Spectroscopic study of the vibrational modes of magnesium nickel chromite, MgxNi1−xCr2O4MgxNi1−xCr2O4

Raman and infrared spectroscopy were performed on synthesized spinel oxide powders of solid solution MgxNi1−xCr2O4MgxNi1−xCr2O4, over the full range of composition 0≤x≤10≤x≤1, to determine the dependence of the vibrational modes on the divalent cation, which occupies the tetrahedral site of the normal spinel lattice. X-ray diffraction shows a nearly linear change in the lattice parameter of the solid solution. Our data agree with literature values for the pure chromites, NiCr2O4NiCr2O4 and MgCr2O4MgCr2O4. Solid solution data are reported here for the first time. All observed vibrational modes exhibit one-mode behavior and increase in wavenumber when nickel is replaced by magnesium. The wavenumbers of the highest-wavenumber Raman mode, A1gA1g, and the two higher-wavenumber infrared modes, ν1ν1 and ν2ν2, do not significantly change with substitution of the divalent cation, while the lower-wavenumber Raman and infrared modes are affected by this cation substitution on the tetrahedral site. The EgEg and F2g(1)F2g(1) modes exhibit a nonlinear increase in wavenumber.

► The mixed spinel MgxNi1−xCr2O4MgxNi1−xCr2O4 characterized using XRD, Raman, and infrared. ► Frequencies of detected vibrational modes increase as nickel substitutes magnesium at the tetrahedral site. ► High frequency A1gA1g mode largely unaffected by tetrahedral substitution. ► Lower frequency vibrational modes more strongly affected by tetrahedral substitution.