First of all I should like to thank the organising committee headed by Countess Bettina
for getting me here as a physicist and the second physicist this morning.
But I should like to say that the discovery of this superconductivity in the cuprate
is a bit borderline case between physics and inorganic chemistry.
And the motivation was the Polaron Concept.
And just as a precursor to my talk which I am going to give I show you 2 transparencies to illustrate
that now the concept which we had to find that the polarons are really there.
So now I sit down before I fall down.
(laughter).
One of the experiments which supported this polaron motion is the isotope effect.
What is the isotope effect?
It is if you replace the oxygen 16 by oxygen 18.
You shift the transition temperature, TC here.
And this TC is proportional to the mass of your ions in your samples time the exponent alpha.
This is this coefficient.
That is isotope exponent which is the logarithmic derivative of the observed temperature against the mass which you can measure.
Now BCS theory tells you it must be a half.
What has been recently been published looks like this.
This was a collaboration with a young, Stephen Weyeneth.
And what you see on this graph is the following.
Here is the reduced temperature.
So this is maximum temperature.
And you go down by reducing the doping of the sample.
And these are data on many of these cuprates from several groups.
And this curve here is not a curve just to fit the data, but this is the theory of Kresin and Wolf.
Kresin is at Berkeley and Vladimir Kresin... And Stuart Wolf is in Washington.
Which they published in 1994.
And people did not take much attention but you see that these measurements fit this curve very well.
And you see up here this is the coefficient of 1.
I told you before the coefficient of...
In BCS there is a half, should be here.
This has been measured in Switzerland by Rustem Khasanov and his group at the Paul Scherrer Institute in Switzerland.
So many theories started because at optimum doping here the effect disappears, is zero.
To assume if there are... The cause is electronic but this is one example which show you that it’s really polaronic.
Now it is not the scope of my talk and therefore I think in the afternoon, 5 or half past 5,
there is a half an hour and those among you who may be interested in that can... we can discuss that.
Now let me get to my talk.
The title is slightly changed a bit.
It is “Photostimulated Solid State Synthesis of Oxide Materials”.
And it was a collaboration between the Tbilisi State University with the people shown there.
And I was also involved, the University of Zurich.
I have to say that Alexander Shengelaya who is the head of this group by now is head of the physics department down there.
Has been there for 5 years.
Before he was 9 years in Zurich Switzerland running how the science is done in Switzerland.
And this collaboration continued.
Here you see the photograph.
This is the entrance of the physics institute in Tbilisi in Georgia, Georgia which is as you know between Turkey and Russia.
Here are 2 of us.
This is Alexander Shengelaya at a time when I visited Tbilisi a bit more than a year ago.
Now, what I am going to talk about is related to perhaps some of the interest here of inorganic chemists.
And by now oxide is becoming quite important.
At the time I was here the first time it was just when Count Bernadotte gave his responsibility over to Countess Silvia
which is unfortunately not anymore among us and I am very sorry about that.
She was very lively and having this meeting really in hand and developed it.
So normally these oxides at a time when we found the superconductivity, the oxides were considered as dirty.
And in fact the samples which Georg Bednorz and myself first did, we had 3 different oxides in it.
And only one of them was superconducting.
By now the standard of oxide chemistry has come practically up to the level
which at the time silicon had and this for various application reasons.
So what you generally do is to produce oxides
which are complex -the superconductor ones are complex ones- by the direct reaction of a mixing of starting reagents
at high temperature depending when the oxide melts of course.
High temperature provides the necessary energy for the reactions.
This is shown down here for the compounds lanthanum copper O4.
This is the compound Georg Bednorz and myself found a quarter of a century ago.
This is the oldest and simplest method to mix together the powdered reactants.
In part you use carbonates of course, press the pellets and heat them for a period of time.
Now, the new thing is the following.
No, before that here you see a typical reaction.
A diagram, this is for the YBCO compound where you heat it up.
This is hours. You see these are hours.
And I hope you see it even on the panel side.
You heat it up say to 900 degrees and you keep it there for several hours.
Then you keep it at this temperature and you cool it down.
So the whole process for such a reaction takes of the order of 1.5 days, 38 hours.
This is quite long. And this is the way you produce these oxides.
Now, the new thing is the following.
In Tbilisi they have such an oven which had halogen lamps here which you can irradiate, here is your sample.
This is quartz tube. And here you can heat it.
And colour temperature of your lamp is 3,200 degrees K.
And what you are doing, you pulse with these halogen lamps this sample.
And if you do that what happens?
So this is synthesis of the original compound, lanthanum oxide.
You put in some strontium on the place of the lanthanum because it is 2-valent and 3-valent.
So this compound lacks charge.
So it’s whole doped. And this is the size of the sample.
And what happens is here. This is a typical measurement which you do.
After the reaction here is the temperature.
You cool it down and here is the magnetic moment which you measure.
So here something starts, it’s becoming more negative.
What does this mean? It means that the sample expels the magnetic field.
This is known as the Meissner-Ochsenfeld effect, found in Germany in 1933.
And this is without an outside magnetic field.
These are 2 one time pulses at this temperature.
And if you apply a magnetic field the susceptibility is smaller.
The reason is that you trap some magnetic flux in the sample.
However, from this susceptibility, this negative susceptibility, you can compute how much superconducting you got.
And here for this sample you got 50%. Fine.
Now you can do that in a systematic way.
And what comes out is the following.
So this was done in 20 seconds, before we had 1.5 days.
And here is the x-rays. You are all familiar with x-rays, you see that the reflections and these stars are external phase.
If you heat it just to 900 degrees you have more of this external phase.
If you go to 1050 degrees you have less. So this is what the x-ray tells you.
And now we compare what you can do with this new method to light irradiate the crystal without it.
And here you see the results. This is for a time of 2 minutes.
If you put the sample just in the oven you get practically no superconductivity.
If at this various temperature you pulse with the light you see that you get 20% or 30% of susceptibility in your sample.
So this was quite... we were quite happy about that.
And the whole research was submitted in June.
And I was very happy that last Monday, this Monday,
I got from the publisher the agreement to publish our article which we have submitted.
So it’s really new. This will be published in the Journal of Superconductivity and Magnetism.
And by the acceptance Springer will put it in the internet.
But so far you are the first to see these results.
Now in the YBCO compound it was different that it didn’t work so well
and because of that in addition to the illumination by this infrared light was added ultraviolet light.
And you see that here. So you had the halogen lamps, I discussed before, here there are only 3.
Here again the sample. And here you have the ultraviolet lamp which is indicated here, what it is.
And by doing so applied to the YBCO compound which is most used for application.
This is what was gotten in Tbilisi.
Namely just furnace, you barely see any magnetism, any superconductivity.
If you irradiate just with halogen there is an effect, this green thing.
And if in addition you irradiate with ultraviolet light.
You get here really a substantial superconducting compound of it.
Now, oxides become more and more important in various ways.
For instance there are compounds which show magnetic and electric effects.
At the same time you can apply an electric field modulated magnetically and vice versa.
This is one of these compounds, bismuth iron O3.
And these are the x-rays of it. This is synthesised at 870 Kelvin for 5 minutes. So it works also there.
Now the conclusions of this finding is, I read it down:
The new method was found for photostimulated solid state reaction called PSSR of oxide materials.
This method involves the irradiation of the mixture of starting oxides
with light in a broad spectral range from infrared to ultraviolet with intensity sufficient to starting the solid state reaction.
So using this method you can produce polycrystalline high temperature superconductors.
You can produce magneto-electric effects.
The outlook: I think there is a broad application
because you can shorten the process of fabrication quite importantly like in magnets, in fuel cells, in solar cells, in catalysts.
And what is the mechanism? We don’t know.
Maybe somebody here of you find sufficient interest, try to find out why this functions.
And of course you can apply it to thin films.
And as an outlook I show you the cut of the films which are now produced, superconducting wires.
This is shown here. You have on the bottom a textured tungsten alloy.
This is to have stability in the whole thing.
And then you have 1, 2, 3 buffer layers.
These buffer layers are there to have a right orientation of the crystalline
because here then the next layer, this is the YBCO compound layer.
Because in order to have best current transport, the crystallines have to be aligned relatively well.
In the moment the crystalline are rotated a bit, say 2, 3 degrees,
the current transport capability is an order of 2 magnitude down.
And then comes at the end here a silver layer.
Here on top. Why silver?
You have to adjust the oxide here in this YBCO compound, in the superconducting compound quite accurately.
And silver is the only metal which transfers oxygen.
And this makes it expensive.
If somebody here finds another metal or alloy who transfers silver, he becomes very wealthy I tell you.
So this is the layer. This is a second generation of these cuprates for cables.
And with these wires they are now able in at least 2 or 3 factories to draw 1 kilometre long wires.
And you can wind them up.
Here is such a cable which you see down here.
This is... you have electrical shielding.
You have here electrical thermal insulation.
Then here are these wires which I just showed you a cut.
And through in the middle you send nitrogen because YBCO has a transition temperature of 90 Kelvin.
And nitrogen is lower so with that you can cool it.
And this appears to have some relevance.
These cables will probably be used as DC cables. Why?
Because you want to carry the electrical energy over long distances.
Examples are: In China they are planning to have their solar panels, factories in the Gobi desert.
And they want to use it in the region of Shanghai which is 3,500 kilometre away.
And they have decided this technology.
They come with DC and then they have to chop it. And this is not just plans.
I have seen photographs of buildings where these choppers are already installed and are working.
Furthermore, because these copper oxides contain rare earths,
China has a large amount of rare earths so for them this is cheap.
Another possibility is the Sahara.
In Algeria they have been planning also large factories of solar cells.
And again this is some 3 to 4,000 kilometres away from here, central Europe where it has to be used.
So you have to transport it.
There are various possibilities to transport this electric energy to here.
And similar situation starts occurring in the United States where some of you
who have been gambling in Las Vegas know that around it there is desert.
And there you can install also solar thing.
So in a way it looks to me like we are kind of having a transition between...
at the beginning we had mills near rivers which were mechanically driven.
Then came the invention of the dynamo by Werner von Siemens.
And then you could produce your electrical power some place and use it a few hundred kilometres someplace else.
And now, at least to me -I don’t know whether Doctor Chu would agree with me or not-
there comes an era where this solar electric energy are produced some 3 or 4,000 kilometres away and has to be transported.
Of course, this will have to be competed with other sources like oil or methane
which you have also lines who come say from central Asia and here to Europe or from Azerbaijan with methane.
But this perspective is a bit the same.
It’s that you produce it or you bring it from some completely different area to some other ones.
And I think, Mr. Chairman, I stop here and I wish everybody a nice day, thank you.
Applause.