Room‐temperature mechanochemical synthesis of RE molybdates: Impact of structural similarity and basicity of oxides

Abstract

RE molybdates and tungstates are very important inorganic materials that have a high potential application in various fields: photoluminescence, optical fibers, laser materials, and mixed conductors. [1][2][3][4][5][6][7] Ln 6-x Zr x MoO 12-δ (Ln = La, Nd, Sm, Dy, Ho) Zr-doped molybdates, pure La 5.5 MoO 11.25 , pure and doped La 5.4 MoO 11.1 , and Ln 10 Mo 2 O 21 (Ln = Nd, Gd -Ho) have mixed electron-ion (electron-proton) conductivity and are promising materials for SOFC electrolytes and proton-conducting membranes. [5][6][7][8][9][10][11][12][13][14] Zirconium doping improves the stability of these materials to

Synthesis of Hexagonal Nanophases in the La2O3–MO3 (M = Mo, W) Systems

“…In our case, this occurs at 600 °C, and we observe the presence of a second crystalline phase: La2O3. Therefore, we conclude that the rate of room-temperature mechanochemical synthesis in the case of the lanthanum tungstate is lower than in the case of the La10Mo2O21 molybdate [46] and that a considerable fraction of the lanthanum oxide does not react with WO3.…”

“…A P-5X potentiostat/galvanostat combined with a frequency response analyzer module (Electrochemical Instruments, Ltd., Saint Petersburg, Russia) was used for dry and wet air electrical conductivity measurements. Details of the conductivity measurements are given in [16,46]. Figure 2 shows the morphology and cation distribution in the La2O3 + WO3 powder mixture after mechanical activation (m/a).…”

“…Based on the latest crystallographic data reported by Xue et al [45], who studied the polymorphism of this molybdate by neutron diffraction, it can be concluded that, like La 2 WO 6 , La 2 MoO 6 exists in two polymorphs: low-temperature phase γ-La 2 MoO 6 (tetragonal structure) and high-temperature phase α-La 2 MoO 6 (monoclinic scheelite structure). Note that lanthanumrich fluorite-like La 6−x MoO 12−δ solid solutions were reported to have considerable proton conductivity [46][47][48][49]. To the best of our knowledge, there is no evidence for the existence of a molybdate analog of hexagonal La Nd, Gd, Dy, and Ho, exhibit paramagnetic behavior.…”

“…This result confirms that, during room-temperature mechanochemical synthesis, La 2 O 3 is more reactive with molybdenum oxide than tungsten oxide. The solid-state reaction between the starting oxides occurs more readily in the case of the RE molybdates, which can be synthesized even via room-temperature mechanochemical processing [46]. Accordingly, La 15 ture, and the mixture contains unreacted La2O3.…”

“…Previously, mechanochemical synthesis of the R 10 Mo 2 O 21 (R = La, Y, Er) molybdates was shown to occur at room temperature [46]. In this process, the crucial factor was structural matching between the starting RE oxide and the synthesized RE molybdate.…”