Review on structural and chemical properties of transition metal phosphorous trisulfides MPS3

The MPS3 phases constitute a large family of layered compounds which properties are extremely varied and original. From a stability point of view and contrary to transition metal layered dichalcogenides MX2 that are mainly encountered for the IV, V and VID transition elements, the thiophosphates exist from vanadium to zinc. The synthesis of the thiophosphates from the elements can be very easily done and leads to phases with a very good stoichiometry, except for the vanadium derivative that yields a phase of mixed valence (V0.78PS3). Because of the transition metal low oxidation state, many heterocharge substitution possibilities exist with, in particular, the substituted phases M12IM12III PS3 (MI = Ag, Cu, MIII = Cr, V, In). Respective to the cationic radii ratio, in these substituted layered materials one can find either order or disorder at the cation sites. One important case corresponds to the occurence of one dimensional arrangement with (ID) magnetic chains trapped within the (2D) sheets of the structure. Such structures that imply strong ployhedral distortions are only possible because of the great adaptability of the anionic (P2S6)4− groups which are able either to distort or to elongate in respect with the intraslab cation size. The lability of the transition metal is correlated to the ligand field stabilization and is clearly shown through the thermal vactor values calculated from structural determinations. The cations with d5 and d10 configuration can thus easily be substituted, at ambient temperature, by more electropositive cations, and this is quite an original chemical behavior of the MPS3. MPS3 electronic band structures indicate that the accepting levels of these phases are constituted by the transition metal d-orbitals. During the intercalation of donor elements, reduction of the host has then to take place on the transition metal, which oxidation state is lowered at unexpected small values. During lithium intercalation in these phases, 31P NMR results and 57Fe Mössbauer spectroscopy are in agreement with a redox scheme occurrence of very reduced cationic species in the host material. Hence the question of the electronic transfer in the LixMPS3 intercalates is solved. That seems to finally correspond to the rather classical scheme of cationic reduction. The electrochemical characteristics of the MPS3 as cathodic materials in room temperature lithium batteries are well related to band and crystal structure factors as well as to the structures bonds ionicity and to some of their chemical properties.