EPR study of Mo-V in the tetragonal and monoclinic phases of zirconia

MoOx/ZrO2 (Mo-95-enriched or not) samples were prepared by adsorption or coprecipitation and were subsequently heated in air or oxygen at 773 or 1073 K, Depending on the heating temperature and the Mo content, clustered Mo-V species (Mo-clust(V)) and isolated Mo-V species in tetragonal (Mo-tetr(V)) and/or monoclinic (Mo-mon(V)) phases were formed. Mo-V species were detected by EPR only at low temperature (77 K), were formed by treatments in oxidizing conditions, and were insensitive to leaching treatment. Computer simulation of the spectra yielded the following spin-Hamiltonian parameters for isolated species: g(parallel to) = 1.960, g(perpendicular to) = 1.843, A(parallel to) = 34 G, and A(perpendicular to) = 90 G for Mo-tetr(V); g(xx) = 1.803, g(yy) = 1.883, g(zz) = 1.965, A(xx) = 81 G, A(yy) = 61 G, and A(zz) = 16 G for Mo-mon(V). The ground state, spin polarization factor, and spin-orbit reduction factor were calculated by the equations of McGarvey.