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MATERIALS ENGINEERING

SEMINAR

“Proton Doping and Characterization of Rare Earth Nickelates”

By

Derek Karl Wittenburg Schwanz

Purdue MSE Ph.D. Final Exam

Advisor: Professor Shriram Ramanathan

ABSTRACT

Perovskite rare earth nickelates with formula RNiO₃ (R = trivalent rare earth lanthanides) feature exceptional electrical behavior and performance in a wide variety of functional applications due to their unique metal-insulator transition. This distinctive phase transition is caused by charge disproportionation as the crystal structure distorts upon temperature change and electron-electron interactions result in a modified band structure. However, electron doping of the same nickelate systems has created a more pronounced phase transition wherein unprecedented resistivity changes on the order of 10¹⁰ Ω*cm are achieved through the opening of a wide bandgap. In this work, a new method for inducing a water-mediated electrically driven phase transition is examined through the use of various processing methods and investigation of subsequent effects on the structural and material properties. Electrochemically driven doping of protons is caused through potentiostatic bias applications and linear sweep voltammetry, while the effects on the electrical and optic properties are observed and correlated with structural data collected through x-ray and neutron scattering. Finally, the effects of A-site substitution (Sm, Nd, Eu) on the doping process are assessed.

Date: Tuesday, June 19, 2018

Time: 10:00 A.M.

Place: ARMS 1028