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A route to room-temperature superconductivity?

  1. Nov 22, 2007 #1
    Scientists using diamond anvils have found that boron in contrast to
    other metals becomes superconducting at higher temperatures when
    compressed:

    Superconductivity: boron goes it alone.
    Jul 12, 2001
    "Boron - one of the lightest elements in the periodic table - becomes
    a superconductor when it is squeezed, according to a team led by
    Russell Hemley of the Carnegie Institute of Washington in the US. They
    found that boron loses its resistance to electrical current below 6
    kelvin and at a pressure of 160 gigapascals. Now theorists must
    explain why the 'transition temperature' of boron rises as the
    pressure increases, in contrast with other metals (M I Eremets et al
    2001 Science 293 272)."
    http://physicsworld.com/cws/article/news/2642

    Reports
    Superconductivity in Boron.
    Mikhail I. Eremets, Viktor V. Struzhkin, Ho-kwang Mao, Russell J.
    Hemley.
    Science, 13 July 2001: Vol. 293. no. 5528, pp. 272 - 274.
    http://www.sciencemag.org/cgi/content/full/293/5528/272

    As shown in Fig. 4 in this Science report, the dependence on
    pressure of the temperature of transition to superconductivity is
    remarkably linear at high pressures. If this holds up we can estimate
    how much pressure would be required for boron to be superconducting at
    liquid nitrogen temperature 77K and at room temperature 300K.
    The report shows that the rate at which the transition temperature
    increases according to pressure is .05K/GPa and that the transition
    temperature is 11 K at 250 GPa. Then to get to a superconducting
    transition temperature of 77 K would require a pressure of 1,570 GPa.
    And to get to room-temperature superconductivity would require a
    pressure of 6,030 GPa.
    However, diamond anvils crack at around 400 GPa = 4 megabars. So to
    test this would require new materials or methods to attain these
    ultrahigh pressures. One possibility might be "tetracarbon" which from
    theoretical calculations has been claimed to be 40 times harder than
    diamond:

    Newsgroups: sci.astro, sci.physics, sci.energy, sci.materials,
    sci.chem
    From: "Robert Clark" <rgregorycl...@yahoo.com>
    Date: 8 Sep 2006 11:35:49 -0700
    Local: Fri, Sep 8 2006 1:35 pm
    Subject: 'Tetracarbon', 40 times harder than diamond?
    http://groups.google.com/group/sci.astro/browse_thread/thread/ff42a43c596088a8

    Bob Clark
     
  2. jcsd
  3. Nov 22, 2007 #2

    ZapperZ

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    Not sure of the point you're trying to make here, especially since this is a rather old news (in high Tc superconductor community, anything more than 2 years old is rather "antique", considering how fast the field of study changes and moves). The community has known for quite a while that having some compounds under lattice strain can induce a higher Tc.

    The physics could be interesting. The practical aspect is almost non-existent since having room temperature superconductor for application under that high of a pressure isn't realistic. That's why you don't see this as one of the "hot" topic in superconductivity research.

    Zz.
     
  4. Nov 24, 2007 #3
    Thanks for responding. I think it's pretty obvious that the only reason this has not been tested at much higher pressures is the lack of static methods of producing pressures much higher than about 3 megabars, 300 GPa, or so.
    My purpose for writing this is that the possibility that this could extend at least into the liquid nitrogen range, the point at which superconductivity becomes economically feasible for large scale applications, is so important that it mandates methods of achieving the required higher pressures be investigated. I suggested one possible way. I'm sure readers of this forum with a little thought could come up with others.


    Bob Clark
     
  5. Nov 24, 2007 #4

    ZapperZ

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    Er.. no, it isn't economically "feasible".

    First of all, we already have superconductors that work above the LN2 temperatures. Secondly, can you imagine the kind of equipment needed to force that kind of pressures? How large do you think you can make an equipment that can produce that type of pressure at the end of such diamond anvil? Do you know how "small" that material is? What is the use of something THAT small in commercial application?

    We already see the drawback in using the cuprate superconductors in applications. That's why it isn't that widely used still. I don't see how another requirement of high pressure simply to achieve LN2 temperatures would be anything "economically feasible", especially for large scale applications.

    So far, these types of experiments are simply to add to the physics/knowledge base.

    Zz.
     
  6. Nov 24, 2007 #5

    f95toli

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    Why would anyone use a superconductor that requires such an extrem pressure to be useful at 77K in an application?
    Existing high-Tc compounds such as YBCO and various Bi compounds such as 2212 work very well at 77K and when used properly can "do" just about everything we need them them for.The main reason why they are not more widely used is problems wihth the "infrastructure" needed for cooling (e.g. reliability of cryocoolers) and "mechanical" issues (especially for high-Tc cables, things like bending radius and stress are real issues)

    Also, there are no guarantees that such a superconductor would have propertoes that made it useful; we know of hundreds of superconducting elements and compounds but only a handful are actually used; most elements/compounds with hight Tc are difficult to grow or have other undesirable properties that make them virtually useless.
    The Hg based cuprates would be a good example, they have highest known Tc of all known compounds but are never used in applications.

    That said, it would of course be interesting from a purely scientific point of view if it could be done. Shouldn't it be possible to calculate all (or at leat most) properties using DFT? Is should be very accurate for a "simple" superconductor such as boron.
     
  7. Nov 24, 2007 #6
    The maximum pressure attainable by the diamond anvil method is typically given around 360 GPa, 4 megabars:

    Diamond anvil cell.
    http://en.wikipedia.org/wiki/Diamond_anvil

    However, recently there have been produced synthetic diamonds 50% harder than natural diamond:

    Large diamonds made from gas are the hardest yet.
    Posted on: Wednesday February 25, 2004.
    http://www.physlink.com/News/022504CVDDiamonds.cfm

    The researchers state these could be used to produce pressures at least up 200 GPa. However, since they are 50% harder, conceivably they could be used to create pressures 50% higher than that for natural diamonds, so perhaps to 540 GPa.
    Then the range to test the linear increase of transition temperature
    of superconductivity with pressure for boron could be doubled.


    Bob Clark
     
  8. Nov 24, 2007 #7
    Another possibility might be to use strong magnetic fields that
    induce a high outward pressure on materials at high intensity to
    counteract the very high compressive forces on the anvil.
    This magnetic field generation method might work when you consider
    that the main reason why static magnetic fields are limited in
    intensity to about 30 tesla or so is because the intense fields cause
    the wires to fall apart. See this page for a formula on the forces
    produced by the magnetic field:

    Magnetic Properties of Ferromagnetic Materials.
    http://hyperphysics.phy-astr.gsu.edu/hbase/tables/magprop.html#c2

    It is quite possible to generate gigabar pressures in the wires
    containing the current for example. The idea then would be to induce
    the very high outward pressure in the diamond or metal in the anvil so
    it would be able to withstand the high pressure far above what it
    would normally take to crack it.
    You might want to use a metal now rather than diamond in the anvil
    since metals would more easily carry the high currents required to
    generate the high magnetic fields. The metals would not be as hard as
    diamond but the hope is this would be outweighed by the outward
    pressure produced by the magnetic field.
    Some recent research also has suggested that osmium might be
    comparable to diamond in resistance to compression, though not in
    hardness:

    Osmium is Stiffer than Diamond.
    27 March 2002
    http://focus.aps.org/story/v9/st16


    Bob Clark
     
  9. Nov 24, 2007 #8

    ZapperZ

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    Right.. so if I want to conduct electricity over ... let's say, 100 km, I have to build this huge and long device similar to a "diamond anvil" and have to apply that much pressure on this material over that length.

    What was it again that you said earlier about it being "economically feasible"?

    Zz.
     
  10. Nov 24, 2007 #9

    f95toli

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    Also, the magnetic field method has one big problem: Presumably the field strength needed to generate that kind of pressure would be MUCH higher than the critical field of the superconductor.
     
  11. Nov 27, 2007 #10

    If "tetracarbon" does indeed have the strength properties claimed, then it may be a means of maintaining the high pressures required on the boron.

    Newsgroups: sci.astro, sci.physics, sci.energy, sci.materials,
    sci.chem
    From: "Robert Clark" <rgregorycl...@yahoo.com>
    Date: 8 Sep 2006 11:35:49 -0700
    Local: Fri, Sep 8 2006 1:35 pm
    Subject: 'Tetracarbon', 40 times harder than diamond?
    http://groups.google.com/group/sci.astro/browse_thread/thread/ff42a43c596088a8


    Bob Clark
     
  12. Nov 27, 2007 #11

    ZapperZ

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    For some odd reason, you seem to be completely blind to the engineering and design aspect of this.

    You want to tout the "economically feasible" aspect of it, but yet, you seem to continually ignore it. I don't get it.

    As has been said, the use of ANY material, and especially superconductors, isn't JUST based on what Tc values one can get. This is the LEAST of such problems. Yet, it appears to be the ONLY parameters that you are obsessed with. And it is highly ironic because for the two of us who responded in this thread and who are physicists that have worked in the PHYSICS of these material, we seem to be the ones who are trying to get through to you of the practical and feasible aspect of this.

    Zz.
     
  13. Nov 27, 2007 #12
    Nobody knows YET what the properties of this room-temperature superconductor will be. The possibility it could be feasible is so important that means of inducing such extreme high pressure states need to be developed in order to find out. (Of course if there were found materials capable of stably maintaining pressures say 15 times higher than diamond, that in itself would be a majorly important advance.)
    I'm aware that current carrying capacity and malleability into wires are also important factors for a superconductor. I'll do a search on citations on the boron superconductivity article to see if it's current carrying capacity for example was determined in the superconducting state.


    Bob Clark
     
  14. Nov 27, 2007 #13

    ZapperZ

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    Don't forget to do a check on the "feasibility" of having a wire 1 km long under such a pressure, and HOW exactly are you going to use it in that scenario. Have you actually seen one of these anvil setup?

    Zz.
     
  15. Nov 27, 2007 #14
    No. I think the idea would be to cast the tetra-carbon insulated boron cable at high pressure, then owing to the tetra-carbons hardness, it will retain high pressure on the boron core without external pressure. Whether or not tetra-carbon has this property, or whether this property can be infered from it's hardness, I don't know.
     
  16. Nov 28, 2007 #15
    Superconducting boron and boron-doped superconducting diamond, a connection?

    I was doing a search on arxiv.org for articles on boron superconductivity and found some articles discussing the fact that diamond becomes superconducting when doped with boron:

    Origin of Superconductivity in Boron-doped Diamond.
    http://front.math.ucdavis.edu/0404.0547

    Then what might be happening with the boron superconductivity is that under the very high pressure of the diamond anvil, boron is infused into the diamond, thus acting as a dopant.
    Apparently for this boron superconductivity to be observed, the high pressure still has to be applied, i.e., the diamond anvils still have to be in contact with the boron. Then it's possible the drop in resistance is coming from the lack of resistance in the diamond immediately surrounding the boron sample because of the boron infused in the diamond.


    Bob Clark
     
  17. Nov 28, 2007 #16

    ZapperZ

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    .. and would you like to quote for us the Tc for this doped diamond? Think how much much ground you have to make to get it to room temperature, and compare that to the difficulty we already have using the cuprates that already have a head start at having very high Tc already!

    There is a disconnect to reality here, and that seems to be a consistent theme.

    Zz.
     
  18. Nov 28, 2007 #17
    Not necessarily. I was only offering this as a possibility. But if it is true AND if the temperature of onset of superconductivity goes up with the increase of the boron dopant, then there are many ways of increasing the boron amount in the diamond, not just high pressure.
    For instance, you could use high velocity boron ions aimed at the diamond for example.
    The key question to determine is does Tc really go up for diamond with increased boron content?


    Bob Clark
     
  19. Nov 28, 2007 #18

    ZapperZ

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    Don't be so sure!

    Look at the cuprate superconductor. As one dope it with holes via the cation substitution, you start seeing Tc increasing. Now one would think, why not just dope with a lot of holes? 2 problems

    (1) Tc gets to a maximum as some value and then it starts DROPPING as one dope it some more. So just because it increases initially doesn't mean it will continue as you continue doping.

    (2) At some point, you run the risk of causing a structural transition when you have introduced too much of the "foreign" dopant! This will cause the material to change characteristics completely, because the crystal symmetry now will be different. Such a change can cause quite an abrupt transition to many different properties, even making it go non-superconducting!

    Things are not as trivial as you make them out to be.

    Zz.
     
  20. Dec 4, 2007 #19
    In many cases physicists try to related pressure studies of Tc to doping of different materials. When doping of different materials it can stretch or squeeze the unit cell to change the electronic properties of the material. One thing that you have not discussed is at what pressure would the structure of the crystal break down. Not to mention that pressures from a diamond anvil are surely non feasible for any practical purpose outside of a diamond anvil. They are very small setups and very hard to use.
     
  21. Dec 4, 2007 #20
    There's just some problems with this idea that makes it impractical -

    First off, higher doping should increase the Tc until you get to a point where any further doping would either lower its Tc or ruin its superconducting properties. However, I don't think this will have as great an effect as you think it would. The effect of having three dimensionality on the density of the bond states keeps the boron doped diamond from having a higher Tc because it lowers the effect of the doping.

    Going more into the quantum effects in play, diamond is three dimensional in its bonds which are in play (three of six phonon branches that are bond stretching). I believe this three dimensionality would cause a very small function increase in fermi level density as more doping happens (compared to other superconductors which only have two dimensional sigma bonds).

    (sorry if that last part didn't make too much sense, in way to little sleep)

    These last two have been said before, but just a little more detail -

    You would need a substance which can maintain a pressure much higher than diamond (over 30x I believe), you would have to worry about the thickness, cost to produce, and safety of the material, if we can even discover something like it in the future.

    Lastly, Economics - making Kilometers of this stuff would not be worth the amount a person would stand to gain from having a diamond-boron superconducting "wire". There has to be a profit somewhere in this business.
     
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