Synthesis, Structure Refinement and Conductivity of Ln_2-xCd_xMoO_6-x/2

Abstract

Substitution rare-earth elements for cadmium in the monoclinic compounds Ln2MoO6 (Ln – Gd, Ho) leads to the formation of fluorite-related cubic structure. Series Ln2xCdxMoO6x/2 was investigated by XRD (with structure refinement), scanning electron microscopy, FTIR-spectroscopy and conductivity measurements.

Investigation of the Heterovalent Substitution Cadmium for Lanthanum in Molybdate La2MoO6

“…IR spectra of cubic lanthanum molybdate modified by cadmium are similar to spectra of neodymium molybdate Nd 5 Mo 3 O 16+δ and its solid solutions [21] as well as a phase of cubic double cadmium and gadolinium molybdate [16] (see Table 4). A larger number of active vibrations in the IR spectra of the La 1.4 Cd 0.6 MoO 5.7 phase compared to La 2 MoO 6 are possibly due to the fact that, in the structure of the cubic phase, MoO 4 -tetrahedra are connected in a special way through the ions of the rare-earth elements (see Figure 7).…”

“…Lanthanum molybdate with the tetragonal structure transforms into the cubic fluorite-like phase of La 5 Mo 3 O 16+δ in which the content of molybdenum is higher (by 4.5% if Journal of Chemistry recalculating per molybdenum anhydride) than in La 2 MoO 6 . An assumption was made earlier that, in such compounds, the atoms of cadmium [16] or REE [18] can substitute (to a small extent) for the atoms of molybdenum in the Ln 5 Mo 3 O 16+δ structure. According to this, a value of the unit cell parameter in this system depends on three factors simultaneously: first, the smaller ionic radius of cadmium than lanthanum (the values of ionic radii for coordination number 8 are 1.16Å (La 3+ ) and 1.10Å (Cd 2+ ) [19], respectively); second, the decrease in the amount of stoichiometric oxygen according to the electroneutrality principle; and the last, the cadmium atoms localization in the molybdenum sites of the crystal structure.…”

“…With the addition of the redundant quantity of molybdenum in the samples La 1.5 Cd 0.5 Mo (1+u) O 5.75+3u , the unit cell parameter of the cubic phase decreases from 11.2170(4)Å to 11.2011(5)Å. is change may be related to the occupation of the molybdenum sites by the bigger atoms of cadmium due to the lack of molybdenum atoms in the sample [16]. With increased molybdenum, content cadmium passes from the molybdenum sites to the lanthanum ones.…”

“…Earlier, we reported the heterovalent substitution of cadmium for REE in monoclinic gadolinium and holmium molybdates Ln 2 MoO 6 resulted in the formation of cubic fluorite-like phases [16]. For these compositions, the Ln : Mo ratio varies but the (Ln + Cd) : Mo ratio remains constant.…”

La2MoO6 Oxymolybdates Doped with Sodium: Crystal Growth, Features of the Structure, and Properties

“…In Figure , IR spectra of samples of hydrated oxymolybdates (Na 2 O) x (La 2 MoO 6 ) (1‑ x )/2 , x = 0, 0.03, and 0.05 are presented. In the range 870–760 cm –1 lie the frequencies of stretching vibrations of bonds of MoO 4 tetrahedra. − The band near 500 cm –1 corresponds to the frequency of stretching vibrations of LaO 8 polyhedra . The frequencies of bending vibrations of MoO 4 tetrahedra and LaO 8 polyhedra are located in the range of 320–130 cm –1 .…”