Raman and IR studies of TaWO_5.5, ASbWO₆ (A = K, Rb, Cs, Tl), and ASbWO₆·H₂O (A = H, NH₄, Li, Na) pyrochlore oxides

Abstract

Raman and infrared (IR) spectra of defect pyrochlores TaWO 5.5 , NH 4 SbWO 6 ·H 2 O, HSbWO 6 ·H 2 O, LiSbWO 6 ·H 2 O, NaSbWO 6 ·H 2 O, KSbWO 6 , RbSbWO 6 , CsSbWO 6 , and TlSbWO 6 were measured. The obtained spectra are discussed using the factor group approach for the cubic Fd-3m space group, and assignment of bands to respective motions of atoms is proposed. Our results show that the phonon properties of the pyrochlores are strongly affected by disorder, and therefore Raman and IR spectroscopies are very useful tools in studying disorder in this family of compounds. In particular, our studies have shown that in these ionic conductors disorder at sites occupied by NH + 4 , H + , or alkali-metal ions decreases with increasing size and mass of these ions.

Preparation, characterization and photocatalytic studies of N, Sn-doped defect pyrochlore oxide KTi0.5W1.5O6

“…The strong and broad band observed in the 500 -800 cm -1 region is attributed to Ti/WO 6 metaloxygen stretching vibrations. The bands seen in the regions 380 -430 and 300 -350 cm -1 correspond to bending modes of Ti/WO 6 [25,26]. The band (medium intensity) found at 1136 cm -1 in SnKTW may be assigned to M-O-H bending vibrations arising due to lattice water [27].…”

“…The two weak bands in the region 420-520 cm -1 are due to bending modes of the WO 6 octahedra while the strong band at 550-800 cm -1 can be assigned to octahedral metal (M/W)-oxygen stretching vibrations [23,25,26]. A broad band in the high wavenumber region, centered at 681 cm -1 for undoped KTW is dominating the Raman spectra.…”

“…In the defect pyrochlore structure, generally the A site atoms can occupy three crystallographic positions 16(d), 8(b), and 32(e). However, X-ray data showed that in disordered defect pyrochlore systems the alkali ions (K, Rb and Cs) occupy 32e sites [24,25], which contribute with A 2u +E u +F 2u +2F 1u +A 1g +E g +2F 2g +F 1g modes.…”

Synthesis, characterisation and photocatalytic activity of Ag+- and Sn2+-substituted KSbTeO6

“…5). These bands are compared with the Raman spectra of KMWO 6 series (M = Sb, Ta and Nb) (Mączka et al, 2011). The weak and shoulder bands in the range of 800-900 cm −1 can be assigned to stretching modes of the terminal -Sb/Te--O bonds which may be due to structural defects in the KSTO lattice.…”

“…The defect pyrochlore-type oxides, AMWO 6 , give the characteristic Raman spectra (Mączka et al, 2011). The Raman spectra of all the compounds were recorded in the range of 50-1000 cm −1 .…”