Structural Study of Li1+x−yNb1−x−3yTix+4yO3 Solid Solutions

The structures of Li_1+x−yNb_1−x−3yTi_x+4yO₃ solid solutions within the so-called M-phase field in the Li₂O-Nb₂O₅-TiO₂ system were investigated using high-resolution transmission electron, microscope (HRTEM) and single-crystal X-ray diffraction. The results demonstrated that the phase field is not a solid solution but rather a homologous series of commensurate intergrowth structures with LiNbO₃-type (LN) slabs separated by single [Ti₂O₃]²⁺ corundum-type layers. The thickness of the LN slab decreases with increasing Ti-content from ∼55 to 3 atomic layers in the metastable H-Li₂Ti₃O₇ end-member. The LN slabs accommodate a wide range of Ti⁴⁺/Nb⁵⁺ substitution, and for a given homolog the distribution of Ti and Nb is not uniform across the slab. A single-crystal X-ray diffraction study of a structure composed of nine-layer LN slabs revealed preferential segregation of Ti to the slab surfaces which apparently provides partial compensation for the charge on the adjacent [Ti₂O₃]²⁺ corundum layers. The extra cations in phases with x>0 are accommodated through the formation of Li-rich Li₂MO₃-type layers in the middle of the LN slabs. The fraction of layers with extra cations increases with increasing Ti-content in the structure.     

Study of phase equilibria in salt and oxide systems by the oscillation method of phase analysis

The phase equilibria data are presented for two binary systems (LiCl-KCl and K₂O-Nb₂O₅) which are received by thermal and oscillation method of phase analysis.     

New cesium titanate layer structures

A phase study of the Cs₂OTiO₂ system in the composition range 75–100 mole% TiO₂ and the temperature range 850–1200°C revealed the existence of two new cesium titanates, with compositions Cs₂Ti₅O₁₁ and Cs₂Ti₆O₁₃. The former compound undergoes a reversible hydration reaction below 200°C to form Cs₂Ti₅O₁₁ · (1 + x)H₂O, 0.5 < x < 1. The structures of the three phases have been determined. They are based on corrugated layers of edge-shared octahedra, with cesium ions (and H₂O) packing between the layers. In Cs₂Ti₆O₁₃, the layers are continuous in two dimensions, whereas in Cs₂Ti₅O₁₁ and Cs₂Ti₅O₁₁ · (1 + x)H₂O, the layers are periodically stepped to give 5-octahedra wide, corner-linked ribbons.     

Identifying characteristics of the fibrous cesium titanate Cs2Ti5O11

Electron microscopic studies of the fibrous cesium titanate Cs₂Ti₅O₁₁ reveal characteristic features not readily apparent using standard methods of phase analysis (optical microscopy, X-ray diffraction). Its fibrous needle-like laths give characteristic diffuse scattering, complicating the indexing of electron diffraction patterns. The hydrated form Cs₂Ti₅O₁₁ · (1 + x)H₂O (0.5 < x < 1) is typically grossly distorted, resembling pyrolytic graphite. Cs₂Ti₅O₁₁ is unstable when stored under ambient conditions at room temperature for ∼1 year when disproportionation into Cs₂Ti₄O₉ and Cs₂Ti₆O₁₁ · nH₂O occurs. The structure of Cs₂Ti₅O₁₁ and intergrowth defects in the unstable forms have been studied by high-resolution electron microscopy. It is evident that these phases would be undesirable in titanate ceramics such as SYNROC, which are designed for immobilization of radioactive ¹³⁷C_s.     

Location of Cs ions in a hollandite-related superstructure

The techniques of electron diffraction, high-resolution electron microscopy, and energy dispersive analysis of X-rays are applied simultaneously to preparations of mixed (Cs,Ba)-titanates. It is shown that Cs does not substitute randomly for Ba in the hollandite-related phase Ba₂Ti₉O₂₀ but instead forms a Cs-titanate having probable stoichiometry Cs₂Ti₄O₉. For some sample preparation conditions (≦ 1200°C) lamellae of a Cs-titanate phase were observed to coherently intergrow with Ba₂Ti₉O₂₀. However, such intergrowths are probably metastable since for preparation temperatures ≧ 1350°C two distinct phases occurred, being essentially pure Ba₂Ti₉O₂₀ and Cs₂Ti₄O₉. The Cs-titanate phase appears to have structure different than previously reported, since neither single crystal electron diffraction patterns nor X-ray powder patterns could be indexed using unit cell parameters reported previously for Cs₂Ti₄O₉.     

Neues über Zweikernige Oxoferrate(II)

News about Binuclear Oxoferrates(II) [1] . By “reaction with the wall” of the Fe-cylinders used here we synthesized the new oxoferrates(II) Cs₆[Fe₂O₅], Cs_3.5Rb_2.5[Fe₂O₅] and Rb₄K₂[Fe₂O₅] in the form of red single crystals. The structure elucidation via four-circle-diffractometer data shows that the new oxoferrates(II) are isotypic with Cs₂(Cs_0.35K_1.65)K₂ [Fe₂O₅]. In the structure we have isolated binuclear groups [(O1)₂Fe—O(2)—Fe(O1)₂]^6?. Structure refinements is possible in the centrosymmetrial space group C2/m as well as in the space groups C2 and Cm without centre of symmetry. The existence of two further oxoferrates(II) Cs_6?xRb_x[Fe₂O₅] and Cs_6?xK_x[Fe₂O₅] which can be described as solid solutions was confirmed by power-data.     

Nucleation and Crystal Formation in Lithium Disilicate‐Apatite Glass‐Ceramic from a Combined Use of X‐Ray Diffraction,Solid‐State NMR,and Microscopy

Glass‐ceramics are multi‐phase materials that are comprised of one amorphous phase and at least one crystalline phase. Their versatile performance and properties can be engineered by alterations of the three fundamental steps – formulation and production of the amorphous base glass, nucleation, and crystallization. Efforts have been made on syntheses of glass‐ceramics with different components, yet little is known about the details of nucleation and crystallization processes that are essential for tailoring glass‐ceramic properties. Herein, we investigate the nucleation and crystallization mechanisms of a multi‐component, that is SiO₂‐Al₂O₃‐CaO‐Li₂O‐K₂O‐P₂O₅‐F, glass‐ceramic system by a combined use of powder X‐ray diffraction (pXRD), solid‐state nuclear magnetic resonance (NMR), and electron microscopic (EM) techniques. The role of P₂O₅ in the nucleation and crystallization processes is particularly studied. We show that the formation of lithium silicate crystals being independent of the P₂O₅‐associated crystals, and the separation of P₂O₅ phases into individual growth domains of lithium orthophosphate and fluorapatite. We also observe the non‐uniform distribution of fluorapatite particles that explains the opalescence effect of this glass‐ceramic.     

Synthesis and structure of a new family of phases, A2MGe5O12: A = Rb,Cs; M = Be,Mg, Co,Zn

A new family of eight germanate phases, A₂MGe₅O₁₂: A = Rb, Cs; M = Be, Mg, Co, Zn, has been synthesized. They are cubic with a in the range 13.7 to 14.0 Å, Z = 8, and space group $\text{I}\text{4}\text{3d}$. These phases, named the β phases, are isostructural with KBSi₂O₆ which has a structure related to that of pollucite, CsAlSi₂O₆. The structure of one, Rb₂ZnGe₅O₁₂, has been refined to an R value of 0.079 using X-ray powder diffraction data. Several of the new phases are polymorphic. Cs₂ZnGe₅O₁₂, Cs₂CoGe₅O₁₂, and Rb₂MgGe₅O₁₂ form low-temperature, δ polymorphs which have primitive cubic unit cells. Rb₂ZnGe₅O₁₂ forms a low-temperature, ε polymorph which is probably a tetragonal distortion of the β structure.     

Metal-insulator transition in VnO2n−1

Research on phase relationships and structure studies by electron diffraction confirm V_nO_2n?1 (n = 3–9) phases between V₂O₃ and VO₂. Metal-insulator phase transitions have been found in all phases but V₃O₅ and V₇O₁₃. Electrical, magnetic and thermodynamic properties associated with the transitions are reported for sintered samples or for single crystals prepared by a vapor-transport method. The results are collated and reviewed in summarized form.     

Sol-gel synthesis of nanocomposite materials based on lithium niobate nanocrystals dispersed in a silica glass matrix

With the final goal to obtain thin films containing stoichiometric lithium niobate nanocrystals embedded in an amorphous silica matrix, the synthesis strategy used to set a new inexpensive sol-gel route to prepare nanocomposite materials in the Li₂O-Nb₂O₅-SiO₂ system is reported. In this route, LiNO₃, NbCl₅ and Si(OC₂H₅)₄ were used as starting materials. The gels were annealed at different temperatures and nanocrystals of several phases were formed. Futhermore, by controlling the gel compositions and the synthesis parameters, it was possible to obtain LiNbO₃ as only crystallizing phase. LiNbO₃-SiO₂ nanocomposite thin films on Si-SiO₂ and Al₂O₃ substrates were grown. The LiNbO₃ average size, increasing with the annealing temperature, was 27 nm for a film of composition 10Li₂O-10Nb₂O₅-80SiO₂ heated 2 h at 800 °C. Electrical investigation revealed that the nanocrystals size strongly affects the film conductivity and the occurrence of hysteretic current-voltage curves.     

Neue Verbindungen zwischen Kalium und Cäsium

Novel Compounds between Potassium and Caesium The hitherto unknown compounds K₂Cs und K₇Cs₆ exist at temperatures below ?90°C. Phase relationships and kinetic aspects of phase formation are investigated by thermal analyses and x-ray work with poly- and single-crystalline samples. K₂Cs is isotypic with the hexagonal LAVES phase Na₂K (MgZn₂ type of structure; a₀ = 9.065, c₀ = 14.755 Å at ?95°C due to modified GUINIER -diagrams). K₇Cs₆ forms hexagonal crystals with a novel kind of FRANK -KASPER structure (single crystals grown at ?100°C; space group P6₃/mmc; a₀ = 9.078; c₀ = 32.950 Å at ?95°C). Structure relationships of K₇Cs₆ and μ-phases are analogues to those of the LAVES phases MgZn₂ and MgCu₂. The interatomic distances in all of the LAVES phases Na₂K, K₂Cs and Na₂Cs are characterized by the identical expression d = Z(2r_A + r_B).     

Liquid Precursor-Guided Phase Engineering of Single-Crystal VO2 Beams

The study of VO₂ flourishes due to its rich competing phases induced by slight stoichiometry variations. However, the vague mechanism of stoichiometry manipulation makes the precise phase engineering of VO₂ still challenging. Here, stoichiometry manipulation of single-crystal VO₂ beams in liquid-assisted growth is systematically studied. Contrary to previous experience, oxygen-rich VO₂ phases are abnormally synthesized under a reduced oxygen concentration, revealing the important function of liquid V₂O₅ precursor: It submerges VO₂ crystals and stabilizes their stoichiometric phase (M1) by isolating them from the reactive atmosphere, while the uncovered crystals are oxidized by the growth atmosphere. By varying the thickness of liquid V₂O₅ precursor and thus the exposure time of VO₂ to the atmosphere, various VO₂ phases (M1, T, and M2) can be selectively stabilized. Furthermore, this liquid precursor-guided growth can be used to spatially manages multiphase structures in single VO₂ beams, enriching their deformation modes for actuation applications.     

Synthese und Struktur eines Caesiumoxonitridomonowolframates(VI), Cs7[WN1,5O2,5]2

Synthesis and Crystal Structure of a Cesium Oxo Nitrido Monotungstate(VI), Cs₇[WN_1.5O_2.5]₂ Mixtures of tungsten powder and WO₃ react with an excess of CsNH₂ in autoclaves at 650 °C to yield hygroscopic yellow crystals of cesium oxo nitrido tungstate(VI) Cs₇[WN_1.5O_2.5]₂ besides Cs₆[W₂N₄O₃] [1]. After the reaction the crystals are embedded in cesium metal (from thermal decomposition of CsNH₂), which was washed out by liquid ammonia. The crystals allowed a successful X‐ray structure determination. Cs₇[WN_1.5O_2.5]₂ crystallizes in the space group P2₁/c with the lattice parameters a = 6.766(1) Å, b = 11.205(3) Å, c = 22.299(4) Å, β = 91.05(1)° and Z = 4. The crystal structure is built up by isolated tetrahedra [WX₄] with X = N, O, which are separeted by cesium cations.     

Synthesis of complex cesium hydrosulfatophosphates

Solubility of the CsH₂PO₄-CsHSO₄-H₂O system has been studied using the isothermal method (25.0°C); the compounds Cs₄(HSO₄)₃(H₂PO₄), Cs₃(HSO₄)₂(H₂PO₄), and Cs₅(HSO₄)₂(H₂PO₄)₃ have been found to form; Cs₅(HSO₄)₂(H₂PO₄)₃ has been obtained for the first time. Single crystals of the isolated phases have been grown. Their composition has been determined, and agreement between the results of studying solid phases in the CsH₂PO₄-CsHSO₄-H₂O and these single-crystal samples has been demonstrated. X-ray diffraction analysis of these phases has been carried out.     

Electronics structures of Rb,Cs and some of their metallic oxides studied by photoelectron spectroscopy

Photoemission measurements with He and Ne resonance lines and Al Kα radiation are reported on bulk samples of the alkali metals Rb, Cs, their suboxides Cs₇O, Cs₁₁O₃ and (Cs₁₁O₃)Rb₇. For comparison, the Hel spectrum of the “normal” oxide Cs₂O is added. The occurrence of ionic clusters in a metallic matrix is typical for the suboxides. Binding energies, Auger transitions, and electron concentrations are discussed. The spectra of the suboxides show a narrow non-bonding oxygen 2p band at 2.7 eV. Different binding energies are found for Cs atoms in the clusters and for the atoms in the metallic regions of (Cs₁₁O₃)Cs₁₀. The compound Cs₁₁O₃ consists of ionic [Cs₁₁O₃]^5? clusters, which are bound by 5 free electrons in accordance with the chemical bond model.     

Electrical and magnetic properties and homogeneity ranges of mixed-valence cesium-vanadium oxides

Single crystals of CsV₂O₅, Cs₂V₅O₁₃, Cs_xV₂O₅, and CsV₃O₇, grown from melts, have been subjected to electrical conductivity and magnetic susceptibility measurements. CsV₂O₅ and Cs₂V₅O₁₃ are insulators exhibiting Curie-Weiss' law behavior with p_eff close to $\text{1.73}\text{V}{}^{\mathrm{4+}}\text{ion}$. They are stoichiometric according to the X-ray studies. CsV₂O₅, which has a very limited composition range (x ≈ 0.30?;0.33), is a semiconductor with temperature-dependent paramagnetism ($\text{p}{}_{\mathrm{<mtext>eff</mtext>}}\text{=}\text{1.83}\text{V}{}^{\mathrm{4+}}\text{ion}$). Cs_xV₃O₇ (0.30 ? x ? 0.40) is antiferromagnetic with a Néel temperature of ≈230 K. The temperature variation of the lattice parameters of Cs_0.33V₃O₇ has been determined with a Bond-type diffractometer. The same crystal was used for the conductivity measurements, and together these studies indicate that the transition from the semiconducting antiferromagnetic state to the semiconducting paramagnetic state takes place stepwise. The observed properties are discussed with reference to the crystal structures of the compounds.     

Effect of solvent on phase composition and particle morphology of lanthanum niobates prepared by polymeric complex sol–gel method

Lanthanum niobates were prepared by a new polymeric complex sol–gel method using Nb-citrate or -tartrate complexes in different solvent (ethanol or methanol) and calcination at 750–1,050 °C. The perovskite La_1/3NbO₃ and pyrochlore LaNb₅O₁₄ phases were formed after calcination at 900 and 1,050 °C from gels synthesized from ethanol and methanol solvents respectively. The very similar xerogel thermal decomposition processes were observed independently on applied solvents, where the pyrochlore monoclinic LaNbO₄ and Nb₂O₅ phases were intermediate products at lower calcination temperatures during transformation. The particle morphologies changed from spherical 20–50 nm particles at 750 °C to granular LN particles (ethanol) or rectangular (methanol) at 1,050 °C. HRTEM images and SAED verified the coexistence of minority monoclinic LaNbO₄ phase with majority phases in individual LN particles after annealing. The strong effect of alcohol solvent on phase formation was shown, while the effect of chelating agent was insignificant.     

ChemInform Abstract: From 1∞ [(UO2)2O(MoO4)4]6‐ to 1∞ [(UO2)2(MoO4)3(MoO5)] 6‐ Infinite Chains in A6U2Mo4O21 (A: Na,K, Rb,Cs) Compounds: Synthesis and Crystal Structure of Cs6 [(UO2)2(MoO4)3(MoO5)] .

Single crystals of the title compound are obtained from a melt of U₃O₈, MoO₃, and excess Cs₂CO₃ (Pt crucible, 950 °C, 12 h, cooling rate 5 °C/h).     

ChemInform Abstract: Two Structure Types Based on Si6O15 Rings: Synthesis and Structural and Spectroscopic Characterization of Cs1.86K1.14DySi6O15 and Cs1.6K1.4SmSi6O15.

Single crystals of Cs_1.86K_1.14DySi₆O₁₅ (I) and Cs_1.6K_1.4SmSi₆O₁₅ (II) are grown by reaction of SmF₃ or Dy₂O₃, DyF₃, SiO₂, K₂CO₃, and Cs₂CO₃ in a MoO₃ or MoO₃/RbF flux (Pt crucible, 950 °C, 3—6 h; controlled cooling).     

Electrochemical crystal growth in the cesium molybdate-molybdenum trioxide system

A systematic investigation of crystal growth in the cesium molybdate/molybdenum trioxide system is described. A previously unknown blue cesium molybdenum bronze phase has been prepared as well as the known red bronze, Cs_0.33MoO₃, and high-quality crystals of the Magneli-phase compound, γ-Mo₄O₁₁. This new blue bronze, with empirical formula, Cs_0.19MoO_2.85, is monoclinic with cell constants, a = 19.198(4) Å, b = 5.519(2) Å, c = 12.213(2) Å, and β = 119.44(2)°. Measurements of the susceptibility and of the resistivity vs temperature are reported. As is the case for other alkali molybdenum bronzes, the product formed is determined by the molar ratio of alkali molybdate to molybdenum trioxide and the melt temperature.