13 Electrical Properties of Crystals
新材料技术研究：介绍电子晶体性质及应用
导读
晶体电学性质（electrical properties of crystals）：晶体介质在外电场作用下所产生的电学物理量随外电场强度变化的性质。其中有：1）压电性：晶体在受到机械力作用时而在某些表面上出现电荷的现象，称正压电效应；在外电场的作用下而产生应变的现象，称反压电效应；2）热电性晶体由于温度的变化而在晶体表面上出现电荷的现象；3）温差电效应，指热能变成电能或电能变热能的转换现象。本文介绍了电子晶体的性质及应用。
One of the simplest and best-known kinds of crystal is the ionic salt, of which a typical example is sodium chloride or ordinary table salt. The fundamental components of an ionic salt are ions: atoms or molecules that have become electrically charged by gaining or losing one or more electrons. In forming sodium chloride, for example, sodium atoms give up an electron (thereby becoming positively charged) and chlorine atoms gain an electron (thereby becoming negatively charged). The ions are attracted to one another by their opposite charges, and they stack together compactly
, like tightly packed spheres.
Recently, scientists at Michigan State University created a new kind of crystal called an electride. In electrides, the anions (negative ions) are completely replaced by electrons, which are trapped in naturally formed cavities within a framework of regularly stacked cations (positive ions). Electrides are the first examples of ionic salts in which all these anionic sites are occupied solely by electrons.
Unlike other types of anions, anionic electrons do not behave as if they were simple charged spheres. In particular, because of their low mass and their tendency to interact with one another over great distances, they cannot be “pinned down” to any one location. Instead, they wander close to and among the atoms lining the cavity and interact with electrons in nearby cavities, perhaps changing places with them.
The properties of an electride depend largely on the distance between the cavities that hold trapped electrons. When the trapped electrons are far apart, they do not interact strongly, and so behave somewhat like an array of isolated negative charges. When they are closer together, they begin to display properties associated with large ensembles of identical particles. When they are still closer, the ensemble properties dominate and the electrons“delocalize”: they are no longer tightly bound within individual cavities but are more or less free to pass through the spaces within the frame-work of positive ions.
By synthesizing electrides from a variety of materials, one can vary the geometry of the anionic cavities and their relation to the surrounding cations. The resulting properties may make it possible for electrides to become a basis for economically useful new materials and devices. For instance, because the electrons in some electrides are very weakly bound, these crystals could be effective as photosensitive detectors, in which an impinging photon liberates an electron, resulting in a small electric current. The same weak binding could also make electrides useful in solar-energy converters and as cathodes in batteries. One obstacle is the tendency of electrides to decompose through reaction with air and water. Researchers are seeking ways to increase their stability.
一种最简单最常见的晶体是离子盐，典型的实例是氯化钠或普通食盐。离子盐基本成分是离子，是得到或失去一个或一个以上的电子而带电的原子或分子。例如，钠原子失去一个电子（因而带正电），而氯原子得到一个电子（因而带负电），以构成氯化钠。离子通过相反电荷而互相吸引，紧密堆积，好像紧紧挤在一起的球体。
最近，密歇根州大学的科学家研制一种新的晶体，称为电子晶体（electride）。在电子晶体中，阴离子（负离子）完全由电子取代。这些电子落入在整齐堆积的阳离子（正离子）结构内自然形成的腔洞中。电子晶体是全部阴离子区仅由电子占据的首批离子盐实例。
与其他型的阴离子不同，阴离子电子的运转并不是好像单纯带电的球体。尤其是因为阴离子电子质量低，倾向于远距离相互作用，因而不可能在某一区域被“固定住”。相反，阴离子电子在沿腔洞排列的原子附近或原子中间徘徊，并与附近腔洞中的电子相互作用，可能与其互换位置。
电子晶体的这种性质主要随具有落入电子的腔洞之间的距离而定。当落入腔洞的电子距离很远，相互作用不强，其运转有点像排列整齐的一排分离的负电荷。当落入电子的距离比较接近时，开始表现出类似大量同类粒子在一起的整体效应性质。当落入电子的距离更加接近，整体效应性质处于支配地位，这些电子发生“离域”（delocalize）现象，不再与个别腔洞紧密结合，而是或多或少通过正离子结构中的空间区域自由活动。
用各种材料合成电子晶体，能够改变阴离子腔洞的几何形状及其与周围阳离子的关系。由此而产生的性质可能使电子晶体成为制造经济实用的新材料、新器件的基础。例如，由于电子晶体中的电子结合很弱，这些晶体可能是高效的感光探测器：在其中，一个冲击的光子释放出一个电子，结果产生一小股电流。同样，这种电子结合能力很弱的性质，也能使电子晶体在制造太阳能变换器中有用，并且能用做电池的阴极。障碍是电子晶体容易与空气和水反应而分解。研究工作者正在探索增强其稳定性的方法。
Sentence Translation
句子翻译
1. In forming sodium chloride, for example, sodium atoms give up an electron (thereby becoming positively charged) and chlorine atoms gain an electron (thereby becoming negatively charged).
2. When the trapped electrons are far apart, they do not interact strongly, and so behave somewhat like an array of isolated negative charges.
Key
1．例如，钠原子失去一个电子（因而带正电），而氯原子得到一个电子（因而带负电），以构成氯化钠。
2．当落入腔洞的电子距离很远，相互作用不强，其运转有点像排列整齐的一排分离的负电荷。