Is there a mixed alkali effect in the low temperature ac conductivity of glasses?

Jain, Himanshu; Lu, Xiangdong

doi:10.1016/0022-3093(95)00601-x

Cited by 51 publications

(24 citation statements)

References 13 publications

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“…The existence of NCL in glassy ionic conductors is well known. Evidences for its existence was suggested repeatedly over the span of several decades [1][2][3][4][5][6][7][8][9][10][11][12] and it is now considered to be a universal characteristic of ionic conductors, 13,14 although till now there are only a few investigations of its properties. [11][12][13][14][15][16][17][18][19] This NCL contribution appears at higher frequency than the ion hopping ac conductivity hop Ј ( ).…”

Section: ͑2͒mentioning

confidence: 99%

Cage decay, near constant loss, and crossover to cooperative ion motion in ionic conductors: Insight from experimental data

2002

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Experimental frequency-dependent conductivity relaxation spectra of a number of molten, glassy, and crystalline ionic conductors that show both the presence of the near constant loss ͑NCL͒ and the cooperative ion hopping contribution are analyzed. On decreasing frequency, the NCL appears first but terminates at some frequency x1 . At still a lower frequency x2 the cooperative ion hopping dispersion takes over. The independent ion hopping frequency 0 of the coupling model is calculated from the parameters characterizing the cooperative ion hopping dispersion. It is found for all ionic conductors that x1 ӷ 0 , and 0 always fall inside the frequency region x1 Ͼ Ͼ x2 . The empirical results leads to a qualitative theory for the origin of the NCL, which gives physical meanings of the two crossover frequencies x1 and x2 , as well as explaining the role of the independent hopping frequency 0 , in determining them. The weak temperature dependence of the NCL has been recaptured by the qualitative theory. An improved understanding is gained of the evolution of the ion dynamics from early times when the cages decay very slowly with time, giving rise to the near constant loss, to long times when ions move cooperatively, leading finally to dc conductivity.

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Section: ͑2͒mentioning

confidence: 99%

Cage decay, near constant loss, and crossover to cooperative ion motion in ionic conductors: Insight from experimental data

2002

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“…͑1͒ originates from a migration of ions by hopping between neighboring potential wells, which eventually gives rise to a dc conductivity at the lowest frequencies. Interestingly, it is usually assumed in the literature 2,[21][22][23][24][25][26] that the Jonscher conductivity and the linear frequency term ͑or NCL͒ are additive contributions, and that the total ac conductivity can be described by the so-called augmented Jonscher form…”

Section: ͑1͒mentioning

confidence: 99%

Crossover from ionic hopping to nearly constant loss in the fast ionic conductorLi0.18La0.61TiO
Rivera-Calzada
¹
,
Yebra
²
,
Sanz
³

et al. 2002
Phys. Rev. B
39
3
22
0
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Electrical conductivity measurements of the fast ionic conductor Li 0.18 La 0.61 TiO 3 have been conducted at temperatures ranging from 8 to 300 K and frequencies between 20 Hz and 5 MHz. A detailed analysis of the ac conductivity shows the existence of a crossover between two different regimes. At high temperatures and/or low frequencies correlated ion hopping is responsible for a power-law frequency dependent and thermally activated ac conductivity. On the other hand, at sufficiently low temperatures and/or high frequencies, the ions do not have enough thermal energy or time to hop between neighboring sites, and remain caged. The ac conductivity is then characterized by a linear frequency dependence ͑i.e., the equivalent of a nearly constant loss͒ and by a weak exponential temperature dependence of the form exp(T/T 0 ). A crossover between the two regimes is found, which is thermally activated with an activation energy Eϭ0.17 eV, significantly lower than that observed for the dc conductivity, E ϭ0.4 eV. From this result, it is shown that the so-called ''augmented Jonscher expression'' fails to describe the ac conductivity in the whole frequency and temperature ranges. All these findings suggest that the nearly constant loss originates from electrical loss occurring during the time regime while the ion is still confined in the potential-energy minimum. Further, it is proposed that the loss mechanism involves some type of process where the potential-energy minimum relaxes in time on a time scale much shorter than the ionic hopping time scale. At longer times, as soon as the ion has significant probability of being thermally activated out of the potential well, the nearly constant loss terminates and correlated ion hopping becomes the only contribution to the ac conductivity.

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“…The left side is the regime when enough thermal energy is available, and mobile ions start to jump over their own sites and subsequently adjacent sites, giving an additional contribution to the ac conductivity, which overshadows the linear frequency term. Moreover, and interestingly enough, we want to emphasize that this result is at odds with the usual assumption [15][16][17][18][19][20][21][22] that the total ac conductivity in ionic conductors can be described by the augmented Jonscher's expression,…”

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confidence: 96%

“…Experimentally, A is not thermally activated and has temperature dependence much milder than s 0 or v p [18][19][20]. Partial replacement by alkali ions of a different kind has the effect of reducing the NCL [3,18,21,22], but the reduction in A is much smaller than the decrease in s 0 due to the well-known mixed alkali effect [3]. From these facts, it has been very recently proposed [18] that local vibrational relaxation reflected in the mean-square displacement of ions could be the origin of the constant loss in ionic conductors.…”

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confidence: 99%

Origin of Constant Loss in Ionic Conductors

et al. 2001

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We have analyzed the constant loss contribution to the ac conductivity in the frequency range 10 Hz -1 MHz and temperatures down to 8 K, for two Li ionic conductors, one crystalline (Li 0.18 La 0.61 TiO 3 ) and the other glassy (61SiO 2 ? 35Li 2 O ? 3Al 2 O 3 ? P 2 O 5 ). As temperature is increased a crossover is observed from a nearly constant loss to a fractional power law frequency dependence of the ac conductivity. At any fixed frequency v, this crossover occurs at a temperature T such that v ഠ n 0 exp͑2E m ͞k B T͒, where n 0 is the attempt frequency and E m is identified with the barrier for Li 1 ions to leave their wells. DOI: 10.1103/PhysRevLett.86.1279 Much effort has been devoted during the last few decades to understand the dynamics of ionic transport in ionically conducting materials. In spite of the advances made, there is still no general agreement on interpretation of the experimental data [1][2][3][4][5][6][7][8][9][10][11]. Most research activity in this field has focused on the origin and properties of the long-range ion motion, and electrical relaxation is the most commonly used experimental tool to access the ion dynamics. The frequency dependence of the ionic conductivity can be usually well described by using Jonscher's expression [12]where s 0 is the dc conductivity, v p is a characteristic relaxation frequency, and n is a fractional exponent. Both s 0 and v p are thermally activated with about the same activation energy, indicating that the dispersive conductivity, s ‫ء‬ ͑v͒, originates from migration of ions. However, there is another ubiquitous contribution to dispersive conductivity that has received much less attention so far. This contribution consists of a nearly frequency independent dielectric loss,´0 0 ͑v͒ ഠ A, which corresponds to an almost linear frequency dependent term of the form s 0 ͑v͒ v´0 0 ͑v͒ ഠ Av in the real part of the complex conductivity. At sufficiently low temperature or high frequencies, the Av term dominates over the power law dependence of exponent n. The existence of this nearly constant loss (NCL) was suggested more than 20 years ago and subsequently verified [13,14]. Since then, few investigations of its properties have been made [15][16][17] and low temperature data with its dominant contribution are still scarce.Although, ultimately, mobile ions seem to be responsible also for the NCL, the experimental facts including its dependence on temperature and the effect of mixed alkalis point to a different origin than ionic hopping [18]. Experimentally, A is not thermally activated and has temperature dependence much milder than s 0 or v p [18][19][20]. Partial replacement by alkali ions of a different kind has the effect of reducing the NCL [3,18,21,22], but the reduction in A is much smaller than the decrease in s 0 due to the well-known mixed alkali effect [3]. From these facts, it has been very recently proposed [18] that local vibrational relaxation reflected in the mean-square displacement of ions could be the origin of the constant loss in ionic conductors...

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Is there a mixed alkali effect in the low temperature ac conductivity of glasses?

Cited by 51 publications

References 13 publications

Cage decay, near constant loss, and crossover to cooperative ion motion in ionic conductors: Insight from experimental data

Cage decay, near constant loss, and crossover to cooperative ion motion in ionic conductors: Insight from experimental data

Crossover from ionic hopping to nearly constant loss in the fast ionic conductorLi0.18La0.61TiO
Rivera-Calzada
¹
,
Yebra
²
,
Sanz
³

et al. 2002
Phys. Rev. B
39
3
22
0
View full text Add to dashboard Cite

Origin of Constant Loss in Ionic Conductors

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Is there a mixed alkali effect in the low temperature ac conductivity of glasses?

Cited by 51 publications

References 13 publications

Cage decay, near constant loss, and crossover to cooperative ion motion in ionic conductors: Insight from experimental data

Cage decay, near constant loss, and crossover to cooperative ion motion in ionic conductors: Insight from experimental data

Crossover from ionic hopping to nearly constant loss in the fast ionic conductorLi0.18La0.61TiORivera-Calzada1, Yebra2, Sanz3 et al. 2002Phys. Rev. B393220View full textAdd to dashboardCite

Origin of Constant Loss in Ionic Conductors

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About

Crossover from ionic hopping to nearly constant loss in the fast ionic conductorLi0.18La0.61TiO
Rivera-Calzada
¹
,
Yebra
²
,
Sanz
³

et al. 2002
Phys. Rev. B
39
3
22
0
View full text Add to dashboard Cite