Tailoring of Colloidal HfO₂ Nanocrystals with Unique Morphologies and New Self‐Assembly Features

Abstract

Advancing the synthesis of HfO2 nanocrystals, a refined anhydrous protocol that enables kinetic trapping of the metastable tetragonal phase and modulates twinning defects in anisotropically grown monoclinic nanoprisms is presented. This evolved sol–gel approach examines the role of the capping agent tri‐n‐octylphosphine oxide (TOPO) and introduces a novel heating strategy with sequential growth stages. Replacement of TOPO with triphenylphosphine oxide (TPPO) leads to the formation of prismatic hafnia nanocrystals exhibiting pristine {011}‐facets of the monoclinic phase. Furthermore, a hot‐injection inspired heating approach yields sub‐4 nm isotropic HfO2 nanocrystals in the tetragonal phase, bypassing the need for aliovalent cation species. In contrast, a heat‐up approach culminates in the generation of well‐characterized HfO2 nanorods. With sophisticated transmission electron microscopy analysis and the Wulff construction method, insights into the structural nucleation of nanoparticle growth are provided. This synthesis offers exceptional control and facilitates the formation of self‐assemblies akin to liquid crystals, opening the door for new applications with nanocolloidal HfO2.

Complexation and disproportionation of group 4 metal (alkoxy) halides with phosphine oxides

“…The same chemistry is relevant for titania and hafnia nanocrystals, where the choice of metal halide, metal alkoxide, and of the Lewis base plays a crucial role in the determination of the final properties of the product. 4,14–18 Although the nature and stability of the formed metal complexes are of direct consequence to the outcome of nanocrystal syntheses, detailed insights into the coordination of alkoxy halides are lacking.…”

Epitaxial Core/Shell Nanocrystals of (Europium-Doped) Zirconia and Hafnia

“…Surfactant-assisted, nonaqueous synthesis methods have allowed the synthesis of ZrO 2 and HfO 2 NCs with control over their size. ,− Even more, solid solutions of various compositions (Zr x Hf 1– x O 2 ) were obtained as colloidal nanocrystals. ,, Hf 0.5 Zr 0.5 O 2 is an interesting ferroelectric material, making it promising for nonvolatile memory devices. , …”