Phosphates M 0.5(1 + x) 2+ Cr x Ti2 − x (PO4)3: Synthesis, structure, and catalytic properties

Complex phosphates of titanium, chromium, and metals(2+) of the general formula M_{0.5(1 + x} )Cr _x Ti_{2 ? x} (PO₄)₃ (M = Mg, Ca, Mn, Ni, Sr, Ba, and Pb) were synthesized. Their phase formation was studied by means of X-ray powder diffraction, electron probe microanalysis, differential thermal analysis, and IR spectroscopy. Individual phases and solid solutions crystallizing in kosnarite and langbeinite structure types were identified; their crystallographic parameters were calculated. The catalytic properties of phosphates Ca_{0.5(1 + x} )Cr _x Ti_{2 ? x} (PO₄)₃ in methanol conversion were studied.     

Solid electrolytes with potassium cation conductivity in K1−2x M x AlO2 (M = Ba, Pb) systems

New solid electrolytes with high potassium cationic conductivity based on potassium monoaluminate were synthesized and studied in the K_1?2x Ba _x AlO₂ and K_1?2x Pb _x AlO₂ systems. A partial substitution of potassium cations with double charged positive cations results in a considerable increase in the conductivity of KAlO₂ in the whole studied range of temperatures. The electric characteristics are somewhat higher in the bariumcontaining system, which is in all probability connected with the effect of the size factor: the size of the Ba²⁺ ion is higher than that of Pb²⁺, which must correlate with the increase of the effective dimensions of the migration channels in the electrolyte structure. The main cause of the conductivity increase at the introduction of the studied additives is the formation of potassium vacancies at the substitution of 2K⁺ → Ba²⁺(Pb²⁺) + V′_K.     

Novel red-emitting phosphors, (Mg(1−x−y)MnxDyy)Al2Si2O8 and (Mg(1−x−y)MnxTmy)Al2Si2O8

Mn⁴⁺ doped and Dy³⁺, Tm³⁺ co-doped MgAl₂Si₂O₈-based phosphors were prepared by conventional solid state reaction at 1,300 °C. They were characterized by thermogravimetry, differential thermal analysis, X-ray powder diffraction, photoluminescence, and scanning electron microscopy. The luminescence mechanism of the phosphors, which showed broad red emission bands in the range of 600–715 nm and had a different maximum intensity when activated by UV illumination, was discussed. Such a red emission can be attributed to the ²E → ⁴A₂ transitions of Mn⁴⁺.     

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.     

Glycolate Ti1 − x Fe x (OCH2CH2O)2 − x/2 as a precursor for the preparation of quasi-one-dimensional (1D) solid solutions Ti1 − x Fe x O2 − 2x/2 (0 ≤ x ≤ 0.1)

Quasi-one-dimensional (1D) solid solutions Ti_{1 ? x} Fe _x (OCH₂CH₂O)_{2 ? x/2} (0 < x ≤ 0.1) with the structure of anatase were prepared by heating the glycolate Ti_{1 ? x} Fe _x (OCH₂CH₂O)_{2 ? x/2} in an atmosphere of air at a temperature of >450°C. The conditions of formation and the properties of the new glycolate Ti₃Fe₂(OCH₂CH₂O)₉ were described. It was found that the synthesized Ti_{1 ? x} Fe _x O_{2 ? 2x/2} solid solutions exhibit photocatalytic activity in the reaction of hydroquinone oxidation in an aqueous solution on irradiation with UV light. A correlation between the rate of oxidation of hydroquinone and the concentration of iron in the catalyst was established. A procedure for the preparation of titanium dioxide with the structure of anatase doped with iron and carbon (Ti_{1 ? x} Fe _x O_{(2 ? x/2) ? yCy)} and also composites on its basis, which contain an excess amount of carbon, was proposed.     

Sol-gel synthesis and structure of MZr2(AsO4)3 arsenates and MZr2(AsO4) x (PO4)3 − x arsenate phosphates (M = K,Rb, Cs)

MZr₂(AsO₄)₃ arsenates and MZr₂(AsO₄) _x (PO₄)_{3 ? x} arsenate phosphates (M = K, Rb, Cs) have been obtained by sol-gel synthesis followed by heat treatment and have been characterized by X-ray diffraction, electron probe microanalysis, and IR spectroscopy. Continuous series of substitutional solid solutions form in the MZr₂(AsO₄) _x (PO₄)_{3 ? x} systems (0 ≤ x ≤ 3). The solid solutions have a kosnarite structure (KZr₂(PO₄)₃, space group \(R\bar 3c\) ). The crystal structures of MZr₂(AsO₄)₃ and MZr₂(AsO₄)_1.5(PO₄)_1.5 have been refined by full-profile analysis. The structural frameworks of these phases are built from ZrO₆ octahedra and AsO₄ tetrahedra or (As,P)O₄ tetrahedra statistically populated by arsenic and phosphorus atoms. The alkali metal atoms occupy extraframework sites. The effect of the crystal chemical properties of alkali metals on the formation of the structures of MZr₂(AsO₄)₃ arsenates (M = Li-Cs) and MZr₂(AsO₄) _x (PO₄)_{3 ? x} solid solutions is discussed.     

Synthesis and phase formation in M 0.5(1+x) 2+ FexTi2−x (PO4)3 phosphate series

New complex phosphates of titanium, iron, and alkaline-earth metals have been synthesized. X-ray powder diffraction, differential thermal analysis (DTA), and IR spectroscopy are used to study phase formation in the series of M_0.5(1+x)Fe_xTi_2?x (PO₄)₃ (M = Mg, Ca, Sr, Ba) phosphates. Individual compounds and solid solutions are found to crystallize in the NaZr₂(PO₄)₃ and K₂Mg₂(SO₄)₃ structure types. Their crystal parameters are calculated. CaFeTi(PO₄)₃ is studied using Mössbauer spectroscopy. Its structure is refined by the Rietveld method: space group $R\bar 3$ c, Z = 6, a = 8.5172(1), Å, c = 21.7739(4) Å, V = 1367.91(4) ų.     

Electroconductivity of Solid Solutions Cs3–2x M x PO4 (M = Ba, Sr, Ca, Mg)

Solid solutions Cs_{3 – 2x} M _x PO₄ (M = Ba, Sr, Ca, Mg) are synthesized and their thermal behavior and electroconductivity are examined. Adding elements of Subgroup IIA of the periodic table into cesium orthophosphate shifts the phase transition, which occurs in pure Cs₃PO₄ at 450–620°, towards lower temperatures and raises the cesium cation conductivity at low temperatures. The electroconductivity of a high-temperature modification of Cs₃PO₄ is weakly dependent on the presence and concentration of such additives, which points to structural disordering of the cesium sublattice.     

Hydrogen content in proton-conducting perovskites CaZr1 − x Sc x O3 − x /2 (x = 0.0–0.2)

The hydrogen content in CaZr_{1 ? x} Sc _x O_{3 ? x/2} (x = 0.00–0.20) and BaZr_0.9Y_0.1O_3-α (for comparison) was studied by powder nuclear microanalysis. The samples were saturated with heavy water (D₂O) vapors at 350 and 400°C in air. The chemical expansion of the CaZr_0.95Sc_0.05O_3-α and BaZr_0.95Y_0.05O_3-α samples at 700°C was measured at different water vapor pressures. A model was suggested to explain the lowered hydrogen content in oxides based on CaZrO₃.     

Electroconduction of Solid Solutions Na3 – 2x M x PO4(M = Cd, Pb)

In the sodium-orthophosphate-based solid solutions in Na_{3 – 2x} M _x PO₄ systems (M = Cd, Pb), the electroconduction is maximum near the upper concentration boundaries of the single-phase regions: x 0.4 for M = Cd and x 0.25 for M = Pb. The conductivity values at 300°C are 6.25 × 10^–3 and 2.5 × 10^–3 S/cm, respectively. The conduction of synthesized solid electrolytes has a co-cation nature. Their electric characteristics, inferior to those of the Na₃PO₄-based solid solutions obtained via heterovalent substitutions of another type, may be a manifestation of an effect similar to the polyalkali effect.     

Electronic structure and related properties for quasi-binary (GaP)1−x (ZnSe) x crystals

The results of pseudopotential calculations of the band structure and related electronic and optical properties of quasi-binary (GaP)_1?x (ZnSe) _x crystals in the zinc blende structure are presented. Trends in bonding and ionicity are discussed in terms of electronic charge densities. Moreover, the composition dependence of the refractive index and dielectric constants are reported. The computed values are in reasonable agreement with experimental data. The results suggest that for a proper choice of the composition x, (GaP)_1?x (ZnSe) _x could provide more diverse opportunities to achieve the desired electronic and optical properties of the crystals which would improve the performances of devices fabricated on them.     

Bioresorbable carbonated hydroxyapatite Ca10−xNax(PO4)6−x(CO3)x(OH)2 powders for bioactive materials preparation

The purpose of this work was to find and investigate a correlation between the carbonate ion content in crystalline lattice and defect structure, and solubility of the materials; finally, to prepare the materials under study for in vitro tests. Various techniques, such as XRD, FTIR, TEM, FESEM/EDX, TG/DTA, AES (ICP), wet chemical analysis, Ca-ionometry, microvolumetric analysis of evolved CO₂, BET adsorption, were applied to determine the efficiency of carbonate substitution, and to quantify the elemental composition, as well as to characterize the structure of the carbonated hydroxyapatite and the site(s) of carbonate substitution,. It was shown that AB-type substitution prevails over other types with the carbonate content increase. According to in vitro tests, the bioactivity of the samples is correlated with the carbonate content in carbonate-doped hydroxyapatite due to accumulation of defects in carbonated hydroxyapatite nanocrystals.      

Multivariate analysis of melting points for homologous series C x H2x − 1NO (x = 3−6)

A multivariate analysis of the empirical structure data for isomeric homologues using principal-component analysis has been carried out, and the correlation with experimental melting points has been shown. Based on the data on the CSD structure, we discuss the impact of molecular H-aggregation.     

Small angle neutron scattering experiments on solid electrolyte (AgI) x (AgPO3)1−x

Superionic conductor glasses have generated considerable technological interest in the applications such as batteries, fuel cell, sensors, etc. In AgPO₃ glass doped by AgI, (AgI) _x (AgPO₃)_1?x , small size of AgI clusters were formed and dispersed in the AgPO₃ glass. The size of clusters in the sample depends on the AgI content and influences the electrical properties of the sample. To understand the microscopic structure, in particular the shape and size of the clusters, a series of small angle neutron scattering experiment on (AgI) _x (AgPO₃) _x with x?=?0.0, 0.5, and 0.7 were performed at the Neutron Scattering Laboratory–National Nuclear Energy Agency, Indonesia. By assuming the clusters are spherical, a radius of gyration R _g of the clusters was determined from a Guinier plot. As there are different clusters sizes in the samples, a polydisperse model is also used to analyze the data. The results show that the average radius of clusters dispersed in (AgI) _x (AgPO₃)_1?x samples with x?=?0.0, 0.5, and 0.7 are around 236.2, 252.6, and 257.5 Å, respectively.     

Atom Exchange Versus Reconstruction: (GexAs4−x)x− (x=2, 3) as Building Blocks for the Supertetrahedral Zintl Cluster [Au6(Ge3As)(Ge2As2)3]3−

The Zintl anion (Ge₂As₂)²⁻ represents an isostructural and isoelectronic binary counterpart of yellow arsenic, yet without being studied with the same intensity so far. Upon introducing [(PPh₃)AuMe] into the 1,2-diaminoethane (en) solution of (Ge₂As₂)²⁻, the heterometallic cluster anion [Au₆(Ge₃As)(Ge₂As₂)₃]³⁻ is obtained as its salt [K(crypt-222)]₃[Au₆(Ge₃As)(Ge₂As₂)₃]⋅en⋅2 tol ( 1 ). The anion represents a rare example of a superpolyhedral Zintl cluster, and it comprises the largest number of Au atoms relative to main group (semi)metal atoms in such clusters. The overall supertetrahedral structure is based on a (non-bonding) octahedron of six Au atoms that is face-capped by four (Ge_xAs_4−x)^x− (x=2, 3) units. The Au atoms bind to four main group atoms in a rectangular manner, and this way hold the four units together to form this unprecedented architecture. The presence of one (Ge₃As)³⁻ unit besides three (Ge₂As₂)²⁻ units as a consequence of an exchange reaction in solution was verified by detailed quantum chemical (DFT) calculations, which ruled out all other compositions besides [Au₆(Ge₃As)(Ge₂As₂)₃]³⁻. Reactions of the heavier homologues (Tt₂Pn₂)²⁻ (Tt=Sn, Pb; Pn=Sb, Bi) did not yield clusters corresponding to that in 1 , but dimers of ternary nine-vertex clusters, {[AuTt₅Pn₃]₂}⁴⁻ (in 2 – 4 ; Tt/Pn=Sn/Sb, Sn/Bi, Pb/Sb), since the underlying pseudo-tetrahedral units comprising heavier atoms do not tend to undergo the said exchange reactions as readily as (Ge₂As₂)²⁻, according to the DFT calculations.     

Synthesis and electrical properties of variable-composition phases Rb1 − x A1 − x R1 + x (MoO4)3 (0 ≤ x ≤ 0.2; A = Mg, Mn, Co, Ni; R = Sc, Yb, Lu)

Subsolidus region of the ternary systems Rb₂MoO₄-AMoO₄-R₂(MoO₄)₃, in which variable-composition phases Rb_{1 ? x} A_{1 ? x} R_{1 + x} (MoO₄)₃ crystallizing in the monoclinic system (space group C2) are formed, was studied. Their crystallographic parameters were calculated; temperature dependences of the electrical conductivity, dielectric constant, and dielectric loss tangent were analized.     

Ferrimagnetic spinels in hydrothermal and thermal treatment of MnxFe2−2x(OH)6−4x

Products of hydrothermal treatment of the initial amorphous system Mn_xFe_2–2x(OH)_6–4x for 0x1 in 0.1x intervals, and products of their further thermal treatment, were examined by chemical analysis, X-ray, IR, and DTA techniques supported by magnetic measurements. After hydrothermal growth for lowx, hematite and goethite phases occurred. Although the goethite phase was still identifiable atx=0.6, formation of a solid solution with the isostructural groutite was not found. The ferrimagnetic spinel phase, which resists heating up to 400C, was present at 0.5x0.9. At higher temperatures, it transformed into the rhombohedral hematite type phase or into the cubic bixbyite phase. AtT900C, a ferrimagnetic spinel structure reappeared up tox=0.8. For x=0.9, the low- and high-temperature forms of the hausmannite phase occurred, forx= 1 passing from one form into another through Mn₅O₈ and partritgeite.For a primary mixture Mn_0.5Fe(OH)₄, corresponding to the manganese ferrite structure, the lattice parameter of which passes from 8.43 å through 8.33 å to 8.50 å, the probable crystallochemical formula was suggested.We are grateful to KBN (The State Committee for Scientific Research, Poland) for grant No. 3 T09A 064 08, which contributed substantially to the materialization of this project.     

Electroconductivity of Solid Electrolytes in the Systems K3–2x M x PO4 (M = Ca, Sr, Ba)

Solid electrolytes K_{3 – 2x} M _x PO₄ (M = Ca, Sr, Ba) are synthesized and the temperature and concentration dependences of their electroconductivity are studied. Adding calcium and strontium stabilizes the high-temperature -form of K₃PO₄ at room temperature, while barium-containing solid electrolytes undergo an eutectoid decomposition below 430°C. Maximum electroconductivity is exhibited by K_{3 – 2x} Sr _x PO₄ (7.1 × 10^–3 and 1.25 × 10^–1 S cm^–1 at 300 and 700°C).     

Anion⋅⋅⋅Anion Attraction in Complexes of MCl3− (M=Zn,Cd, Hg) with CN−

High-level ab initio calculations show that the MCl₃⁻ anions comprising Group 2B M atoms Zn, Cd, and Hg form a stable complex with the CN⁻ anion, despite the like charge of the two ions. The complexation occurs despite a negative π-hole region above the M atom of MCl₃⁻. The dimerization distorts the planar geometry of MCl₃⁻ into a pyramidal shape which reduces the negative potential above the M atom, facilitating a close approach of the two anions, with R(M⋅⋅⋅C)∼2 Å, and an overall attractive electrostatic attraction within the dimer. In the gas phase, this dimer is less stable than the pair of separated ions by some 30 kcal/mol. However, the dissociation must surmount an energy barrier of roughly 25 kcal/mol which occurs at an intermolecular distance of 4 Å. In aqueous solution, the dimerization process is exothermic and barrier-free, with a binding energy in the 11–18 kcal/mol range.     

Synthesis and characterization of a NASICON phase of variable composition Na1 − x Ni1 − x Sc1 + x (MoO4)3 (0 ≤ x ≤ 0.5)

Subsolidus phase ratios in the Na₂MoO₄-NiMoO₄-Sc₂(MoO₄)₃ system have been studied using X-ray diffraction, differential thermal analysis, and vibrational spectroscopy. A phase of variable composition Na_{1 ? x} Ni_{1 ? x} Sc_{1 + x} (MoO₄)₃ (0 ≤ x ≤ 0.5) having NASICON structure (space group \(R\bar 3c\) ) and a triple molybdate crystallizing in triclinic system (space group \(P\bar 1\) ) have been obtained. The high conductivity of Na_{1 ? x} Ni_{1 ? x} Sc_{1 + x} (MoO₄)₃ allows the phase of variable composition to be regarded as a promising sodiumion-conductive solid electrolyte.