CuAlO2 thermoelectric compacts by SPS and thermoelectric performance improvement by orientation control

We fabricated CuO/Al2O3 green compacts from plate-like Al2O3 and granular CuO powders by multi-press forming and investigated the alumina orientation using Lotgering's method. The results showed that Al2O3 particles preferentially aligned perpendicular to the pressure direction and the orientation degree increased as the forming pressure was increased. We proposed a model describing the movement of the alumina particles to explain the pressure effect on their orientation. The orientation calculation was in good agreement with those by Lotgering's method. Furthermore, we prepared the CuAlO2 compacts by regular or spark plasma sintering (SPS). However, the compacts sintered by SPS exhibited higher orientation degree and density than those produced by regular sintering. The electrical conductivity values of the orientation-controlled compacts sintered by SPS reached 770 S m−1 at 928 K, which was close to that of CuAlO2 single crystal. The power factor of the CuAlO2 compacts with highest orientation degree is as high as 5.95 × 10−5 W m−1 K−1 at 928 K. Therefore, we can conclude that orientation control is an effective method to enhance the thermoelectric performance of compact polycrystalline CuAlO2 bulks.