EFFECTS OF DOPING AND DEFECTS IN BaSnO3 AND COVETIC ALLOYS

Abstract

Doping and defects have played major roles for optimizing the structural, electrical, optical and mechanical properties of materials over the centuries. With the advent of modern fabrication and characterization tools, we are engineering materials by modifying the fundamental structure at the nano-scale. Such research and innovations are necessary to find alternatives of the known materials to meet technological, economic and environmental challenges. In this dissertation, we will discuss two classes of materials to identify the effects of atomic level engineering on the enhanced properties of Covetic alloys and BaSnO3 perovskites.

The first part of the thesis is based on the nanoscale and surface characterizations of the carbon doped metal alloys of aluminum and silver produced by the Covetic process. We have found the presence of sp2 bonded 3D epitaxial carbon in graphene nano-ribbon form on the aluminum and silver atomic planes. Such directional presence of sp2 carbon in the crystalline form along with other allotropes will be studied. Here, we have detailed the bonding, strain, defect concentrations, and oxidation characteristics of these compositions, and distinguished Covetic materials from other carbon based composites. Covetic process is significant as it defies the traditional metal-carbon phase diagrams under non-equilibrium conditions.

The second part of the dissertation focuses on the BaSnO3, a major candidate in s-band electronics and transparent conducting oxide industry. Here, we will demonstrate the role of oxygen vacancies for inducing high conductivity in the BaSnO3 thin films from insulating state and their stability on single crystal substrates deposited by pulsed laser deposition. To further investigate the role of multi-valent rare earth element doping on optical and electronic properties, results of Lead (Pb), Bismuth (Bi) and Strontium (Sr) substitution by combinatorial synthesis of BaSnO3 are presented. We have tuned the bandgap from 3 to 4 eV based on the substitutions, and observed clustering and in-gap states for Pb and Bi-substitutions, respectively. Lastly, experiments regarding the search of the BaSnO3 based superconductors by carrier injection, multi-valent states and strain engineering will be discussed.