The effect of the synthesis conditions on the structure and phase transitions in Ln2(MoO4)3

Solid-State Synthesis and Phase Transitions in the RE2(MoO4)3 Family Monitored by Thermodiffraction

“…Popov and co-authors also found the incommensurable component along the other direction of the tetragonal scheelite (the a* direction) in the incommensurable phases. 20 This complicates the model, as new defects must appear along the other diagonal of the structure, which is more difficult to assume because, in this direction, neither lanthanide polyhedra nor vacancy-forming bands and clusters are connected. Therefore, it is more appropriate to model a mixture of the αand LaMophases which, in turn, could be incommensurable only concerning the second component of the modulation vector.…”

“…Also, very recently, Tang and co-authors 33 studied changes in luminescence intensities depending on the transition temperature synthesized by solid-state reaction of three polymorphs of Eu 2 (MoO 4 ) 3 regulating the sintering temperature: the scheelite phase at 873 K, a new monoclinic modulated scheelite phase between 973 and 1073 K and the βphase between 1173 and 1273 K. They also presented DTA curves where an exothermic peak appears above 873 K, assigned to the scheelite-new modulated scheelite phase transition, and an endothermic peak near 1173 K, assigned to the newly modulated scheelite-β transition. 33 While we were working on this manuscript, Popov and coauthors 20 published a work on the formation and evolution of the local and long-range structures in almost the entire RE 2 (MoO 4 ) 3 series (with RE ≡ La, Pr, Nd, Eu, Gd, Dy, Ho, and Yb) using XRD with synchrotron radiation, Raman, infrared, and photoluminescence spectroscopies and simultaneous thermal analysis with ICP spectroscopy. They prepared the samples by co-precipitation with subsequent calcination of the precursors.…”

“…18,19 Compounds with the same chemical composition but obtained by different preparation methods (solid-phase synthesis, growth in melt, co-precipitation from solutions, sol−gel method, hydrothermal synthesis) can show significant changes in structure under other conditions. 20 However, since Bixner in 1979 until today, there has been quite a consensus on the assumption of the phase diagram showing the thermal stability zones versus the ionic radii of the trivalent metals. 1 All known crystalline structures in this family of compounds belong to three polytypes with no symmetry relationship.…”

“…These authors reviewed and proposed a new phase diagram for this family according to the newly observed phase sequence. 20 There is less knowledge about other m/n compositions of the m REd 2 Od 3 −n MoOd 3 system. The discovery of the fast ionic conductivity in the La 2 Mo 2 O 9 compound (m/n = 1:2), together with the determination of its structure, is relatively recent.…”

Features of the Phase Preferences, Long- and Short-Range Order in Ln2(WO4)3 (Ln = Gd, Dy, Ho, Yb) with Their Relation to Hydration Behavior

“…We apply a complex of physico-chemical methods, including synchrotron X-ray powder diffraction, XAFS spectroscopy, Raman and Fourier transform infrared (FT-IR) spectroscopies, supplemented by simultaneous thermal analysis. Earlier, we have successfully shown the potency of such multi-technique structural analysis of lanthanoid hafnates [28], zirconates [29,30], titanates [30], molybdates [31], light and intermediate Ln tungstates [32].…”