Elaboration and characterization of glassy cobalt phosphomolybdates

摘要

Selecting two series of P_2O_5-based oxide glasses containing at the same time the MoO_3 and CoO oxides, an investigation of structural properties has been undertaken by infrared (IR) and electron paramagnetic resonance (EPR) spectroscopies. The structure of glasses inside the CoO-MoO_3-P_2O_5 system may be considered as made of several types of molybdenum and phosphorous structural groups, the ratios of which depend on composition. The EPR spectra of Mo(V) ions are characterized by the large anisotropy of g- and A-tensors along the local z axis. The values of the covalency parameters k_‖ and k_⊥ determined for some glasses are correlated to the axial distortion of (Mo~V O_6) octahedron along the z axis. EPR spectra carried out at lower temperatures show additional broad line near g ≈ 4 and a narrow one at g ≈ 2. The former is attributed to the HS form of cobalt(II) in octahedra site. The latter is associated with LS electron configuration of Co~(2+) ions and/or Mo~(5+) centers. The existence of Co~(2+) in octahedral environment in both HS and LS forms is interpreted in term of a spin-crossover for Co(II) in these glasses.