Structural Features and Physical Properties of Tetragonal Ln₂MoO₆ (Ln = La, Pr) Oxymolybdates Doped with Cadmium Atoms

Abstract

Cadmium-doped lanthanum and praseodymium oxymolybdates were synthesized as single crystals and polycrystalline samples. X-ray diffraction analysis confirmed that Cd cations replace rare-earth atoms in the oxymolybdate structure (sp. gr. I4̅c2), shifting from the main position to a distance of approximately 0.6 Å. It is shown that in the temperature range of 20–600 °C, Cd-doped Ln 2MoO6 (Ln = La, Pr) samples expand linearly, and their thermal expansion coefficients (10–12) × 10–6 K–1 are close in values to the coefficients of standard solid-oxide fuel cell electrolytes, for example, yttria-stabilized zirconia. Cadmium heterovalent doping of lanthanum oxymolybdate increases the conductivity of the compound by an order of magnitude but reduces its hygroscopicity, as evidenced by the data of thermogravimetric analysis.

Polymorphism and physical properties of pure and lead-doped monoclinic Sm2MoO6 oxymolybdates

“…The formation of oxygen vacancies by heterovalent substitution can significantly increase the conductivity of oxymolybdates. This has been demonstrated by doping the tetragonal La 2 MoO 6 phase with divalent cadmium 19,20 and monovalent sodium atoms, 21 and the monoclinic Sm 2 MoO 6 phase with divalent calcium or strontium. 6 Doping lanthanum and neodymium oxymolybdates with lead resulted in several interesting and practically valuable outcomes.…”