Perfect crystal - is there such thing?

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Discussion Overview

The discussion revolves around the concept of a perfect crystal, exploring whether such a thing exists in nature or if it is merely a theoretical construct. Participants delve into the definitions, implications, and conditions surrounding the idea of perfection in crystalline structures.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants argue that a perfect crystal is a theoretical idea, similar to a perfect circle, suggesting that nothing in nature can be truly perfect.
  • Others propose that while imperfections are common due to various defects at the atomic level, very small crystals may approach perfection due to fewer opportunities for defects to occur.
  • One participant mentions that imperfections can be influenced by gravity, while another counters that gravity's effect on crystal growth is negligible compared to other forces.
  • There is a discussion about the conditions under which perfect crystals might be created, such as in zero gravity environments, though this is challenged by concerns over depletion zones affecting growth.
  • Some participants highlight that intrinsic semiconductors and silicon boules for integrated circuits may represent the closest man-made approximations to perfect crystals, but acknowledge that defects like vacancies are thermodynamically unavoidable at finite temperatures.
  • A distinction is made between the concept of a perfect crystal having no defects and the idea that all physical objects, including crystals, inherently possess boundaries.

Areas of Agreement / Disagreement

Participants generally do not reach a consensus on the existence of perfect crystals, with multiple competing views remaining about the nature of perfection and the conditions under which crystals might be considered "perfect."

Contextual Notes

Discussions include varying definitions of what constitutes a "perfect crystal," the implications of defects, and the conditions under which crystals are grown, indicating that assumptions about perfection are context-dependent.

blacklily
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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 theoretical 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?
 
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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.
 
Can we construct a perfect crystal? Like constructing a perfect circle.
 
"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.
 
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 category 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.
 
Imperfections are created due to gravity. In space and in zero gravity environments perfect crystals can be created as on the International Space Station.
 
cyberjackh3 said:
Imperfections are created due to gravity.

No. Gravity has a negligible effect on crystal growth. At the atomic level, other forces are FAR more powerful.
 
cyberjackh3 said:
Imperfections are created due to gravity. In space and in zero gravity environments perfect crystals can be created as on the International Space Station.

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"?
 
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
 
  • #10
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.
 
  • #11
blacklily said:
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 theoretical 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?

billiards said:
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.

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.
 
  • #12
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:
 
  • #13
Define perfect?
 
  • #14
Dadface said:
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:

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.
 
  • #15
Vanadium 50 said:
A perfect crystal has no defects, and has no boundaries.
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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