ELECTRICAL-CONDUCTIVITY IN AMORPHOUS MOLYBDENUM SULFIDES

Non-stoichiometric amorphous molybdenum sulphides MoS2+x (0 less-than-or-equal-to x less-than-or-equal-to 1) have been prepared from thermal decomposition of synthetic ammonium thiomolybdate. The evolution from amorphous MoS3 to amorphous MoS2 can be followed by a study of the d.c. and a.c. conductivities. This method leads us to assume that electrical conductivity arises from electronic hopping between localized states. A theoretical model is used, and W(M), the potential energy of the electron, can be determined (0.7-1.3 eV), as well as N, the number of sites (about 10(-24) m-3) involved in the polarization conductivity mechanism. For the composition MoS2.6, W(M) and N decrease sharply, showing a pseudo-transition which can be clearly related to a short-range reorganization within the amorphous material.