Electrical conductivity of nonstoichiometric Ba β-alumina single crystals prepared by a floating zone method

Abstract

Nonstoichiometric Ba β-alumina single crystals, Ba 1−0.25 x Mg 1− x Al 10+ x O 17+0.25 x (0≦ x≦1), were prepared in the BaO–MgO–Al 2O 3 system by a floating zone method. The single crystals were cleaved parallel to a (001) plane. The electrical conductivity parallel to the cleavage plane ( σ //) was 10 to 20 times greater than that perpendicular to the cleavage plane ( σ ⊥). The σ // and σ ⊥ had the maximum at around x=0.5. The activation energy of σ ⊥, 240 to 270 kJ/mol, was slightly greater than that of σ //, 170 to 190 kJ/mol. The σ // was almost independent of oxygen partial pressure ( P O 2 ), while σ ⊥ showed a P O 2 −1/6 dependence in a low P O 2 region of P O 2 =10 −4 to 10 −13 Pa.