Grain Boundary Segregation and Blocking Effects in Polycrystalline TiO2
Open Access
- Author:
- Wang, Qinglei
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 16, 2008
- Committee Members:
- Elizabeth C Dickey, Committee Chair/Co-Chair
Clive A Randall, Committee Member
Long Qing Chen, Committee Member
Theresa Stellwag Mayer, Committee Member - Keywords:
- grain boundary segregation
TiO2 - Abstract:
- Titanium dioxide was studied as a model material to investigate the grain boundary segregation of yttrium and niobium as a function of dopant concentration. Local grain boundary defect chemistry was quantitatively determined by analytical transmission electron microscopy. Electrical properties associated with both bulk and the grain boundaries were obtained using impedance spectroscopy. Experimental findings were compared to the high-temperature equilibrium thermodynamic space-charge models that incorporated both electrostatic and elastic driving forces for solute segregation. For yttrium, solute excess density at the grain boundaries was found to increase with the dopant concentration until the solid state solubility was reached. The activation energy for electrical conduction increased with dopant concentration, which implied a blocking barrier at the grain boundaries introduced by the solute interfacial excess. Local grain boundary defect chemistry, including core and space-charge layers, was employed to understand the relationship between the specific grain boundary resistivity and solute excess. The thermodynamic models showed that the elastic driving force was dominant in this system and electrostatic driving force only contributed a 10-20% correction to the total solute segregation. In comparison to the experimental results, the models provided good predictions for several grain boundary parameters including local stoichiometry, solute interfacial excess, barrier height and space charge layer thickness.