LOW DIMENSIONAL CONDUCTORS : A NEW SERIES OF TRANSITION METAL TETRACHALCOGENIDES (MX_4)_nY (M = Nb, Ta ; X = S, Se ; Y = halogen) : STRUCTURAL DETERMINATIONS AND PHYSICAL PROPERTIES(EXPERIMENTS ON (MX_4)_nY COMPOUNDS, International Symposium on NONLINEAR TRANSPORT AND RELATED PHENOMENA IN INORGANIC QUASI ONE DIMENSIONAL CONDUCTORS)
In studies concerning low-dimensional conductors, the chemist plays an important role. He has to prepare new materials taking in account some structural rules and ionicity structure relationship about the relative stability of atomic fibers or slabs in a given structure. Then he has to look for new polytypes associating in different ways the same slabs or fibers. He can also act upon the lateral bonds which link chains together, thus modifying the real dimensionality of the compounds. Finally, he also has to be concerned with the depinning of C.D.W. because the depinning field is impurity or defect dependent (defects being created by irradiation technique). In this paper, I would like to illustrate these points with some materials elaborated in our group at NANTES University. I will briefly remind you some aspects concerning trichalcogenides before presenting a new class of materials, the halogened tetrachalcogenides of transition metal (MX_4)_nY.