New ternary molybdenum chalcogenides containing Mo6 and Mo9 clusters: M2Mo15Se19 (M = K,Ba, In,Tl) and K2Mo15S19

New superconducting Mo^II compounds M₂Mo₁₅X₁₉ (M = K, Ba, In, Tl and X = Se; M = K and X = S have been found. These materials crystallize in a new structural type containing isolated Mo₆X₈ and Mo₉X₁₁ units. They are superconducting (T_c = 3.32 K for K₂Mo₁₅S₁₉), and have high initial slopes $\text{dHc}{}_2\text{dT}$ of the upper critical field.     

New ternary Mo(II) - compounds InxMo15Se19 containing Mo6Se8 and Mo9Se11 units

A new ternary molybdenum chalcogenide has been found with composition In_xMo₁₅Se₁₉. This compound crystallizes in the hexagonal space group P6₃/m, and shows both types of blocks Mo₆Se₈ and Mo₉Se₁₁. To our knowledge, this is the first Me₉X₁₁ unit ever observed in a material. It presents a homogeneity domain: 2, 9 < x < 3, 4. Substitution of sulphur and tellurium for selenium in In_3.3Mo₁₅Se_19-yX_y (X = S, Te) is possible in the limits 0 < y < 12 and 0 < y < 2 respectively. The new compound becomes a high field superconductor at low temperature.     

A facile synthesis of pseudo one-monodimensional ternary molybdenum chalcogenides M2Mo6X6 (X = Se,Te; M = Li,Na..Cs)

Compounds of this family are of great interest because of their pseudo one-dimensional structure of linear chains of (Mo₃)¹_∞ clusters. High temperature solid state reactions (1100°C) are generally used to prepare members of this class, such as In₂Mo₆Se₆. This paper describes ion exchange reactions of In₂Mo₆X₆ with alkali iodide and chloride salts at 550°C to give M₂Mo₆X₆ and mixed solid solutions In_2?xM_xMo₆X₆ (M=Li, Na, K, Rb, Cs; X=Se, Te). Furthermore, we show that ion exchange provides a low temperature route to prepare phases which are not stable at high temperature, such as In_2?xM_xMo₆Se₆ 0 ≤ x ≤ 2 and M = alkali. When M = Li, the lithium can be partially removed by oxidation with iodine producing non stoichiometric ternary molybdenum chalcogenides In_2?xMo₆Se₆ (0 ≤ x ≤ 1.8). Superconducting measurements indicate that only Tl₂Mo₆Se₆ is superconducting above 1K.     

New compounds of the type Mo2Re4X8 (M = S,Se) containing octahedral Mo2Re4 clusters

We report the preparation and some properties of new compounds with the composition Mo₂Re₄X₈ (X = S, Se) and Mo₄Re₂Te₈. These compounds are isostructural to Mo₆Se₈ and present mixed octahedral clusters : Mo₂Re₄ or Mo₄Re₂. The solid solutions Mo₂Re₄S_8?xSe_x (0 ? x ? 8) and Mo₂Re₄Se_8?xTe_x (0 ? x ? 1.2) are semiconducting, whereas Mo₄Re₂Te₈ is metallic and becomes superconducting at T_c = 3.55 K.     

Preparation, structure and dielectric properties of Ba4LaMNb3O15 (M = Ti, Sn ) ceramics

Two new cation-deficient hexagonal perovskites Ba₄LaMNb₃O₁₅ (M = Ti, Sn) ceramics were prepared by high temperature solid-state reaction route. The phase and structure of the ceramics were characterized by X-ray diffraction, scanning electron microscopy (SEM). The microwave dielectric properties of the ceramics were studied using a network analyzer. The Ba₄LaTiNb₃O₁₅ has high dielectric constant of 52, high quality factors (Q) 3500 (at 4.472 GHz), and temperature variation of resonant frequency (τ_f) +93 ppm °C⁻¹ at room temperature; Ba₄LaSnNb₃O₁₅ has dielectric constant of 39 with high Q value of 2510 (at 5.924 GHz), and τ_f −29 ppm °C⁻¹.     

Polyol mediated synthesis of nanocrystalline M3SbS3 (M=Ag, Cu)

A simple and convenient polyol-mediated route has been developed to produce nanocrystalline Ag₃SbS₃ and Cu₃SbS₃ from AgNO₃ and Cu(NO₃)₂ and SbCl₃ with thiourea at 197 °C. The products were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Analysis shows that glycol agitated state and injection rate have a great effect on the purity of the final products.     

Ternary and pseudoternary AB2X4 compounds (A = Zn,Cd; B = Ga,In; X = S,Se)

Multication compounds are considered to have interesting applications. Among the variety of possible A_mB_nX_p materials, however, the research work has been unevenly distributed, as the ABX₂ chalcopyrites have attracted the majority of the efforts. The related family of AB₂X₄ defect chalcopyrites, which is characterized by an ordered sublattice of vacancies and then by a further degree of freedom as to tailoring possibilities, has on the other hand received much less attention.Here we discuss the results obtained in the crystal growth and in the structural and dynamical (Raman) analysis of about sixty different ternary and pseudoternary AB₂X₄ compounds or phases.The reaction products can be grouped in three different structural families: cubic-spinel AB₂X₄ structures (CdIn₂S₄ like), AB₂OX₄ layered hexagonal structures (ZnIn₂S₄ like) and AB₂□X₄ defective tetragonal structures (CdGa₂S₄ like).Our attention has been primarily devoted to the defective phases, which have been obtained in the great majority of the starting compositions studied.     

Growth conditions and crystal structure parameters of layer compounds in the series Mo1−xWxSe2

Single crystals of layer compounds with compositions Mo_1?xW_xSe₂, where x varies within the range 0 to 1, have been grown by the direct vapour transport technique to a minimum size of 6 mm × 5 mm × 0.2 mm. The series forms a complete range of isomorphous solid solutions, showing good agreement with Vegard's law. Growth conditions and lattice parameters are given for the series.     

Effects of annealing temperatures on optical and electrical properties of vacuum evaporated Ga15Se77In8 chalcogenide thin films

The optical constants (absorption coefficient, optical band gap, refractive index, extinction coefficient, real and imaginary parts of dielectric constants) of amorphous and thermally annealed thin films of Ga₁₅Se₇₇In₈ chalcogenide glasses with thickness 4000 Å have been investigated from absorption and reflection spectra as a function of photon energy in the wave length region 400-800 nm. Thin films of Ga₁₅Se₇₇In₈ chalcogenide glasses were thermally annealed for 2 h at three different annealing temperatures 333 K, 348 K and 363 K, which are in between the glass transition and crystallization temperature of Ga₁₅Se₇₇In₈ glasses. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It was found that the optical band gap decreases with increasing annealing temperature. It has been observed that the value of absorption coefficient and extinction coefficient increases while the values of refractive index decrease with increasing annealing temperature. The decrease in optical band gap is explained on the basis of the change in nature of films, from amorphous to crystalline state. The dc conductivity of amorphous and thermally annealed thin films of Ga₁₅Se₇₇In₈ chalcogenide glasses is also reported for the temperature range 298-393 K. It has been observed that the conduction is due to thermally assisted tunneling of the carriers in the localized states near the band edges. The dc conductivity was observed to increase with the corresponding decrease in activation energy on increasing annealing temperature in the present system. These results were analyzed in terms of the Davis-Mott model.     

Microwave dielectric properties of alkaline earth orthosilicates M2SiO4 (M=Ba, Sr, Ca)

Alkaline earth orthosilicates M₂SiO₄ (M=Ba, Sr, Ca) ceramics were prepared by solid state ceramic route and their microwave dielectric properties were investigated. M₂SiO₄ ceramics have ε_r in the range 8.5-13. At microwave frequencies, the Q_u × f obtained were 17,900 GHz, 19,100 GHz and 26,100 GHz for Ba₂SiO₄, Sr₂SiO₄ and Ca₂SiO₄ respectively. The τ_f of Ba₂SiO₄ was − 17 ppm/°C, whereas Sr₂SiO₄ and Ca₂SiO₄ exhibited high values of τ_f, − 205 ppm/°C and − 89 ppm/°C respectively. The coefficient of thermal expansion (α_l) of the orthosilicates was also studied.     

M3O4(M=FeCoCrMnMg)高熵氧化物粉体的简易制备及超电容性能研究

高熵氧化物以其独特的结构和潜在的应用前景引起了越来越多的关注。本工作采用简单易行的固相反应法制备了M₃O₄(M=FeCoCrMnMg)高熵氧化物粉体, 采用不同手段对粉体进行表征, 并采用涂覆法制备了 M₃O₄/泡沫镍(M₃O₄/NF)复合电极, 研究其超电容性能。结果表明, 随着煅烧温度升高, Fe₂O₃(H)/Co₃O₄(S)/Cr₂O₃(E)和Mn₂O₃(B)相继固溶进入尖晶石主晶相晶格; 在900 ℃煅烧2 h所得M₃O₄粉体的平均粒径为0.69 μm, 具有单一尖晶石结构(面心立方, Fd-3m, a=0.8376 nm), 且Fe、Co、Cr、Mn和Mg五种元素在晶粒内均匀分布, 呈典型的高熵氧化物特征。此外, M₃O₄/NF复合电极在1 mol/L KOH的电解液中, 当电流密度为1 A·g^-1时, 其质量比电容达到193.7 F·g^-1, 可见M₃O₄高熵氧化物在超级电容器电极材料领域具有良好的应用前景。     

A model for the structure of 1.31BaO.6M2O3; M = Al,Ga; an electron microscopic study

Two bariumhexaaluminates are reported in literature (2–9) with the approximate compositions 0.82BaO.6Al₂O₃ and 1.31 BaO.6Al₂O₃. In this paper an electron microscopic and X-ray powder diffraction study of 1.31BaO.6Ga₂O₃ is reported. 1.31BaO.6Ga₂O₃ (a′ = 10.081(5), $\text{c}\text{′ = 70.60(2)}\text{A}\text{?}$) has an a?3,a?3,3c superstructure of NaAl₁₁O₁₇. High resolution electron microscope images show two types of BaO layers to exist.A model for the structure of 1.31BaO.6Ga₂O₃ is proposed, based on high resolution images, electron diffraction, the observed composition and crystal binding. This model with the formule Ba₇M₆₄O₁₀₃ has Ba₃O₃ layers and Ba₄O₄ layers occurring alternatingly along the c axis. In the last layer the substitutions M₂O → Ba and M₂O → M₂O₃ are found.     

A study of the systems M2SAl2S3, M = Li,Na, K; preparation,phase study and electrical conductivity

A study of the systems M₂SAl₂S₃ (M = Li, Na, K) was undertaken to determine the phases present in these systems. New phases identified were LiAlS₂, NaAlS₂, Na₂S·(10±1)Al₂S₃, KAlS₂ and K₂S·(10±1)Al₂S₃, none of which were analogous to the beta-alumina structure. Electrical conductivity measurements were made on the potassium phases, and the former phase is an electronic conductor, while the latter is an ionic conductor (2 × 10^?5 (S/m) at 573 K).     

Microstructure and properties of MoSi2–MoB and MoSi2–Mo5Si3 molybdenum silicides

MoSi₂-based intermetallics containing different volume fractions of MoB or Mo₅Si₃ were fabricated by hot-pressing MoSi₂, MoB, and Mo₅Si₃ powders in vacuum. Both classes of alloys contained approximately 5 vol.% of dispersed silica phase. Additions of MoB or Mo₅Si₃ caused the average grain size to decrease. The decrease in the grain size was typically accompanied by an increase in flexure strength, a decrease in the room temperature fracture toughness, and a decrease in the hot strength (compressive creep strength) measured around 1200 °C, except when the Mo₅Si₃ effectively became the major phase. Oxidation measurements on the two classes of alloys were carried out in air. Both classes of alloys were protected from oxidation by an in-situ adherent scale that formed on exposure to high temperature. The scale, although not analyzed in detail, is commonly recognized in MoSi₂ containing materials as consisting mostly of SiO₂. The MoB containing materials showed an increase in the scale thickness and the cyclic oxidation rate at 1400 °C when compared with pure MoSi₂. However, in contrast with the pure MoSi₂ material, oxidation at 1400 °C began with a weight loss followed by a weight gain and the formation of the protective silica layer. The Mo₅Si₃ containing materials experienced substantial initial weight losses followed by regions of small weight changes. Overall, the MoB and Mo₅Si₃ additions to MoSi₂ tended to be detrimental for the mechanical and oxidative properties.     

La liaison metal-metal dans les clusters M12O36: I - Preparation et etude structurale des phases La4M6O19 (M = Ru,Os)

La₄Ru₆O₁₉ and La₄Os₆O₁₉ are prepared for the first time by the oxidation of stoechiometric mixtures of (La₂O₃ + RuO₂) and (La₂O₃ + Os) with excess KC10₃. The crystal structure of both compounds are solved by conventional Fourier and least-squares methods to R = 0.022 and R = 0.024, respectively, using automated four-circle diffractometer data. Both are isostructural with La₄Re₆O₁₉. M-M distances (2.488 Å for M = Ru and 2.499 Å for M = Os) show evidence of strong metal-metal interaction. Comparison of data for M = Ru, Os or Re reveals the evolution of some interatomic distances with Z.     

M3MgSi2O8(M=Sr, Ba)中Ce3+的发光性质

本文合成了掺Ce     

The preparation of some ternary sulphides MR2S4 (M = Ca,Cd; R = La,Sm,Er) and the melt growth of CaLa2S4

The Preparation of the binary sulphides CaS, La₂S₃, Er₂S₃, and Sm₂S₃ in high purity powder form from the elements is described, with the subsequent synthesis of ternary sulphides with Th₃P₄ and spinel structures. Single crystals of CaLa₂S₄ and CaLa₂S₄La₂S₃ solid solutions, up to 10 mm³ volume, have been grown from the melt in sealed crucibles using the Stöber technique.     

Conductivite electrique et spectres de diffusion raman des verres mixtes AgPO3 − MI2 AVEC M = Cd,Hg, Pb. Correlation entre conductivite et structure

The glass-forming regions in the AgPO₃ ? MI₂ systems with M = Cd,Pb,Hg were determined. Electrical conductivity measurements and Raman spectra were carried out. A maximum conductivity value of $\text{10}{}^{\mathrm{?2}}\text{(Ω}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 25°C is obtained for a mole fraction of 0,19 in PbI₂ or in CdI₂, whereas a value of $\text{3×10}{}^{\mathrm{?5}}\text{(Ω}\text{cm}\text{)}{}^{\mathrm{?1}}$ at 25°C is found for a mole fraction of 0,5 in HgI₂. The conductivity results and Raman spectra are examined and compared with those of AgPO₃ ? AgI. An exchange between Ag⁺ and M²⁺ ions is proposed leading to AgI species in AgPO₃ ? CdI₂ and AgPO₃ ? PbI₂ glasses. It could explain the high conductivity values obtained and the similarities observed in Raman spectra.     

Electrical properties of amorphous Ge15Se60M25 where (M = As or Sn or Bi) films

Thin film samples were prepared from the synthesized amorphous Ge₁₅Se₆₀M₂₅ (where M = Sn or As or Bi) chalcogenide glass compositions by thermal evaporation technique. X-ray analysis shows the amorphous nature of the obtained films. The dc-electrical conductivity was studied for different thicknesses (89-903 nm) as function of temperature in the range (303-413 K) below T_g (glass transition temperature). The obtained results showed that the conduction activation energy has two values indicating the presence of two conduction mechanisms through the investigated range of temperature which can be explained in accordance with Mott and Davis model. The current-voltage characteristics of the investigated samples present a switching phenomenon of memory type. The mean value of the threshold switching voltage increases linearly with increasing film thickness and decreases exponentially with temperature in the investigated range below T_g. The obtained results are explained in accordance with the electrothermal model for the switching process.     

Une nouvelle structure hexagonale compacte ordonnee Les oxydes |SnX3|octa |MLi|tétraO8, avec X = Sn(Ti) + M + Li et M = Zn,Mg

New oxides Sn_2.8Li_1.6M_1.6O₈ (M = Zn, Mg) with a four layers (ABAC) hexagonal closest packing of oxygen atoms have been isolated. The structural study shows a double order of the cations; Sn and X |X = Sn(Ti) + M + Li| are located respectively on two sets of octahedral sites whereas Li and M are located respectively on two sets of tetrahedral sites. The original linkage of tetrahedral and octahedral units gives a close approach of tetrahedral lithium and octahedral X. A partial substitution of zinc and magnesium by copper has been successfully tried.