A novel thin film phase of oriented MgO grown from a liquid solution

Close lattice matching with a MgAl2O4 (0 0 1) substrate has been used to synthesize thin films of a rare spinel-like polymorph of MgO (b-MgO) that is unstable in bulk form. The film is produced by spin casting an acetate-substituted Mg-ethoxide precursor, which forms a crystalline magnesium acetate phase at room temperature. Pyrolysis of most organic constituents occurs during continuous heating from room temperature to 4001C and is followed by formation of phase-pure b-MgO at To7001C. Four-circle X-ray diffraction indicates that the film is highly oriented with the substrate lattice, with o0:051 tilt or twist between the (0 0 1) planes of the film grains and the (0 0 1) planes of the substrate. Kinetic and/or energetic constraints arising from the presence of a substrate are responsible for stabilizing b-MgO: bulk powders formed from the same precursor yield only the usual rock salt MgO structure and, although the formation of some b-MgO occurs on widely different substrate types, its volume fraction crystallographic orientation can be tuned by using closely lattice-matched substrate crystals. r 2001 Published by Elsevier Science B.V. PACS: 68.55.–a; 81.15.Lm; 61.10.–i