Abstract
Ferropericlase (Mg1–xFex)O solid solution was prepared by ball milling of the mixture of MgO with a rock-salt structure and metal Fe powders in atmosphere and at room temperature. Differing from (Mg1–xFex)O prepared at high temperature by using MgO and FeO as starting materials, the solution of Fe in MgO is not continuous but limited in the ball milling process, and the solubility limit is less than 30 at. pct. About 92 pct of the Fe ions occupy the site of tetrahedral oxygen coordination in trivalent Fe (Fe3+) with high spin, whereas about 8 pct of the Fe ions occupy the site of octahedral oxygen coordination in bivalent Fe (Fe2+) with high spin. The Fe3+ and Fe2+ ions do not show a ferromagnetic but show a paramagnetic state. The as-milled (Mg1–xFex)O is metastable and decomposes to ferropericlase (Mg1–yFey)O (where y < x) and MgFe2O4 with spinel structure as annealed above 773 K (500 °C), and the content of Fe in the (Mg1–yFey)O increases with increasing annealing temperature. A bulk (Mg1–xFex)O was fabricated by annealing the as-milled (Mg1–xFex)O powders at 973 K (700 °C). It shows n-type conductivity, which is attributed to an electronic small polaron with an activation energy of 0.135 eV.
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