Raman spectroscopic study of the tellurite minerals: emmonsite Fe₂³⁺Te₃⁴⁺O₉·2H₂O and zemannite Mg_0.5[Zn²⁺Fe³⁺(TeO₃)₃]4.5H₂O

Abstract

Raman spectroscopy has been used to study zemannite Mg 0.5 [Zn 2+ Fe 3+ (TeO 3 ) 3 ]4.5H 2 O and emmonsite Fe2 3+ Te3 4+ O 9 ·2H 2 O. Raman bands for zemannite and emmonsite, observed at 740 and 650 cm −1 and at 764 and 788 cm −1 , respectively, are attributed to the n 1 (TeO 3 / 2− symmetric stretching mode. The splitting of the symmetric stretching mode for emmonsite is in harmony with the results of X-ray crystallography which shows three non-equivalent TeO 3 units in the crystal structure. Two bands at 658 and 688 cm −1 are assigned to n 3 (TeO 3 / 2− anti-symmetric stretching modes. Raman bands observed at 372 and 408 cm −1 for zemannite and 397 and 414 cm −1 for emmonsite are attributed to the (TeO 3 / 2− n 2 .A 1 / bending mode. The two Raman bands at 400 and 440 cm −1 for emmonsite are ascribed to the n 4 .E/ bending modes, while the band at 326 cm −1 is due to the n 2 .A 1 / bending vibration.