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

Nonstoichiometric Ba β-alumina single crystals, Ba1−0.25xMg1−xAl10+xO17+0.25x (0≦x≦1), were prepared in the BaO–MgO–Al2O3 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 (PO2), while σ⊥ showed a PO2−1/6 dependence in a low PO2 region of PO2=10−4 to 10−13 Pa.