Résumé : Mo films were deposited on sintered polycrystalline MgO. These films exhibited, depending on deposition conditions, two different structures, namely the normal body-centered cubic and an abnormal face-centered cubic. The analysis performed by electron diffraction and Auger electron spectroscopy indicated that the fcc structure assumed by molybdenum is an impurity-stabilized phase rather than a simple polymorphic transformation or dimolybdenum nitride (γMo2N) as previously stated by some authors. © 1994.