Surface conduction versus bulk conduction in pure stoichiometric NiO crystals

Abstract From the measurement of three-probe resistivities, which are much larger than two-probe resistivities, we conclude that annealed, nominally pure and nearly stoichiometric NiO single crystals normally have a low-resistivity surface layer which masks the behaviour of the bulk in most electrical measurements. Bulk resistivities larger than 1016 Ω cm have been measured below 100°C. It is possible that the results of nearly all previous Hall, resistivity and thermoelectric-power measurements made on high-resistivity samples are indicative of the surface rather than the bulk properties of NiO.