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.

Pure and sodium-containing lanthanum oxymolybdates were synthesized as polycrystalline samples and single crystals. The compounds have been characterized by several methods including SEM, inductively coupled plasma MS, X-ray single crystal diffraction analysis, thermogravimetry, differential scanning calorimetry, IR-spectroscopy, and impedance spectroscopy. ICP-MS has shown the presence of sodium cations in single crystals. According to X-ray diffraction analysis, sodium cations replace lanthanum atoms in the structure. The I4̅c2 (Z = 8) space group was established for sodium-containing crystals. The feature of Na-doped polycrystalline La2MoO6 samples is a reversible phase transition at about 650 °C recorded by DSC. La2MoO6 ceramics with sodium absorb water as evidenced by TG and IR-spectroscopy data. Investigated materials exhibit proton conductivity in a humid environment.

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