Перевод текста тех. тематики (англ. - рус) - CONDUCTORS AND INSULATORS

TEXT III

CONDUCTORS AND INSULATORS
We can now understand why some solids are conductors and others are insulators. If the valence band is only partially full, there are many empty states in the band and the electrons in the band can easily be raised to a higher energy state by an electric field. Accordingly, this material is a good conductor. If the valence band is full and there is a large energy gap between it and the next available band, a typical applied electric field will be too weak to excite an electron from the upper energy levels into the energy levels of the empty band, so the material is an insulator. The lowest band in which there are unoccupied states is called the conduction band. In a conductor the valence band is partially filled, so the valence is also the conduction band. An energy gap between allowed bands is called a forbidden energy band.
Superconductivity
There are some materials for which the resistivity suddenly drops to zero below a certain temperature Tc, called the critical temperature. This amazing phenomenon, called superconductivity, was discovered in 1911 by the Dutch physicist H. Kamerlingh Onnes, who had developed a technique for liquefying helium (boiling point 4.2 K) and was putting his technique to work exploring the properties of materials at extremely low temperatures. The critical temperature for mercury is the same as the boiling point for helium, 4.2 K. Critical temperatures for other superconducting elements range from less than 0.1 K for hafnium and iridium to 9.2 K for niobium. The temperature range for superconductors goes much higher for a number of metallic compounds. For example, the superconducting alloy NB3Ge, discovered in 1973, has a critical temperature of 23.2 K, which was the highest known until 1986, when the discoveries of Bednorz and Muller launched the era of high temperature superconductors, which exhibit superconductivity at temperatures above 77 K.

solid – твердое тело
band – зона (уровней энергии); энергетическая зона
valence band – валентная зона
energy gap – запрещенная энергетическая зона, энергетическая щель
forbidden energy band – запрещенная энергетическая зона
conduction band – зона проводимости
superconductivity – сверхпроводимость
alloy – сплав