M. Gargouri

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.

NMR study of the proton mobility in RbH(SO4)0.81(SeO4)0.19 protonic conductor

Abstract Crystals of RbH(SO4)0.81(SeO4)0.19 formulation are studied by 1H NMR spectroscopy. The 1H line-shape, the line width and the T1 and T2 relaxation times are determined as a function of temperature. The activation energies deduced from the temperature dependence of line width and relaxation times are compared with the activation energy issued from conductivity measurements by impedance spectroscopy. The results obtained are discussed and supported by the help of the Ngai model.

Structural and Vibrational Study of (NH4)3H(SO4)1.42(SeO4)0.58 Mixed Crystals

At room temperature (T = 293(2) K) (NH 4 ) 3 H(SO 4 ) 1.42 (SeO 4 ) 0.58 (NHSSe) M m = 274.34 g possesses a monoclinic structure with space group Cc. The unit cell parameters are: a = 15.564(6) A, b = 5.9180(6) A, c = 10.275(2) A, β = 102.09(2)°, V = 925.4(4) A, Z = 4, D x = 1.97 g/cm 3 . The structure was determined with R = 0.0529 and wR2 = 0.1373 for 826 observed reflections. The Raman and infrared spectra at room temperature were investigated in the frequency ranges 10 to 1300 cm -1 and 400 to 1600 cm -1 , respectively. The assignment of most of the bands is given. We note for this compound two kinds of disorder to be expected: a statistical or dynamic disorder of the acidic proton O-H-O hydrogen bond and another one which is connected with a reorientational motion of NH 4 + ions.

Structural phase transitions and vibrational study of CsH(SO4)0.76(SeO4)0.24

CSH(SO 4 ) 0.76 (SeO 4 ) 0.24 , M m = 241.2, single crystals were grown and appear to be isomorphous with CsHSeO 4 . The space group is P2 1 /a, the lattice constants are: a = 7.8340(10) A, b = 8.2147(6) A, c = 7.4440(10) A, β = 110.910(10)°, V = 447.50(9) A 3 , Z = 4, D x = 3.582 Mg m -3 , λ (MoK α ) = 0.71069 A, μ(MoK α ) = 10.269 mm -1 . F(000) = 818, T = 293(2) K (room temperature phase), R = 0.023 and wR = 0.0563 for 883 observed reflections. The hydrogen sulphate or hydrogen selenate groups are connected by hydrogen bonds. The separated chains of asymmetric hydrogen bonds run parallel to the c-axis. The O-H...O distance utilized in the hydrogen bonding is 2.608 A which is 2.603 A for CsHSeO 4 . Mixed cesium hydrogen sulphate selenate CsH(SO 4 ) 0.76 (SeO 4 ) 0.24 undergoes two phase transitions at T = 333 and 408 K. The values of the enthalpies are 2.02 and 4.37 kJ/mol, respectively.

Structural and vibrational study of a new protonic conductor (Cs)0.26(Rb)0.74H(SO4)0.89(SeO4)0.11

Abstract The crystal structure of (Cs) 0.26 (Rb) 0.74 H(SO 4 ) 0.89 (SeO 4 ) 0.11 (CsRbHSSe) has been determined by X-ray single-crystal analysis. This compound crystallizes in the space group Pc with unit cell dimensions a=14.733(4) A , b=4.6437(9) A , c=15.102(4) A , β =120.94(3)°, and Z =8. The refinement converged to R =0.0391 and wR 2 =0.0964. The mixed compound CsRbHSSe is a chain-based structure. The Cs + and Rb + cations are intercalated between chains of HBO 4 − (B=S, Se) groups linked with O–H⋯O hydrogen-bonding. CsRbHSSe presents a new type of structural arrangement different from RbH(SO 4 ) 0.81 (SeO 4 ) 0.19 (RbHSSe) and CsH(SO 4 ) 0.76 (SeO 4 ) 0.24 (CsHSSe). Infrared (IR) and Raman spectroscopic studies were performed to confirm results of the radiocrystallographic method.

Conductivity and structural studies of new mixed potassium hydrogeno-sulphate selenate KH(SO4)0.8 (SeO4)0.2

Single crystals and polycrystalline samples of KH(SO 4 ) 0.8 (SeO 4 ) 0.2 were obtained by slow evaporation at 300 K. The samples were characterized by X-ray diffraction, examined by Raman vibrational spectroscopy and impedance spectroscopy technique. At high temperatures, no phase transition leading to a superionic phase was found. KH(SO 4 ) 0.8 (SeO 4 ) 0.2 is characterized by a medium conductivity σ 3 x 10 -8 Ω -1 cm -1 and an activation energy E a m 0.5 eV.