Perfect crystal - is there such thing?

  1. Hi, I am just wondering is there such thing as perfect crystal. I don't know much about this stuff. It seems to me it's just a theorical idea, because nothing is really "perfect" in this world.

    Anyways, I just want to know more about perfect crystal. If they do exist, what is a perfect crystal?
     
  2. jcsd
  3. In the same way that there is no such thing as a perfect circle (in nature), I do not believe that there is such a thing as a perfect crystal. As you say, it is merely a theoretical idea.
     
  4. Can we construct a perfect crystal? Like constructing a perfect circle.
     
  5. "Perfect" is a very strong word. I don't believe there is anything that is "perfect". Even if we measure it to be perfect, some thing somewhere is probably going to be out of alignment.
     
  6. Depends on size

    In the world of crystallography there are specific defects at the atomic level that make a crystal imperfect. These include missing atoms (vacancies), extra atoms (interstitials), wrong species of atoms (impurities) all under the catagory of "point" defects. There are "line like" defects called dislocations, there are also planar defects, called stacking faults. Finally there are 3 dimensional defects which are inclusions of another type of crystall within the one in question. In general all crystalls have some of these defects but with great care, crystalls have been grown nearly defect free. When a very small crystal is grown, that may have just a few hundered atoms or so, I suspect that perfection is attainable since there is only a limited number of chances of getting things wrong.
     
  7. Imperfections are created due to gravity. In space and in zero gravity environments perfect crystals can be created as on the International Space Station.
     
  8. negitron

    negitron 842
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    No. Gravity has a negligible effect on crystal growth. At the atomic level, other forces are FAR more powerful.
     
  9. Andy Resnick

    Andy Resnick 6,015
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    That's not true- in many cases, the lack of bouyancy-driven convection of solute leads to a depletion zone around the crystal, which can adversely affect the growth habit (or prevent it altogether).

    And there's still possible to have impurities.

    Maybe a better question is "What's the current lower experimental/production limit of defect density in crystals"?
     
  10. I was quoting a website
    unfortunately, now that I look again I see that the website in question was you guessed it; wikipedia. my apologies
     
  11. Vanadium 50

    Vanadium 50 18,153
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    A perfect crystal has no defects, and has no boundaries. People have focused on the first part, but the second part makes it obvious that there is no perfect crystal in nature. That doesn't mean it's not a useful concept - just that, like the frictionless plane, it's an idealization that's not reached in nature.
     
  12. ZapperZ

    ZapperZ 30,451
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    Maybe you should backtrack just a little bit and make sure you understand what is meant as a "crystal" in physics, and see if this is what you mean by a "crystal". Note that in physics, this does not necessarily mean shinny, colorful, reflective objects that people sometime use as costume jewelery.

    Only after we have established a clear understanding of what a "crystal" is in physics, can we then proceed to what we mean by a "perfect crystal".

    Zz.
     
  13. Dadface

    Dadface 2,090
    Gold Member

    Am I right in guessing that intrinsic semiconductors are the closest we can get to perfection with man made crystals?I think that cables used in fibre optics have less imperfections but these have only short range crytaline structure being more amorphous/glassy.:confused:
     
  14. Define perfect?
     
  15. Mapes

    Mapes 2,532
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    Silicon boules intended for IC wafers are probably the most perfect structures ever made by humans. But impurities are only one type of imperfection. Vacancies (mentioned by bdrosd) are another, and because their presence adds entropy they are thermodynamically required; they can never be eliminated at finite temperatures.
     
  16. DaveC426913

    DaveC426913 16,439
    Gold Member

    This seems to be bifucating bunnies. When we talk about "a crystal" we implicitly mean an object, which by definition has a boundary. I would agree with you that a perfect crystal lattice would extend without bound.
     
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