High conductivity porous oxides formed on Zr-2.5 wt% Nb

Influence of Oxidation Media on the Transport Properties of Thin Oxide Layers of Zirconium Alloys

“…The oxide layer was not uniform. There was black hypostoichiometric layer of relatively high conductivity near the oxide-metal interface, whereas the outer layer was white and of high resistivity, as was shown metallographically by Cox et al [14]. It is well known [7][8][9] that bulk ZrO 2 is predominantly an electronic high-resistivity semiconductor with a certain amount of ionic conduction at higher temperatures [7].…”

“…The oxide films are not homogeneous, but consist of a substoichiometric black oxide layer of high conductivity, near the metal-oxide interface, as stated by Cox et al [14], and of an almost stoichiometric white layer of high resistivity. At larger film thickness the high resistivity layer dominates.…”

“…Fully oxidized layers are of monoclinic structure, whereas substoichiometric black layers with oxygen deficiency can have a tetragonal structure [15]. Moreover, part of the layer near the surface can be porous [14], so that painted-on electrode material could enter into the pores and alter the effective thickness of the layers. The relative permittivity computed from capacitance measurements of specimens of different electrode metals often deviated from the accepted value of e r = 22 for bulk zirconium oxide.…”

“…The relative permittivity computed from capacitance measurements of specimens of different electrode metals often deviated from the accepted value of e r = 22 for bulk zirconium oxide. This may be due to partly to the porosity of the layers or to wetting difficulties of the contacts, or to inhomogeneities of the layers [14]. Oxidation in aqueous surroundings leads to the development of hydrogen and can enter into the layers and even into the bulk zirconium [16].…”