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

• DOI: 10.3390/en16155637
• Publication Date: 2023-07-27T06:07:17Z
• Authors: Egor Baldin; Nikolay Lyskov; Galina Vorobieva; Igor Kolbanev; Olga Karyagina; Dmitry Stolbov; Valentina Voronkova; Anna Shlyakhtina
• Keywords: Nanocrystalline material; Rietveld Refinement; Hexagonal phase; Orthorhombic crystal system; Microcrystalline; Tetragonal crystal system; Atmospheric temperature range

We report a study of nanophases in the La2O3–MO3 (M = Mo, W) systems, which are known to contain variety good oxygen-ion and proton conductors. Mechanically activated La2O3 + MO3 mixtures final ceramics have been characterized by differential scanning calorimetry (DSC) X-ray diffraction (XRD) with Rietveld refinement. The microstructure materials has examined electron microscopy (SEM), their conductivity dry wet air determined using impedance spectroscopy. In both formation hexagonal La15M8.5O48 (phase II, 5H polytype) is observed for composition 1:1, exothermic peaks DSC curve range ~480–520 °C La15Mo8.5O48 ~685–760 La15W8.5O48, respectively. crystallite size nanocrystalline tungstates ~40 nm, that molybdates ~50 nm. At higher temperatures (~630–690 ~1000 °C), we observe irreversible reconstructive phase transitions tetragonal γ-La2MoO6 La15W8.5O48 orthorhombic β-La2WO6. compare temperature dependences nanoparticulate microcrystalline phases high-temperature differing density. Above 600 °C, oxygen ion conduction prevails coarse-grained La18W10O57 I, 6H ceramic. Low-density nanoceramics exhibit predominantly an activation energy 1.36 1.35 eV, respectively, air.