Roling, Martiny, and Murugavel Reply:

Roling, Bernhard; Martiny, C.; Murugavel, Sevi

doi:10.1103/physrevlett.89.079602

Cited by 38 publications

(66 citation statements)

References 2 publications

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] The frequency dependent conductivity is characterized by an approximate power law behavior ͑͒ ϰ s in which s is observed to be 0 Ͻ s ഛ 1. By rescaling the frequency dependent conductivity at various temperatures following Taylor-Isard scaling, master curves can be created that appear to be independent of the actual disordered material.…”

Section: Introductionmentioning

confidence: 99%

Universality of ac conduction for generalized space-charge transport in ordered solids

2005

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Section: Introductionmentioning

confidence: 99%

Universality of ac conduction for generalized space-charge transport in ordered solids

2005

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“…9 The properties of the NCL are lesser known compared with the dc conductivity at room temperature in ionic conductors, and, at present there is an ongoing debate on the origin of the NCL. 8,10,11 On the other hand, it was pointed out that superionic conductors, characterized by their exceptional high dc conductivity at room temperature, show also the highest values of the near constant loss at low temperatures. 9 We show in this work that there exists a strong correlation, for a variety of ionic conductors, between the magnitude of the NCL observed at low temperatures and the dc conductivity and its activation energy at roomtemperature.…”

Section: ͑1͒mentioning

confidence: 99%

Correlation between ion hopping conductivity and near constant loss in ionic conductors

2004

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For ionic conductivity relaxation in ionically conducting materials we predict in the framework of the coupling model that the magnitude of the ubiquitous near constant loss correlates with the activation energy E a for independent ion hopping. Using experimental data of a variety of ionic conductors, this correlation has been borne out. The model also explains the observed correlation between the magnitude of the near constant loss and the value of the dc conductivity at room temperature, as well as the temperature dependence for the near constant loss. DOI: 10.1103/PhysRevB.69.134303 PACS number͑s͒: 66.30.Hs Due to their technological importance in state-of-the-art batteries, sensors, and other devices, there is an increasing research activity on ion-conducting materials during last decades. 1,2 The challenge is to clarify the mechanism that limits the mobility of ions and consequently break new grounds for practical applications. Therefore, efforts have been focused on the dynamics of ionic hopping transport at low frequencies and near room temperature. 3,4 Only recently, the ac conductivity of ionic conductors at high frequencies and low temperatures has attracted the attention of workers in the field. 5-8 A ubiquitous nearly linear frequency dependent term Ј( )ϷA o 1Ϫ␣ with ␣ almost zero and o the permittivity of a vacuum, becomes the dominant contribution in the ac conductivity at sufficiently high frequencies or low enough temperatures. This term is equivalent to a nearly frequency independent dielectric loss, ͑1͒and naturally this contribution is known as the near constant loss ͑NCL͒. 9 The properties of the NCL are lesser known compared with the dc conductivity at room temperature in ionic conductors, and, at present there is an ongoing debate on the origin of the NCL. 8,10,11 On the other hand, it was pointed out that superionic conductors, characterized by their exceptional high dc conductivity at room temperature, show also the highest values of the near constant loss at low temperatures. 9 We show in this work that there exists a strong correlation, for a variety of ionic conductors, between the magnitude of the NCL observed at low temperatures and the dc conductivity and its activation energy at roomtemperature. Therefore, understanding the origin of the NCL also may help to improve the understanding of the dynamics of ionic conductivity and the factors limiting the roomtemperature dc conductivity in ionic conductors. 12 The NCL appears at higher frequencies than the ion hopping ac conductivity, hop Ј ( ). The latter is assumed by some workers to be represented by the Jonscher expression 13where n J is a fractional exponent, 0 is the dc conductivity, and p a characteristic relaxation frequency. Both 0 and p are found to be thermally activated with about the same activation energy E . Alternatively, in terms of the electric modulus, 14 the ion hopping ac conductivity is also well described by the one-sided Fourier transform,of the time derivative of a stretched exponential function ⌽(t)ϭexp͓Ϫ(t/...

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“…Different models for ionic conduction in solids have recently explained this experimental finding based on the NCL behavior arising from the cage decay or caged ion dynamics, which result in a logarithmic time dependence of the mean-square displacement and thus in a linear frequency dependence of the ac conductivity. 14,15 However, there is still some debate on the origin of the NCL in ionic conductors, [16][17][18][19][20] arising most probably from the scarceness of accurate experimental ac conductivity data of ionic conductors showing a linear frequency dependence in a broad temperature and frequency range, since the dielectric loss value, A, and consequently tan ␦ values ͑tan ␦ = Љ/ Ј͒ are usually very low in the NCL regime. In particular, it is not easy to obtain enough resolution in measuring the ac conductivity ͑dielectric loss͒ values to determine precisely the crossover to the NCL behavior by changing temperature or frequency.…”

Section: ͑1͒mentioning

confidence: 99%

Crossover to nearly constant loss in ac conductivity of highly disordered pyrochlore-type ionic conductors

Díaz-Guillén

Díaz-Guillén²,

Fuentes³

et al. 2010

Phys. Rev. B

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We report on ac conductivity measurements of oxide ion conductors with composition Gd 2 ͑Zr y Ti 1−y ͒ 2 O 7 , at temperatures between 170 and 500 K and in the frequency range 1 Hz-3 MHz, and show that a crossover from a sublinear power law to a linear frequency dependence ͑or nearly constant loss behavior͒ in the ac conductivity can be clearly observed in a wide temperature range. This crossover is found to be thermally activated, and its activation energy E NCL to be much lower than the activation energy E dc for the dc conductivity. We also found that the values of E NCL are almost independent of composition, and therefore of the concentration of mobile oxygen vacancies, unlike those of E dc . Moreover, for each composition, the values of E NCL = 0.67Ϯ 0.04 are very similar to those estimated for the energy barrier for the ions to leave their cages, E a = 0.69Ϯ 0.05. These results support that the nearly constant loss behavior, ubiquitous in ionic conductors, is originated from caged ion dynamics. ͑1͒where A is a constant with weak temperature dependence 3,4 and 0 the permittivity of vacuum. The term "nearly constant loss" is due to the corresponding nearly frequency independent behavior of the dielectric loss NCL Љ ͑ ͒ = NCL Ј ͑ ͒ / 0 Ϸ A. Despite the great interest in ionically conducting materials during the last decades, most experimental and theoretical work has been devoted to understand the dynamics of mobile ions at much higher temperatures, when the ions eventually give rise to a long-range charge transport characterized by a frequency-independent conductivity dc , and an NCL contribution to the ac conductivity is usually absent from experimental data. Therefore, until recently, conductivity data showing an NCL behavior were scarce in the literature. [5][6][7][8][9] It was in 1999 that Ngai first pointed out the correlation existing between the high values of the dc conductivity dc and the high values of the NCL magnitude A found in superionic conductors with technological interest for their application as electrolytes in solid-state batteries and fuel cells. 4,10 Based on this fact and on several other properties of the NCL experimentally observed in ionic conductors, Ngai proposed its physical origin might be due to the displacement of the mobile ions in their local vibrational motion at low temperature and/or high frequency. León et al. [11][12][13] later found experimental evidence, in two different lithium ionic conductors, consistent with such an origin for the NCL contribution to the ac conductivity. From the measurement of the crossover temperature ͑frequency͒ at which the NCL behavior terminates at different fixed frequencies ͑temperatures͒, they were able to determine an activation energy E NCL for the crossover which was found to be much lower than the activation energy E dc for the dc conductivity, governed by ion hopping dynamics, and in fact E NCL was found to be similar to the value estimated for the energy barrier for the ions to leave their cages, E a . Different models for ionic co...

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Roling, Martiny, and Murugavel Reply:

Cited by 38 publications

References 2 publications

Universality of ac conduction for generalized space-charge transport in ordered solids

Universality of ac conduction for generalized space-charge transport in ordered solids

Correlation between ion hopping conductivity and near constant loss in ionic conductors

Crossover to nearly constant loss in ac conductivity of highly disordered pyrochlore-type ionic conductors

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