Defects in Fe1-xO and the Fe1-xO to Fe3O4 phase transition studied by the perturbed angular correlation method

Abstract

The time differential perturbed angular correlation (PAC) method has been applied to study defects in iron monoxides, using iron-implanted 111In probes. Besides a broad distribution of electric field gradients two well-defined quadrupole coupling constants have been detected nu Q=97(4) MHz, eta =0 and nu Q=71(2) MHz, eta =0.32(2). The first one was associated with an indium-iron vacancy complex, while the second one, visible in a high-temperature measurement, was tentatively assigned to indium having trapped two iron vacancies and one interstitial iron atom (the so-called Roth-type cluster). Structural transformations between different complexes and the Fe1-xO to Fe3O4 phase transition are discussed. From the analysis of the vacancy/interstitial ratio, a sizeable fraction of 4:1 defect clusters at low temperatures can be excluded. The proposed defects are compared with those recently observed in the chemically and structurally similar cobalt monoxide CoO.