Accessing Metastable Solid-Solution Nanoparticles from Solution-Phase Condensation Reactions: Applications in High-K Dielectrics, Geopolymerization, and X-Ray Phosphors

Abstract

This dissertation focuses on the design, synthesis, and functional applications of ceramic materials prepared with precise compositional, dimensional, and structural control from molecular precursors using a versatile sol—gel condensation process. Three primary thrusts have stemmed from this central idea: (i) mapping the size-dependent phase diagram of HfOv2 and stabilizing the metastable tetragonal phase of HfOv2 at room temperature as a result of dimensional confinement, thereby obtaining a technologically important high-dielectric-constant polymorph that is only accessible above a temperature of 1720°C in the bulk; (ii) developing a method to cross-link plant fibers through creation of siloxane frameworks, resulting in the stabilization of a mechanically resilient load-bearing composite for roadworks in the Alberta Oil Sands; and (iii) stabilizing solid-solution rare earth oxychloride (REOCl) nanocrystals across a broad compositional range to obtain a full palette of X-ray phosphors, allowing for elucidation of activation channels, sensitization mechanisms, and recombination pathways underpinning X-ray-activated optical luminescence. The dissertation develops a versatile synthetic toolbox for defining oxide and oxyhalide frameworks. The choice of molecular precursors and ligands added during synthesis strongly influence kinetics of particle growth and allow for compositional control as well as tunability of particle dimensions. The metastable materials synthesized in this work have allowed for exploration of the size-dependent phase diagram of HfO2 and have enabled the development of quaternary and quintary solid-solution phosphors based on the PbFCl-type LaOCl and GdOCl frameworks.