Infrared reflectivity of γ-(spinel)Ni2SiO4

The infrared reflectance spectrum of a polycrystalline sample of the high pressure Ni 2 SiO 4 -spinel polymorph has been recorded from 100 to 1200 cm −1 . The four infrared active modes expected from symmetry analysis (F 1u ) have been observed and their approximate TO-LO frequencies are 231-234 (±2), 350-420 (±5), 500-540 (±5) and 810-955 (± 10) cm −1 . These data are compared with previous infrared studies of normal spinels with tetravalent cations (silicates and germanates). A simple harmonic model is used to infer the position of the lowest frequency infrared mode of Mg 2 SiO 4 -spinel at ≃ 300 cm −1