Raman spectroscopic study of the mixed anion mineral yecoraite Bi₅Fe₃O₉(Te⁴⁺O₃)(Te⁶⁺O₄)₂·9H₂O

Abstract

Tellurates are rare minerals as the tellurate anion is readily reduced to the tellurite ion. Often minerals with both tellurate and tellurite anions are found. An example of such a mineral containing tellurate and tellurite is yecoraite. Raman spectroscopy has been used to study this mineral, the exact structure of which is unknown. Two Raman bands at 796 and 808 cm −1 are assigned to the ν 1 (TeO 4 ) 2− symmetric and ν 3 (TeO 3 ) 2− antisymmetric stretching modes and Raman bands at 699 cm −1 are attributed to the ν 3 (TeO 4 ) 2− antisymmetric stretching mode and the band at 690 cm −1 to the ν 1 (TeO 3 ) 2− symmetric stretching mode. The intense band at 465 cm −1 with a shoulder at 470 cm −1 is assigned the (TeO 4 ) 2− and (TeO 3 ) 2− bending modes. Prominent Raman bands are observed at 2878, 2936, 3180 and 3400 cm −1 . The band at 3936 cm −1 appears quite distinct and the observation of multiple bands indicates the water molecules in the yecoraite structure are not equivalent. The values for the OH stretching vibrations listed provide hydrogen bond distances of 2.625 Å (2878 cm −1 ), 2.636 Å (2936 cm −1 ), 2.697 Å (3180 cm −1 ) and 2.798 Å (3400 cm −1 ). This range of hydrogen bonding contributes to the stability of the mineral. A comparison of the Raman spectra of yecoraite with that of tellurate containing minerals kuranakhite, tlapallite and xocomecatlite is made.

Lattice dynamics and pressure-induced phase transitions in α-BaTeMo2O9

“…It is worth noting that the wavenumber range established for the stretching modes of Te-O-Mo bridges in α-BaTeMo 2 O 9 is in very good agreement with the range where stretching vibrations of TeO 3 groups were reported, i.e. 550-800 cm −1 [25,26]. This result proves that vibrations of the Te-O-Mo bridges are governed primarily by the character and strength of the Te-O bonds.…”

Rich Non-centrosymmetry in a Na–U–Te Oxo-System Achieved under Extreme Conditions

“…Owing to OH – stretching vibrations, both uranyl tellurite compounds have weak broad bands located from 2800 to 3100 cm –1 . These bands are comparable to those found in many tellurite minerals, such as sonoraite (Fe III Te IV O 3 (OH)·H 2 O) and yecoraite (Bi 5 Fe 3 O 9 (Te IV O 3 )­(Te VI O 4 ) 2 ·9H 2 O) . A close resemblance between the Raman spectra of Na 2 [(UO 2 )­(Te VI 2 O 8 )] and Na 2 [(UO 2 )­Te VI O 5 ] can be detected.…”

Growth and characterization of nonlinear optical telluromolybdate CoTeMoO 6 single crystals

“…According to literature data, translations of molybdenum and tellurium atoms contribute to lattice modes observed below 200 cm À 1 [6,7,[21][22][23][24]. Translations of Co 2 þ are usually observed in the same region as Mn, Ni, Fe, i.e.…”

“…The former range can be attributed to stretching modes and the latter to bending and lattice modes. Based on literature data for molybdates, tellurates containing TeO 4 units and telluromolybdates, we may assign the 890-960 cm À 1 bands to stretching vibrations of the short Mo-O bonds, whereas the bands in the range and 610-790 cm À 1 correspond to stretching vibrations of Mo-O bonds and Mo-O-Te bridges [6,7,[21][22][23][24]. In a similar way, we may propose assignment of the 250-480 cm À 1 bands to bending modes of the Mo-O and Te-O bonds as well as Mo-O-Te bridges.…”