A. Kabadou

Crystal structure and dielectric measurements of mixed caesium-ammonium mercury chloride : Cs0.7(NH4)0.3HgCl3

The title compound crystallises in the space group P3 2 and has the unit cell dimensions a = 13.295(11) A, c = 9.419(8) A, V = 1441.82(2), Z = 9, D exp = 4.17, D caic = 4.153. The structure at room temperature is considered as distorted perovskite tentatively with R = 0.057 and WR 2 = 0.153 for 700 observed reflections. The dielectric permittivity measured in the frequency and temperatures ranges 10 3 to 10 6 Hz and 307 to 613 K, respectively, reveals a transition at T = 449 K. Transport properties in this material appear to be due to the high mobility of NH 4 + in the tunnels.

Electrical properties of the mixed compound K2.51(NH4)1.49Hg3Cl10.2H2O

Abstract Crystals of K2.51(NH4)1.49Hg3Cl10.2H2O undergo two phase transitions at T1=395 and T2=424 K. phase I—(395 K)→phase II—(424 K)→phase III These transitions have been detected by differential scanning calorimetry, impedance and modulus spectroscopy techniques. The first transition at T=395 K is related to NH4+ reorientation and H+ diffusion. The conductivity relaxation parameters associated with some K+/NH4+ and H+ conduction have been determined from an analysis of the M″/M″ max spectra measured in a wide temperature range. Transport properties in this material appear to be due to an K+/NH4+ and H+ ions hopping mechanism.

Structural and vibrational studies of mixed potassium-ammonium chloromercurate(II) dihydrates K2.51(NH4)1.49Hg3Cl10.2H2O

Abstract The crystal structure of K 2.51 (NH 4 ) 1.49 Hg 3 Cl 10 .2H 2 0 has been determined by X-Ray single-crystal analysis. The title compound crystallises in the space group Pmcm and has the unit cell dimensions a =4.5110(15)A, b =14.489(2), c =16.074(4) A, Z =2. The refinement converged to R =0.03 8 and WR 2 =0.105. The structure may be described as consisting of alternating layers and chains built up from HgCl 6 octahedra. The ammonium groups (or K + ) and water molecules are located between the chains and layers. IR and RAMAN spectroscopic studies were performed to confirm results of the radiocristallographic method.

DSC, X-Ray diffraction and Raman studies in the compound K2.51(NH4)1.49Hg3Cl10.2H2O

Abstract The mixed compound potassium–ammonium mercurate exhibits two phase transitions at T1=395 K and T2=424 K: phase I−(395 K)→phase II−(424 K)→phase III These transitions have been detected by differential scanning calorimetry, X-ray diffraction and Raman scattering on polycrystalline samples of K2.51(NH4)1.49Hg3Cl10.2H2O. The room temperature phase has space group Pmcm (a=4.511(4) A, b=14.489(9) A and c=16.074(12) A). Phase II is disordered and exhibits orthorhombic symmetry (a=4.500(1) A, b=17.758(5) A and c=22.895(5) A). Hydrogen bonding, the nature and the degree of structure (dis)order and the mechanisms of the phase transitions are discussed. The NH4+ ions show an important orientation disorder at the high temperatures.

Rietveld refinement of the gadolinium strontium oxide SrGd 2 O 4

Powder X-ray diffraction (XRD) data were collected for a new phase of SrGd 2 O 4 . Analysis using the Rietveld method was carried out and it was found that the sample crystallizes in the orthorhombic symmetry with CaFe 2 O 4 related structure. The lattice parameters are found to be a =12.0521(2) A, b =10.1327(2) A, c =3.4757(4) A and Z =4. For X-ray data R F =4.9%, R B =7.6%, R P =8.1% and χ 2 =1.51. The structure can be described as an assembly of bioctahedron [Gd 2 O 10 ] which are linked together by O 2− anions and of dodecahedron of SrO 8 .

X-ray powder diffraction study of Sn0.59Ti0.41Te3O8

The crystal structure of titanium-tin tellurium oxide Sn 0.59 Ti 0.41 Te 3 O 8 has been determined using X-ray powder diffraction techniques. At room temperature, the title compound crystallizes in cubic space group Ia -3, with lattice parameter a =11.05515(6) A. Rietveld refinement of the structure led to final confidence factors R p =0.0395 and R wp =0.0577. The structure of Sn 0.59 Ti 0.41 Te 3 O 8 consists of isolated Ti/SnO 6 -octahedra slightly deformed in the a direction. The TeO 4 E [ E =lone pair of Te(IV) atoms] groups are located between the octahedra ensuring the stability of the structure by Ti/Sn-O-Te bonding contacts. Only one peak in thermal behavior was detected for this compound at 488 K by differential scanning calorimetry experiment. An IR spectroscopic study is employed as a means to obtain preliminary structural information and shows the presence of the Ti/SnO 6 and TeO 4 E groups. This result is later confirmed by X-ray diffraction studies.

X-ray powder diffraction study of cesium ammonium hexachlorotellurate [Cs 0.86 (NH 4 ) 0.14 ] 2 TeCl 6

The crystal structure of cesium ammonium hexachlorotellurate [Cs 0.86 (NH 4 ) 0.14 ] 2 TeCl 6 , has been determined using X-ray powder diffraction techniques. At room temperature, the title compound crystallizes in the cubic space group F m 3 m , with a lattice parameter a =10.470(17) A. The Rietveld refinement of the structure led to final confidence factors R p =0.0338 and R w p =0.0487. The structure of [Cs 0.86 (NH 4 ) 0.14 ] 2 TeCl 6 belongs to the large family of K 2 PtCl 6 -related structures. The H atoms of the ammonium group are orientated with its apex toward Te atoms as seen in the related compound (NH 4 ) 2 SiF 6 . An IR spectroscopic study was performed to confirm the results of the diffraction method, notably concerning the presence of the ammonium group.

Crystal structure, phase transitions and dielectric properties of the mixed compound [Cs0.92(NH4)0.08]2HgBr4

Abstract The crystal structure of [Cs 0.92 (NH 4 ) 0.08 ] 2 HgBr 4 was determined by three-dimensional X-ray diffraction analysis. The space group is Pnma with a = 10.210(2), b = 7.928(1), c = 13.883(1)A and Z = 4 at 293K. The structure was refined to R = 0.067. The distribution of atoms can be described as isolated HgBr 4 2− tetrahedra , Cs + and NH 4 + cations. The main feature of this structure is the coexistence of two types of bonds: Cs +  Br − ionic bonds and NH…Br hydrogen bonds ensuring the cohesion of the crystal. Dicaesium-ammonium tetrabromomercurate exhibits three phase transitions at T 1 = 237K, T 2 = 244K and T 3 = 513K. These transitions were detected by differential scanning calorimetry and analysed by dielectric measurements using the impedance and modulus spectroscopy techniques. The phase change at high temperature is related with the orientational disorder of NH 4 + cations. Transport properties in this material appear to be due to a H + ion hopping mechanism.

Crystal Growth and Structural Characterization of a Thiocyanato-Bridged Copper(I/II) Mixed-Valence Coordination Polymer

A new mixed-valence coordination polymer [Cu3(SCN)4(DMSO)2]n (SCN– = thiocyanato and DMSO = dimethyl sulfoxide) was prepared and characterized by single crystal X-ray diffraction method. The in situ formation of thiocyanate during the synthesis induces reduction of a part of Cu(II) to Cu(I). The three-dimensional structure of the binuclear thiocyanato bridged compound provided an example of pseudohalide materials containing two different environments for both copper centers.

Structural, thermal behaviour and vibrational study of a new mixed cesium–ammonium tellurate

AbstractSynthesis, crystal structure, thermal characterization, FTIR and Raman measurements are given for a new mixed compound cesium–ammonium tellurate. X-ray study showed that the [Cs0.92(NH4)0.08]2TeCl4Br2 compound crystallizes in the tetragonal space group P4/mnc, with a = 7.452 (1) Å, c = 10.544 (3) Å and Z = 2. The refinement converged at room temperature to Rp = 0.093 and Rwp = 0.076. The structure is considered as isolated octahedral TeCl4Br