Structure of copper-potassium hexacyanoferrate (II) and sorption mechanisms of cesium

A mixed potassium-copper hexacyanoferrate (II) K₂CuFe(CN)₆ was prepared by local growth on solid cupric sulfate in an aqueous solution of potassium hexacyanoferrate (II) and by growth in a gel. Powders having this composition and separable by filtration could not be obtained by normal precipitation from aqueous solution. This compound has a triclinic P-1 structure, described for the first time, and made up of non-linear -Fe-C-N-Cu-chains which form a puckered layered network. Sorption mechanisms for cesium have been studied in batch experiments including kinetics and isotherms, X-ray diffraction, infra-red spectroscopy and scanning electron microscopy. In neutral solutions the initial crystal structure is maintained and sorption proceeds through a K/Cs ion exchange. In acid solutions, even without addition of cesium, the initial structure is destroyed. The main phase formed in acidic media is Cu₂Fe(CN)₆. In the presence of cesium the structure is also destroyed and new solid phases are formed. All these processes have slow kinetics, the evolution of the solid being observed over a period of 6 months. This study confirms previous results, which have shown that the sorption mechanisms on hexacyanoferrates strongly depend on the composition and structure of the solid, together with the composition of the solution. Sorption mechanisms have considerable consequences on the use of these products for the decontamination of radioactive wastes.     

Characterization of solid solutions composed of oxides of Cu,Zn, and Cr for methanol synthesis

Solid solutions of Cu₂O alone and Cu₂O with ZnO or Cr₂O₃ in ZnO · Cr₂O₃ as well as solid solutions of ZnO in Cu₂O · Cr₂O₃ have activities and selectivities for methanol synthesis comparable to solid solutions of Cu₂O in ZnO. Addition of a secondary phase to these solid solutions limits the grain growth and produces higher surface areas.     

Solid solutions between β-Ca3(PO4)2 and sodium-containing whitlockite

Mixtures of CaHPO₄, CaCO₃, and Na₂CO₃ were heated at 870°C under steam or under dry CO₂ until phase composition and weight were constant. According to chemical analysis and X-ray diffractometry the stability field of the β-Ca₃(PO₄)₂ phase is limited by the molar P/Ca ratio of 0.664 ± 0.003 and 0.675 ± 0.010 irrespective of the partial water vapour pressure. A continuous series of solid solutions was found between β-Ca₃(PO₄)₂ and a new whitlockite with the composition Ca₁₀Na(PO₄)₇. The IR spectrum of these solid solutions shows that the point symmetry of the PO₄ groups and their environment increases with increasing sodium content. This is in agreement with data published about the structure of β-Ca₃(PO₄)₂ and whitlockite. The composition of these solid solutions suggests that Na⁺ ions can replace H⁺ ions in the whitlockite structure. Carbonate and pyrophosphate ions are not incorporated in these whitlockites.     

Potassium-conducting solid electrolytes in K<Subscript>1 − 2<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>GaO<Subscript>2</Subscript> system

New solid electrolytes with a high conductivity by K⁺ ions in the K_{1 − 2x} Sr _x GaO₂ system are synthesized and studied. It is found that the introduction of Sr²⁺ ions into potassium monogallate leads to the formation of solid solutions with KGaO₂ structure in a wide range of additive concentration. These solid solutions exhibit a high conductivity; the conductivity increases monotonically with increasing concentration of strontium within the single-phase range. The electrical characteristics are related to the electrolyte structure. The results are compared with the earlier data for the gallate solid electrolytes with the additives of four-charged cations and the systems based on potassium monoferrite and monoaluminate.     

Synthesis and Characterization of Spinel‐Type Gallia‐Alumina Solid Solutions

By precipitation with ammonia of ethanolic solutions containing the appropriate proportions of gallium and aluminium nitrate, following by calcination of the resulting gels at 773 K, mixed Ga₂O₃/Al₂O₃ oxides having Ga:Al ratios of 9:1, 4:1, 1:1, 1:4 and 1:9 were obtained. Powder X‐ray diffraction showed that these mixed metal oxides form a series of solid solutions having the spinel‐type structure; also shown by γ‐Al₂O₃ and γ‐Ga₂O₃. The specific surface area (determined by nitrogen adsorption at 77 K) was found to range from 160 m² g^?1 for the mixed oxide having Ga:Al = 9:1 up to 370 m² g^?1 for that having Ga:Al = 1:9. High resolution MAS NMR showed that Ga³⁺ and Al³⁺ ions occur at both tetrahedral and octahedral sites in the spinel‐type structure of the mixed metal oxides, although there is a preferential occupation of tetrahedral sites by Ga³⁺ ions. A proportion of penta‐coordinated Al³⁺ ions was also found. IR spectra of carbon monoxide adsorbed at 77 K showed that the mixed metal oxides have a considerable Lewis acidity, related mainly to tetrahedrally coordinated metal ions exposed at crystal surfaces. The characteristic infrared absorption band of coordinated (adsorbed) CO appears in the range 2205–2190 cm^?1, and its peak wavenumber is nearly independent of Ga:Al ratio in the mixed gallia‐alumina oxides.     

Ionic mobility and electrophysical properties of solid solutions in PbF<Subscript>2</Subscript>–SbF<Subscript>3</Subscript> and PbF<Subscript>2</Subscript>–SnF<Subscript>2</Subscript>–SbF<Subscript>3</Subscript> systems

Ionic mobility and electrical conductivity of solid solutions with fluorite structure, obtained with solid-state approach in PbF₂–SbF₃ and PbF₂–SnF₂–SbF₃ systems, are studied by 19F NMR and electrochemical impedance spectroscopy methods. The 19F NMR spectra parameters, types of ion motions in the fluoride sublattice, and the ionic conductivity magnitude are shown to be determined by the temperature and fluoride concentration in the solid solutions. The solid solution specific conductivity in the PbF₂–SbF₃ and PbF₂–SnF₂–SbF₃ systems at 420–450 K is as high as ~10^–2 S/cm, which allows accounting the solid solutions as a base for preparation of functional materials.     

Interactions in the NdF<Subscript>3</Subscript>-Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>-MF<Subscript>2</Subscript> (M = Ba,Sr) systems

Isothermal anneals (at 873 K) and powder X-ray diffraction were used to study isothermal sections of phase diagrams of the NdF₃-Nd₂O₃-MF₂ (M = Ba, Sr) systems. In studying the NdF₃-Nd₂O₃-BaF₂ system, classical solid-phase synthesis was supplemented with mechanochemical activation of feedstock mixtures or BaF₂ activated with gaseous hydrogen fluoride was used. In both systems, a solid solution with the fluorite structure based on MF₂ and NdOF phases, a solid solution with the tysonite structure based on NdF₃, and an ordered fluorite-related phase Ba₄Nd₃F₁₇ were found. The NdOF-based solid solutions were shown to have polymorphism: β_trig ai α_cub at ≈800 K; a new trigonal phase of these solid solutions has been discovered. The effect of a dimensional factor $\left( {R_{Ba^{2 + } } > R_{Sr^{2 + } } } \right)$\left( {R_{Ba^{2 + } } > R_{Sr^{2 + } } } \right) on phase formation and unit cell parameters of the solid solutions was traced.     

Ferromagnetic material CdGeP2:Mn for spintronics

Solid solutions Cd_1?x Mn_xGeP₂ (x=0?0.19) have been synthesized and identified. In these solutions, the unit cell parameters decrease with an increase in the manganese content. The solid solution Cd_0.81Mn_0.19GeP₂ is a ferromagnet with the Curie temperature T _C ≈ 311 K. The paramagnetic moment of Mn²⁺ ions equal to 5.8 μ_B, as well as the spontaneous magnetization constituting 76% of the total magnetization of a crystal, has been determined with the use of the Langevin function. The origin of ferromagnetism in CdGeP₂:Mn is exchange mediated by charge carriers (holes). These holes are caused by cationic defects in the structure of chalcopyrite.     

Potassium–conducting K<Subscript>1 − 2<Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>GaO<Subscript>2</Subscript> solid electrolytes

Solid electrolytes with potassium-cation conductivity in the K_{1 − 2x} Pb _x GaO₂ system were synthesized and studied. It was found that solid solutions based on potassium monogallate are formed in a wide range of compositions. They contain vacancies in the potassium sublattice that provide for high conductivity of electrolytes. The relationship is considered between electric characteristics of solid electrolytes and the composition and structure of solid solutions. The results are compared to the earlier obtained data for similar solid electrolytes based on potassium monoaluminate and monoferrite.     

Magnetic studies on (U,La)O2+x solid solutions

Magnetic susceptibilities of La_yU_1−yO_2+x solid solutions with fluorite structure were measured from 4.2 K to room temperature. An antiferromagnetic transition was observed for the solid solutions with lanthanum concentration0 ≤ y ≤ 0.3 in both stoichiometric (x = 0) and hypostoichiometric oxygen range (x < 0). From comparison of the magnetic properties of solid solutions with different oxygen amounts (x < 0, x = 0, x > 0), both oxygen vacancies and interstitial oxygens were found to weaken the magnetic exchange interactions between uranium ions. The Ne´el temperature decreased with decreasing uranium concentration. The variation of the Ne´el temperature of (U, La)O₂ solid solutions with uranium concentration was different from that of (U, Th)O₂ solid solutions. The magnetic moment decreased with decreasing uranium concentration. Its rate was larger than that of (U, Th)O₂ solid solutions and was comparable with that of (U, Y)O₂ solid solutions. The oxidation state of uranium in the solid solutions was examined from the magnetic susceptibility data. The uranium ions were found to be in either the tetravalent or the pentavalent state. The effect of magnetic dilution was larger with La₂O₃ than with Y₂O₃ and/or Sc₂O₃.     

The complex synthesis and solid state chemistry of ceria-lanthana solid solutions prepared via a hexamethylenetetramine precipitation

Mixed oxide solid solutions are becoming ever more commercially important across a range of applications. However, their synthesis can be problematical. Here, we show that ceria-lanthana solid solutions can be readily prepared via simple precipitation using hexamethylenetetramine. However, the solution chemistry can be complex, which results in the precipitated particles having a complex structure and morphology. Great care must be taken in both the synthesis and characterisation to quantify the complexity of the product. Even very high heat treatments were not able to produce highly homogeneous materials and X-ray diffractions reveals the non-equilibrium form of particles prepared in this way. Unexpected crystal structures are revealed including a new metastable cubic La₂O₃ phase.     

Ce1－xNdxO2－δ固溶体的电子顺磁共振谱和阻抗谱的研究

利用溶胶-凝胶方法在800 ℃焙烧10 h后, 合成了固溶体Ce_1－xNd_xO_2－δ (x＝0.05～0.55), X射线衍射(XRD)测试表明固溶体已经形成立方萤石结构; 电子顺磁共振谱(EPR)研究表明在固溶体Ce_1－xNd_xO_2－δ中随着掺杂量x的增大, Ce^3＋离子含量减少, 说明掺杂Nd^3＋离子可以抑制Ce^4＋的还原; 交流阻抗谱的测量表明固溶体Ce_0.9Nd_0.1O_2－d 具有离子导电特性, 600和700 ℃时的电导率分别为4.25×10^－3和1.12×10^－2 S•cm^－1, 活化能为0.68 eV.     

Crystal Structures and Packing of 4-Cyanocubanecarboxylic Acid,Its Methyl Ester,and the Solid Solution of 1,4-Dicyanocubane and 1,4-Dibromocubane

The crystal structure of 4-cyanocubanecarboxylic acid contains the same syn–anti carboxyl group catemer that is found in other cubane monocarboxylic acids. The cyano groups are arranged according to the type-II geometry, in that they are 2₁ screw-axis related. Curiously, there is a 5% orientational disorder of the cyano and anti carboxyl groups. The ester of the title acid packs isostructurally with the corresponding chloro and fluoro analogs because of the importance of the C—H...O hydrogen bond patterns. 1,4-Dicyanocubane forms solid solutions with 1,4-dibromocubane, but, interestingly, the crystal structure of the solid solution is distinct from that of either component. The formation of these solid solutions seems to be governed by shape and size factors.     

Zr1−xLnxW2O8−x/2 (Ln=Eu, Er, Yb): Solid solutions of negative thermal expansion-synthesis, characterization and limited solid solubility

Zr_1−xLn_xW₂O_8−x/2 solid solutions (Ln=Eu, Er, Yb) of different substitution fractions x have been synthesized. Their X-ray diffraction (XRD) patterns have been indexed and lattice parameters calculated based on the α-ZrW₂O₈ structure. The coefficients of thermal expansion (CTEs) of these solid solutions were estimated to be −10.3×10⁻⁶ K⁻¹ in temperature range of 30-100 °C. The solubility of lanthanide ions in these solid solutions decreases linearly with the increase in the radius of substituted lanthanide ions. Based on the concentration dependence of phase transition temperatures, a novel method for determination of solubility of the lanthanide ions in Zr_1−xLn_xW₂O_8−x/2 solid solutions has been developed. This method seems to be more sensitive as compared with that based on XRD technique.     

Transition-metal bimaleates and their solid solutions: Synthesis,structural, and thermoanalytical study

Transition-metal hydrogen maleates of composition M(C₄H₃O₄)₂ · 4H₂O, where M = Mn, Fe, Co, and Ni, and their solid solutions were synthesized and characterized by X-ray crystallography, IR spectroscopy, mass spectrometry, and thermal analysis. X-ray crystallography and IR spectroscopy showed that both intramolecular and intermolecular H-bonds exist in these compounds. The generation of continuous substitutional solid solutions with cation substitution in these compounds was studied. The thermolysis mechanism was studied for both transition-metal hydrogen maleates and their solid solutions. The composite produced by thermolysis is stable up to 1200°C in flowing helium.     

Isolation of Rare-Earth Elements from Mixtures of Calcium and Lanthanide Oxalates

The temperature regions for separate crystallization of rare-earth element (REE) oxides of the cerium group in the presence of CaCO₃ have been determined using X-ray diffraction, differential thermogravimetric analysis, inductively coupled plasma mass spectroscopy, and X-ray fluorescence. The possibility to separate REE oxides from CaCO₃ in H₂SO₄ solutions after heat treatment (450–600°C) has been studied. The solid phase of the precipitate is represented by slightly soluble calcium sulfate, whereas the REE oxides pass into the liquid phase in the form of highly soluble sulfates. After heat treatment of the test mixture of REE oxalates and calcium oxalate at a temperature higher than 750°C, calcium compounds pass into 1–2% HNO₃ liquid phase in the form of nitrates, whereas lanthanide oxides remain in the insoluble phase of REE oxide solid solution having CeO₂ structure.     

A microdomain description of defective fluorite-type phasesCaxM1−xO2−x(M =Zr,Hf; x = 0.1–0.2)

Electron diffraction patterns from cubic solid solutions of lime in zirconia and hafnia contain weak diffuse features in addition to the strong reflections expected from the fluorite structure type. A comparison of these features with those found in patterns from annealed specimens suggests that the solid solutions contain domains embedded coherently in a number of specific orientations within the cubic matrix. Each domain is about 30A?in diameter, and its structure corresponds to that of CaHf₄O₉. Calculations based on this model agree with the observed diffraction data.     

Co-cation conduction in solid electrolytes based on AAlO2 (A = Li, Na)

Regions of the formation of tetragonal solid solutions with the γ-LiAlO₂ structure and the co-cation conduction are studied in the systems 0.9Na_1-xLi_xAlO₂-0.1EO₂ (E = Ti, Ge, Si) and 0.8Na_1-xLi_xAlO₂-0.2TiO₂. The single-phase regions of solid electrolytes narrows down with decreasing size of cations of a rigid lattice. No polyalkaline effect exists in the above systems. In the single-phase region of solid solutions, variations in the conductivity is caused largely by variations in the partial conductivity of the more mobile sodium cation.     

Beiträge zur Untersuchung anorganischer nichtstöchiometrischer Verbindungen. XXIII. Neue Bauelemente bei metastabilen Blockstrukturen im System Nb2O5/WO3 Elektronenmikroskopische Untersuchung in Hochauflösung

Contributions to the Investigation of Inorganic Non-stoichiometric Compounds. XXIII. New Building Elements of Metastable Block Structures in the System Nb₂O₅/WO₃, Investigation by High Resolution Electron Microscopy Under equilibrium conditions the region of existence of block structures in the system Nb₂O₅/WO₃ ends with a phase having the composition 9 Nb₂O₅:8 WO₃ corresponding to values of O/ΣM = 2.654 (M = Nb, W) and W/Nb = 0.44. We now investigated to what extent this region of existence of block structures could be expanded towards a higher content of WO₃. Starting out from the known phases Nb₂O₅:WO₃ = 6:1, 7:3, 8:5 and 9:8 in which Nb and W are present in their maximum states of oxidation, we obtained series of solid solutions by substituting W for Nb. Thereby the initial structure (block sizes [3×4], [4×4], [4×5] and [5×5] M–O-octahedra) and also the respective O/ΣM remained unchanged. Upon complete oxidation of these series of solid solutions which led into reduced systems (e. g. NbO₂/Nb₂O₅/WO₃) at ～500°C metastable products were gained, which also have block structures. Corresponding to the extent of substitution of the initial series of solid solution and the resulting ratio O/ΣM of the oxidation products the new structures are to a wide extent built of large blocks that have an extension (at maximum [5X15] M–O-octahedra) we have not observed so far. These blocks could be seen using high resolution transmission electron microscopy. The investigations on the oxidation products of the solid solutions of thc 8:5 and 9:8 series and illso it model concerning the mechanism of oxidation are described.     

Formation of continuous solid solutions near the minimum point of a phase diagram

A model of structure ordering in alloys of the compositions corresponding to the minimum points of phase diagrams with continuous series of solid solutions was proposed based on calculating the concentration dependence of the energy of mixing and the results of X-ray powder diffraction study of solid solutions in the systems Sb-As, Sb₂Se₃-Bi₂S₃, and Cu-Mn.