Infinite dielectric permittivity

[Stanley514]

I read that in some ferroelectrics,such as Barium Titanate,
dielectric permittivity approaches infinity near Curie point.
For example,for Barium Titanate it`s closer to 120 centigrads.
Do those effect allow as (in theory) create capacitor with
almost unlimited energy density?Or there are even theoretical
obstacles to do it?

 

[Antiphon]

It really means that the dielectric deformation of the matererial happens very easily with the imposed field and that the electric field in the material is nearly completely eliminated by the deformation. It is almost as if there are unbound charges as in a conductor but there aren't and the material is still an insulator. (this is how an infinite permittivity acts like a conductor when looking at wave reflections at a surface.)

What will happen is that the dielectric strength of the material will go way down as the permittivity goes up and it will only be able to store a reasonable amount of energy which is probably even less than when it is not near it's Curie temperature.

 

[Curl]

what happens if you have a conductor wrapped in an insulator for a dialectic? Isn't it a similar effect?

 

[Stanley514]

What if we use combination of material with high dielectric strenghts at 120 centigrads and Barium Titanate with dielectric permittivity appraching infinity at that point?

 

[htg]

If you use layers, one of barium titanate, the other of your high strength dielectric, then it will give you the same result as connecting two capacitors in series - the capacitance will be smaller than the capacitance of the smaller capacitor.
If you use mixture of dielectrics, things get complicated, but you will not have very high capacitance without significant decrease of dielectric strength.

 

[Stanley514]

I read mind of some student on scientific forum who stated that energy storage similar to
capacitors,flywheels,superconductors, (which he generalized as mechanical energy storage); principaly cannot exide energy density of fuel (such as gasoline).He clamed energy storage of fuel is based on brokening of intermolecular forces while capacitors and other mechanical storage on their deformations.I don`t know, but scientists still didn`t find the best dielectric in the world.I would be glad to know if there is some physical theoretical limits to dielectric strengts of matter.Did I understood you right that for capacitor with unbelievebly huge energy density we need almost infinite dielectric strenghts,not only permittivity?

 

[Antiphon]

E = 1/2 C * V^2.

Either C or V can be big but for practical energy storage you usually have a very large C and moderate to high V.

 

[Stanley514]

Is it possible to use triboelectric effect for practical energy storage?
For example ebonite could store negative electric charge, I guess it depends on surface
area.What is material that could have the largest known triboelectric charge potential?

 

[Dickfore]

There are different definitions of dielectric susceptibility. One is a "static" (I don't know if this is the correct term), defined as:

$$P_{i} = \epsilon_{0} \, \sum_{k}{\chi_{i k} \, E_{k}}$$

for linear media, i.e. media where the polarization is always proportional to the existing electric field; and the other is "dynamic" (agaim, terminology), defined as the tensor:

$$\chi_{i k} = \frac{1}{\epsilon_{0}} \, \frac{\partial D_{i}}{\partial E_{k}}$$

For isotropic materials, $\chi_{i k} = \chi \, \delta_{i k}$.

The dielectric permittivity tensor is defined through the susceptibility tensor as:

$$\epsilon_{i k} = \epsilon_{0} \, \left(\delta_{i k} + \chi_{i k}\right)$$

or for isotropic media ($\epsilon_{i k} = \epsilon \, \delta_{i k}$):

$$\epsilon = \epsilon_{0} \, (1 + \chi)$$

so, in infinite permittivity would correspond to infinite susceptibility. I would suspect that this refers to the second definition, i.e. a susceptibility of the "dynamical" kind and corresponds to a vertical tangent on the P - E plot (or D - E plot).

If you know thermodynamics, you will see that the susceptibility corresponds to a second derivative of the Helmholtz free energy with respect to the field, and according to the Ehrenfest classification of phase transitions, this would indicate a second order phase transition (or a critical point).

 

[htg]

Van de Graaf generators practically use triboelectric effect for generation of high voltages. But not for energy storage.

 

[Stanley514]

I have question regarding electric hazard.For example a person touches live electric wire on fifth floor of a building made of concrete.To get shock, charge should flow through person.But where will it flow,into the ground? Charges usually flow to opposite,but what is charge of the Earth? And how charge could penetrate tens of meters of air and concrete which seems to be a dielectric? Or there is some different principle?

2)Is it possible to make energy storage (capacitor) with carges of only one kind,for example negative?Could you discharge it to the grownd through electric motor and make it work?

 

[htg]

1) A human body can be viewed as a conductor. It has its capacitance and when connected to a non-zero potential it will get charged. In the process of charging current will flow.
2) You can make a unipolar capacitor, but to use it to power a motor you would have to make it huge and discharge it through e.g. a voltage regulator.

 

[Stanley514]

1) A human body can be viewed as a conductor. It has its capacitance and when connected to a non-zero potential it will get charged. In the process of charging current will flow.

What do you meen as potential?I read that if person will hang on one hand on a live wire and
will not touch ground he will not be killed.Birds could freely seat on high power wires without being killed,because of low difference in potentials.Why person doesn`t get serious shock when getting charged from carpet,but only when discharges this charge?You said current should flow into person?

2) You can make a unipolar capacitor, but to use it to power a motor you would have to make it huge and discharge it through e.g. a voltage regulator.

Do you think it will allow to store more energy than usual capacitor?There is a greater distance between capacitor and Earth than between two plates of capacitor.

3)Is it possible to make capacitor which would store energy solely in polarisation of material but would not have electrons displaced?
Isn`t ferroelectric RAM working in a similar way?
If material is electracaly polarized but doesn`t have electrons difference between plates,could electric breakdown still occur?

4)What to you think about digital quantum battery?
http://www.physorg.com/news180704455.html"
Will that thing really work?

 

[htg]

Bird's body capacitance is quite small. That's why they can sit on high voltage lines.
If you get charged slowly (e.g. from a carpet) then small current flows and does not cause shock. During sudden discharge relatively large current flows.

 

[Stanley514]

If I no make mistake, dry skin is rather prone to charge positevly - e.g. to give up electrons,not to accept them.What about other parts of human body?How could human body charge negatively?

 

[Stanley514]

100.000 Volts at 1 Amp=100.000 Wats?
Will 100.000 Volts at 1 Amp Direct current kill a person?

 

[htg]

About 10 mA may kill a person. 1 A certainly will (unless it is very high frequency, so that skin effect has a protective effect).

 

[Dickfore]

Electric current is a flux measurement, i.e. it measures the total stream of current carriers from the source of emf to its other end. What is more important is how this current is distributed. Did you mean the whole of 1 A passes through the human body? Because, as the previous poster had suggested, even 10 mA (although I think the correct value is 100 mA through vital organs) is sufficient to kill you. Then, it also depends on the frequency.

 

[Antiphon]

100.000 Volts at 1 Amp=100.000 Wats?
Will 100.000 Volts at 1 Amp Direct current kill a person?

Yes.

 

[Stanley514]

What is sense to use high voltage motors in electric vehicles such as Toyota Prius which works from few hundreds of volts?
Could we use low voltage and high current motor similar to starter in gasoline car?
I mean could we compensate reduced length of wires by making them thicker and obtain the same power?Because you will need some licensed electrician to work on high voltage equipment.

 

[superczar0]

It really means that the dielectric deformation of the matererial happens very easily with the imposed field and that the electric field in the material is nearly completely eliminated by the deformation. It is almost as if there are unbound charges as in a conductor but there aren't and the material is still an insulator. (this is how an infinite permittivity acts like a conductor when looking at wave reflections at a surface.)

What will happen is that the dielectric strength of the material will go way down as the permittivity goes up and it will only be able to store a reasonable amount of energy which is probably even less than when it is not near it's Curie temperature.

I can't agree with this assessment. Since piezoelectricity goes to zero at Curie temp (i.e cubic phase transition) there is no deformation. Also breakdown strength is not determined by the mechanism you suggest, rather barium titanate is a band-gap insulator and can withstand unlimited electric fields directly. Breakdown is related to macroscopic electric field which can be kept quite low. Infinite permittivity would give infinite energy storage with any finite electric field. As an example of high permittivity and energy storage take the example of EEStor which has achieved 10,000J/cc storage with a 33,500 permittivity material.

 

[Stanley514]

1) A human body can be viewed as a conductor. It has its capacitance and when connected to a non-zero potential it will get charged. In the process of charging current will flow.

How then you explain that electriciens like to use thick rubber rugs and shoes to prevent a strike?If voltage strike would happen by internal capacitance mechanism it would not help anyway.

 

[Stanley514]

If you use mixture of dielectrics, things get complicated, but you will not have very high capacitance without significant decrease of dielectric strength.

What do you think on metal nanoparticles embedded in ceramic dielectric?Distance between metal nanoparticles could be smaller than 10 nm to prevent arching by quantum effects.What dielectric constant and strength could we expect from such an artificial dielectric?