Synthesis, structure and properties of layered Pr₂MoO₆-based oxymolybdates doped with Mg

Abstract

Undoped and Mg-doped Pr 2 MoO 6 oxymolybdate polycrystals and single crystals have been prepared by solid-state reactions and flux growth. The compounds have been characterized by powder X-ray diffraction, energydispersive spectroscopy, inductively coupled plasma mass spectrometry, scanning transmission electron microscopy, single crystal X-ray structure analysis, differential scanning calorimetry and thermogravimetry. The (MgO) x -(Pr 2 O 3 ) y (MoO 3 ) z (x + y + z = 1) solid solution series has been shown to extend to x = 0.03. The structure of the Mg-doped Pr 2 MoO 6 single crystals can be represented as superimposed lattices of the main matrix (Pr 2 MoO 6 ) and lattices in which Mo atoms are partially replaced by Mg. The incorporation of Mg atoms into the structure of Pr 2 MoO 6 results in the disordering of the praseodymium and oxygen lattices. Both the polycrystalline and single-crystal Mg-doped samples are hygroscopic.

Structure and Properties of Ln2MoO6 Oxymolybdates (Ln = La, Pr, Nd) Doped with Magnesium

“…In the SEM image of a Mg-doped Pr 2 MoO 6 single crystal, no domains and block boundaries were found (Figure 2b). The chemical composition of Mg-doped Nd 2 MoO 6 and Pr 2 MoO 6 was determine in [24,25] using energy dispersive X-ray spectrometry. More precisely, the low concentration of magnesium in Pr 2 MoO 6 single crystals was determined by inductively coupled plasmamass-spectrometry (ICP-MS technique) [25].…”

“…The conductivity of oxymolybdates does not exceed 10 -4 S cm -1 [23]. Thermogravimetry shows that molybdates Ln 2 MoO 6 (Ln = La, Pr, Nd) have hygroscopic properties up to 1000-1200 • C, which may indicate the possible proton conductivity in these compounds [24][25][26].…”

“…Currently, a number of works are known in which the rare earth element in oxymolybdates with large cations is partially replaced by divalent elements-lead or magnesium [21,[24][25][26]. Solid solutions (PbO) x (Nd 2 MoO 6 ) (1-x)/2 are formed in a wide range 0 ≤ x ≤ 0.6.…”

“…The second divalent element, magnesium, during the synthesis of solid solutions according to the scheme (MgO) x (Ln 2 MoO 6 ) (1-x)/2 , where Ln = La, Pr, Nd [24][25][26], led to the formation of a very narrow field of solid solutions with x < 0.10. Mg-doped single crystals were prepared by flux growth.…”

“…According to the X-ray diffraction study of the compounds obtained, the Mg atom replaces Mo and leads to the splitting of the positions of rare earth elements, while the phase transition does not occur. In [24][25][26], the features of the structure and properties of Mg-doped oxymolybdates are considered. The presented work is a brief review in which we summarize, analyze and compare the structural features and properties of Mg-doped Ln 2 MoO 6 oxymolybdates with large rare earth cations (Ln = La, Pr, Nd), previously published and supplemented by studies of a number of new properties using powder X-ray diffraction, thermogravimetry, and infrared spectroscopy.…”