Selective Growth of Monoclinic and Tetragonal Zirconia Nanocrystals

Abstract

The growth of metal oxide nanocrystals with a well-organized crystalline phase is of fundamental and technological interest because in this way it is possible to tune their size-dependent unique properties. In this communication, we demonstrate the selective growth of monoclinic and tetragonal ZrO₂ nanocrystals of 3)₄⁺. The nanocrystals were grown in aqueous solution at 150 °C. It was revealed, by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and optical absorption studies, that the nanocrystals capped by N(CH₃)₄⁺ have a less defective pure monoclinic phase, while those without capping have a pure tetragonal phase with highly disordered oxygen vacancies. The N(CH₃)₄⁺ capping on the surface oxygen site can reduce the surface energy low enough to stabilize the monoclinic phase. By contrast, the bare surface oxygen site has higher energy; thereby, the lower surface energy tetragonal phase is formed spontaneously. The present concept is a promising universal approach to control the crystal phases of technologically important oxide nanocrystals