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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]

Fluorite‐like oxyfluorides NaLn4Mo3O15F (Ln = La, Pr, Nd), which relate to the Nd5Mo3O16 structural type, were obtained by solid‐phase synthesis in the air. Codoping of the Nd5Mo3O16+δ family with sodium and fluorine led to the appearance of a piezoelectric effect and a reversible phase transition in oxyfluorides, accompanied by a jump in the conductivity and an anomaly of the permittivity of the ferroelectric type. It is assumed that the compounds NaLn4Mo3O15F in contrast to Nd5Mo3O16+δ, which possess mixed oxide‐ion/electronic interstitial conductivity, can have oxygen conductivity of vacancy type. The highest conductivity offered by these materials is 3.2 × 10–2 S/cm at 700 °C. NaLn4Mo3O15F compounds were found to be hygroscopic and can be considered as potential proton conductors. Codoping of fluorite‐like cubic Ln5Mo3O16 (Ln = La, Pr, Nd) with Na and F leads to stabilization of NaLn4Mo3O15F compounds. The appearance of superionic phase transition, piezoelectric effect and hygroscopic properties are observed in NaLn4Mo3O15F compounds. [ABSTRACT FROM AUTHOR]

Polycrystalline (PbO)x(La2MoO6)(1-x)/2 (x = 0, 0.05, 0.1, 0.2, 0.34, 0.4) samples have been prepared by solid-state reactions near 900 °C. Phase-pure compounds with the layered tetragonal La2MoO6 structure have been obtained in the range 0 ≤ x ≤ 0.34. Pb doping of La2MoO6 has been shown to cause an unusual effect: a reversible phase transition at 775 °C, accompanied by a jump in electrical conductivity by two orders of magnitude (superionic transition) and an anomaly in permittivity, which is related to the structural features of oxymolyb-dates. [ABSTRACT FROM AUTHOR]

Polycrystalline (PbO)x(La2MoO6)(1-x)/2 (x = 0, 0.05, 0.1, 0.2, 0.34, 0.4) samples have been prepared by solid-state reactions near 900 °C. Phase-pure compounds with the layered tetragonal La2MoO6 structure have been obtained in the range 0 ≤ x ≤ 0.34. Pb doping of La2MoO6 has been shown to cause an unusual effect: a reversible phase transition at 775 °C, accompanied by a jump in electrical conductivity by two orders of magnitude (superionic transition) and an anomaly in permittivity, which is related to the structural features of oxymolyb-dates. [ABSTRACT FROM AUTHOR]

The phase relations along the Nd2MoO6-PbO join of the ternary Nd2O3-MoO3-PbO system have been studied by means of solid-state synthesis in air. The samples with high Pb content underwent a reversible first-order phase transition near 820 °C. XRD analysis revealed two tetragonal phases, the high-temperature centric phase ( I41/ acd) and the low-temperature acentric phase ( I $\bar {4}$2 m). In the region of the phase transition, the permittivity of the Pb-containing samples show a strong lambda-type anomaly and electrical conductivity increases sharply by one and half orders of magnitude. The conductivities of the Pb-containing samples reach 10-2 S/cm at 850 °C, which is two orders of magnitude greater than the conductivity of pure Nd2MoO6. The conductivity in such compounds may be due to oxygen ions. A permittivity anomaly, existence of a piezoelectric effect, and the symmetry change from acentric I $\bar {4}$2 m to centric I41/ acd may indicate an antiferroelectric nature of the phase transition. [ABSTRACT FROM AUTHOR]

A single crystal of Nd5Mo3O16 with lead partly substituting for neodymium, which has a fluorite-like structure, was studied by precision X-ray diffraction, high-resolution transmission microscopy and EDX microanalysis. The crystal structure is determined in the space group . It was found that the Pb atoms substitute in part for Nd atoms in the structure and are located in the vicinity of Nd2 positions. Partial substitutions of Mo cations for Nd positions and of Nd for Mo positions in crystals of the Ln5Mo3O16 oxide family are corroborated by X-ray diffraction for the first time. The first experimental verification of the location of an additional oxygen ion in the voids abutting MoO4 tetrahedra was obtained. [ABSTRACT FROM AUTHOR]

The La2Mo2O9 (LM) and Pr2Mo2O9 (PM) single crystals are studied using precision X-ray diffraction and high-resolution transmission microscopy at room temperature. The crystal structures are determined in the space group P213. La and Pr atoms, as well as Mo1 and O1 atoms, are located in the vicinity of the threefold axes rather than on the axes as in the high-temperature cubic phase. In both structures studied, the O2 and O3 positions are partially occupied. The coexistence of different configurations of the Mo coordination environment facilitates the oxygen-ion migration in the structure. Based on the X-ray data, the activation energies of O atoms are calculated and the migration paths of oxygen ions in the structures are analysed. The conductivity of PM crystals is close to that of LM crystals. The O2 and O3 atoms are the main contributors to the ion conductivity of LM and PM. [ABSTRACT FROM AUTHOR]

Undoped and Mg-doped Pr 2 MoO 6 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 (Pr 2 O 3 ) y (MoO 3 ) z (x + y + z = 1) solid solution series has been shown to extend to x = 0.03. The structure of the Mg-doped Pr 2 MoO 6 single crystals can be represented as superimposed lattices of the main matrix (Pr 2 MoO 6 ) and lattices in which Mo atoms are partially replaced by Mg. The incorporation of Mg atoms into the structure of Pr 2 MoO 6 results in the disordering of the praseodymium and oxygen lattices. Both the polycrystalline and single-crystal Mg-doped samples are hygroscopic.

A single crystal of Nd5Mo3O16 with lead partly substituting for neodymium, which has a fluorite-like structure, was studied by precision X-ray diffraction, high-resolution transmission microscopy and EDX microanalysis. The crystal structure is determined in the space group Pn3¯n. It was found that the Pb atoms substitute in part for Nd atoms in the structure and are located in the vicinity of Nd2 positions. Partial substitutions of Mo cations for Nd positions and of Nd for Mo positions in crystals of the Ln5Mo3O16 oxide family are corroborated by X-ray diffraction for the first time. The first experimental verification of the location of an additional oxygen ion in the voids abutting MoO4 tetrahedra was obtained.

The La2Mo2O9 (LM) and Pr2Mo2O9 (PM) single crystals are studied using precision X-ray diffraction and high-resolution transmission microscopy at room temperature. The crystal structures are determined in the space group P2(1)3. La and Pr atoms, as well as Mo1 and O1 atoms, are located in the vicinity of the threefold axes rather than on the axes as in the high-temperature cubic phase. In both structures studied, the O2 and O3 positions are partially occupied. The coexistence of different configurations of the Mo coordination environment facilitates the oxygen-ion migration in the structure. Based on the X-ray data, the activation energies of O atoms are calculated and the migration paths of oxygen ions in the structures are analysed. The conductivity of PM crystals is close to that of LM crystals. The O2 and O3 atoms are the main contributors to the ion conductivity of LM and PM.