• Billinge, Simon J. L.
• Bøjesen, Espen Drath
• Birgisson, Steinar
• Christensen, Mogens
• Jensen, Kirsten M. Ø.
• Bremholm, Martin
• Tyrsted, Christoffer
• Dippel, Ann Christin
• Saha, Dipankar

Abstract

<p>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.</p>

Topics

• nanoparticle
• impedance spectroscopy
• amorphous
• phase