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δ-Bi2O3-based materials have long been a focus of interest as potential solid oxide fuel cell materials due to their high electrical conductivity. Here, extensive studies of thermal stability, polymorphism and conductivity have been carried out for the first time on Bi3.24Ln2W0.76O10.14 (Ln = La, Pr or Nd) compounds in the ternary Bi2O3–Ln2O3–WO3 system, mentioned more than 20 years ago by Watanabe. The obtained single-phase materials were found to be sufficiently dense (more than 94%) and thermally stable (up to 900 °C). Emphasis was placed on studying the nature of the electrical transport of these phases, which was investigated through high-throughput calculations and experimental measurements. Theoretical studies included a crystal chemical evaluation of conductivity channels and migration energy, calculation of ionic conductivities using the kinetic Monte Carlo method, and determination of band gaps using a quantum-chemical approach. Experimental conductivity investigations were carried out over a wide temperature range (up to 900 °C) and at various oxygen partial pressures. For Bi3.24Ln2W0.76O10.14, the anionic type of conductivity is predominant with a share of the electronic component. The total conductivity values reached about 10−2 S cm−1 at 900 °C for all samples, confirmed by both calculation and measurement. These theoretical and experimental findings enhance the understanding of the nature and mechanism of Watanabe's phase conductivity. [ABSTRACT FROM AUTHOR]

The Sm2MoO6 compounds, also known as oxymolybdates, were synthesized in air using a solid-phase method. A series of techniques were employed to characterize the undoped and, for the first time, lead-doped samples. It has been demonstrated that lead-containing samples form a wide range of solid solutions, which are isostructural (sp. gr. C2/c) to the pure monoclinic Sm2MoO6 compound. The thermal stability, polymorphism, and conductive properties of the obtained samples were studied in detail. Doping Sm2MoO6 ceramics with lead results in a notable increase in conductivity compared to the pure sample, with conductivity reaching 10−3 S cm−1 at 900 °C. This improvement is due to the formation of oxygen vacancies through the heterovalent substitution of cation sublattice. In contrast to undoped samarium oxymolybdates, Pb-containing Sm2MoO6 ceramics demonstrate the capacity to transfer protons, resulting in an overall increase in conductivity in a wet environment. [ABSTRACT FROM AUTHOR]

The conductive properties of fluorite-like structures KLn4Mo3O15F (Ln = La, Pr, Nd: KLM, KPM, KNM) have been studied theoretically and experimentally. Theoretical studies included the geometrical-topological analysis of voids and channels available for migration of working ions; bond valence site energy calculations of the oxygen ions' migration energy; quantum-chemical calculations for the estimation of the oxygen vacancies formation energy. Experimental measurements of conductivity were made using impedance spectroscopy and as a function of oxygen partial pressure. The total conductivity was ∼10−3 S cm−1 for KLM and ∼10−2 S cm−1 for KPM and KNM at 800 °C. Measurements with changes in partial pressure proved the mixed nature of electric transport in KLM, KPM, and KNM phases, with predominantly ionic conductivity. The measured ion transference numbers in air reached approximately 0.9 at 800 °C for the KPM and KNM ceramics. Also, evaluated proton transfer numbers were less than 10%, indicating a small contribution to the total conductivity. [ABSTRACT FROM AUTHOR]

Fluorine-containing rare earth compounds of the LiLn4Mo3O15F (Ln = Eu, Gd, or Dy) composition have been obtained using solid-phase synthesis in vacuum-sealed quartz ampoules. It was found that only LiEu4Mo3O15F samples are isostructural to cubic Ln5Mo3O16 (Ln = La–Gd) molybdates with a fluorite-like structure. Luminescence, hygroscopic, and electrophysical characteristics of the LiEu4Mo3O15F phase were studied for the first time. The double replacement of europium with lithium and oxygen with fluorine leads to the appearance of a reversible phase transition accompanied by a jump in conductivity by 2 orders of magnitude. The conductivity of the LiEu4Mo3O15F compound exceeds the value of 10−2 S cm−1 at 700 °C. A relationship between the size of the Ln cation and the hygroscopic and conductive properties of LiLn4Mo3O15F compounds has been established: as the lanthanide radius decreases, the compounds lose their ability to absorb water and transfer protons. [ABSTRACT FROM AUTHOR]

We report a study of nanophases in the La2O3–MO3 (M = Mo, W) systems, which are known to contain a variety of good oxygen-ion and proton conductors. Mechanically activated La2O3 + MO3 (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 La15M8.5O48 (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 La15Mo8.5O48 and ~685–760 °C for La15W8.5O48, 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 La15Mo8.5O48 to tetragonal γ-La2MoO6 and of hexagonal La15W8.5O48 to orthorhombic β-La2WO6. 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 La18W10O57 (phase I, 6H polytype) ceramic. Low-density La15W8.5O48 and La15Mo8.5O48 (phase II, 5H polytype) nanoceramics exhibit predominantly electron conduction with an activation energy of 1.36 and 1.35 eV, respectively, in dry air. [ABSTRACT FROM AUTHOR]

Rare-earth fluorine-containing molybdates of the Ln5Mo3O16+δ oxygen–electron conductor family with the LiLa4Mo3O15F composition were synthesized for the first time as single crystals by the flux method. An accurate X-ray diffraction analysis of the obtained crystals was carried out at 20 and −183 °C. The LiLa4Mo3O15F compound is isostructural to the fluorine-free analogue with a cubic structure (space group Pn 3 ¯ n). It is shown that lithium atoms replace one of the two positions of lanthanum in the more distorted LaO8 polyhedron. According to X-ray diffraction analysis, fluorine atoms replace the positions of over-stoichiometric oxygen located in the vast cavities of the structure. So, fluorine anions can promote the interstitial conductivity of F-containing LiLa4Mo3O15F molybdates. [ABSTRACT FROM AUTHOR]

The transcription factor Adr1 directly activates the expression of genes encoding enzymes in numerous pathways that are upregulated after the exhaustion of glucose in the yeast Saccharomyces cerevisiae. ADH2, encoding the alcohol dehydrogenase isozyme required for ethanol oxidation, is a highly glucose-repressed, Adr1-dependent gene. Using a genetic screen we isolated > 100 mutants in 12 complementation groups that exhibit ADRI-dependent constitutive ADH2 expression on glucose. Temperature-sensitive alleles are present among the new constitutive mutants, indicating that essential genes play a role in ADH2 repression. Among the genes we cloned is MOT1, encoding a repressor that inhibits TBP binding to the promoter, thus linking glucose repression with TBP access to chromatin. Two genes encoding proteins involved in vacuolar function, FAB1 and VPS35, and CDC10, encoding a nonessential septin, were also uncovered in the search, suggesting that vacuolar function and the cytoskeleton have previously unknown roles in regulating gene expression. Constitutive activation of ADH2 expression by Adr1 is SNF1-dependent in a strain with a defective MOT1 gene, whereas deletion of SNF1 did not affect constitutive ADH2 expression in the mutants affecting vacuolar or septin function. Thus, the mutant search revealed previously unknown Snf1-dependent and -independent pathways of ADH2 expression.

LixLn5–xMo3O16.5–1.5xFx (0.8 ≤ x ≤ 1.4 (Ln = La), 0.4 ≤ x ≤ 1 (Ln = Pr), 0.6 ≤ x ≤ 1 (Ln = Nd)) solid solutions on the Ln5Mo3O16–LiLn4Mo3O15F joins of the Ln2O3–MoO3–LiF ternary systems, similar to the fluorite‐related cubic compound Nd5Mo3O16, have been prepared by solid‐state reactions. Substitutions of lithium on the rare‐earth site and fluorine on the oxygen site have been shown to lead to a reversible phase transition accompanied by an anomaly in permittivity and a jump in conductivity by one and half orders of magnitude. In a wet atmosphere, the LixLn5–xMo3O16.5–1.5xFx compounds may have proton conductivity. [ABSTRACT FROM AUTHOR]

LixLn5–xMo3O16.5–1.5xFx (0.8 ≤ x ≤ 1.4 (Ln = La), 0.4 ≤ x ≤ 1 (Ln = Pr), 0.6 ≤ x ≤ 1 (Ln = Nd)) solid solutions on the Ln5Mo3O16–LiLn4Mo3O15F joins of the Ln2O3–MoO3–LiF ternary systems, similar to the fluorite‐related cubic compound Nd5Mo3O16, have been prepared by solid‐state reactions. Substitutions of lithium on the rare‐earth site and fluorine on the oxygen site have been shown to lead to a reversible phase transition accompanied by an anomaly in permittivity and a jump in conductivity by one and half orders of magnitude. In a wet atmosphere, the LixLn5–xMo3O16.5–1.5xFx compounds may have proton conductivity. [ABSTRACT FROM AUTHOR]

Undoped and Mg‐doped Pr2MoO6 oxymolybdate polycrystals and single crystals have been prepared by solid‐state reactions and flux growth. The compounds have been characterized by powder X‐ray diffraction, energy‐dispersive spectroscopy, inductively coupled plasma mass spectrometry, scanning transmission electron microscopy, single crystal X‐ray structure analysis, differential scanning calorimetry and thermogravimetry. The (MgO)x(Pr2O3)y(MoO3)z (x + y + z = 1) solid solution series has been shown to extend to x = 0.03. The structure of the Mg‐doped Pr2MoO6 single crystals can be represented as superimposed lattices of the main matrix (Pr2MoO6) and lattices in which Mo atoms are partially replaced by Mg. The incorporation of Mg atoms into the structure of Pr2MoO6 results in the disordering of the praseodymium and oxygen lattices. Both the polycrystalline and single‐crystal Mg‐doped samples are hygroscopic. [ABSTRACT FROM AUTHOR]

Crystals with the La18W10O57‐type structure (6H and 5H polytypes) were obtained by a self‐flux method from high‐temperature solutions. Some of the crystal samples were studied by single‐crystal X‐ray structure analysis. The diffraction patterns indicated that two phases co‐exist in each sample. The hexagonal lattices have a common period of a ≈ 9.0 Å and are non‐equal in length but have equally oriented superstructure periods 6c (phase I) and 5c (phase II), c ≈ 5.4 Å. The structures of phases I and II were solved in the symmetry groups P2c and P321, respectively, based on the X‐ray data for crystals I and II, with predominant content of the first and second phase. The motif of isolated WO6 prisms with W atoms on the cell edges is common to both phases. WO6 octahedra, both isolated and joined by faces, are distributed along the c axis within the unit cells. Phase I contains extra layers of isolated WO6 octahedra compared to phase II. Tungsten sites in joined octahedra are disordered and partially occupied. Disordering is more expressed in phase II, which in return contains rather more W and O per atom of La. The refined chemical compositions are La18W10O57 for I and La15W8.5O48 for II. [ABSTRACT FROM AUTHOR]