Anisotropic electrical conductivity of delafossite-type CuAlO2 laminar crystal

Delafossite-type CuAlO2 laminar crystals (R3̄m) were prepared through melt by a cooling method from 1423 K. The layer-by-layer structure of the crystal was observed. Because of the structural anisotropy of the crystal, electrical conductivity along the ab plane (σab) was higher than that along the c axis (σc), σab≳25σc. The anisotropy unveiled that the main conduction path of the crystal is closed-packed Cu+ layers. The values of the activation energies which were estimated from the Arrhenius plot were ∼0.20 and ∼0.13 eV for σc and σab, respectively. The linearity in the log σ vs (1/T)1/4 plot and the positive thermoelectric power (>+300 μV/K) of the crystal suggested p-type variable-range hopping conduction.