D. Gharailou, A. Abbasi,
Volume 12, Issue 3 (9-2015)
Abstract
Effect of electro migration on crystal structures of platinum nanowire (Nano bridge) during Nano-gap
formation is investigated by means of Transmission Electron Microscopy (TEM). Selected area diffraction patterns as
well as bright field images are used for this investigation. There were severely recessions in the polycrystalline Nano
bridge and crystal structures around the nanogap changed completely during electro migration. Due to Joule heating,
original small crystal with random orientation disappeared and newly crystals with a preferred orientation grew. They
have [111] orientations (respect to beam direction) with slight misorientations. α and θ was defined to calculate the
misorientation and used to represent Nano-gap formation mechanism. The calculation gives the breaking of Nano
bridge occurred along grain boundaries in most of Nano bridges. The controlling system during eletromigration may
affect on the shapes of tips so that the shape of tips in Nano bridges, in which feedback control is applied, is more
symmetric than others. The effect of temperature on atomic diffusivity might be the reason of the behaviour. {422}
could be a preferred surface plane for mass transport in platinum Nano bridge in which atoms move along it
H. Mohebbi, S.m. Mirkazemi,
Volume 17, Issue 4 (12-2020)
Abstract
Flash sintering of 8 mol% yttria-stabilized zirconia (8YSZ) as solid oxide fuel cell (SOFC) electrolyte is studied. The relation between relative density, shrinkage, sample temperature during the flash, and incubation time, with the electric field strength, current density, as well as contact paste, are modeled by response surface methodology (RSM). The electric field strength and current density varied from 50 to 400V.cm-1 and 50 to 200mA.mm-2, respectively. Also, platinum (Pt) and lanthanum strontium manganite (LSM) used as contact paste. Results show that using LSM paste lead to higher density and more shrinkage compare with Pt paste. Contrary, the electric field strength has no significant effect on density and shrinkage. However, a minimum electric field strength equal to 80 V.cm-1 is necessary for flash onset. As the field increases, the incubation time decreases dramatically. Compare with samples with LSM paste, samples with Pt contact paste reach to a higher temperature during the flash. Flash sintered 8YSZ shows the mean grain size of 0.3μm, which is about half of the conventionally sintered 8YSZ. Electrochemical Impedance Spectroscopy reveals despite lower mean grain size, the resistivity of flash sintered 8YSZ is lower than conventionally sintered 8YSZ.
