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

Abstract Raman and infrared spectroscopy were performed on synthesized spinel oxide powders of solid solution Mg x Ni 1 − x Cr 2 O 4 , over the full range of composition 0 ≤ 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, NiCr 2 O 4 and MgCr 2 O 4 . 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, A 1 g , and the two higher-wavenumber infrared modes, ν 1 and ν 2 , 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 E g and F 2 g ( 1 ) modes exhibit a nonlinear increase in wavenumber.