Cationic Order-Disorder in Double Scheelite Type Oxides: the Case Study of Fergusonite LaSiMoO.

Up to now, the possible occurrence of a cationic ordering on the tetrahedral sublattices of stoichiometric double scheelite-type oxides was not settled, with somewhat contradictory X-ray diffraction and optical measurements [Blasse, G. . , , 2091].

Reducing the thermal conductivity of LaMoO with a trivalent praseodymium substitution for its potential use as a thermal barrier coating.

(La1-xPrx)2Mo2O9 powders were synthesized by solid state reaction for x = 0.00, 0.10, 0.

Extension of the A B O Slicing/Oxidizing Process from 2D Layered to 1D Columnar Perovskites: The LaWM O Structural Family with Di-, Tri-, and Tetravalent Transition Metal M Substitutes to Tungsten.

The ABO structural type is a columnar-perovskite-type arrangement originally evidenced in LaMoO [Goutenoire et al. J. Solid State Chem.

On the local order of amorphous LaMoO.

The amorphous reduction product of the oxide ion conductor LaMoO was previously shown to be a good, sulphur-tolerant, anode material for solid oxide fuel cell devices (X. C. Lu, J.

Cationic Intermixing and Reactivity at the La2 Mo2 O9 /La0.8 Sr0.2 MnO3-δ Solid Oxide Fuel Cell Electrolyte-Cathode Interface.

Among standard high-temperature cathode materials for solid oxide fuel cells, La0.8 Sr0.2 MnO3-δ (LSM) displays the least reactivity with the oxide-ion conductor La2 Mo2 O9 (LMO), yet a reaction is observed at high processing temperatures, identified by using XRD and focused ion beam secondary-ion mass spectrometry (FIB-SIMS) after annealing at 1050 and 1150 °C.

Reduction Kinetics of La2Mo2O9 and Phase Evolution during Reduction and Reoxidation.

An amorphous reduced form of oxide ion conductor La2Mo2O9 had been proposed as sulfur-tolerant anode material for solid oxide fuel cell, but its oxygen content was not known. In this paper, we investigate the reduction kinetics by diluted hydrogen of La2Mo2O9 to amorphous, and the oxygen range of the amorphous form. The reduction kinetics is studied as a function of the powder specific surface area and of the temperature, on powders synthesized by solid state reaction and by polyol process using two different solvents.

Thermodynamic stability of La2Mo2-yWyO9, La2Mo2-yWyO8.96+0.02y and La7Mo7(2-y)/2W7y/2O30 (y = 0, 0.5 and 1.0).

The role of W content on the limit oxygen partial pressure (pO2) for stability of fast oxygen-ion conductors La2Mo2-yWyO9 with y = 0, 0.5 and 1.0 has been studied by means of thermogravimetric analysis (TGA) under controlled atmospheres.

Thermodynamic stability, structural and electrical characterization of mixed ionic and electronic conductor La2Mo2O(8.96).

Thermogravimetric analysis (TGA) technique in controlled oxygen partial pressure (pO(2)) atmospheres has been used to obtain equilibrium oxygen content data as a function of pO(2) on the La(2)Mo(2)O(9-δ) system resulting from the partial reduction of fast oxide-ion conductor La(2)Mo(2)O(9) (LM). Thermodynamic conditions for stabilization of crystalline La(7)Mo(7)O(30) and amorphous La(2)Mo(2)O(7-y) at 718 °C have been determined and discussed. At 608 °C, the compound reported for the first time La(2)Mo(2)O(8.

Analysis of the local structure of phosphorus-substituted LAMOX oxide ion conductors.

The effect of partial substitution of molybdenum by phosphorus on the global and local structural arrangement of the fast oxide-ion conductor La(2)Mo(2)O(9) (LAMOX) has been studied by X-ray powder diffraction as well as (139)La and (31)P solid state NMR. The diffraction patterns show that La(2)Mo(2-y)P(y)O(9-y/2) forms a solid solution at low phosphorus concentrations, and that there is a structural phase transition upon increasing phosphorus concentration. This phase transition is also reflected in (139)La and (31)P NMR spectra.

Topological metastability and oxide ionic conduction in La(2)-(x)Eu(x)Mo(2)O(9).

The effect of partial substitution, up to x = 0.4, of La by trivalent Eu on the phase stability, thermal expansion, and transport properties of La2Mo2O9 are investigated using temperature-controlled X-ray powder diffraction, differential thermal analysis, and complex impedance spectroscopy. At low europium content (x < or = 0.

On the flexibility of the structural framework of cubic LAMOX compounds, in relationship with their anionic conduction properties.

A mathematical analysis of the cubic crystal structure of fast oxide-ion conductor beta-La(2)Mo(2)O(9) (and derived members of the LAMOX family) shows that its cationic sublattice can behave as a semirigid framework. Tilt/rotation of rigid [O1La(3)Mo] anti-tetrahedral units about their 3-fold axis can open up tunnels in the cationic framework, therefore favoring the mobility of O2 and O3 oxide ions located in these tunnels, as confirmed by molecular dynamics simulations. Such a process is likely to assist the anionic transport and explain the postulated transition from Arrhenius-type to VTF (Vogel-Tamman-Fulcher)-type behavior propounded to account for the peculiar conductivity curvature observed at high temperature in all the cubic LAMOX compounds.

17O NMR in room temperature phase of La2Mo2O9 fast oxide ionic conductor.

A room temperature (17)O NMR study of La(2)Mo(2)O(9), a fast oxide ionic conductor exhibiting a phase transition at 580 degrees C between a low-temperature alpha-phase and a high-temperature beta-phase, is presented. Four partly overlapping quasi-continuous distributions of oxygen sites are evidenced from 1D magic angle spinning (MAS) and 2D triple quantum MAS NMR experiments. They can be correlated with the three oxygen sites O1, O2 and O3 of the high-temperature crystal structure.