The sample material volume or bulk electrical conductivities
were measured in terms of their volume or bulk electrical
resistivity using a four-point probe technique; the lower the
resistivity, the higher the conductivity since conductivity is
the reciprocal of resistivity. For resistivity calculations, the
samples would ideally be semi-infinite, i.e., the sample
extends for all intents and purposes to infinity in all directions
(and hence sample dimensions) below the plane upon which
the four probes are to be located because then the true samp