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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 Pn3¯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.

In this work, we present results on the growth of centimeter-scale pentacene crystals using the physical vapor transport method in a dual-temperature zone horizontal furnace. It was established that intensive crystal growth processes occurred in transition regions with sudden temperature changes, while crystal growth was practically not observed in regions with slightly varying temperatures. During crystal growth, co-precipitating golden needle-like crystals reaching lengths of more than 10 mm were obtained. Using the method of single-crystal X-ray diffraction at 85 and 293 K for dark-blue lamellar pentacene crystals, the crystal structure was refined in a triclinic system with sp.gr. P1¯. It was established that the golden needle crystals consisted of molecules of the pentacene derivative—5,14-pentacenedione, the crystal structure of which was solved for the first time in a rhombic system with sp.gr. P212121. The absorption and luminescence spectra of pentacene and 5,14-pentacenedione in toluene solutions were obtained and analyzed. The electrical properties of the prepared pentacene thin films and single crystals grown under physical vapor transport conditions were evaluated by fabricating and characterizing field-effect transistors (FETs). It was shown that the presence of impurities in the commercial pentacene material had a significant effect on the morphological quality of thin polycrystalline films and noticeably reduced the hole mobility.

The crystal structure of samarium iron borate was analyzed with regard to growth conditions and temperature. The inclusion of about 7% Bi atoms in the crystals grown using the Bi2Mo3O12-based flux was discovered and there were no impurities in the crystals grown using the Li2WO4-based flux. No pronounced structural features associated with Bi inclusion were observed. The different absolute configurations of the samples grown using both fluxes were demonstrated. Below 80 K, a negative thermal expansion of the c unit-cell parameter was found. The structure of (Sm0.93Bi0.07)Fe3(BO3)4 belongs to the trigonal space group R32 in the temperature range 90–400 K. A decrease in the (Sm,Bi)—O, Sm—B, Sm—Fe, Fe—O, Fe—B and Fe—Fe distances is observed with a lowering of the temperature, B1—O does not change, B2—O increases slightly and the B2O3 triangles deviate from the ab plane. The strongest decrease in the equivalent isotropic atomic displacement parameters (U eq) with decreasing temperature is observed for atoms Sm and O2, and the weakest is observed for B1. The O2 atoms have the highest U eq values, the most elongated atomic displacement ellipsoids of all the atoms and the smallest number of allowed vibrational modes of all the O atoms. The largest number of allowed vibrational modes and the strongest interactions with neighbouring atoms is seen for the B atoms, and the opposite is seen for the Sm atoms. The quadrupole splitting Δ(T) of the paramagnetic Mössbauer spectra increases linearly with cooling. The Néel temperature [T N = 31.93 (5) K] was determined from the temperature dependence of the hyperfine magnetic field B hf(T), which has a non-Brillouin character. The easy-plane long-range magnetic ordering below T N was confirmed.

Pure and sodium-containing lanthanum oxymolybdates were synthesized as polycrystalline samples and single crystals. The compounds have been characterized by several methods including SEM, inductive...

Oxymolybdates La2MoO6, both pure and doped with magnesium, have been obtained by the flux crystallization method and solid-phase synthesis as single crystals and polycrystals, respectively. The compounds are described by X-ray diffraction analysis, thermogravimetry, and differential scanning calorimetry; their conducting properties have been investigated. A model of the structure of magnesium-doped La2MoO6 single crystals is proposed. Incorporation of divalent magnesium atoms into the sites of hexavalent molybdenum atoms in the La2MoO6 structure leads to the formation of oxygen vacancies and a slight increase in the conductivity of doped samples in comparison with pure crystals. The compounds under study have hygroscopic properties.

Undoped and Mg-doped Pr2MoO6oxymolybdate 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 tox= 0.03. The structure of the Mg-doped Pr2MoO6single 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 Pr2MoO6results in the disordering of the praseodymium and oxygen lattices. Both the polycrystalline and single-crystal Mg-doped samples are hygroscopic.

A new linear luminophore consisting of five conjugated units of oxazole, phenylene and a central benzothiadiazole fragment, 4,7-bis[4-(1,3-oxazol-5-yl)phenyl]-2,1,3-benzothiadiazole, has been synthesized and characterized. Needle-like single-crystal samples up to 10 mm in length were obtained by physical vapor transport. The crystal structure was determined at 95 K and 293 K using single-crystal X-ray diffraction. With decreasing temperature, the space group P21/n does not change, but the unit-cell volume of the crystal decreases. The presence of intra- and intermolecular hydrogen bonds was established. Melting parameters (T m = 305.5°C, ΔH m = 52.2 kJ mol−1) and the presence of a liquid-crystalline mesophase (T LC = 336.3°C, ΔH LC = 1.4 kJ mol−1) were determined by differential scanning calorimetry and in situ thermal polarization optical microscopy studies. The presence of linear chains of hydrogen bonds ensures high stability of the crystal structure in a wide temperature range. The luminophore is characterized by a large Stokes shift (5120–5670 cm−1) and a high quantum yield of fluorescence, reaching 96% in solutions (λmax = 517 nm) and 27% in thin crystalline films (λmax = 529 nm). The calculated absorption and emission spectra are in good agreement with the experimental data. Because of the excellent optical properties and high thermal stability, the new linear luminophore has great potential for application in organic photonics and optoelectronic devices.

Undoped and Mg-doped Nd 2 MoO 6 oxymolybdate single crystals and polycrystalline samples have been prepared by flux growth and solid-state reactions. The materials have been characterized by X-ray diffraction, EDS microanalysis, X-ray structure analysis, differential scanning calorimetry, thermogravimetry, and impedance spectroscopy. The (MgO) x (Nd 2 MoO 6 ) (1– x )/2 solid solution series has been shown to extend to x = 0.20. Doping of Nd 2 MoO 6 single crystals with Mg leads to splitting of the Mo, Nd1, and O2 sites. A structural model in which the Mg atoms partially substitute for Mo atoms and reside near the Mo site, 0.28 A from it, ensures the best agreement with the observed diffraction pattern. The conductivity of the undoped and doped polycrystalline samples approaches 10 −4 S/cm at 800 °C and is assumed to have an anionic nature.

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 P\overline{6}2c 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.

The literature data and the results obtained by the authors on the study of the structure and properties of a series of polycrystalline and single-crystal samples of pure and Mg-doped oxymolybdates Ln2MoO6 (Ln = La, Pr, Nd) are analyzed. Presumably, the high-temperature phase I41/acd of Nd2MoO6 single crystals is retained at room temperature. The reason for the loss of the center of symmetry in the structures of La2MoO6 and Pr2MoO6 and the transition to the space group I4¯c2 is the displacement of oxygen atoms along the twofold diagonal axes. In all structures, Mg cations are localized near the positions of the Mo atoms, and the splitting of the positions of the atoms of rare-earth elements is found. Thermogravimetric studies, as well as infrared spectroscopy data for hydrated samples of Ln2MoO6 (Ln = La, Pr, Nd), pure and with an impurity of Mg, confirm their hygroscopic properties.

Undoped and Mg-doped Pr

Crystals with the La