Hello,
This is a good and interesting question.
Most often mxied ion-electron conductors are essentially electronic conductors.
So if you have the possibility to generate electronic conductivity (with 3d metals for instance), think in priority that the main contribution is electronic.
This comes from the fact that electron mobility is usually much higher than ionic one.
so a bit of mixed valency is sufficient to generate higher electronic conductivity.
I dont believe temperature behaviour is sufficient.
In many metal oxides, electronic conductivity is polaronic in nature.
In this case, the electronic (hole) conductivity many times increases
with temperature since the electron jump is assisted by phonons.
I know also some cobaltites where the conductivity is flat over a range of temperature of 500K.
So not sufficient.
In all cases, oxygen ion conductivity will be in the range 0.6-1.1 eV so
a much smaller activation energy is probably associated to electron conductivity.
Simple ways to distinguish are:
1. Do variations of pO2. If your conductivity changes a lot with pO2, it is essentially electronic. Defects equations must be written anyway.
2. do impedance spectroscopy measurments. if you see almost no electrode contribution, your material is probably essentially electronic. Use a bad oxygen electrode material, it would be even better (Pt or Au are good examples at low LT; Ag is not because it is a rather good oxygen electrode material).
hoping it helps.
Guilhem
ionic conductivity decreases with increase of pressure and the electronic conductivity increases with application of pressure. Please refer the papers from my contributions in Research gate: Philosophical Magazine 1983; Phys. Rev. Letters, 1984; J. Materials Research 1987.
If you prepare a membrane and place it between two volumes with the different pressure of oxygen (P1 and P2), EMF measurement on the different sides of a membrane E will be expressed by a formula E = (RT/4F) ln(P1/P2), F - Faradey constant. If you know pressure P1 and P2, you can calculate theoretical value of EMF (Etheor). The measured value of EMF (Eexp) will differ from theoretical at a value of an electronic contribution (te) to the general conductivity: Eexp/Etheor = (1-te)/(ti+te), ti - ionic contribution in general conductivity.
As your experiment is Faraday- dependent and you want to separate ionic contribution from the overall measured conductivity, I agree with the suggestion given by Alexander Titov.
To know the extent of ionic and electronic contribution to the total conductivity, transference number measurements can be carried out by two different techniques: (i) Wagner's dc polarisation method, (ii) electrochemical potential method.
Hello,
This is a good and interesting question.
Most often mxied ion-electron conductors are essentially electronic conductors.
So if you have the possibility to generate electronic conductivity (with 3d metals for instance), think in priority that the main contribution is electronic.
This comes from the fact that electron mobility is usually much higher than ionic one.
so a bit of mixed valency is sufficient to generate higher electronic conductivity.
I dont believe temperature behaviour is sufficient.
In many metal oxides, electronic conductivity is polaronic in nature.
In this case, the electronic (hole) conductivity many times increases
with temperature since the electron jump is assisted by phonons.
I know also some cobaltites where the conductivity is flat over a range of temperature of 500K.
So not sufficient.
In all cases, oxygen ion conductivity will be in the range 0.6-1.1 eV so
a much smaller activation energy is probably associated to electron conductivity.
Simple ways to distinguish are:
1. Do variations of pO2. If your conductivity changes a lot with pO2, it is essentially electronic. Defects equations must be written anyway.
2. do impedance spectroscopy measurments. if you see almost no electrode contribution, your material is probably essentially electronic. Use a bad oxygen electrode material, it would be even better (Pt or Au are good examples at low LT; Ag is not because it is a rather good oxygen electrode material).
hoping it helps.
Guilhem
Hello,
I totally agree with the views of Prof.Dezanneau.
Prof. K.V.Sivakumar
Hello,
I quite agree with AlexanderTitov, G, Dezanneau and Dmitry Medvedev. Some additional method is based on the mathematical (digital) solution of the equation including two exponents:
σ = σi + σe = σ0i exp(-ΔΕi / RT) + σ0e exp(-ΔΕe / RT).
This method is applicable in a case when: σi ≈ σe.
The answer of Andrei Rogoza is entirely wrong.
The relation between ln sigma & 1/T may be a method to diffrentiate between both ways of conductin specially in glass.That is where this relation appears lenear and sigma could calculated from the slop of this line.When this line became tow lines with different slopes; the firest at low ttemperature which represents the electonic conductiom.The2nd has larger slop because it represents both ionic and electronic
condution at high temperature; that is because ionic conuction eds high energy dun
ELECTRONIC CONDUCTIVITY IS ATTRIBUTED BY ELECTRONS AND THUS THERE FORMS STRAIGHT PART OF THE CONDUCTIVITY VERSUS FREQUENCY CURVE WHILE THE SHARP RISE FORMS THE PART OF IONINC CONDUCTIVITY.
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