Polycrystalline samples of LixNi1-yCoyO2-delta(x = 0.6, 0.9 and y = 0.5, 1, with delta much less than 1 depending on the stoichiometry) with and without the addition of 50 wt% alpha-Al2O3 were prepared and examined by XRD, TGA, DTA and a.c. electrical techniques. LixCoO2 and its mixture with alpha-Al2O3 is unstable above 1050 K. Materials containing Ni were stable up to 1173 K and no interaction with alpha-Al2O3 was found after 6 h at 1173 K. Maximum conductivity in Ar was obtained for Li0.9Ni0.5Co0.5O2-delta between 100 Hz and 1 MHz up to 950 K. The high temperature conductivity of Li0.9Ni0.5Co0.5O2-delta could be modified with the addition of alpha-Al2O3 to render it suitable for an RF reactor. At 650 K the conductivity reversibly increased in CO2 and rapidly decreased in H-2 followed by a slow increase on removal of H-2, behaviour typical of a p-type semiconductor. At 870 K the conductivity increased in H-2 due to slow and irreversible reduction of the oxides.