A mixed valence compound in the two dimensional MPS3 family: V0.78PS3 structure and physical properties

Abstract The non stoichiometric compound V0.78PS3 has been obtained as single crystals from a preparation corresponding to the atomic ratio V/P/S = 1/1/3. It cristallizes with monoclinic symmetry, space group C2/m, with the unit cell parameters a = 5.867(1) A , b = 10.160(2) A , c = 6.657(1) A , β = 107.08(2)°, V = 379.3(1) A 3 and Z =4. The structure refinement was made down to a reliability factor value R = 3.3% from 445 reflexions (I > 3 σ (I)) and 31 variables. The material has same layer structure as FePS3 with the occurrence of the thiophosphate anion (P2S6)4−-including a P2 pair. In V0.78PS3, the charge equilibrium implies the following developped formula : V0.34II V0.44III □0.22 PIV S3−II. The phase is a semi-conductor with a small activation energy of 0.24 eV, in accord with a vanadium mixed valence, and it presents, at low temperature, an antiferromagnetic order (TN = 62 K).