甚麼是半金屬?

metal, non-metal同semi-metal是以元素最外層的電子來分metal : 1-3semi-metal：4non-metal：5-8
類金屬總共有B、Si、Ge、As、Sb、及At等七個元素，在週期表中呈階梯狀的排列，它們的性質介於金屬和非金屬之間，僅具有部分金屬或非金屬的性質，例如銻(Sb)外觀有金屬的光澤，但是易碎不具延展性，導電和傳熱性也差。類金屬的導電性比非金屬稍微好一點，但隨溫度之增高而增加，和金屬的導電性隨溫度之增高而下降的性質正好相反。另外和金屬不相同的一點，當金屬中有雜質存在時會使其導電性降低，而類金屬的導電性常因含有微量的雜質而劇增，例如矽及鍺，室溫下純度高時導電性很差，溫度提高時則導電性增高，當加入微量的鎵或磷便成為很好的半導體，目前這些元素已成為製造電子元件的重要元素。
這要看金屬的合金性質,一般為金屬鍵,但是氧化鋁就是共價鍵,如果像氧化鋁一樣純度高的化合物金屬多是共價鍵,如氧化鋯
參考資料:
tw.knowledge.yahoo.com

Semimetal From Wikipedia, the free encyclopedia (Redirected from Semi-metal) Jump to: navigation, search
圖片參考：http://upload.wikimedia.org/wikipedia/commons/9/9c/Semimetal.PNG
This diagram illustrates a direct semiconductor (A), an indirect semiconductor (B), and a semimetal (C). A semimetal is a material with a small overlap in the energy of the conduction band and valence bands.[1]
However, the bottom of the conduction band is typically situated in a different part of momentum space (at a different k-vector) than the top of the valence band. One could say that a semimetal is a semiconductor with a negative indirect bandgap. Schematically, the figure shows
A) a semiconductor with a direct gap (like e.g. CuInSe2),B) a semiconductor with an indirect gap (like Si) andC) a semimetal (like Sn or graphite). The figure is schematic, showing only the lowest-energy conduction band and the highest-energy valence band in one dimension of momentum space (or k-space). In typical solids, k-space is three dimensional, and there are an infinite number of bands.
Unlike a regular metal, semimetals have charge carriers of both types (holes and electrons), typically in smaller numbers than a real metal. The electrical properties of semimetals are partway between those of metals and semiconductors. The classic semimetallic elements are arsenic, antimony, and bismuth. These are also considered metalloids but the concepts are not synonymous. Semimetals, in contrast to metalloids, can also be compounds such as HgTe,[2] and tin and graphite are typically not considered metalloids.
Graphite and hexagonal boronnitride (BN) are an interesting comparison. The materials have essentially the same layered structure and are isoelectronic. However BN is a white semiconductor and graphite a black semimetal, because in one case the bandgap is positive (like case B in the figure) in the other negative (see C).
As semimetals have fewer charge carriers than metals, they typically have lower electrical and thermal conductivities. They also have small effective masses for both holes and electrons because the overlap in energy is usually the result of the fact that both energy bands are broad. In addition they typically show high diamagnetic susceptibilities and high lattice dielectric constants.

[edit] References ^ Burns, Gerald (1985). Solid State Physics. Academic Press, Inc., 339-40. ISBN 0-12-146070-3. ^ Wang, Yang; N. Mansour, A. Salem, K.F. Brennan, and P.P. Ruden (1992). "Theoretical study of a potential low-noise semimetal-based avalanche photodetector". IEEE Journal of Quantum Electronics 28 (2): 507-513. DOI:10.1109/3.123280. Retrieved on 2006-06-08.
[edit] See also MetalMetalloidSemiconductorSolid-state physics