The electrochemical formation of magnesium nitride (Mg3N2) films in LiCl-KCl containing Li3N at 723 K was investigated. From a thermodynamic point of view, a potential-pN(3-) diagram was constructed for the Mg-N system in an analogous fashion to Pourbaix diagrams for aqueous solutions. As a result, the thermodynamically stable region of Mg3N2 in LiCl-KCl-Li3N was identified. XRD analysis revealed that Mg3N2 film was obtained by potentiostatic electrolysis of a magnesium electrode between 0.4 and 0.8 V (versus Li+/Li), and the structure of obtained Mg3N2 was anti-bixbyite (a = 1.001 nm). Reflectance measurements clarified that assuming direct transition, the bandgap energy was 3.15 eV and assuming indirect transition, the bandgap energy was 2.85 eV. (C) 2005 Elsevier Ltd. All rights reserved.