31P AND 2H NMR Spectra of A Lyomesophase Containing Phosphoric Acid Monodecylester and H3PO4

This is a report on ³¹P nmr spectra of phosphoric acid monodecylester, PDE, and ²H quadrupolar splitting of D₂O in a lyomesophase developed from n-decylammonium chloride, PDE/H₃PO₄ and D₂O.Polarizing microcopic and ²H nmr studies showed that the mesophase was of lamellar-like structure but alignes as the temperature is increased. As the mesophase contained a minute amount of free H₃PO₄, the ³¹P nmr spectra gave a sharp peak and a hump. The latter was interpreted to arise from a slow tumbling process of PDE between different agglomerates in this system.     

Proton conductivity of Al(H2PO4)3–H3PO4 composites at intermediate temperature

Composites of Al(H₂PO₄)₃ and H₃PO₄ were synthesised by soft chemical methods with different Al/P ratios. The Al(H₂PO₄)₃ obtained was found to have a hexagonal symmetry with parameter a = 13.687(3)Å, c = 9.1328(1)Å. The conductivity of this material was measured by a.c. impedance spectroscopy between 100 °C and 200 °C in different atmospheres. The conductivity of pure Al(H₂PO₄)₃ in air is in the order of 10^? 6–10^? 7 S/cm between 100 and 200 °C. For samples containing small excess of H₃PO₄, much higher conductivity was observed. The impedance responses of the composites were found to be similar with AlH₂P₃O₁₀·nH₂O under different relative humidity. The conductivity of Al(H₂PO₄)₃–H₃PO₄ composite with Al/P = 1/3.5 reached 6.6 mS/cm at 200 °C in wet 5% H₂. The extra acid is found to play a key role in enhancing the conductivity of Al(H₂PO₄)₃–H₃PO₄ composite at the surface region of the Al(H₂PO₄)₃ in a core shell type behaviour. 0.7% excess of H₃PO₄ can increase the conductivity by three orders of magnitude. These composites might be alternative electrolytes for intermediate temperature fuel cells and other electrochemical devices. Conductivity (9.5 mS/cm) changed little, when the sample was held at 175 °C for over 100 h as the conductivity stabilised.     

Cl35 NQR study of the structural phase transition in (CH3NH3)HgCl3

The Cl³⁵ nuclear quadrupole resonance spectra of (CH₃NH₃)HgCl₃ have been measured between -150°C and + 100°C. The spectra clearly show that a structural phase transition of first order takes place around T_c? 60°C. The transition may be related to a disordering of the CH₃NH₃ groups which are reorienting both above and below T_c. The positive temperature coefficient of the Cl NQR frequency, dv/dT may be also explained by the CH₃NH₃ motion.     

A new story in the structural chemistry of cerium(IV) phosphate

Two different cerium(IV) phosphates have been prepared by ageing at 95 °C an aqueous solution made from Ce(NO₃)₆(NH₄)₂, nitric acid, and phosphoric acid with the following conditions: P/Ce=2, [HNO₃]=5.8 M and [Ce⁴⁺]=0.1 M. The control over the formed solid was achieved through the ageing time. After 18 h, a metastable compound (A), corresponding to Ce(PO₄)_1.5(H₂O)(H₃O)_0.5(H₂O)_0.5, is obtained, while after 5 days a stable one (B), corresponding to Ce(PO₄)(HPO₄)_0.5(H₂O)_0.5, is recovered. Both solids exhibit a P/Ce ratio of 1.5. Their structures, ³¹P solid state NMR, and thermal behaviors are compared.     

Optical absorption studies on cobalt doped struvite

Abstract

Optical absorption spectrum of cobalt doped MgNH₄PO₄ · 6H₂O (struvite) is investigated in UV-VIS-NIR regions. The spectrum in UV-VIS-NIR region is attributed to Co²⁺ in octahedral symmetry whereas the IR spectrum is attributed to vibrations due to PO₄ ^3-, NH₄ ⁺ and H₂O. The following crystal field (Dq) and interelectronic repulsion (B, C) parameters are evaluated: Dq = 940cm^?1, B = 870cm^?1 and C = 3970cm^?1.     

NMR Investigations of the Protonic Transport Mechanism in Composed Materials on the Basis of Cesium Acid Sulfates and Phosphates

The composite materials Cs(HSO₄)_1?x (H₂PO₄) _x were investigated by X-ray phase analysis, differential scanning calorimetry, nuclear magnetic resonance (NMR) relaxation, pulsed field gradient NMR (PFG-NMR) and impedance spectroscopy. Three composite materials types x = 0.1 ÷ 0.3 mixture CsHSO₄, α-Cs₃(HSO₄)₂(H₂PO₄), β-Cs₃(HSO₄)_2.5(H₂PO₄)_0.5—compositions of area I; x = 0.4 ÷ 0.5 mixture α-Cs₃(HSO₄)₂(H₂PO₄) and Cs₂(HSO₄)(H₂PO₄)—compositions of area II; x = 0.6 ÷ 0.9 mixture Cs₂(HSO₄)(H₂PO₄) and CsH₂PO₄—compositions of area III, were synthesized. The phase transition temperature from the low-to-high conductive phase for obtained composite materials is notably below (about 100 °C) than that for the individual components. The proton self-diffusion coefficients measured by PFG-NMR are lower than the diffusion coefficients calculated from proton conductivities data. The correlation times τ _d controlling the ³¹P–¹H magnetic dipole–dipole interaction were calculated according to data of the spin–lattice relaxation on ³¹P nuclei. The self-diffusion coefficients estimated from the Einstein equation are in good agreement with the experimental self-diffusion coefficients measured by PFG-NMR. It confirms the fact that the proton mobility is caused by the rotation of PO₄ anion tetrahedra.     

Dielectric properties of CsH2PO4 and CsD2PO4

Orthorhombic CsH₂PO₄ undergoes a ferroelectric transition at T_c = ?119.5°C, whereas the ferroelectric transition temperature in isomorphous CsD₂PO₄ is T_c = ?5.55°C. The transitions are of first order in both cases. The rather large isotope effect demonstrates the importance of the OHO bonds in the transition mechanism.     

Theoretical studies of the spin Hamiltonian parameters and local structures for WO3 doped Zn3(PO4)2ZnO nanopowders

The spin Hamiltonian parameters (SHPs) and the local structures for impurity W⁵⁺ in the Zn₃(PO₄)₂ZnO nanopowders doped with WO₃ under different concentrations are theoretically investigated using the perturbation calculations of these parameters. The exponential functions of the related quantities (cubic field parameter Dq, covalency factor N, relative tetragonal compression ratio τ and core polarisation constant κ) of concentration x with totally four adjustable coefficients a, b, c and d are adopted to fit the concentration dependences of the experimental d-d transition bands and SHPs. The impurity W⁵⁺ centres demonstrate moderate tetragonal compression ratios τ (～3.1%) due to the Jahn–Teller effect. With the increase of WO₃ concentration, Dq and N show moderately decreasing rules, while τ and κ exhibit slightly and moderately increasing tendencies with x, respectively. The mechanisms of the above concentration dependences of these quantities are analysed from the modifications of the local crystal-field strength and electron cloud density around the impurity W⁵⁺ with the variation of x. Present theoretical studies would be useful to the exploration of the structural properties and optical applications for WO₃ doped Zn₃(PO₄)₂ZnO nanopowders.     

The Mössbauer spectrum of synthetic hureaulite: Fe5 2+(H2O)4(PO4H)2(PO4)2

The crystal structure of synthetic ferrous hureaulite, Fe₅ ²⁺ (H₂O)₄(PO₄H)₂(PO₄)₂, was refined from single-crystal X-ray data. It is monoclinic, space group C2/c, with a=17.487(4), b=9.017(2), c=9.338(2) Å, β=96.27(3)°, V=1463.6(6) Å³, Z=4 and D _calc=3.327 g/cm³. This end member of the hureaulite series was crystallized under distinctly acidic conditions, by a method that gives perfect crystals, large enough for X-ray single crystal studies. The main feature of the hureaulite structure is that it has an equal number of normal (PO₄)³⁺ and acid (PO₄H)²⁺ tetradentate groups. These are centered on Fe²⁺ atoms and share corners with edge-linked octahedra, forming pentamer units. The five Fe²⁺ atoms are distributed on three distinct sites in these units. This can be directly observed in the Mössbauer spectrum at 295 K, which contains three doublets whose relative intensities correspond to the 1:2:2 distributions of crystallographic sites.     

EPR study of the symmetry breaking effect in ferroelectric cesium dihydrogen phosphate doped with Cr5+ ions

The (PO₄)^3? units in a CsH₂PO₄ (CDP) crystal were replaced in a small fraction of sites by (CrO₄)^3? groups and the EPR of the Cr⁵⁺ center was investigated. Splitting of the EPR line appears at T¹_c=245 K, 91 K higher that the ferroelectric transition temperature T_c=154 K. The electronic wave function of Cr⁵⁺ (3d¹) is identified as d_x2_?y2. The d_x2_?y2 function couples with the near protons and the reorientation of this unit in the two possible configurations occurs in the paraelectric phase and breaks the symmetry far above T_c. The observed correlation time 10^?9 sec and associated activation energy ΔU=0.215 eV are discussed.     

Structural,vibrational study and superprotonic behavior of a new mixed dipotassium hydrogenselenate dihydrogenphosphate K2(HSeO4)1.5(H2PO4)0.5

Ongoing studies of the KHSeO₄–KH₂PO₄ system aiming at developing novel proton conducting solids resulted in the new compound K₂(HSeO₄)_1.5(H₂PO₄)_0.5 (dipotassium hydrogenselenate dihydrogenphosphate). The crystals were prepared by a slow evaporation of an aqueous solution at room temperature. The structural properties of the crystals were characterized by single-crystal X-ray analysis: K₂(HSeO₄)_1.5(H₂PO₄)_0.5 (denoted KHSeP) crystallizes in the space group P 1¯ with the lattice parameters: a = 7.417(3) Å, b = 7.668(2) Å, c = 7.744(5) Å, α = 71.59(3)°, β = 87.71(4)° and γ = 86.04(6)°. This structure is characterized by HSeO₄⁻ and disordered (H_xSe/P)O₄⁻ tetrahedra connected to dimers via hydrogen bridges. These dimers are linked and stabilized by additional hydrogen bonds (O–H–O) and hydrogen bridges (O–H…O) to build chains of dimers which are parallel to the [0, 1, 0] direction at the position x = 0.5.The differential scanning calorimetry diagram showed two anomalies at 493 and 563 K. These transitions were also characterized by optical birefringence, impedance and modulus spectroscopy techniques. The conductivity relaxation parameters of the proton conductors in this compound were determined in a wide temperature range. The transport properties in this material are assumed to be due to H⁺ protons hopping mechanism.     

Complex formation and phosphate-H2O interactions in a concentrated aqueous Mg(H2PO4)2 solution.

X-ray diffraction data from a solution of Mg(H₂PO₄)₂ were examined. The experimental distribution curve shows peaks at about 2.10, 2.7–2.9, 3.6, 3.9 and 4.25 Å. The 3.6 Å peak reveals the formation of inner sphere magnesium-phosphate complexes Mg(H₂O)_6-z(H₂PO₄)^+2-z_z, in which oxygens from phosphate groups substitute z water molecules of the hydrated Mg(H₂O)²⁺₆ ions. Least squares refinements of the i(s) curve are consistent with a structural unit in which the phosphate tetrahedron shares a corner with one magnesium octahedron with MgOP angle of 147 deg. Each phosphate ion interacts with about eight water molecules.     

Structure and proton conductivity of mechanochemically treated 50CsHSO4·50CsH2PO4

Mixtures of CsHSO₄ and CsH₂PO₄ were mechanochemically treated using a planetary type of ball mill. The changes in structure and proton conductivity of the solid acid compounds with the treatment have been investigated. Cs₃(HSO₄)₂(H₂PO₄) and Cs₅(HSO₄)₃(H₂PO₄)₂ were formed during milling. The mechanochemically treated composite consisting of Cs₃(HSO₄)₂(H₂PO₄) and Cs₅(HSO₄)₃(H₂PO₄)₂ showed higher conductivity than the untreated mixture. In addition, a high temperature phase of Cs₂(HSO₄)(H₂PO₄) was generated from the composite at around 100 °C on heating. Conductivity of the mechanochemically treated composite significantly increased at temperatures around 90 °C on heating. The value becomes 2 × 10^− 3 S cm^− 1 at around 180 °C. On the other hand, no steep decrease is observed on cooling. The activation energies of the mechanically milled sample with high conductivities were estimated to be about 0.3 eV for both heating and cooling processes. The relatively high proton conductivity and a low activation energy for the proton conduction should be ascribed to the presence of the high temperature phase of Cs₂(HSO₄)(H₂PO₄).     

Study of hopeite coatings: II. Study of polycationic hopeites: structure and dehydration process

The structures and the dehydration processes of phosphates, formed on galvanized steel sheets treated in polycationic solutions containing Zn²⁺, Ni²⁺ and Mn²⁺ as dihydrogenophosphates, are studied using differential and gravimetric thermal analysis (DTA, TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The compounds constituting the phosphated layers, and the crystals precipitated in a stove at 70° C from the same solutions, are structurally substituted-hopeites, (Zn, Mn, Ni)₂(PO₄)₂·4H₂O. Their thermal behaviour is strongly influenced by the presence of Ni²⁺ and Mn²⁺ ions. The dihydrate (Zn₃(PO₄)₂·2H₂O), whose structure conformation has been determined at first, is identified as the main component in the dehydration products of these compounds. The knowledge of the dihydrate conformation allows the understanding of the specificity of the dehydration processes of substituted hopeites whose transformation temperatures and dehydration modes depend on the nature of the substituting cations.     

A new type of phase transition in M(ClO4)2(H2O)6M = Fe,Co, Ni and Mn

Mössbauer studies on Fe(ClO₄)₂(H₂O)₆ salt showed anomalous quadrupole splitting around (230 ± 15)°K which we have established to be due to a new type of phase transition from pseudohexagonal to monoclinic system. Exactly similar type of transition was observed magnetically in all the isomorphous Ni²⁺, Co²⁺ and Mn²⁺ perchlorate hexahydrate single crystals at different critical temperatures.     

Preparation,structural characterization and conductivity of LiZr2(PO4)3

Amorphous LiZr₂(PO₄)₃ has been prepared at room temperature starting from aqueous solutions of ZrOCl₂, H₃PO₄, and LiOH and then crystallized by heating at temperatures between 600 and 900°C. The material obtained at 900°C has been characterized by X-ray powder diffractometry, DSC analysis, and ac conductivity. It is monoclinic from 20 up to about 300°C and orthorhombic at higher temperatures. A change in the activation energy for conduction (from 0.79 to 0.43 eV) and a weak endothermic effect (0.9–1.7 cal/g) are associated with the phase transition. The ac conductivity of sintered pellets is, on average, 7×10⁻⁴ S cm⁻¹ at 300°C.     

Structural and electrical characterization of the NASICON-type Li2FeZr(PO4)3 and Li2FeTi(PO4)3 compounds

In order to develop new electrolytes for all-solid-state rocking chair lithium batteries, the NASICON-type compounds Li₂FeZr(PO₄)₃ and Li₂FeTi(PO₄)₃ were investigated by powder X-ray diffraction technique and impedance spectroscopy. Li₂FeZr(PO₄)₃ is orthorhombic Pbna (a=8.706(3), b=8.786(2), c=12.220(5) Å) and Li₂FeTi(PO₄)₃ is orthorhombic Pbca (a=8.557(3), b=8.624(3), c=23.919(6) Å). They show no phase transitions from RT to 800 °C. In the same temperature range logσT vs. 1/T show no slope variations. The activation energies for the ionic conductivity were 0.62 and 0.64 eV for Li₂FeTi(PO₄)₃ and Li₂FeTi(PO₄)₃, respectively. In order to better evaluate the present results they were compared with those of α and β-LiZr₂(PO₄)₃ phases, which were also prepared and characterised. A change of activation energy from 0.47 eV to 1.03 eV was observed in the case of β phase, at about 300 °C; attributed to the β (orthorhombic) ? β′ (monoclinic) phase transition. In the α phase the activation energy 0.47 eV in the temperature range 150 – 850 °C. The Li₂FeZr(PO₄)₃ and Li₂FeTi(PO₄)₃ compounds can be interesting for applications as solid electrolytes in high temperature (>300 °C) lithium batteries.     

Theoretical investigations on the g factors and local structures for Cu2+ in the ZnX (X= O,S and Se) nanocrystals

ABSTRACT

The g factors and local structures for Cu²⁺ in the ZnX (X = O, S and Se) nanocrystals at room temperature are theoretically investigated by the perturbation calculations for a tetragonally distorted tetrahedral 3d⁹ cluster in a consistent way, and the isotropic g factor is predicted for the ZnS:Cu²⁺ nanocrystals at room temperature. The bond angles θ between the four equivalent Cu²⁺?X^2? bonds and the C₄ axis are found to be about 1.26°, 1.24° and 1.07°, respectively, larger in the ZnO, ZnS and ZnSe nanocrystals than that (θ₀ ≈ 54.74°) for an ideal tetrahedron, inducing tetragonally compressed tetrahedra. The declining tendency (ZnO > ZnS > ZnSe) of the tetragonal angular distortion Δθ (= θ ? θ₀) can be ascribed to the decreasing strength of the dynamic Jahn–Teller effect via the vibration interactions of the [CuX₄]^6? groups due to the weakening Cu²⁺?X^2? bonding. The isotropic g factors are attributable to the appropriate Δθ due to the dynamic Jahn–Teller effect and the internal stress. The slightly increasing (ZnO < ZnS < ZnSe) g factors can be illustrated by the declining cubic field parameter Dq, angular distortion Δθ and covalency factor N of the systems.     

Crystal growth and characterization of a new co-ordination complex—barium tetrakis(maleate) dihydrate

Crystals of barium tetrakis(maleate) dihydrate [Ba₄(C₄H₂O₄)₄]^?2H₂O are grown in gelated hydrosilica matrix. Single crystal X-ray diffraction studies show that the crystal system is monoclinic with space group P2₁/c. The unit cell dimensions are a=9.3721(2)  Å, b=20.5880(7)  Å, c=14.0744(4) Å, α=γ=90°, β=90.289(2)°. Powder XRD studies confirmed the single phase nature of the grown crystals. The FTIR data is in conformity with the XRD results. The TG–DTA curves of the material indicate a three-step thermal decomposition. The response of the dielectric properties in the temperature range 30 °C to 500 °C is correlated with the TG–DTA results.