Synthesis of Hexagonal Nanophases in the La 2 O 3 –MO 3 (M = Mo, W) Systems

Egor Baldin, Nikolay Lyskov, Galina Vorobieva, Igor Kolbanev, Olga Karyagina, Dmitry Stolbov, Valentina Voronkova and Anna Shlyakhtina ()
Additional contact information
Egor Baldin: N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow 119991, Russia
Nikolay Lyskov: Federal Research Center of Problems of Chemical Physics and Medical Chemistry RAS, Chernogolovka, Moscow 142432, Russia
Galina Vorobieva: N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow 119991, Russia
Igor Kolbanev: N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow 119991, Russia
Olga Karyagina: Emanuel Institute of Biochemical Physics RAS, Russian Academy of Sciences, Moscow 119334, Russia
Dmitry Stolbov: Department of Chemistry, Lomonosov Moscow State University, Moscow 119991, Russia
Valentina Voronkova: Department of Physics, Lomonosov Moscow State University, Moscow 119991, Russia
Anna Shlyakhtina: N.N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow 119991, Russia

Energies, 2023, vol. 16, issue 15, 1-17

Abstract: We report a study of nanophases in the La 2 O 3 –MO 3 (M = Mo, W) systems, which are known to contain a variety of good oxygen-ion and proton conductors. Mechanically activated La 2 O 3 + MO 3 (M = Mo, W) mixtures and the final ceramics have been characterized by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) with Rietveld refinement. The microstructure of the materials has been examined by scanning electron microscopy (SEM), and their conductivity in dry and wet air has been determined using impedance spectroscopy. In both systems, the formation of hexagonal La 15 M 8.5 O 48 (phase II, 5H polytype) (M = Mo, W) nanophases is observed for the composition 1:1, with exothermic peaks in the DSC curve in the range ~480–520 °C for La 15 Mo 8.5 O 48 and ~685–760 °C for La 15 W 8.5 O 48 , respectively. The crystallite size of the nanocrystalline tungstates is ~40 nm, and that of the nanocrystalline molybdates is ~50 nm. At higher temperatures (~630–690 and ~1000 °C), we observe irreversible reconstructive phase transitions of hexagonal La 15 Mo 8.5 O 48 to tetragonal γ-La 2 MoO 6 and of hexagonal La 15 W 8.5 O 48 to orthorhombic β-La 2 WO 6 . We compare the temperature dependences of conductivity for nanoparticulate and microcrystalline hexagonal phases and high-temperature phases differing in density. Above 600 °C, oxygen ion conduction prevails in the coarse-grained La 18 W 10 O 57 (phase I, 6H polytype) ceramic. Low-density La 15 W 8.5 O 48 and La 15 Mo 8.5 O 48 (phase II, 5H polytype) nanoceramics exhibit predominantly electron conduction with an activation energy of 1.36 and 1.35 eV, respectively, in dry air.

Keywords: mechanochemical synthesis; nanomaterials; lanthanum tungstate; lanthanum molybdate; polytypism; oxygen ion conductivity; proton conductivity (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
References: View complete reference list from CitEc
Citations:

Downloads: (external link)
https://www.mdpi.com/1996-1073/16/15/5637/pdf (application/pdf)
https://www.mdpi.com/1996-1073/16/15/5637/ (text/html)

Related works:
This item may be available elsewhere in EconPapers: Search for items with the same title.

Export reference: BibTeX RIS (EndNote, ProCite, RefMan) HTML/Text

Persistent link: https://EconPapers.repec.org/RePEc:gam:jeners:v:16:y:2023:i:15:p:5637-:d:1203388

Access Statistics for this article

Energies is currently edited by Ms. Agatha Cao

More articles in Energies from MDPI
Bibliographic data for series maintained by MDPI Indexing Manager ().