Point defect clusters in transition metal monoxides

It was already known that the non-stoichiometry in Fe1-xO consists not only of vacant Fe sites, due to the composition, but also Fe ions in tetrahedral sites. We discovered that these vacancies and tetrahedral ions were not randomly arranged or ordered, as had ben suggested, but instead were clustered, in large groups, which were in fact groups of vacancy tetrahedra, each occluding an Fe interstitial. this was quite exciting at the time, because until then very little thought had been given to this possibility. The Magneli phases (shear structures that lead to composition changes by shearing the octahedral building blocks of many oxides so that they share edges and faces rather than corners) were known, but otherwise pint defects were thought to be isolated. Our result was determined mainly from the extra diffuse scattering away from Bragg peaks. In this brief paper, the authors summarize out latest efforts which have evolved around two remaining questions: Many proposals have been made as to the exact configuration of the clusters in Fe1-xO but the experimental evidence these clusters were, in turn, periodical arranged on the corners of 3 x 3 x 3 NaC/ cells. Mn1-xO is another cation deficient oxide but, unlike Fe1-xO, the stoichiometric composition exists at atmospheric pressure. It is also a semiconductor like Fe1-xO