A. Daoud

Synthesis and crystal structure of a new form of potassium–bismuth polyphosphate KBi(PO3)4

Abstract Synthesis and complete structural characterization by X-ray diffraction, IR and Raman are given for a new form of potassium–bismuth polyphosphate. This compound is monoclinic P 2 1 / n with a structural type IV and with the following unit cell dimensions: a =10.443(4) A, b =8.989(2) A, c =10.757(4) A, β =105.76(2)°, V =971.8(5) A 3 , Z =4 and ρ cal =3.855 g/cm 3 . The structure was solved from 3390 independent reflections with R 1 =0.0420 and WR 2 =0.0910, refined with 164 parameters. The atomic arrangement can be described as a long chain polyphosphate organization. Two infinite (PO 3 ) n chains with a period of eight tetrahedra run along the [101] direction. Bismuth atoms have an eightfold coordination while potassium atoms have nine oxygen neighbours. Infrared and Raman spectra were investigated at room temperature in the frequency range, 250–1500 and 200–1600 cm −1 , respectively, showing some characteristic bands of infinite chain structure of PO 4 tetrahedra linked by a bridging oxygen.

Structural, vibrational and calorimetric study of a new ammonium dihydrogen phosphate–arsenate: NH4H2(PO4)0.52(AsO4)0.48

Mixed crystals NH4H2(PO4)1−x(AsO4)x (ADAP) of the two antiferroelectric NH4H2PO4 (ADP) and NH4H2AsO4 (ADA) were grown with x=0.48 by slow evaporation from aqueous solution at room temperature. The structural properties of the crystals were analyzed by means of X-ray diffraction, which revealed that the title compound is isostructural with the tetragonal phases of ADP and ADA. This mixed compound crystallizes in space group I42d and has lattice parameters a=7.5920(13) A, c=7.6260(2) A with four formula units in the unit cell. Two kinds of disorder can be expected in this structure: a statical or dynamical disorder of the acidic proton in the O–H…O hydrogen bond and another one which is connected with a reorientational motion of NH4+ ions. Broader peaks in the IR spectrum confirm a structural disorder in this material. Crystals of ADAP undergo two phase transitions at T1=193 K and T2=423 K which are detected by differential scanning calorimetry (DSC).

Conductivity relaxation parameters of some H+ and K+ conducting in the polycrystalline compound KDyHP3O10

Abstract Polycrystalline samples of KDyHP 3 O 10 was obtained by heating for 12 hour at 553 K a mixture containing K 2 CO 3 , Dy 2 O 3 and H 3 PO 4 . Samples were characterized through X-ray diffraction, examined by IR vibrational spectroscopy and impedance and modulus spectroscopy techniques. The conductivity relaxation parameters of some H + and K + conducting in this compound have been determined from an analysis of ac conductivity data measured in a wide temperature range. Transport properties in this material appears as due to H + and K + ions hopping mechanism. The stretched exponential function exp[−( t / τ σ ) β ] has been used to describe the conductivity relaxation. The relaxation parameters have been investigated as a function of the nature of mobile ions. The results obtained are shown to be in good agreement with the predictions of the Ngai coupling model.

Studies by thermally stimulated current (TSC) of hydroxy- and fluoro-carbonated apatites containing sodium ions

Carbonated hydroxyapatites (HAPCO3Na) and fluoroapatites (FAPCO3Na) containing sodium ions have been precipitated by the hydrothermal method. The effect of carbonate and sodium substituted for phosphate and calcium respectively on the dipolar mobility of the OH- and F- ions located inside the apatitic channels of those samples has been studied by thermally stimulated current (TSC). In both apatites two relaxation modes, around -100 and + 50 °C, have been observed. In the HAPCO3Na sample, the relaxation mode fine structure reveals the existence of two cooperative phenomena with compensation temperatures in the vicinity of the hydroxyapatite monoclinic-hexagonal transition. After preheating of samples at 400 °C, the presence of cooperative movements is confirmed by the observation of a compensation phenomenon with a compensation temperature equal to 214 °C. An x-ray diffraction study is in agreement with this attribution. As for the FAPCO3Na sample, the fine structure of the lower temperature relaxation mode only reveals a compensation phenomenon at 5 °C attributed to water molecule reorientations inside apatitic channels.

Ferroelectric and electric properties of Rb0.6(NH4)0.4HSO4 single crystal

Abstract Dielectric investigations in the temperature and frequency ranges 150–450 K and 10 2 –10 5 Hz, respectively show that Rb 0.6 (NH 4 ) 0.4 HSO 4 composition is ferroelectric below T c =290 K. A.C. complex impedance measurements were performed on this ferroelectric and superconductor material at high temperatures. An impedance relaxation was observed. In addition, to the ferroelectric properties, an important level of conductivity at high temperatures attributed to the motion of H + proton at least in the off-stoichiometric material, was observed. This behavior indicates the presence of superionic protonic phase transition in this material.

Manganese Ethylenediammonium Bis(sulfate) Tetrahydrate

[NH 3 (CH 2 ) 2 NH 3 ][Mn(SO 4 ) 2 (H 2 O) 4 ] shows an alternate stacking of inorganic layers of tetraaquabis(sulfato-O)manganese anions, [Mn(SO 4 ) 2 (H 2 O) 4 ] 2- , and organic layers of [NH 3 (CH 2 ) 2 NH 3 ] 2+ cations. Anions and cations are linked together through N-H...O hydrogen bonds to form a three-dimensional network.

Phase transitions and electrical properties of CsH(SO4)0.76(SeO4)0.24 mixed crystals

The study by X-ray diffraction, calorimetry, vibrational and impedance spectroscopy of CsH(SO4)0.76(SeO4)0.24 new solid solution is presented. Crystals of this composition undergo two phase transitions at T = 333 and 408 K. The last one at 408 K is a superionic-protonic transition (SPT) related to a rapid [HS(Se)O4−] reorientation and fast H+ diffusion. A sudden jump in the conductivity plot confirms the presence of this transition. Above 408 K, this high temperature phase is characterized by high electrical conductivity (7 × 10t-3 Ω− cm−1) and low activation energy (Ea < 0.3 eV).

INVESTIGATION OF THE PROTON MOBILITY IN CSH(SO4)0.76(SEO4)0.24 CRYSTAL BY 1H NMR SPECTROSCOPY

Abstract Crystals of CsH(SO 4 ) 0.76 (SeO 4 ) 0.24 formulation were studied by 1 H NMR spectroscopy. The 1 H line-shape, the T 1 and T 2 relaxation times were determined as a function of temperature. The activation energies deduced from the temperature dependence of relaxation times were compared with the activation energy issued from conductivity measurements. The results obtained are discussed and supported by the Ngai model.

Phase transition and analysis of AC conductivity data of the (Cs)0.26(Rb)0.74H(SO4)0.89(SeO4)0.11 compound

Abstract The X-ray diffraction, vibrational and impedance spectroscopy studies of (Cs) 0.26 (Rb) 0.74 H(SO 4 ) 0.89 (SeO 4 ) 0.11 (CsRbHSSe) new solid solution are presented. The title compound undergo a superionic phase transition (SPT) at T=395 K . This transition was confirmed by an abrupt increase of conductivity. The bulk impedance parameters of CsRbHSSe, RbH(SO 4 ) 0.81 (SeO 4 ) 0.19 (RbHSSe) and CsH(SO 4 ) 0.76 (SeO 4 ) 0.24 (CsHSSe) were determined from an analysis of AC conductivity data measured in a wide temperature range. The charge carriers concentration in the samples investigated has been evaluated using the Almond–West formalism and shown to be independent of temperature.

Structural and Electrical Properties of the NH4DyHP3O10 Compound

Low-frequency dielectric dispersion phenomena in NH 4 DyHP 3 O 10 (ammonium dysprosium hydrogen phosphate type) polycrystalline compounds have been analyzed by impedance spectroscopy. The thermal evolution of the dielectric constant shows a phase transition at 305 K which is ferroelectric-paraelectric type. The ferroelectric phase is isotypic with KDyHP 3 O 10 and exhibits the triclinic symmetry P1 (at room temperature: a = 6.820 A, b = 7.583 A, c = 8.467 A, a = 104.396°, β = 103.545°, y = 90.349°, Z = 2). An empirical expression has been deduced for the complex permittivity e * (ω), e * (ω) = e∞ + e s -e∞/ 1 + (iω/ω 1 ) + σ 0 /e 0 ω [1 + (iω/ω 2 ) n ], where the (ω 1 , m) and (ω 2 , n) couples characterize the lattice and the charge carriers responses, respectively. This relation may be considered as a generalisation of the Cole-Cole dielectric expression. The influence of the charge carrier contribution on the dielectric permittivity at low frequency is significant, as shown when both lattice and carrier polarization mechanisms are simultaneously considered.