Equilibrium-thickness amorphous films on (1 1 (2)over-bar 0) surfaces of Bi2O3-doped ZnO

Model experiments and thermodynamic calculations revealed that a nanometer- thick liquid/amorphous film is the equilibrium configuration of the {1 1 (2 ) over bar 0} surfaces of Bi2O3-rdoped ZnO. In samples equilibrated both ab ove and below the eutectic temperature, bismuth enriched amorphous films we re observed. The film thickness is fairly uniform. The average thickness of ninety-seven films formed at 780 degrees C (above the eutectic temperature , 740 degrees C) is 1.54 nm, with a narrow standard deviation of 0.28 nm. I n addition, the thickness was found to be independent of firing time or sec ond phase fraction. Therefore, we conclude that the surface film has an 'eq uilibrium- thickness.' A thermodynamic model is presented. This new observa tion may have relevance to the understanding and control of surface coating s in ceramics and related properties. (C) 1999 Elsevier Science Limited All rights reserved.