Infrared phonon study of the S = 1 spinel oxide ZnV₂O ₄

We have obtained infrared phonon spectra of spinel structure vanadium oxide ZnV₂O₄ over the temperature range 10K<T<100K from reflectivity measurements. When the material undergoes the structural transition at T_s = 51K each of the four phonon peaks is split into a doublet (eight phonons) and additionally two new phonons appear at ω = 187 and 488cm^-1. Point group analysis shows that such phonon change is consistent with the crystal symmetry I4₁/amd at T<T_s. We compare this result against recent theories about the orbital ordering mechanism in tetragonal ZnV₂O₄.