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

Close lattice matching with a MgAl2O4 (001) substrate has been used to synt hesize thin films of a rare spinel-like polymorph of MgO (beta -MgO) that i s unstable in bulk form. The film is produced by spin casting an acetate-su bstituted Mg-ethoxide precursor, which forms a crystalline magnesium acetat e phase at room temperature. Pyrolysis of most organic constituents occurs during continuous heating from room temperature to 400 degreesC and is foll owed by formation of phase-pure beta -MgO at T < 700 degreesC. Four-circle X-ray diffraction indicates that the film is highly oriented with the subst rate lattice, with < 0.05 degrees tilt or twist between the (001) planes of the film grains and the (001) planes of the substrate. Kinetic and/or ener getic constraints arising from the presence of a substrate are responsible for stabilizing beta -MgO: bulk powders formed from the same precursor yiel d only the usual rock salt MgO structure and, although the formation of som e beta -MgO occurs on widely different substrate types, its volume fraction crystallographic orientation can be tuned by using closely lattice-matched substrate crystals. (C) 2001 Published by Elsevier Science B.V.