Isomorphous substitutions and conductivity in molybdates Nd5−xLnxMo3O16+y (y∼0.5), where Ln = La, Ce, Pr

The Fluorite-Like Phase Nd5Mo3O16±δ in the MoO3–Nd2O3 System: Synthesis, Crystal Structure, and Conducting Properties

“…However, as the structural and conducting properties of the Nd 5 Mo 3 O 16+δ system at high temperature are sensitive to the surrounding atmosphere, further studies are required to establish its suitability for technological applications within SOFCs. There is also considerable scope to improve its conducting properties by appropriate doping of the Nd and Mo sites, and a number of studies along these lines have been reported recently. − …”

“…Compounds with a closely related stoichiometry, R 5 Mo 3 O 16.5 , with R = La, Pr, Nd, Sm, and Gd, were shown to possess high conductivities by Tsai et al in 1989 . In the case of Nd 5 Mo 3 O 16.5 , the system was more recently “rediscovered” by Voronkova et al (without citing the earlier work) and shown to achieve values of conductivity close to 10 –2 Ω –1 cm –1 at 1073 K. This has led to significant interest in the structural and conducting properties of Nd 5 Mo 3 O 16.5 − and, to a lesser extent, its Pr analogue, ,, including studies of the effects of cation doping onto the Nd 3+ − and Mo 6+ sites. The crystal structure of Nd 5 Mo 3 O 16.5 can be described as a supercell of the cubic fluorite structure with the lattice parameter a ≈ 2 a fluorite , space group Pn 3̅ n , long-range ordering of the Nd 3+ and Mo 6+ over the cation sites, and significant displacements of the anions away from their locations within an ideal fluorite lattice. , However, on the basis of the formal cation valences, the metal to oxygen ratio is 1:2.0625, implying anion excess with respect to the conventional 1:2 ratio for stoichiometric fluorite-structured compounds.…”

Effect of Sodium and Fluorine Co‐Doping on the Properties of Fluorite‐Like Rare‐Earth Molybdates of Nd5Mo3O16 Type

“…The conductivity of these compounds was reported to exceed 10 –2 S/cm at 800 °C . In mixed rare‐earth molybdates Nd 4 SmMo 3 O 16 and Nd 4.5 La 0.5 Mo 3 O 16 , an increase in the electrical conductivity to 0.06–0.1 S/cm was observed , …”

Substitutions in Nd5−xTbxMo3O16+δ Series: Phase Formation, Atomistic Modeling, and Crystal Structure of Nd5Mo3O16+δ-Based Solid Solutions

“…Substitution of neodymium or molybdenum for elements with a lower charge does not lead to an increase in conductivity [3,13,14]. Previously, we studied the substitution of neodymium for a number of elements, including lanthanum, cerium, praseodymium, samarium, erbium, bismuth, and lead [11,13,[15][16][17]. It was shown that the most promising way to enhance the conductivity is to replace neodymium with large cations (lanthanum, praseodymium) or cerium and thorium [15,18], which can exhibit a +4 oxidation state in oxide compounds.…”

“…Previously, we studied the substitution of neodymium for a number of elements, including lanthanum, cerium, praseodymium, samarium, erbium, bismuth, and lead [11,13,[15][16][17]. It was shown that the most promising way to enhance the conductivity is to replace neodymium with large cations (lanthanum, praseodymium) or cerium and thorium [15,18], which can exhibit a +4 oxidation state in oxide compounds. Among rare earth elements, terbium can also exhibit oxidation states of +4 [19], so its introduction into the crystal structure of neodymium molybdate can lead to a rise in conductivity.…”