Co-cation Conduction in Solid Solutions (K1 – xRbx)4P2O7–M2P2O7(M = Ca,Sr, Cd,Ba): Dependence on the Nature and Concentration of Cations M2+

Solid solutions of the structure -K₄P₂O₇, which have the composition (K_{1 – x} Rb _x )_3.8M_0.1P₂O₇(M = Ca, Sr, Cd, Ba) and (K_{1 – x} Rb _x )_{4 – 2y} Ca _y P₂O₇(y= 0.025–0.20), are synthesized. The solutions' electroconductivity is studied in the temperature range 400–600°C. The concentration dependences of the conductivity and the activation energy for conduction have extremums at x 0.6, which points to the polyalkaline effect. The effect increases with decreasing radius of cation M²⁺and with increasing concentration of calcium cations, which is explained by an increased energy nonequivalence of positions in the cation sublattice accessible to alkali ions.     

Electric conductivity of RbFeO2 modified with Nb5+ and Ta5+ cations

Solid solutions based on RbFeO₂ in Rb_{2 ? 2x} Fe_{2 ? x} Nb(Ta) _x O₄ (0 ?? x ?? 0.2) systems were synthesized. Their crystal structure and the temperature and concentration dependences of the total and ion conductivities were studied. The ranges of composition and temperature with dominant rubidium-cation conductivity were determined. For the Rb_1.9Fe_1.95Ta_0.05O₄ solid solution, the rubidium-cation conductivity was found to be 2.3 × 10^?2 S/cm at 200°C, which exceeds the electric conductivity of other known polycrystalline rubidium-cation solid electrolytes.     

Co-cation conduction of the (Na1-x K x )3.8M0.1P2O7 (M = Ca, Sr, Cd) solid solutions

Samples of systems (Na _1-x K _x )_3.8M_0.1P₂O₇ (M = Ca, Sr, Cd; 0 ≤x ≤ 1) are synthesized. It is established that solid solutions with the structure of γ-K₄P₂O₇ form in these systems. At room temperature, the solutions exist atx ≥ 0.7. In the calcium-containing system, they form a continuous series at temperatures exceeding ∼500°C. The co-cation character of conduction of the solutions is confirmed by measured transport numbers. The concentration dependences of the electroconductivity and its activation energy point to a polyalkali effect, which decreases with an increase in the M²⁺ ion radius. Partial conductivities of sodium and potassium cations in the (Na _1-x K _x )_3.8Ca_0.1P₂O₇ system are calculated and their dependences on the balance between alkali cations in the solid solution are discussed     

Rubidium-cationic conductivity of Rb2−2x Ga2−x A x O4 (A = P, V, Nb, Ta) solid electrolytes

Solid solutions based on rubidium monogallate RbGaO₂ with a general formula Rb_2?2x Ga_2?x A _x O₄ (A = P, V, Nb, and Ta) are synthesized. Their crystal structure and temperature and concentration dependences of conductivity are studied. The highest rubidium-cationic conductivity is (1.8–3.9) × 10^?3 S cm^?1 at 400°C and (1.4–2.1) × 10^?2 S cm^?1 at 700°C. These results are compared with the data for rubidium monogallate doped with four-charged cations and solid solutions based on RbAlO₂.     

Nitrilotriacetato-monoperoxo complexes of vanadium(V): formation in aqueous solution,synthesis and structure

Summary M₂[VO(nta)(O₂)]·xH₂O, where M⁺ is NH _inf4 ^p+ , K⁺ or Rb⁺ and nta is nitrilotriacetate, and Sr[VO(nta)(O₂)]·2H₂O were synthesized. The electronic spectra of aqueous KVO₃-H₂O₂-H₃nta-HClO₄(KOH) solutions (pH 1.45–5.62) and the thermal decomposition of K₂[VO(nta)(O₂)]· 2H₂O with active oxygen release at 275° C showed that the nta-monoperoxo complex is the most stable vanadium(V) peroxo complex so far investigated. The anhydrous potassium salt was prepared on heating the crystallohydrate under dynamic conditions. The i.r. spectra indicate the same anion structure in solution and in the solid state where nta is coordinated as a tetradentate ligand.     

Synthesis and crystal structure of mixed metal(III) tungstenyl(VI) ortho-pyrophosphates

The series of isotypic anhydrous ortho-pyrophosphates M^III(W^VIO₂)₂(P₂O₇)(PO₄) (M: Sc, V, Cr, Fe, Mo, Ru, Rh, In, Ir) was obtained via vapor phase moderated solid state reactions in sealed ampoules. The crystal structure of the phosphates M^III(W^VIO₂)₂(P₂O₇)(PO₄) (M: V, Ru, Rh) was solved from single crystal X-ray data (C2/c, Z = 16). Fairly regular MO₆ and distorted WO₆ octahedra share vertices with PO₄ and P₂O₇ units to form a 3D network. For the ortho-pyrophosphates with M: V³⁺, Cr³⁺, and Fe³⁺ the oxidation state of M is confirmed by magnetic measurements. ³¹P-MAS-NMR spectra of the diamagnetic phosphates M^III(W^VIO₂)₂(P₂O₇)(PO₄) (M: Sc, In, Ir) show surprisingly different isotropic chemical shifts for the seven phosphorus sites. V^III(W^VIO₂)₂(P₂O₇)(PO₄) occurs as equilibrium phase in the quasi-binary system (V_1–xW_x)OPO₄ at x = 0.67 and exhibits a small homogeneity range 0.60 ≤ x ≤ 0.67. The scandium compound shows a fully inverted occupancy of the M sites according to the formulation W(Sc_1/2W_1/2O₂)₂(P₂O₇)(PO₄).     

Phase equilibria,charge transport,and mass transport in Sr<Subscript>4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript>-“M<Subscript>4</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript>” (M = Cd,Cu, Ni,and Zn) systems

Homogeneous fields of Sr_{4 − x} M _x Nb₂O₉ (M = Cd, Cu, Ni, or Zn) solid solutions were determined using powder X-ray diffraction. Phase fields were plotted proceeding from the tolerance factor t and electronegativity ratio $ \bar k_A /\bar k_B $ \bar k_A /\bar k_B with a satisfactory fit of experimental results. Thermogravimetry was used to establish the major kinetic laws of solid-phase synthesis (conversion, rate-controlling stage, and effective activation energy) in (4 − x)SrCO₃ + xMO + Nb₂O₅ powdery mixtures. Direct radiometry was used to determine ⁹⁰Sr, ⁶³Ni, and ⁶⁵Zn self-diffusion coefficients in solid solutions based on the Sr₄Nb₂O₉ phase. Electrical conductivity was measured as a function of temperature for all Sr₄Nb₂O₉-“M₄Nb₂O₉” samples. The conductivity of Sr_{4 − x} M _x Nb₂O₉ (M = Cd, Cu, Ni, or Zn) solid solutions has a mixed ion-electron character.     

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.     

Fe x Ti1−2x M x O2 (M=Nb,Ta) rutile solid solutions from gels

In this study, Fe _x Ti_1–2x M _x O₂ (M=Nb, Ta) rutile solid solutions have been synthesized from gels made from Fe(III) acetylacetonate, NbCl₅, TaCl₅, Ta(V) ethoxide, TiCl₄ and Ti(IV) isopropoxide. The results obtained are compared with those obtained by the ceramic method. The solid solutions synthesized from gels were obtained at lower temperatures than these synthesized by the ceramic method.     

Synthesis, structure and dielectric properties of Ba1-xSrxMyTi1-yO3 (M = Zr, Sn)

A series of Ba_1-xSr_xM_yTi_1-yO₃ (M = Zr, Sn, 0?x?0.4, 0?y?0.3) solid solutions were synthesized with the soft chemical method below 100 °C. XRD pattern and cell parameters-composition figures of the prepared powder demonstrate that they are completely miscible solid solutions based on BaTiO₃. Furthermore, TEM shows that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of the powder doped with Sr²+and Zr⁴⁺ or Sn⁴⁺ have dielectric constant eight times higher and dielectric loss thirty per cent lower than those of pure BaTiO₃ phase at room temperature.     

Study of the Solid Solutions of LiNbO3and LiTaO3with Mn

Two unusual, extensive new solid solutions of LiNbO₃and LiTaO₃with MnO have been prepared, where 4Mn²⁺replace a combination of 3Li⁺and a pentavalent cation: Nb⁵⁺or Ta⁵⁺. The formulas are Li_1−xM_1−xMn_4xO₃, 0<x<0.13, forM=Nb and 0<x<0.23 forM=Ta. The solid solutions were characterized by X-ray powder diffraction and density measurements. The manganese oxidation states were determined by X-ray photoelectron spectroscopy.     

Co-cation Conduction in Solid Solutions (K1 – xRbx)4P2O7–M2P2O7(M = Ca,Sr, Cd,Ba): Transport Numbers and Partial Ionic Conductivities

Transport numbers for potassium and rubidium cations in solid electrolytes (K_{1 – x} Rb _x )_3.8M_0.1P₂O₇(M = Ca, Cd, Ba) are measured, and the co-cation nature of the electrolytes" conduction is confirmed. The concentration dependences of transport numbers are used to draw a conclusion about the ratio between mobilities of potassium and rubidium cations. The presence of an extremum in the concentration dependence of the activation energy for the rubidium-cation constituent of conduction is confirmed by the NMR method. The obtained results are explained by assuming that the polyalkaline effect is largely due to an ordering of mobile alkali cations.     

Missing Member in the MIIMIIISi4N7 Compound Class: Carbothermal Reduction and Nitridation Synthesis Reveal Substitution of Nitrogen by Carbon and Oxygen in CaLu[Si4N7–2xCxOx]:Eu2+/Ce3+ (x≈0.3)

The nitridosilicate CaLu[Si₄N_7–2xC_xO_x] (x≈0.3) was synthesized by carbothermal reduction and nitridation starting from CaH₂, Lu₂O₃, graphite and amorphous Si₃N₄ at 1550 °C in a radiofrequency furnace. CaLu[Si₄N_7–2xC_xO_x] (x≈0.3) crystallizes isotypically to many previously known M^IIM^IIISi₄N₇ compounds in the space group P6₃mc, as was confirmed by Rietveld refinement based on powder X-ray diffraction data. Incorporation of carbon into the crystal structure as a result of the carbothermal synthesis route was confirmed by ¹³C and ²⁹Si MAS NMR spectroscopy. For the first time in the M^IIM^IIISi₄N₇ compound class, complementary EDX measurements suggest that simultaneous incorporation of oxygen compensates for the negative charge excess induced by carbon, resulting in an adjusted sum formula, CaLu[Si₄N_7–2xC_xO_x] (x≈0.3). When excited with UV-to-blue light, CaLu[Si₄N_7–2xC_xO_x] (x≈0.3) shows an emission maximum in the blue spectral region (λ_em=484 nm; fwhm=4531 cm⁻¹) upon doping with Ce³⁺, whereas Eu²⁺-doped CaLu[Si₄N_7–2xC_xO_x] (x≈0.3) exhibits a yellow-green emission (λ_em=546 nm; fwhm=3999 cm⁻¹).     

Determination of indium,chromium, and iron in double alkali phosphate compounds

A procedure is presented for the determination of indium, chromium, and iron in complex phosphate compounds of the type M^IM^IIIP₂O₇, M^I is Li, Na, or K; M^III is Fe, Cr, or In and in solid solutions based on the above phosphates. The procedure is based on X-ray fluorescence spectrometric analysis. It was demonstrated that this method exhibits adequate accuracy of the determination of In, Fe, and Cr and can be recommended for the rapid analysis of samples.     

Mechanism of ionic transport in cesium-conducting solid electrolytes based on cesium orthophosphate

The earlier obtained data on the transport properties of cesium-conducting solid electrolytes based on cesium orthophosphate in the Cs_3–2xM_x^II PO₄ (M^II = Mg, Ca, Sr, Ba), Cs_3–3x PO₄ (M_x^III = Sc, Y, La, Sm, Nd) and Cs_3–xP_1–xZ_x^VI O₄ (Z = S, Cr, Mo, W) systems are analyzed. It is shown that, in addition to the conventional jump mechanism, the “paddle wheel” mechanism can play an important role in the ionic transport. This mechanism is associated with the orientation disordering of [PO₄] tetrahedrons at the elevated temperatures, which leads to their rotation promoting “pushing” cesium ions into the accessible neighboring positions.     

Synthesis, structure and dielectric properties of Ba1-xSrxMyTi1-yO3 (M = Zr, Sn)

A series of Ba_1-xSr_xM_yTi_1-yO₃ (M = Zr, Sn, 0⩽x⩽0.4, 0⩽y⩽0.3) solid solutions were synthesized with the soft chemical method below 100 °C. XRD pattern and cell parameters-composition figures of the prepared powder demonstrate that they are completely miscible solid solutions based on BaTiO₃. Furthermore, TEM shows that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of the powder doped with Sr²+and Zr⁴⁺ or Sn⁴⁺ have dielectric constant eight times higher and dielectric loss thirty per cent lower than those of pure BaTiO₃ phase at room temperature.     

Structural and dynamical studies of δ-Bi2O3 oxide ion conductors: III. Phase relationships in the system (Bi2O3)1−x(M2O3)x as a function of pressure and temperature (M = Y,Er, or Yb)

We report the results of a structural investigation of the nonstoichiometric solid solutions (Bi₂O₃)_1−x(M₂O₃)_x (M = Y, Er, or Yb) treated at temperatures of between 298 and 1023 K and at pressures of up to 4 GPa. For x = 0.25 and M = Er or Y, 4 GPa pressure at 873 K causes the fluorite-related phase stable under ambient conditions to transform to a monoclinic phase which on subsequent annealing transforms to a rhombohedral phase isostructural with that adopted by the solid solution (Bi₂O₃)_1−x(Sm₂O₃)_x under ambient conditions. For x = 0.4 and M = Er or Y, application of 4 GPa at 1073 K causes the fluorite phase to undergo a distortion to another rhombohedral structure with a smaller unit cell. No transitions were found in the Yb³⁺-doped system.     

Investigation of s, p, d-element Niobates and Their Solid Solution Formation Processes by Thermal Analysis

The binary and ternary systems M'O(M'CO₃)-Nb₂O₅ and M'O(M'CO₃)-MO-Nb₂O₅, where M'=Ca,Sr and Ba and M=Cu, Ni, Cd, Zn and Pb, were investigated by means of thermal analysis in the temperature range 20–1500°C. The boundaries of stability of the solid solutions Sr_2−xMe_xNb₂O₇,Sr_2−xM_xNb₂O₇, Sr_4−xM_xNb₂O₉ and Sr_6−xM_xNb₂O₁₁ were determined by means of X-ray diffraction, and IR and Raman spectroscopy. The possibility of prognostication of the phase fields of stable solid solutions by calculation from the diagrams of the ‘comparative electronegativity of atoms vs. tolerance factor’ was demonstrated. The kinetic parameters of the interactions in theSrCO₃+MO+Nb₂O₅ powder mixtures were established. This revised version was published online in August 2006 with corrections to the Cover Date.     

Some studies on the solid solutions in the systems Sr2Nb2O7Eu2Nb2O7 and Sr2Ta2O7Eu2Ta2O7

Preparation of new solid solutions containing divalent europium have been tried in the systems Eu₂Nb₂O₇Sr₂Nb₂O₇ and Eu₂Ta₂O₇Sr₂Ta₂O₇. These solid solutions described as Eu_2xSr_2(1?x)M₂O₇ (M = Nb and Ta) exist in a pure orthorhombic phase in a limited region of x from 0 to about 0.5. The compounds with compositions close to Eu₂M₂O₇ exist but techniques have not been found to prepare them in pure form.     

Microporous Framework (Nb,Fe)-Silicate with Much Potential to Remove Rare-Earth Elements from Waters

Nanoparticles of a new small-pore metal silicate formulated as Na_2.9(Nb_1.55Fe_0.45)Si₂O₁₀ ⋅ xH₂O and exhibiting the structure of previously reported Rb₂(Nb₂O₄)(Si₂O₆) ⋅ H₂O have been synthesized under mild hydrothermal conditions. Replacement of the bulky Rb⁺ by smaller Na⁺ ions was accomplished by stabilizing the framework structure via partial occupancy of the Nb⁵⁺ sites by Fe³⁺ ions. Exploratory ion-exchange assays evidence the considerable potential of this new silicate to remove rare-earth elements from aqueous solutions.