Insulators Can Conduct Current , Electron and Band thoeries

in #steemstem6 years ago (edited)

imagesource: pixabay

As we know insulator can be define as a device or substances which does not conduct electricity. Which is they do not allow the flow of current.
Its time to look basically on how to enable insulators to allow the flow of currents. To get it more clearer we look into its components as a substance "electrons". As we know electrons are subatomic particle with a unit negative electric charge.

Insulators, of course, keep all their electrons in the basement. Under ordinary conditions, their conduction band is empty, the first forbidden band is too broad for any of the electrons to find the energy needed to jump across it. But when the insulator is heated properly, the oscillation energy of its ions at the lattice nodes becomes very great. This energy can be imparted to the electrons which occasionally become energetic enough to jump up into the
conduction band. The insulator then begins to conduct current. This is called heat breakdown
Actually, to account for this breakdown we don't need quantum mechanics, for it only means that the electron has broken out of its narrow atomic world and has got into the conduction band and become practically a free man.
The same way if we push it chemically. HgO can break down by heat into Hg and O, each independently free to exist.
The energy required for its release was simply equal to the width of the forbidden band separating the basement from the ground floor.

All this can be pictured as follows

imagesketched by me

a thermal 'knock' ejected the electron from its atom,
ionizing the latter, while the electron released from its atom is now moving freely but is yet able to leave the chunk of insulator.
But it turns out that an insulator also becomes a conductor of electricity when a very strong electric field is applied to it. Wait a minute isn't this just like the cold emission of electrons from a metal?
But this isn't a metal, it's an ionic crystal! In the emmission of electrons from metals, the electrons escaped the metal altogether, whereas here they only jump from the valence band to the conduction band.
Still despite the differences, this is one and the same phenomenon.

The miracle in both instances is the tunnel effect.
Indeed, what is a forbidden zone if it isn't a potential barrier?

forbidden zone is the energy gap between valence band and conduction band in solids .this gap is large in insulators and small in semi conductors . there is no forbidden zone in metals because in metals valence and conduction band overlap
Yes, it is simply a potential barrier of practically infinite (for the electrons, naturally) width. It's simply a step with only one 'front side. An electric field, as before, bends it and creates a rear side. As a result, the barrier now has a finite width.
![image]()skeched by me
The rest is all the same. The electrons begin to seep through from the valence band across the barrier into the conduction band. First we get a small electric current: the probability of penetration is low and few electrons get into the conduction band. But this current, as it moves through the crystal, heats it like the wire in a hot-plate. This heating, in turn, adds fresh armies of electrons to the conduction band, and the current in the insulator builds up of its own accord. In just no time there is an electric rupture of the insulator accompanied by a simultaneous thermal breakdown-the insulator melts. It is no good any more and has to be thrown out. This is interesting and beautiful.

But there is a more peaceable manner of generating electric currents in insulators.
These currents are very weak and absolutely harmless. They are produced by illuminating ionic crystals. Photons strike the crystal, knocking fall electrons from the valence band into the conduction band. This is a real photoelectric effect, but there is no emission, it all takes place inside, so to speak. There is no harm done, and at the same time it is just the thing for practical applications.

Reference
Reference
Reference
Other Reference : Offline lecture notes.





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ok welcome (edited)

Hello! I find your post valuable for the wafrica community! Thanks for the great post! @wafrica is now following you! ALWAYs follow @wafrica and use the wafrica tag!

Because an insulator can also conduct electricity, that is why we have insulators usually rated by the maximum amount of voltage they can withstand without breaking down. For instance, a friend just bought an insulating glove capable of handing up to 9KV. Voltages higher than that may be risky to use such a protection device to work on it.

Yes you are right. Its termed R-value which is the which is a value that determines how objects resist the flow of current. Higher the R value larger the resistivity. Thanks for stopping by

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