Anisotropic electrical conductivity of delafossite-type CuAlO2 laminar crystal

Delafossite-type CuAlO2 laminar crystals (R (3) over barm) 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 (sigma (ab)) was higher than that along the c axis (sigma (c)), sigma (ab)greater than or similar to 25 sigma (c). 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 similar to0.20 and similar to0.13 eV for sigma (c) and sigma (ab), respectively. The linearity in the log sigma vs (1/T)(1/4) plot and the positive thermoelectric power (> +300 muV/K) of the crystal suggested p-type variable-range hopping conduction. (C) 2001 American Institute of Physics.