Defect clusters in wustite, Fe1−xO

Interdiffusion induced defect microstructures of Co(1-x)O near confined zirconia particles

Diffusion couples of metal alloys were commonly used to study Kirkendall pore formation and amorphization near the interface of composition discontinuity. In this work, yttria-partially stabilized zirconia (Y-PSZ) powders mixed with Co(1-x)O (1:99 molar ratio, denoted as Z1C99) were sintered and annealed at 1600 degrees C for 1-75 h to study interdiffusion-induced defect microstructures of Co(1-x)O near confined Y-PSZ particles. Analytical electron microscopic analysis indicated a much larger flux of Co(2+) from Co(1-x)O into Y-PSZ compared to the reverse flux of Zr(4+) and Y(3+). In addition, there is a significant inward flux of oxygen from Y-PSZ into Co(1-x)O. A net vacancy flux in the opposite direction of ion flux then caused the formation of Kirkendall pores and dislocations in Co(1-x)O near corrugated Y-PSZ/Co(1-x)O interface. Amorphous regions and [111] faulting were also found in Co(1-x)O near Kirkendall pores, which can be rationalized by diffusion-induced amorphization and assembly of cation vacancies along close-packed [111] planes vulnerable to crystallographic shear, respectively. Y-PSZ particles were found to migrate-coalesce as corrugated slabs and rods at Co(1-x)O grain boundaries and junctions, respectively, when the composite with more Y-PSZ additive (Z(1)C(89)) was annealed.

Positive holes in magnesium oxide. Correlation between magnetic, electric, and dielectric anomalies

Magnetic susceptibility measurements of high purity MgO single crystals (<50-wt. ppm transition metals) by means of a vibrating-sample magnetometer shows an anomaly at 800 K. At the same temperature the electric conductivity increases anomalously, the static dielectric constant epsilon increases from 9 to approximately 150, a pronounced positive surface charge appears, and Fe2+ in the MgO matrix oxidizes to Fe3+. The data are consistent with O2(2-) (peroxy) defects, representing self-trapped, spin-paired positive holes at Mg2+ vacancy sites. Diamagnetic at low temperatures, the holes start to decouple their spins > 600 K, probably forming at first V0 centers (two O- at an Mg2+ vacancy), then V- centers (single O- at an Mg2+ vacancy), and releasing mobile O- states. These O- represent itinerant charge carriers on acceptor levels near the O 2p-dominated valence band and conduct by O- /O2- valency fluctuations. The O- concentration is of the order of 8 X 10(19) cm-3.