Non-periodic local motion of silver ions in ßAg3SI from far-infrared conductivity measurements

Gras, B.; Funke, K.

doi:10.1016/0167-2738(81)90037-0

Cited by 13 publications

(4 citation statements)

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“…The observed increase of σ(ω) must correspond to a negative tail of the velocity correlation function and is thus indicative of some fast forward-backward motion, suggesting spatial localization. Similar features had been detected in both α-RbAg 4 I 5 [88,89] and β-Ag 3 SI [91,92]. However, the ionic movements causing them had turned out to be quite different.…”

supporting

confidence: 67%

“…However, the ionic movements causing them had turned out to be quite different. While in the case of α-RbAg 4 I 5 there was evidence for correlated forwardbackward hops between tetrahedral sites [89], the effect detected in β-Ag 3 SI was successfully described in terms of a Brownian motion performed by the silver ions in flat potentials [91,92]. It remains to be seen which explanation appears more appropriate in α-AgI, see below.…”

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confidence: 99%

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Marking the Centennial of the Discovery of Alpha Silver Iodide

Funke

2016

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In 2014, present-day scientists had the opportunity of marking the centennial of a discovery that triggered the development of a new field of research, which is now called Solid State Ionics.In their 1914 paper, Carl Tubandt and Erich Lorenz reported on the extraordinary properties of the alpha phase of silver iodide. Although α-AgI was a crystalline material, it resembled a molten salt with regard to the liquid-like value and weak temperature dependence of its ionic conductivity. With their transference measurements, Tubandt and Lorenz proved that the electric current in α-AgI was completely carried by the silver ions, while the iodide ions formed a rigid lattice. Up to the present day, α-AgI has been considered the fast ion conductor par excellence.In the mid-1930s, L.W. Strock was the first to use x-ray diffraction to investigate the crystal structure of α-AgI. The anion sublattice was found to be body centered cubic, but the arrangement of the silver ions remained a puzzling question. On the one hand, Strock could assign a large number of possible crystallographic sites to them. On the other hand, the state of the silver ions appeared to be rather ‘quasi-molten’ or ‘liquid-like’. This structural puzzle was resolved in 1977, when Cava, Reidinger and Wuensch used the results of a single-crystal neutron-diffraction experiment to construct contour plots for the probability density of the silver ions in α-AgI, which turned out to have broad maxima at the tetrahedral voids of the anion structure, with saddle points between them.A number of novel experimental approaches toward a better understanding of the ion dynamics in α-AgI were suggested by Wilhelm Jost in the 1960s and 1970s. These included high-accuracy specific heat measurements, measurements of the ionic conductivity in the microwave and far-infrared frequency regimes, and quasielastic neutron scattering. The results of the ensuing experiments, involving the present author, did not always provide immediate answers to the long-standing open questions, but rather created new puzzles instead. In this Chapter, an overview is given of the essential steps that were taken in experiment and modeling, eventually leading to the emergence of a self-consistent picture of the structure and dynamics of the mobile silver ions in α-AgI. Notably, that picture included both solid-like and liquid-like aspects. Strictly speaking, however, either category, ‘solid’ and ‘liquid’, had to be considered inappropriate for characterizing the actual state of the silver-ion sublattice.Recently, the transition to a more solid-like behavior of the mobile silver ions was observed in low-temperature α-AgI, which could be stabilized by confinement in glass, as first shown by Tatsumisago et al. Far below the regular phase transition temperature, 147 °C, measurements were performed of the frequency-dependent conductivity of α-AgI, yielding relevant information on the silver-ion dynamics. A conjecture put forward by Jost in 1937 could thus be corroborated by the present author and his coworkers. Below 147 °C, the ‘liquid-like’ activation energy for ionic transport was found to be replaced by a larger, more ‘solid-like’ value, although the anion structure and, therefore, the barriers for elementary displacements of the cations remained essentially unchanged. The underlying mechanism is sketched at the end of the Chapter.

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Marking the Centennial of the Discovery of Alpha Silver Iodide

Funke

2016

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“…4. Ag 3 SI was subject to intensive studies of the non-periodic local motion of the cations and anions [59] and intensive experiments were performed to tune their physical properties by partial and full ion exchange. These results are discussed later on in this section.…”

Section: Ionic Chalcogen Substructure -Coinage Metal Chalcogenide Halmentioning

confidence: 99%

Silver(I)-(poly)chalcogenide Halides – Ion and Electron High Potentials

Nilges¹,

Bawohl

Osters

et al. 2010

Zeitschrift Für Physikalische Chemie

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Materials with high dynamics in the solid state are of potential interest in semiconductor science and for a great variety of energy applications. In most of the cases the majority of physical properties of such compounds are directly related to their electronic structure. Optimization of properties is therefore correlated with direct or indirect control of this parameter. Compounds with highly mobile ions like the coinage metal cations and the heavy chalcogenide anions can easily be modified chemically or physically to fine tune their electronic structures. The range of adjustable properties lasts from ion conductivity, magneto resistance, thermoelectricity to a reversible redox-driven switch of semiconductivity. Today, the strong demand on clean energy production, the efficient energy transport and energy storage is a major goal for present and oncoming generations. Stable, mixed-conducting materials will play a major role in this process. The ongoing development of coinage metal chalcogenide halides during the last 50 years reflects the fundamental interest in this field. Many interesting and sometimes unexpected properties have been determined recently which substantiates the great potential of this class of materials. Especially the new class of coinage metal polychalcogenide halides is of potential interest due to their drastic modulations of physical properties driven by a fundamental tuning of its electronic structures. Thermopower and thermal diffusivity, two major properties to tune thermoelectricity can be varied in such a way that drastic changes can be addressed in very small temperature ranges close to room temperature. Herein we report on the recent progress of polychalcogenide and chalcogenide halides with the mobile d 10 ions Ag and Cu putting the main focus on silver compounds.

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“…Locally, for instance, they may participate in the vibratory lattice modes, act as Einstein-type oscillators, or behave like Brownian particles confined to restricted regions of space. Examples of the two latter kinds of motion are a-RbAg415 [l] and ,B-Ag,Si [2], respectively.…”

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confidence: 99%

Cooperative Localized Hopping in β-AgI

Shukla¹,

Funke²

1989

Europhys. Lett.

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The ionic conductivity of p-AgI has been measured at frequencies from 1 kHz to 2.6 GHz, at different temperatures. A marked increase of the conductivity is observed at about 1 MHz. The spectra are interpreted in terms of localized hopping processes of the silver ions, performed between neighbouring tetrahedral sites. From the spectra it is concluded that these processes are largely cooperative in character.

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Non-periodic local motion of silver ions in ßAg3SI from far-infrared conductivity measurements

Cited by 13 publications

References 6 publications

Marking the Centennial of the Discovery of Alpha Silver Iodide

Marking the Centennial of the Discovery of Alpha Silver Iodide

Silver(I)-(poly)chalcogenide Halides – Ion and Electron High Potentials

Cooperative Localized Hopping in β-AgI

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