Preparation of Na 19-Alumina Thin Films by RE-Sputtering and Their Ionic Conduction

NOBUGAI Kohji, KANAMARU Fumikazu

doi:10.1246/nikkashi.1987.2242

Thin amorphous films of composition Na₂O.xAl₂O₃(5 x 13) were prepared by RF-sputtering1and converted to Na β-alumina by heat treatment. The effects of the sputtering conditions on chemical composition, microtexture, and ionic conductivity of the films were examined. The Na content in the film varied not only with the Na content of the target, but by the surface temperature of the target. In the case of low surface temperature, the atomic ratio of Na to Al in the films was lower than that of the target. The Na deficiency was due to low sputtering yield of Na atoms. However, the Na content in the films increased with the rise in surface temperature of the target. This fact is considered as. a result of thermal evaporation of Na atoms on the target surface. The microtexture of the sputtered films depended on both the RF-power and the gas pressure, and amorphous films of homogeneous texture were obtained at a lower RF-power(50 W) and lower gas pressure(0.53 Pa).<BR>Thin film Na p-alumina of composition Na₂O.6.9 Al₂O₃ obtained by cryst allization of amorphous films exhibited an ionic conductivity of 5.8 x 10^-2 Sicm at 300°C with an activation energy of 0.26 eV the former value is higher than the conductivity of bulk sintered Na β-alumina. This high ionic conductivity, close to that of a single crystal, is due to both the dense microtexture formed, by crystallization of the poreless amorphous films and the preferred orientation of crystallites with the (001) plane parallel to the film surface. The ionic conduction mechanism of an intermediate phase appearing on the amorphous to β-phase transition is discussed in terms of its nonstoichiometry.

Preparation of Na 19-Alumina Thin Films by RE-Sputtering and Their Ionic Conduction

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