Adams S
GZG, Abt. Kristallographie, Universität Göttingen, Goldschmidtstrasse 1, D37077 Göttingen, Germany.
Acta Crystallogr B. 2001 Jun;57(Pt 3):278-87. doi: 10.1107/s0108768101003068. Epub 2001 Jun 1.
Established bond-valence parameter tables rely on the assumption that the bond-valence sum of a central atom is fully determined by interactions to atoms in its first coordination shell. In this work the influence of higher coordination shells is tested in detail for bonds between lithium and oxygen. It is demonstrated that the sum of the weak interactions with atoms of the second coordination shells significantly contributes to the valence sum and should therefore not be neglected. Since the independent refinement of the two parameters R(0) and b is hardly possible from the limited range of bond lengths occurring in the first coordination shell, the restriction of bond-valence sums to contributions from nearest neighbours implicated another far-reaching simplification: the postulation of a universally fixed value of the bond-valence parameter b which characterizes the shape of the bond-valence pseudopotential for the respective atom pair. However, recent more sophisticated applications of the bond-valence concept, e.g. to model ion-transport pathways in solid electrolytes, demand sensible estimates of the bond-valence sums for mobile ions not only at their equilibrium sites but also at interstitial sites and bottle-necks of transport pathways. Calculations of bond valences at these non-equilibrium sites require the knowledge of the actual shape of the bond-valence pseudopotential. A systematic route to a more realistic estimate of b for alkali halides and chalcogenides is developed in this work from an empirical correlation between b and the absolute softnesses of the interacting particles.
已建立的键价参数表依赖于这样一种假设，即中心原子的键价总和完全由其第一配位层中与原子的相互作用决定。在这项工作中，详细测试了更高配位层对锂和氧之间键的影响。结果表明，与第二配位层原子的弱相互作用总和对价和有显著贡献，因此不应被忽视。由于从第一配位层中出现的有限键长范围很难独立精修两个参数R(0)和b，将键价总和限制为仅来自最近邻的贡献意味着另一个影响深远的简化：假设键价参数b具有普遍固定的值，该值表征了相应原子对的键价赝势的形状。然而，键价概念最近更复杂的应用，例如用于模拟固体电解质中的离子传输路径，不仅需要对移动离子在其平衡位置，而且在间隙位置和传输路径瓶颈处的键价总和进行合理估计。在这些非平衡位置计算键价需要了解键价赝势的实际形状。在这项工作中，通过b与相互作用粒子的绝对软度之间的经验相关性，开发了一种系统的方法来更实际地估计碱金属卤化物和硫族化物的b。
