MICROSTRUCTURAL CHANGES IN A POLYCRYSTALLINE, SEMICONDUCTING OXIDE UNDER DC ELECTRIC-FIELDS

Microstructural changes have been examined in a polycrystalline, semic onducting oxide, e.g., CoO, under de electric fields in an air-electro de condition. A change always starts at a singularity such as an inter face or phase boundary where the divergence of partial cationic curren t does not vanish (i.e., del . i(ion) not equal 0). The changes (at de l . i(ion) < 0, in particular) are characterized by the growth of the oxide beyond the permeable, original boundary of the system oxide, the grain growth and densification of the initially porous matrix, and th e growth of a single-crystalline region at the expense of the polycrys talline matrix. These are qualitatively explained by chemical diffusio n that is caused by the electrotransport-induced, chemical polarizatio n at those singularities.