Understanding and Controlling Reaction Pathways for Synthesis of Oxynitride Materials

Goldfine, Elise Ann

doi:https://doi.org/10.21985/n2-2629-3y20

Work

Understanding and Controlling Reaction Pathways for Synthesis of Oxynitride Materials

Public

Download PDF

Download All Files (.zip)

Heteroanionic materials are a class of materials of interest for their unique and tunable electronic, ionic, thermal, and optical properties, which are distinct from their homoanionic counterparts due to their multi-anionic nature. Oxynitrides, a type of heteroanionic material, are useful catalysts due to the effect of mixing oxygen and nitrogen atoms on their bandgap and catalytic binding energy. Oxynitride materials have been relatively underutilized because of the difficulty in synthesizing them. In this work, in situ x-ray diffraction is used to study the ammonolysis reaction for the synthesis of bulk oxynitride materials. Two promising catalytic oxynitride materials are studied in depth: MoON and TaON. Once the reaction mechanisms are elucidated, methods for controlling the syntheses to produce materials with desirable properties are explored. Additionally, methods for the thin film growth of targeted oxynitride materials predicted by computational discovery are explored.Chapter 1 provides an in depth look at the ammonolysis of MoO3 to form MoON by combined in situ XRD and TEM. The reaction pathway, roles of reaction intermediates, and crystallographic relationships among the phases are mapped. Building off the understanding of the ammonolysis reaction gleaned in Chapter 1, Chapter 2 explores the use of alternate precursors to bypass a critical intermediate phase and thus produce the target oxynitride phase at low temperature with high surface area and Chapter 3 details the use of alternate heating conditions to produce the target phase with ultra-low oxygen content. In Chapter 4, the in situ synthesis technique is applied to the ammonolysis of Ta2O5 to synthesize TaON, and several key insights into the reaction are determined. Chapter 5 details three methods investigated for the growth of MoON and TaON thin films, including (1) PLD of oxide films with post-deposition ammonolysis, (2) N-plasma assisted PLD, and (3) reactive sputtering. The thesis concludes with a summary of and outlook on the progress towards the goal of synthesis-on-demand of oxynitrides.

Creator