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arXiv 0903.0848cond-mat.mtrl-scicond-mat.dis-nn
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再论混合移动离子效应的缺陷模型:形变率的重要性

Defect model for the mixed mobile ion effect revisited: an importance of deformation rates

Vladimir Belostotsky

摘要:

报道了在混合移动离子效应的缺陷模型的概念内理解玻璃混合离子导体的行为的进展(V. Belostotsky,J. Non-Cryst. Solids 353(2007)1078)。表明在混合离子导体(例如,混合的碱金属玻璃),其包含两种或多种不同类型的不同尺寸的可移动离子,由进入外来位置的可移动离子的尺寸失配引起的足够的局部应变原则上不能被周围的网络形成基质吸收而不对其造成损害。通过在最近的玻璃网络中形成本征缺陷,在接近离子迁移过程的时间尺度上立即发生主位点重排。在这种情况下,既不能预期在玻璃化转变温度Tg以下观察到滞弹性松弛,也不能预期在Tg或高于Tg下观察到粘弹性或粘性行为,因为在宽温度范围内的应力松弛的特性首先由邻近的网络形成基质局部采用的变形速率决定。由于离子迁移发生在皮秒时间尺度上,邻近离子位点的玻璃网络的主要重排发生在比临界最小值高的数量级的速率下,因此即使在远高于Tg的温度下,基质也表现出对所产生的应变的脆弹性响应,这尤其解释了为什么在玻璃熔体中可观察到混合碱效应。

英文摘要:

The progress in understanding the behavior of glassy mixed ionic conductors within the concept of the defect model for the mixed mobile ion effect (V. Belostotsky, J. Non-Cryst. Solids 353 (2007) 1078) is reported. It is shown that in a mixed ionic conductor (e.g., mixed alkali glass) containing two or more types of dissimilar mobile ions of unequal size sufficient local strain arising from the size mismatch of a mobile ion entering a foreign site can not be, in principle, absorbed by the surrounding network-forming matrix without its damage. Primary site rearrangement occurs immediately, on the time scale close to that of the ion migration process, through the formation of intrinsic defects in the nearest glass network. Neither anelastic relaxation below glass transition temperature, Tg, nor viscoelastic or viscous behavior at or above Tg can be expected being observed in this case because the character of the stress relaxation in a wide temperature range is dictated above all by the deformation rates employed locally to the adjacent network-forming matrix. Since the ion migration occurs on the picosecond time scale, the primary rearrangement of the glass network adjacent to an ionic site occurs at rates orders of magnitude higher than those of the critical minimum values, so the matrix demonstrates brittle-elastic response to the arising strain even at temperatures well above Tg, which explains, among other things, why mixed alkali effect is observable in glass melts.

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