It was recalled that, in an electronically conducting oxide, an electronic flow might theoretically be induced not only directly by the electronic electrochemical potential gradient itself, but also indirectly by the ionic electrochemical potential gradient. It was noted that it had long been believed, without evidence, that the indirect cross-effect was negligible. It was pointed out here that it had recently been discovered that the cross-effect was non-negligible in non-stoichiometric CoO. Three different experiments which revealed the non-zero cross-effect were described.

H.I.Yoo: Key Engineering Materials, 1997, 125-126, 331-54