C-axis oriented β″-alumina ceramics with anisotropic ionic conductivity prepared by spark plasma sintering

• SPS method is effective for lowering sintering temperature of β″-alumina.
• Uniaxial pressure application causes an alignment of conduction planes.
• Total Na+ ion conductivity on the order of 10− 2 S·cm− 1 is available at RT.

High-density β″-alumina with relative density exceeding 98% was obtained by spark plasma sintering (SPS) at 1400 °C for 15 min. X-ray diffraction measurements and scanning electron microscopy demonstrated that the c-axis of the β″-alumina grains oriented along the direction of pressure application during SPS. Na volatilization was well suppressed by encapsulation in a carbon die and a short sintering time. Higher ionic conductivity was observed along the vertical direction than along the direction of pressure application owing to the alignment of the conduction plane in β″-alumina crystals. The highest total conductivity at 25 °C was 1.9 × 10− 2 S⋅cm− 1.