It was found that the temperature dependence of the conductivity exhibited 2 characteristic discontinuities: at -52 and -113C. It was assumed that phase transformations, accompanied by a sudden change in the activation energy for conduction, corresponded to these temperatures. It was concluded that the product of conductivity and temperature, over the various ranges of behavior, could be described by:

-136 to -113C:     σT (SK/cm) = 3.9 x 107 exp[-0.25(eV)/kT]

-113 to -52C:     σT (SK/cm) = 2.45 x 105 exp[-0.184(eV)/kT]

-52 to 163C:     σT(SK/cm) = 1.26 x 104 exp[-0.127(eV)/kT]

N.N.Vershinin, J.I.Malov, E.A.Ukshe: Elektrokhimiya, 1984, 20[11], 1538-40