Ionic ordering and infrared spectra of some II-IV spinels

The infrared absorption spectra in the range from 200 to 700 cm−1 are reported for the spinels NiMn2O4, NiMnZnO4, LiZnNbO4, and M2TiO4 with MMg, Mn, Fe, Co, and Zn. The compounds Mn2TiO4 and Zn2TiO4 could be obtained with 1:1 order on octahedral sites. This ordering gives a superstructure in the IR spectrum, which was not observed in the case of the cobalt and iron compound because of the normal-inverse disorder occurring in the cobalt titanate and the oxygen nonstoichiometry of the iron titanate. The infrared spectra of NiMn2O4 and NiMnZnO4 give evidence of the short-range order in these materials from which the cation valencies in NiMn2O4 can be deduced to be NiMn(1−v)2+(Ni2+vMnMn) O4.