The electronic structure of CrO43− as studied by EPR in K2SO4 single crystals

EPR and ENDOR investigations are carried out on irradiated K₂SO₄ crystals doped with CrO₄^2? ions. They indicate the formation of CrO₄^3? centers interacting with a nearby proton. The identification of the CrO₄^3? centers is based on their g values, the orientation of the g tensor and the symmetry requirements. The results are compared with related studies on MnO₄^2? in K₂SO₄ and K₂CrO₄ hosts.     

Conduction and tritium diffusion studies in single crystals of potassium hydrogen sulfate

Direct-current electrical conductivity of single crystals of KHSO₄ doped with 5, 11, 30, and 437 ppm of cobalt-II is studied in the temperature range 25 to 165°C. The point defect parameters are calculated by graphical analysis of the conductivity data. Various parameters are obtained: enthalpy for the migration of proton (referred to as the enthalpy for the rotation of HSO₄ ion), H_M = 0.55 ± 0.01 eV; the enthalpy for the formation of the intrinsic defects (referred to as the enthalpy for the breaking of the HSO₄ dimers), H_F = 1.30 ± 0.01 eV; and the enthalpy for the impurity-vacancy association H_a = ?0.14 ± 0.01 eV. The tritium diffusion studies in the pure KHSO₄ single crystals give 0.22 ± 0.01 eV and ?1.09 × 10^?3 eV K^?1 as the activation enthalpy and entropy for the process, respectively. The Nernst-Einstein relation is not obeyed. The mechanisms for the conduction and diffusion preocesses in this crystal are discussed.     

Dilead(II) trimercury(II) tetraoxide chromate(VI), Pb2(Hg3O4)(CrO4)

Pb₂(Hg₃O₄)(CrO₄) consists of [CrO₄]²⁻ tetra­hedra, linear O—Hg—O dumbbells and divalent Pb atoms in [3+5]‐coordination. The HgO₂ dumbbells are condensed into [Hg₃O₄]²⁻ units and can be regarded as a section of the HgO structure. The [Hg₃O₄]²⁻ complex anions are connected by inter­stitial Pb²⁺ ions, while the [CrO₄]²⁻ tetra­hedra are isolated.     

Structure and electric properties of Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>-NaPO<Subscript>3</Subscript> glasses

The influence of the SO₄²⁻ ion on the temperature and concentration dependences of electric conductivity and the structure of sodium phosphate oxide glasses was studied. The increased electric conductivity of sulfate-phosphate glasses was explained by the formation of mixed sulfate-phosphate fragments with terminal SO₄²⁻ ions in the structure of glasses in the Na₂SO₄-NaPO₃ system. The dissociation energies of the sodium sulfate fragments are lower than those of pure oxide sodium phosphate structural units. As a result, the number of dissociated sodium ions increases, the activation energy of electric conductivity falls, and the conductivity (at 25°C) increases approximately 270-fold relative to the conductivity of NaPO₃. The arrangement of SO₄²⁻ ions in the structure was evaluated from the IR spectra of the glasses.     

Heterometric microdetermination of cobalt using nitron as titrant

Small amounts of cobalt (0.1–0.25 mg in 15 ml solution) were determined heterometrically in the presence of potassium thiocyanate by titration with nitron acetate solution. A strong electrolyte (Na₂SO₄) must be added to obtain a clear end point. The titration can be carried out in the presence of a number of diverse ions e.g., Cd²⁺, Ni²⁺, Pb²⁺, Mn²⁺, Cr³⁺, MoO₄^2?, WO₄², CrO₄^2?, NO₃^?, Au³⁺, Pt⁴⁺ without interference; Fe³⁺ can be masked with NaF. Copper and zinc interfere and must be absent. The titration takes about 2–3 min. and the maximum error was 1.5%.     

Dilead mercury chromate(VI), Pb2HgCrO6

The structure of Pb₂HgCrO₆ (space group P) can be described as consisting of isolated [CrO₄]^2? tetrahedra and nearly linear [HgO₂]^2? dumb‐bells, which form layers of composition [HgCrO₆]^4?. These are intercalated with corrugated pseudo‐hexagonal Pb²⁺ layers. The Pb²⁺ cation is stereochemically active and has coordination 3+5.     

Proton dynamics in superionic phase of Tl3H(SO4)2

Electrical properties and ¹H-NMR absorption line have been measured, in order to investigate proton dynamics in a superionic phase in Tl₃H(SO₄)₂. From the measurement of the thermoelectric power, it is found that a majority carrier in electrical conductivity is a proton. Moreover, from ¹H-NMR measurement it is also found that the activation energy 0.33 eV of the hopping motion of protons is close to 0.38 eV as observed in the electrical conductivity measurement. These results indicate that the electrical conductivity in the superionic phase is caused by the hopping motion of protons accompanied by the breaking of the hydrogen bonds.     

Sorption of chromate ions on oxyhydroxides prepared from iron(III) and aluminum sulfates

Sorption properties with respect to the chromate ions of ferro- and alumogels prepared from Fe(III) and aluminum sulfates, and the composition of oxyhydroxides (OH), are studied. It is determined that the sorption values of chromate ions on ferrogels and alumogels (with NaCl) are notably higher than those on OH prepared from other precursors. It is shown that the sorption of CrO ₄ ^2? on alumogels with Na₂SO₄ is almost completely inhibited. It is found that gels retain substantial amounts of sulfate ions during precipitation from precursor solutions, while alumogels retain substantially more than ferrogels. The sorption of SO₄-gels is explained from the viewpoint of their composition and interaction with Na₂SO₄ solution. The competitive sorption of chromate and phosphate ions is studied and it is demonstrated that phosphate ions completely inhibit the sorption of chromate ions at comparable concentrations.     

An experimental investigation of ionic transport properties in CuI-Ag2WO4 and CuI-Ag2CrO4 mixed systems

The phenomenon of ionic transport in the case of two different mixed systems (CuI)_(1−x)-(Ag₂WO₄)_x(0.15?x?0.6) and (CuI)_(1−y)-(Ag₂CrO₄)_y(0.15?y?0.5) has been investigated. Powder X-ray diffraction (XRD) analysis coupled with differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR), FT-Raman and electrical transport studies involving ionic transport number and temperature-dependent electrical conductivity measurements have been carried out in order to identify the various phases responsible for the conduction process. The occurrence of typical ionic conductivity values of 4.5×10⁻³ Scm⁻¹ for the composition (CuI)_0.45-(Ag₂WO₄)_0.55 and 1.1×10⁻⁴ Scm⁻¹ in the case of (CuI)_0.55-(Ag₂CrO₄)_0.45 at room temperature has been discussed in terms of the observed characteristics.     

Electrochemistry of Na2SO4 (I) solid solutions with aliovalent cation substitution

Conductivity data of several Na₂SO₄(I) solid solutions with cation substitutions are presented. The substitution of sodium by bi- and trivalent atoms generates cation vacancy concentrations up to 30% in the structure of Na₂SO₄(I) thus creating high mobility of Na⁺. Electrochemical measurements showed that Na⁺ ion conductivity prevails and that the electronic partial conductivity is negligible. Complex impedance diagrams were used to determine the influence of the vacancy concentration on the ionic conductivity of Na₂SO₄(I) solid solutions. It was found that the conductivity is strongly correlated to the vacancy concentrations, whereas the size and the charge of the substituting ions show no effect within the accuracy of the measurements. The activation energy as function of the vacancy concentration exhibits a minimum of 0.7 eV at a vacancy concentration of 1%. The maximum of conductivity was found to be 1.5 × 10^?2 Ω^?1 cm^?1 at 500°C with 7% vacancies.     

Kinetic and thermal studies of removal of CrO 4 2− ions by ettringite

Ettringite was prepared in the presence of various dosages of CrO ₄ ^2? ions at three different temperatures. X-ray diffraction (XRD) and differential scanning calorimetery (DSC) results showed shift in the peaks characterized to ettringite as the result of formation of Cr-substituted ettringite. Substitution of SO ₄ ^2? by CrO ₄ ^2? ions in ettringite crystal resulted in delay in the rate of its formation, as well as reduction in the crystal diameters. However, the crystal diameters and rate of formation of both ettringite and Cr-substituted ettringite were increased by increasing temperature of preparation, and this was confirmed by scanning electron microscope (SEM) micrographs. The thermodynamic parameters: the enthalpy, entropy, and Gibbs free energy changes for substitution process were studied. It is concluded that the removal of chromate ions by ettringite is an endothermic spontaneous process. The positive value of ΔS° suggests increasing in randomness during the removal process.     

A Design Strategy for Single‐Stranded Helicates using Pyridine‐Hydrazone Ligands and PbII

The reactions of py‐hz ligands ( L1–L5 ) with Pb(CF₃SO₃)₂?H₂O resulted in some rare examples of discrete single‐stranded helical Pb^II complexes. L1 and L2 formed non‐helical mononuclear complexes [Pb L1 (CF₃SO₃)₂]?CHCl₃ and Pb L2 (CF₃SO₃)₂][Pb L2 CF₃SO₃]CF₃SO₃?CH₃CN, which reflected the high coordination number and effective saturation of Pb^II by the ligands. The reaction of L3 with Pb^II resulted in a dinuclear meso‐helicate [Pb₂ L3 (CF₃SO₃)₂Br]CF₃SO₃?CH₃CN with a stereochemically‐active lone pair on Pb^II. L4 directed single‐stranded helicates with Pb^II, including [Pb₂ L4 (CF₃SO₃)₃]CF₃SO₃?CH₃CN and [Pb₂ L4 CF₃SO₃(CH₃OH)₂](CF₃SO₃)₃?2 CH₃OH?2 H₂O. The acryloyl‐modified py‐hz ligand L5 formed helical and non‐helical complexes with Pb^II, including a trinuclear Pb^II complex [Pb₃ L5 (CF₃SO₃)₅]CF₃SO₃?3CH₃CN?Et₂O. The high denticity of the long‐stranded py‐hz ligands L4 and L5 was essential to the formation of single‐stranded helicates with Pb^II.     

Comparative study on energetic distortions of SO42− ions matrix-isolated in compounds with kröhnkite-type chains,K2Me(CrO4)2·2H2O and Na2Me(SeO4)2·2H2O (Me = Mg,Co, Ni,Zn, Cd)

Infrared spectra of compounds with kröhnkite-type infinite octahedral–tetrahedral chains, K₂Me(CrO₄)₂·2H₂O and Na₂Me(SeO₄)₂·2H₂O (Me = Mg, Co, Ni, Zn, Cd), as well as infrared spectra of the title double salts containing matrix-isolated SO₄^2? guest ions are presented and discussed in the regions of the X–O stretching modes.The SO₄^2? guest ions matrix-isolated in selenate and chromate matrices exhibit four infrared bands corresponding to the four site-group components of the stretching modes in good agreement with the low site symmetry of the host ions (C₁ site symmetry). The values of Δν₃ (site-group splitting) and Δν_max (the difference between the highest and the lowest wavenumbered components of the stretching modes) are used as an adequate measure for the extent of energetic distortion of the matrix-isolated SO₄^2? guest ions.The influence of different crystal-chemical parameters (Me²⁺–OXO₃ bond strengths, sizes of the Me²⁺ and Me⁺ ions, electronic configurations of the Me²⁺ ions, hydrogen bond strengths, and unit-cell volumes of the host compounds) on the extent of energetic distortion of both the host SeO₄^2? and CrO₄^2? ions, and the SO₄^2? guest ions is analyzed. Correlations between the values of Δν₃ and Δν_max of the guest ions and both the degree of covalency of the respective Me²⁺–OXO₃ bonds and the electronic configurations of the Me²⁺ ions have been found and will be discussed. For example, the energetic distortion of SO₄^2? ions included in the chromate lattices decreases in the order Zn > Cd > Mg as a result of the decreasing covalency of the respective Me²⁺–O bonds in the same order (Δν₃ have values of 73, 58 and 36 cm^?1, respectively). Furthermore, the values of Δν₃ and Δν_max are larger when the metal ions have CFSE ≠ 0 (crystal field stabilization energy, Co²⁺, Ni²⁺). These cations are more resistant to angular deformations of the MeO₆ octahedra (i.e. changes in the O–Me–O bond angles), thus facilitating the extent of distortion of the matrix-isolated SO₄^2? ions as compared to those having CFSE = 0 (Mg²⁺, Zn²⁺ and Cd²⁺). For example, Δν₃ and Δν_max of SO₄^2? ions matrix-isolated in K₂Zn(CrO₄)₂·2H₂O have values of 73 and 163 cm^?1, and 116 and 207 cm^?1 in Na₂Zn(SeO₄)₂·2H₂O, whereas in the respective nickel lattices Δν₃ and Δν_max have values of 88 and 173 cm^?1 (K₂Ni(CrO₄)₂·2H₂O) and 127 and 212 cm^?1 (Na₂Ni(SeO₄)₂·2H₂O).The SO₄^2? guest ions included in selenate matrices, Na₂Me(SeO₄)₂·2H₂O, are remarkably much distorted than in chromate ones, K₂Me(CrO₄)₂·2H₂O, as deduced from the values of Δν₃ and Δν_max owing to a stronger static field caused by the smaller Na⁺ ions as compared to that caused by the larger K⁺ ions. The smaller unit-cell volumes of the selenate host compounds, i.e. the higher repulsion potential at the lattice sites at which the guest ions are situated additionally favor the extent of energetic distortion of the sulfate guest ions in the selenate matrices.     

Point defects in potassium thiocyanate: Impurity diffusion and conduction in lead-doped crystals

The diffusion rates of ${}^{210}\text{Pb}{}^{\mathrm{2+}}$ and ${}^{35}\text{S}{}^{\mathrm{2?}}$ into single crystals of nominally pure potassium thiocyanate have been measured. The impurity diffusion coefficients are about 1% of the values for the host anion and cation (reported previously), and this supports the view that ionic diffusion in this solid occurs mainly via a vacancy pair process. The electrical conductivity of polycrystalline samples of KSCN doped with Pb²⁺ has been measured as a function of temperature and of lead content. The results show that cation vacancies are mobile in the solid and that the overall conduction behavior of KSCN is dominated by impurity effects.     

Contribution à l'étude du système quaternaire K+—NH4+—CrO4−−—SO4−−—H2O: I. les isothermes de 25° des systèmes ternaires limites

The four ternary limiting isotherms of the system K⁺− NH₄⁺ CrO₄⁻⁻ SO₄⁻⁻ H₂O are given for 25° C. In the systems K₂SO₄ (NH₄)₂SO₄ H₂O and K₂SO₄ K₂CrO₄ H₂O only one solid phase has been encountered; both systems belong to the type I of the ROOZEBOOM classification. A miscibility gap is present in the systems (NH₄)₂CrO₄ K₂CrO₄ H₂O and (NH₄)₂CrO₄ (NH₄)₂SO₄ H₂O; they belong to ROOZEBOOM'S type V.     

Electrical conductivity and thermopower of Fe-phosphate compounds with the lazulite-type structure

Measurements of the electrical DC and AC conductivities were performed on three Fe-phosphate compounds in the temperature range ∼210 K?T?∼450 K. The Fe-phosphates are semiconducting with activation energy of DC conductivity σ_DC of E_A∼0.35-0.45 eV. For α-Fe₂PO₄O, the AC conductivity σ_AC in the low-temperature range is considerably enhanced relative to σ_DC. The frequency dependence of σ_AC can be described by an approximate power law. For the same compound, the thermopower Θ (Seebeck effect) was found to be positive in the range ∼330 K?T?∼700 K, i.e. seemingly p-type conduction occurs; at T>700 K, Θ appears to become negative. The results are described in terms of a small polaron hopping model between localized states with electron transfer of the type Fe²⁺→Fe³⁺ with Fe²⁺ as donors. In this model Θ can be described suggesting equal concentrations of Fe²⁺ and Fe³⁺ to take part in conduction.     

Crystal Structure,Dielectric Characteristics and Conduction Mechanism of a New Hybrid Material,Tetra(Phenylpiperazinium) Decachlorotriplumbate(II)

Monocrystalline (C₁₀H₁₅N₂)₄Pb₃Cl₁₀ was obtained via an aqueous solution reaction and characterized by single-crystal X-ray diffraction technique, elemental analyses, IR spectroscopy, UV–Vis spectrum, photoluminescence properties and thermal analysis. Structural characterization reveals that the title compound is built from [Pb₃Cl₁₀]^4? units sharing Cl2 atom to form 2-D [Pb₃Cl₁₀] _n ^4n? layers, these anions are linked to the organic cations via N–H···Cl and C–H···Cl hydrogen bonding. Moreover, dielectric relaxation spectroscopy has also been determined to show different molecular motions. Measurements of AC conductivity as a function of frequency at different temperatures indicated the hopping conduction mechanism.     

Magnetic,optical and electrical properties of Mn-doped CuCrO<Subscript>2</Subscript> thin films prepared by chemical solution deposition method

CuCrO₂ and CuCrO₂:Mn thin films were prepared on sapphire substrates by chemical solution deposition method. The effects of the annealing temperatures and Mn concentration on the structural, electrical and optical properties were investigated. The X-ray diffraction measurement was used to confirm the c-axis orientation of CuCrO₂ and CuCrO₂:Mn thin films. The maximum transmittances of the films in the visible region are about 65% with direct band gaps of 3.25 eV. All films showed the p-type conduction and semiconductor behavior. The electrical conductivity decreases rapidly with the increase of Mn content, the maximum of the electrical conductivity of 1.35 × 10⁻² S cm⁻¹ is CuCrO₂ film deposited at 600 °C temperature in 10⁻³ Torr vacuum, which is about four orders of magnitude higher than that of the Mn-doped CuCrO₂ thin film. The energy band of the samples is constructed based on the grain-boundary scattering in order to investigate the conduction mechanism. Moreover, the samples exhibit a clear ferromagnetism, which was likely ascribed to originating from the double-exchange interaction between the Mn³⁺ and Cr³⁺ ions.     

Electrical conductivity and dielectric behaviour of PPG4�CAgCF3SO3:Al2O3 nanocomposite gel polymer electrolyte system

In this report, the synthesis of solvent-free poly(propylene glycol) 4000 (PPG₄)?Csilver triflate (AgCF₃SO₃):xAl₂O₃ nanocomposite gel polymer electrolytes containing four different amounts of Al₂O₃ nanoparticles corresponding to x?=?1, 3, 5 and 7?wt.%, respectively, with an ether oxygen-to-metal cation ratio (O?CM) of 4:1 together with their vibrational spectroscopic characteristics derived from Fourier transform infrared (FT-IR ) spectroscopic analysis at room temperature (25?°C) is described. Furthermore, a detailed investigation concerning their mechanism of ion transport performed by means of complex impedance analysis in the frequency range 20?Hz to 1?MHz and over the temperature region 25?C90?°C and analysed in terms of electrical conductivity spectra, electrical modulus spectra and impedance spectra has indicated that the typical composition PPG₄?CAgCF₃SO₃:5?wt.% Al₂O₃ would exhibit the best room temperature electrical conductivity of 6.2?×?10^?4?S cm^?1 owing to the mobility of coordinated silver cations through the mechanism of enhanced segmental motion of the PPG₄ polymer chains as aided by the various coordinating sites available within the polymer network. It is also demonstrated from the present FT-IR results that significant changes in the intensity, shape and position of the different vibrational bands corresponding to ?COH stretching, C?CO?CC stretching, C?CH stretching and C?CO?CC in C?CH stretching modes occur as a result of the incorporation of Al₂O₃ nanofiller particles into the PPG₄?CAgCF₃SO₃ complex. It is evident from the conductivity data that the observed enhancement in electrical conductivity would result from appropriate changes in ionic association occurring in the form of probable ion?Cion and ion?Cpolymer interactions involving Al₂O₃ nanofiller additive in accordance with the Lewis acid?Cbase model of polymer?Csalt?Cfiller interactions.     

Halbquantitative analyse durch messung der entfärbungs-zeit von tüpfelflecken

A rapid semiquantitative method is described based on measurement of the time required for decolorization of spotreactions on filter paper strips by suitable reagents, This very simple method yields results which are accurate to ± 10%. The method has been verified for several ions (Ag⁺, Pb²⁺, JO₃^-,Cu²⁺, CrO₄^2-). The utility of this method for the characterization and differentiation of filter papers is indicated.