The causes of the decrease in electrical conductivity with aging in 11203-stabilized zirconia, an oxygen-ion conductor, were studied. This study was carried out using the dc four-probe technique for measuring electrical conductivity and the activation energy for the migration of oxygen ions. The results show that conductivity decreased with aging below certain temperatures in all specimens. Moreover, it was found that conductivity decreases significantly as the temperature decreases. Samples that were aged at relatively low temperatures exhibited a decrease in conductivity and an increase in activation energy. It was concluded that short range ordering of oxygen ion vacancies toward the zirconium to relax the anistropy of the lattice distortion is the cause of the decrease in electrical conductivity and the increase in activation energy. When aging was carried out at a relatively high temperature, fully stabilized zirconia showed no change in activation energy and only a slight increase in conductivity. This is because oxygen ion vacancies are in the disordered state and the cubic phase is the only phase at this temperature. Short range ordering of oxygen ion vacancies takes such a long time presumably because these oxygen ion vacancies are still able to move even after aging. This was explained using the concept of mean first passage time Infroduction Since Nernst reported Y203-doped Zr03 in 18991 and the

Microstructural changes in yttria-stabilized zirconia with aging were investigated by X-ray diffraction, high resolution transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy under TEM, and electron diffraction. First, various microstructural changes reported in the literature as the causes of the decrease in conductivity were carefully examined. As a result, almost all of them proved not to be the direct cause. Therefore, the changes with aging were analyzed mainly by calling attention to a characteristically broad area that appears on the left shoulder of the X-ray diffraction peaks as well as the superlattice reflections and diffuse scattering seen on electron diffraction patterns, and the relationship between microstructural changes and conductivity was clarified. It is concluded that various phenomena due to aging at relatively lower temperatures are caused by short range ordering of oxygen ion vacancies, which occurs in order to relax the anisotropy of periodical lattice distortion. We also studied changes in microstructures occurring with changing dopant concentrations and concluded that the changes in microstructures responsible for the decrease in conductivity associated with increasing dopant concentration are caused by short range ordering of oxygen ion vacancies in order to relax the anisotropy in strain fields, similarly to those with aging. InfroductionA number of microstructural studies of stabilized zirconia have been conducted using various methods, including neutron diffraction and scattering,1'6 X-ray diffraction and scattering7-9 electron diffraction,10'14 and transmission electron microscopy (TEM).15"8 Because partially stabilized zirconia is a useful material with incomparably high toughness due to stress-induced phase transformation, many microstructural studies of it have been conducted, examining phase transformations, characterizing lattice defects,

No abstract

Changes in local structures with aging in yttria-stabilized zirconia were examined by extended x-ray absorption fine structure (EXAFS) and internal friction measurement. An analysis of EXAFS shows that a decrease in the first nearest neighbor coordination number of Zr ions, which means short range ordering of oxygen ion vacancies, a decrease in distance between a Zr ion and its first nearest atoms, and an increase in distance between a Zr ion and its second nearest atoms occurred in aged 8YSZ. Aging caused a noticeable decrease in the relaxation peak of internal friction in 8YSZ. These phenomena are attributed to the short range ordering of oxygen ion vacancies around a Zr ion that results from relaxation in the anisotropy of periodical lattice distortion. Therefore, it is concluded that the trapping of oxygen ion vacancies at Zr ions in order to relax such distortion is responsible for a decrease in conductivity with aging. The relaxation peak of internal friction before aging changed with increasing dopant concentrations, and the behavior of this change from 8YSZ to 1OYSZ was very similar to that when 8YSZ was aged, and that from 1OYSZ to 15YSZ was similar to that when a single crystal of 1OYSZ was aged. This marked similarity indicates that the changes in crystal structure which cause the decrease in conductivity with increasing dopant concentration are caused by the short range ordering of oxygen ion vacancies brought about by relaxation of the distortion, similar to those when conductivity decreases with aging.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 138.251.14.35

No abstract

No abstract

No abstract

No abstract