Date of Award
Fall 1993
Document Type
Dissertation - Restricted
Degree Name
Doctor of Philosophy (PhD)
Department
Electrical and Computer Engineering
Abstract
Yttria stabilized zirconia(YSZ), one of the zirconia-based solid electrolytes, is well known for its high ionic conductivity. As an oxygen ionic conductor over a wide range of temperature and oxygen partial pressures, YSZ has a wide application as an oxygen sensor, an oxygen pump and in solid oxide fuel cells(SOFC). In recent years, fine powder YSZ starting materials have become available. These powders have significantly improved the fabrication of products with high purity and high density. Furthermore, the transformation toughening behavior was found in the partially stabilized zirconia. This discovery led to the special interest in 3Y-TZP(3 m/o Y2O3-ZrO2) which contains primarily the tetragonal structure. Along with its ultra-high strength, its excellent thermal shock resistance provides another stimulus for investigating the electrical behavior of 3Y-TZP. 3Y-TZP also has a higher ionic conductivity at low temperature than other YSZ electrolytes. The high ionic conductivity is desirable for applications involving gas sensors and SOFC. However, there is a dearth of information regarding the defect structure and non stoichiometric thermodynamic behavior of 3Y-TZP. In this study two types of solid state electrochemical cell techniques were used to investigate the defect structure and non stoichiometric thermodynamic behavior of 3Y-TZP. The electronic transport behavior at low oxygen pressure was also investigated. At elevated temperatures, the electrical conductivity is determined primarily by the ionic point defects(i.e. oxygen vacancies). However, electrons or electronic defects generated by the nonstoichiometric reaction at low oxygen pressure increase the electronic conductivity which reduces the ionic transference number. The minority carriers in YSZ are produced by the nonstoichiometric behavior which is controlled by the temperature, oxygen partial pressure, and doping concentration of Y203...