Impedance spectroscopy study of phase transitions to ionic and superionic conductivity states in Ag₂S and Ag₂Se

Abstract

The percolation threshold (PT) temperatures Tc1,c2 of two non‐equivalent Ag+1,2 ions in Ag2S and Ag2Se lattices were determined from the temperature dependence of low‐frequency (25‐106Hz) impedance spectroscopy measurements. At PT temperatures Tc1≈200 K and Tc2≈ 334 K, an abrupt increase of the dielectric function ε1(ω) of Ag2Se crystal from a very large negative value, ε1 ≈‐109, to a very large positive value ε1≈ 106 was observed, which is assumed to result from the dipole relaxation. The strong peaks of the dielectric losses ε2(ω), tgδ(ω) and impedance Z in Ag2Se were also determined at Tc1,c2. Two significant peaks in ε1(ω), ε2(ω)and tgδ(ω) were observed at Tc1≈ 312‐320 K. and Tc2≈ 380‐430 K in the temperature dependences of these parameters. The measured parameters decreased significantly with increasing frequency, confirming the long relaxation times. The drastic decrease at T > 430 K of ε1from a very large positive value 109to a very large negative one ‐108 is in accordance with infrared (IR) ellipsometry measurements; this indicates that electrons of Ag+‐ ions are ionized because of the high dielectric function screening of lattice sites before the known β→α structural phase transition from monoclinic to a body‐centered cubic (bcc) structure. In addition, the activation energies of Ag+1,2 ions were estimated for Ag2S and Ag2Se crystals. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Impedancemetry of Ag-=SUB=-2-=/SUB=-S nanocrystallites embedded in nanoporous glasses

“…Interesting results of superionics study are observed using dielectric spectroscopy (DS) method, that is often called impedance spectroscopy in literature [6]. This method is used for studying the temperature dependencies of functional features of frequency dependencies of dielectric loss tangent and dielectric relaxators distributions by relaxation time (Gavrilyak−Negami function).…”

First‐principles lattice dynamics and Raman scattering in ionic conductor β‐Ag2S

“…Phase transitions and their influence on the electrical conductivity in Ag 2 S have been extensively studied experimentally in Ref. .…”

Импедансметрия нанокристаллитов Ag-=SUB=-2-=/SUB=-S, внедренных в нанопористые стекла

“…Интересные результаты исследований супериоников получены с помощью метода диэлектрической спектроскопии (ДС), который в литературе часто называют импедансной спектроскопией [6]. Этим методом исследуются температурные зависимости особенностей функций частотных зависимостей тангенса угла диэлектрических потерь и распределения диэлектрических релаксаторов по временам релаксации (функции Гавриляка−Негами).…”