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