Synthesis, Crystal Structure and Ionic Conductivity of Ag₈I₂(CrO₄)₃

Abstract

Ag 8 I 2 (CrO 4 ) 3 has been synthesized by solid state reaction, starting from stoichiometric mixtures of Ag 2 O, AgI and Cr 2 O 3 , at elevated oxygen pressures. The compound crystallizes in the hexagonal space group P6 3 /m, with the unit cell dimensions a = 9.4474(4) Å, c = 10.2672(4) Å, γ = 120°, V = 793.61(6) Å 3 , and Z = 6. The crystal structure was solved by direct methods and refined, basing on single crystal diffraction data (815 independent reflections, R1 = 2.45 %). The structure is fully ordered. The CrO 4 2-anions are arranged in the mode of an hcp packing. Such a building principle is providing channels of face sharing octahedral voids. In the case of the title compound, there are three of such channels in the unit cell. Two of them accommodate two iodine atoms and one silver each, with iodine occupying the octahedral voids, and silver centering the triangular faces connecting the octahedra. Thus, for silver a trigonal bipyramidal coordination by three oxygen and two iodine ions result. In the third column of face sharing octahedra, silver is in the centre of the octahedra. The remaining silver atoms are located in the tetrahedral voids, between the CrO 4 2-anions. According to the results of impedance measurements, Ag 8 I 2 (CrO 4 ) 3 is a silver ion conductor. The compound shows an increase in the ionic conductivity in the temperature range from 25 to 175 °C, and has a silver ion conductivity of 6.5 X 10 -4 Ω -1 cm -1 at 30 °C. The activation energy for silver ion conduction is 0.21 eV, in the temperature range from 25 to 50 °. IntroductionFast-ion electrolytes based on Ag-containing solids have been of interest in that they often show high ionic conductivity already at room temperature [1,2]. The search for new silver-ion conductors continues, considering various chemical systems, which include halides, chalcogenides and others [3][4][5]. The most famous members in this class of electrolytes are AgI and RbAg 4 I 5 . These materials are characterized by their high ionic conductivities, comparable to those observed in molten salts [5][6][7]. RbAg 4 I 5 shows the highest ionic conductivity ever observed for a solid at ambient temperature (σ(i) = 0.27 Ω -1 cm -1 ) [8]. The structures of both, AgI and RbAg 4 I 5 , have been studied thoroughly, in particular with respect to the disorder of the cation partial structure [7]. Among the good silver ion conductors, there is a class of compounds with compositelike topologies, containing silver iodide, and silver oxyacid salts, like Ag 3 PO 4 , Ag 2 WO 4 , Ag 3 AsO 4 etc., at the same time [9][10][11][12][13][14][15][16]. The incorporation of silver ions in an immobile framework of complex oxoanions has proven to be an effective route to raise the silver ion conductivity. Recently, we expanded this field to composites containing AgI and silver selenates and tellurates, this way identifying Ag 3 ITeO 4 , Ag 4 I 2 SeO 4 and Ag 9 I 3 (SeO 4 ) 2 (IO 3 ) 2 as new silver solid electrolytes [17,18]. In the course of our structural investigation of crystalline an...

Crystal structure of silver carbonate iodide Ag10(CO3)3I4

“…The crystal structures of quaternary inorganic compounds composed of silver and iodide ions and oxyanionic groups, such as Ag 2 I(NO 3 ) 2 (Birnstock & Britton, 1970), Ag 16 I 12 P 2 O 7 (Garrett et al, 1982), Ag 5 IP 2 O 7 (Adams & Preusser, 1999), Ag 4 IPO 4 (Oleneva et al, 2008), Ag 8 (CrO 4 ) 3 I 2 (Pitzschke et al, 2009b), Ag 9 (GeO 4 ) 2 I (Pitzschke et al, 2009c), Ag 8 I 4 V 2 O 7 (Adams, 1996), Ag 13 (AsO 4 ) 3 I 4 (Pitzschke et al, 2009a), Ag 4 I 2 SeO 4 (Pitzschke et al, 2008a), Ag 3 ITeO 4 (Pitzschke et al, 2008a), Ag 9 I 3 (IO 3 ) 2 (SeO 4 ) 2 (Pitzschke et al, 2008b) and Ag 26 I 18 (WO 4 ) 4 (Chan & Geller, 1977) have been reported.…”

Reversible Property Switching, Thermoelectric Performance, and d10−d10 Interactions in Ag5Te2Cl

“…Silver(I) chalcogenide halides like Ag 3 S X (with X = Br, I), − Ag 5 Te 2 Cl, − or Ag 19 Te 6 Br 7 , and silver(I) polychalcogenide halides like Ag 10 Te 4 Br 3 , − Ag 23 Te 12 X ( X = Cl, Br), , or Ag 20 Te 10 BrI are mixed conducting materials with a high ion conductivity comparable with related compounds like Ag 7 Fe 3 ( X 2 O 7 ) 4 with ( X = P, As), Ag 8 I 2 (CrO 4 ) 3 , Ag 4 I 2 SeO 4 , or Ag 3 ITeO 4 in this field. Although all the above-mentioned polychalcogenides contain anionic structure units, capable of performing a Peierls-distortion in the solid state, the chalcogenide halides do not fulfill the structural requirements for such a partial covalent bonding in the anion substructure.…”

Painting and Direct Writing of Silver Nanostructures on Phosphate Glass with Electron Beam Irradiation

“…However, the rapid decomposition of the material in the presence of moisture makes its use as a substrate material impractical. Several silver oxyacid based compounds of the form AgI x (Ag y MO z ) 1− x where M = P, As, Se, Te, Cr, Mo, and W have been found to be ionic conductors and are significantly less reactive to moisture compared to RbAg 4 I 5 . In particular, the structure and tunability of the glass transition, activation energy, and ionic conductivity of (AgI) x (AgPO 3 ) 1− x glass mixtures have been well studied due to the wide transparent glass forming region from x = 0 to 0.6 .…”