Theses and Dissertations

Date of Award

7-1-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

First Advisor

Nicholas Dimakis

Second Advisor

Constantine Tarawneh

Third Advisor

Mkhitar Hobosyan

Abstract

The development of reliable sensing materials is essential for infrastructure maintenance and early-warning detection technologies. This work investigates two ceramic-based sensing materials: rare-earth-doped lithium tantalate (LiTaO₃, LT) for near-infrared optical sensing relevant to crack detection, and silver-modified hexagonal boron nitride nanocomposites (Ag/defect h-BN) for carbon monoxide (CO) gas sensing. A computational and experimental approach was used to evaluate their structural, electronic, optical, and sensing properties.

Density functional theory (DFT) was used to study various rare-earth doped LT configurations, while GW-Bethe–Salpeter equation (GW-BSE) calculations were used to investigate the electronic and optical properties of pristine, defective, and Ag-modified defect h-BN. In LT, rare-earth doping introduced localized 4f states that modified the electronic structure and tunable optical response. Quantum Theory of Atoms in Molecules (QTAIM) and Electron Localization Function (ELF) analyses were used to characterize chemical bonding and electron localization in the doped LT structures. For Ag/defect h-BN, band-structure and optical property calculations showed that CO adsorption is strongly defect-dependent. CO binds strongly at Ag-decorated B-vacancy sites, whereas the interaction is weak at Ag-decorated N-vacancy sites.

Experimentally, LT-based powders and Ag/h-BN nanocomposites were synthesized and characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Photoluminescence (PL), and conductivity measurements. The Ag/h-BN nanocomposites exhibited preliminary CO-responsive conductive behavior. The h-BN-30 wt.% Ag pellet showed a decrease in conductivity during CO exposure, followed by a recovery during purging. In contrast, the h-BN-80 wt.% Ag pellet showed an incomplete recovery under the present test conditions, indicating that a higher Ag content hinders reversibility.

Overall, rare-earth doping was shown to tune the optical response of LT for near-infrared crack detection, while Ag incorporation enhanced the CO-sensing performance of defect h-BN based ceramic nanocomposites. These findings demonstrate the potential of advanced ceramic nanomaterials for optical and gas-sensing applications in structural health and environmental monitoring.

Comments

Copyright 2026 Andrea Pelayo Carvajal. All Rights Reserved. https://proquest.com/docview/3409025088

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