- 記錄人類文明的那些美文（環(huán)球時代美文讀本）
- 吳中東 宮玉波
- 1593字
- 2020-08-20 09:57:23
13 Electrical Properties of Crystals
新材料技術研究：介紹電子晶體性質及應用
導讀
晶體電學性質（electrical properties of crystals）：晶體介質在外電場作用下所產(chǎn)生的電學物理量隨外電場強度變化的性質。其中有：1）壓電性：晶體在受到機械力作用時而在某些表面上出現(xiàn)電荷的現(xiàn)象，稱正壓電效應；在外電場的作用下而產(chǎn)生應變的現(xiàn)象，稱反壓電效應；2）熱電性晶體由于溫度的變化而在晶體表面上出現(xiàn)電荷的現(xiàn)象；3）溫差電效應，指熱能變成電能或電能變熱能的轉換現(xiàn)象。本文介紹了電子晶體的性質及應用。
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.
一種最簡單最常見的晶體是離子鹽，典型的實例是氯化鈉或普通食鹽。離子鹽基本成分是離子，是得到或失去一個或一個以上的電子而帶電的原子或分子。例如，鈉原子失去一個電子（因而帶正電），而氯原子得到一個電子（因而帶負電），以構成氯化鈉。離子通過相反電荷而互相吸引，緊密堆積，好像緊緊擠在一起的球體。
最近，密歇根州大學的科學家研制一種新的晶體，稱為電子晶體（electride）。在電子晶體中，陰離子（負離子）完全由電子取代。這些電子落入在整齊堆積的陽離子（正離子）結構內自然形成的腔洞中。電子晶體是全部陰離子區(qū)僅由電子占據(jù)的首批離子鹽實例。
與其他型的陰離子不同，陰離子電子的運轉并不是好像單純帶電的球體。尤其是因為陰離子電子質量低，傾向于遠距離相互作用，因而不可能在某一區(qū)域被“固定住”。相反，陰離子電子在沿腔洞排列的原子附近或原子中間徘徊，并與附近腔洞中的電子相互作用，可能與其互換位置。
電子晶體的這種性質主要隨具有落入電子的腔洞之間的距離而定。當落入腔洞的電子距離很遠，相互作用不強，其運轉有點像排列整齊的一排分離的負電荷。當落入電子的距離比較接近時，開始表現(xiàn)出類似大量同類粒子在一起的整體效應性質。當落入電子的距離更加接近，整體效應性質處于支配地位，這些電子發(fā)生“離域”（delocalize）現(xiàn)象，不再與個別腔洞緊密結合，而是或多或少通過正離子結構中的空間區(qū)域自由活動。
用各種材料合成電子晶體，能夠改變陰離子腔洞的幾何形狀及其與周圍陽離子的關系。由此而產(chǎn)生的性質可能使電子晶體成為制造經(jīng)濟實用的新材料、新器件的基礎。例如，由于電子晶體中的電子結合很弱，這些晶體可能是高效的感光探測器：在其中，一個沖擊的光子釋放出一個電子，結果產(chǎn)生一小股電流。同樣，這種電子結合能力很弱的性質，也能使電子晶體在制造太陽能變換器中有用，并且能用做電池的陰極。障礙是電子晶體容易與空氣和水反應而分解。研究工作者正在探索增強其穩(wěn)定性的方法。
Sentence Translation
句子翻譯
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，鈉原子失去一個電子（因而帶正電），而氯原子得到一個電子（因而帶負電），以構成氯化鈉。
2．當落入腔洞的電子距離很遠，相互作用不強，其運轉有點像排列整齊的一排分離的負電荷。