On the microwave conductivity of α-AgI part I: The effect of sample preparation

Funke, K.; Gacs, A.; Schneider, Heidrun; Ansari, S.M.; Martinkat, N.; Roemer, H.; Unruh, H.‐G.

doi:10.1016/0167-2738(83)90030-9

Cited by 16 publications

(5 citation statements)

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“…The ionic conductivity of α -AgI was found to display no frequency dependence up to at least 40 GHz [38]. This implies that the mobile silver ions move so fast that any memory of individual movements is erased after a time which is the inverse of 2 π × 40 GHz, i.e.…”

Section: The Discovery and Extraordinary Properties Of Alpha Silver Imentioning

confidence: 99%

Solid State Ionics: from Michael Faraday to green energy—the European dimension

Funke¹

2013

Science and Technology of Advanced Materials

147

102

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Solid State Ionics has its roots essentially in Europe. First foundations were laid by Michael Faraday who discovered the solid electrolytes Ag2S and PbF2 and coined terms such as cation and anion, electrode and electrolyte. In the 19th and early 20th centuries, the main lines of development toward Solid State Ionics, pursued in Europe, concerned the linear laws of transport, structural analysis, disorder and entropy and the electrochemical storage and conversion of energy. Fundamental contributions were then made by Walther Nernst, who derived the Nernst equation and detected ionic conduction in heterovalently doped zirconia, which he utilized in his Nernst lamp. Another big step forward was the discovery of the extraordinary properties of alpha silver iodide in 1914. In the late 1920s and early 1930s, the concept of point defects was established by Yakov Il'ich Frenkel, Walter Schottky and Carl Wagner, including the development of point-defect thermodynamics by Schottky and Wagner. In terms of point defects, ionic (and electronic) transport in ionic crystals became easy to visualize. In an ‘evolving scheme of materials science’, point disorder precedes structural disorder, as displayed by the AgI-type solid electrolytes (and other ionic crystals), by ion-conducting glasses, polymer electrolytes and nano-composites. During the last few decades, much progress has been made in finding and investigating novel solid electrolytes and in using them for the preservation of our environment, in particular in advanced solid state battery systems, fuel cells and sensors. Since 1972, international conferences have been held in the field of Solid State Ionics, and the International Society for Solid State Ionics was founded at one of them, held at Garmisch-Partenkirchen, Germany, in 1987.

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Section: The Discovery and Extraordinary Properties Of Alpha Silver Imentioning

confidence: 99%

Solid State Ionics: from Michael Faraday to green energy—the European dimension

Funke¹

2013

Science and Technology of Advanced Materials

147

102

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“…Apparently, many of those microstructures were still present after the β to α phase transformation, then affecting (reducing) the measured Joule losses. In fact, it could be shown that they acted like a close-packed arrangement of capacitors in the α-AgI sample, thus producing the measured dispersion [83].…”

mentioning

confidence: 93%

“…The 'microwave puzzle' could then be solved in a joint effort to clarify the contradiction between the different microwave data. In two common papers [83,84], experimental evidence was reported for the conclusion that the discrepancy in the spectra was entirely due to the different ways of sample preparation, the applied microwave techniques being inherently sound.…”

mentioning

confidence: 99%

“…The inverse transformation being transcendental, it could not be achieved with the help of closed equations. Therefore, transformation charts (|t| , |r|) ⇔ ( σ , ε ) had to be prepared for each frequency in order to find the proper values of σ and ε [83]. Fig.…”

mentioning

confidence: 99%

“…16Ionic conductivity of α-AgI at 250 °C, measured at microwave, millimeter-wave and far-infrared frequencies. For ν ≤ 40 GHz, see Refs [81][82][83][84][85]…”

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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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