Naoaki Kuwata

Structure and ionic conductivity of rapidly quenched AgI-Ag2WO4 superionic conductor glasses

Abstract Silver ion conducting glasses composed of (AgI)x–(Ag2WO4)1−x (x=0.80–0.55) were prepared by a rapid melt quenching method. Their physical properties were investigated by X-ray, DSC, impedance and Ag-109 NMR measurements. The glass transition temperatures were in the range from 110°C to 187°C. The glasses show unusually high ionic conductivities of 2.5xa0×xa010−3 S/cm at x=0.55 and 2.3xa0×xa010−1 S/cm at x=0.80, which varied exponentially with increasing AgI content. Ag-109 NMR spectra also support the high mobility of silver ions in the glasses. Structures of the glasses were investigated by FTIR and W-L1 edge XANES. From these results it is concluded that the tungsten ions are octahedrally coordinated by oxygen ions as in crystalline Ag2WO4 and Ag26I18W4O16, which is quite different from the structure of AgI–Ag2MoO4 glasses.

Ag-109 NMR study of AgI-based glasses containing frozen α-AgI nanocrystals

Abstract Ag-109 MAS-NMR spectra of AgI-based glasses containing frozen α-AgI nanocrystals were measured extensively for AgI–Ag 2 O–M x O y (M x O y =B 2 O 3 , GeO 2 ) systems. The spectrum of α-AgI frozen glass composite observed at room temperature was separated into three components, which were ascribed to glass matrix, α-AgI nanocrystals and crystalline β-AgI. The temperature dependencies of the spectra suggest the formation of more α-AgI nanocrystals by heating.

New organic - inorganic hybrid superionic conductor glasses consisting of silver iodide and alkylbis-trimethylammonium diiodides

New organic - inorganic hybrid superionic conductor glasses were developed, which consisted of silver iodide (AgI) and alkylbis-trimethylammonium diiodides. The glasses were prepared from low-temperature molten salts of them by melt quenching method, which were confirmed in glassy state by X-ray diffraction (XRD), DSC and optical microscope observation. The ionic conductivity of these glasses are about 10 22 V 21 cm 21 at room temperature which is the best in the organic- inorganic hybrid superionic conductor glasses obtained so far. Ag-109 NMR spectra of the glasses showed a motionally narrowed peak at about 800 ppm regardless of their compositions, which is almost equal to the value of AgI crystals. These results are in good agreement with the prediction of the percolation model, where the silver cations are assumed to diffuse through the conduction channels of face-sharing iodide tetrahedra, which are randomly blocked by organic substances. q 2002 Published by Elsevier Science Ltd.

Frequency dependent conductivity of organic–inorganic mixed superionic conductor glasses

Abstract In order to detect local motion of mobile silver cations in organic–inorganic mixed glasses composed of AgI and alkylammonium iodides, their electrical conductivity at radio and microwave frequencies was measured in different compositions. Although their DC conductivity shows a clear transition from insulator to superionic conductor at AgI volume fraction φ ∼0.35, the high frequency value is continuous at the threshold. Details of frequency dependence were measured at room temperatures from DC to 10 GHz. Only a small dependence was seen in the high conducting glasses, however, the sample near the percolation threshold showed power-law dependence σ [ ω ]∼ ω n at low frequency whose slope n ∼0.6 and approaches to unity at high frequencies.