Loading...
Estimating valence states of transition metal dopants in polycrystalline strontium titanate and barium zirconate with magnetometry
Knight, Michael Robert
Knight, Michael Robert
Citations
Altmetric:
Advisor
Editor
Date
Date Issued
2022
Date Submitted
Keywords
Collections
Research Projects
Organizational Units
Journal Issue
Embargo Expires
Abstract
Doping with transition metal cations is known to impact processing and performance of polycrystalline strontium titanate (STO) and yttrium-doped barium zirconate (BZY). Lightly Fe-doped STO is commonly used as a model representative for acceptor-doped large band gap electroceramics. BZY is a promising proton conductor for applications in protonic ceramic fuel cells (PCFCs) operating on methane or other hydrocarbon fuels. BZY is difficult to sinter below 1700 degrees Celcius, however, when small amounts of Ni are incorporated, sintering temperatures are significantly reduced. In both systems, the valence state of the dopant may affect transport properties and redox reactions in electrochemical applications. Valence states can be estimated from their magnetic properties because the only major species having unpaired valence electrons are the dopants, which manifests an electronic magnetic moment. In particular, superconducting quantum interference device (SQUID) magnetometry is demonstrated to provide new information about these two technologically relevant material systems. In STO, the ratio Fe4+/Fe3+ increases with PO2 of the sintering atmosphere and with increasing Fe-doping from 0.2 mol% to 1.2 mol%. In BZY, Ni3+ is shown to exist in a low-spin state and anisotropic coordination environment. Dopant segregation near grain boundaries is suggested by the presence of superexchange interactions in both systems, and experimentally observed by STEM-EDS mapping in 4 mol% Ni-doped BZY. Additionally, this work reveals that greater concentrations of the secondary active-sintering BaY2NiO5 phase remain in the BZY microstructure upon completion of solid-state reactive sintering when NiO is added as a sintering aid versus when Ni is substituted for Zr.
Associated Publications
Rights
Copyright of the original work is retained by the author.