# Talk:Crystal structure

## Untitled

I suggest adding "lattice constant" or "grating constant". I just do not know the exact name for it in english (whether the name in materials or optics) and I am not sure about adding it with definition in the article or link it to an own one. what do yo think?

--morgenrot42 23:12, 22 Aug 2004 (UTC)

the idea was to delete that page, then to rename the" mineral structure" -> "crystal structure".

But suit yourself. If you do it, it will take one second
if I do, it will take maybe two weeks. So do as you wish.

I'll put it on the vote for deletion as usual

ant

History moved. I still think that unit cell should be merged here. --mav
There is no "what the hell". If the history (at least of the richest article) has to be preserved, and the two pages exist at the same time, I cannot do a redirect to an already existing page. Right ? And I cannot delete a page either. So, what I have been doing for a year now, is either to drop the subject as it is very relaxing to do so, or to head for the votes

for deletion page to have one of the pages deleted. Wait until someone is kind enough to do it, then make the move. That is precisely what any non-sysop user has to do each time he wants to do something similar :-)

Replaced mav's diagrams with smoother ones, and added the missing ones. I'm no crystallographer, so let me know if I did something wrong with them -- DrBob 02:25, 20 May 2004 (UTC)

I'm not a crystallographer either, but they look great to me! The only nitpick I have is that the difference between triclinic and rhombohedral is that all the sides are the same in rhombohedral. It's reasonably clear in the diagram, but could you add a little a next to each side of mav's rhombohedral diagram? Tantalate 19:48, 20 May 2004 (UTC)
OK, I've uploaded a tweaked version -- DrBob 20:02, 20 May 2004 (UTC)
Thanks, looks awesome! Tantalate 20:37, 20 May 2004 (UTC)

It would be nice to have the pictures at Wikipedia-Commons. --80.185.28.63 11:13, 11 Feb 2005 (UTC)

## Miller Indices

The text, as it is, implies Miller Indices are only applicable to cubic systems. As far as I know this is incorrect- they are applied to non mutually orthogonal axes as well.

Changed. Thank you. Materialscientist (talk) 00:30, 1 March 2010 (UTC)

Still struggling to understand this topic. Existing diagram is very helpful, but it would help to have the "origin" in the diagram pointed out. (Yes, it's probably irrelevant once you understand this stuff, but it's a useful stepping stone to full understanding.) Assume that the a1, a2, a3 in this description apply to the different axes of the "unit cube" when it's not cubic. Does the order matter in (say) a triclinic crystal? Would be useful to see a diagram labeled with these axes. More useful to see a non-cubic diagram labeled with these axes. Also useful to discuss the equivalent of Miller indices for hexagonal crystals (or state that there isn't one). 76.102.149.228 (talk) 15:03, 26 August 2013 (UTC)

## Lattice vectors

There doesn't appear to be anywhere on Wikipedia where primitive lattice vectors for various lattices are explicitly stated. E.g for FCC,BCC etc. I think it would be useful for any student looking for such information. I added the FCC vectors to the diamond page but they were removed! I could add a list in a new section on this page if thought appropriate.

Thanks Lukehounsome

There is something like this on Cubic (crystal system), you could add info there and on similar pages.--Patrick 12:43, 8 February 2006 (UTC)

## Crystal illustrations

Has anyone taken on the task of making them SVG images? This would be nescessary in any case if the periodic table of Wikipedia:WikiProject_Elements would be converted to SVG. --Dschwen 22:18, 2 March 2006 (UTC)

I've made a .svg of the hexagonal lattice. Image was based on Cubic structures by User:Baszoetekouw - Danieljamesscott 13:23, 23 October 2006 (UTC)

## Making some changes

I'm making some changes to this article. We already have articles for crystal system, Bravais lattice, crystallographic point group and space group. Some of these articles are ok, but we need to tie all of these concepts together, and I believe this article is the right place to do that. So I'm trying to structure this article so that it will give a good overview of the different concepts, while still being short and concise. I'd be happy to have som help in this though. O. Prytz 22:05, 7 June 2006 (UTC)

## Motif/Unit Cell

Introduced concept of 'motif' and distinguished it from 'unit cell' (which is strictly a geometric construct). Dr Thermo 19:13, 19 July 2007 (UTC)

## Rhombohedral

The rhomohedral unit cell should show that the three angles are equal. Dr Thermo 19:14, 19 July 2007 (UTC)

## Point and Space Groups

Introduced improper rotatation and distinguished between symmety operations and symmetry elements. Dr Thermo 19:46, 19 July 2007 (UTC)

## Monoclinic pictures not displaying

The two images of monoclinic structure in the table aren't displayed. Instead there are text links to the correct image pages. Any idea what's going on? I'm using Firefox 2.0.0.6. I have no experience dealing with images on Wikipedia; sorry! Matt 17:01, 18 September 2007 (UTC)

## Biological Relevancy

While I admire the physicists, geologists, and chemists on this page, in the biology and structural biology fields, a crystal structure is uniformily known as the biomolecular product of X-Ray Crystallography. I suggest a link at the top to disambiguate this. Amboo85 (talk) 01:49, 20 December 2007 (UTC)

## unit cell in other materials

Unit cell redirects here, but that concept is broader than strictly crystal structure. For example, foams can be characterized by their unit cells (e.g. to distinguish closed-cell and open-cell foam). --Delirium (talk) 03:05, 13 April 2008 (UTC)

## Description of crystal structures

(colab. MOVED FROM Crystallization)

By considering the arrangement of atoms relative to each other, their coordination numbers, interatomic distances types of bonding etc, we can form a general view of the structures and alternative ways of visualizing them. There are two useful approaches:

### Close packing approach

(cubic and hexagonal close packing)
The principles involved can be uderstood by considering te most efficient way of packing together equal-sized spheres in three dimensions.

According to the image, if layer A lies beneath layer B, there are two possible ways of placing an additional atom on top of layer B. Atoms could be placed on the S labelled positions or the T labelled position, but not both. If an additional layer was placed on the S positions, this would create a layer that is directly over A, giving rise to the following series :

... ABABABAB....

This is known as hexagonal close packing.

If however, the third layer is placed at T, all three layers are staggered relative to each aother and it is not until the fourth layer is positioned at A that the sequence is repeated. If the position of the theird layer is called C, the following sequence arises:

... ABCABCABC...

This is known as cubic close packing

The unit cell of the c.c.p arrangement is the face centred cubic (f.c.c) unit cell. This is not immediately obvious as the close pack layers are parallel to the {111} planes of the f.c.c unit cell. There are four different orientations of the c.p. layers).
The packing efficiency could be worked out by calculating the area of the spheres and dividing that by the area of the cell: (4 spheres and the cell edge is ${\displaystyle 2{\sqrt {2}}r}$ )

${\displaystyle {\frac {4\times 1.33\pi r^{3}}{16{\sqrt {2}}r^{3}}}=0.7405}$

The 74.05% packing efficiency is the maximum density possible in structures constructed of spheres of only one size.

Examples of Closed Packed Structures- Most metals are h.c.p, c.c.p or body centred cubic. These distribution of structure types among the metals is irregular and no clear-cut trends are observed

## Correction of reference to volume as an intensive variable

I changed a sentence early on in the Polymorphism section that read:

"According to Gibbs' rules of phase equilibria, these unique crystalline phases will be dependent on such intensive variables as pressure, temperature, and volume."

"According to Gibbs' rules of phase equilibria, these unique crystalline phases will be dependent on intensive variables such as pressure and temperature."

Volume is not an intensive variable; it is extensive, as it is dependent on the size of the system. Jthechemist (talk) 16:14, 29 July 2010 (UTC)

## "Prediction of structure" section

This section, as of 8 April 2011, seems too long and too complicated for this article. It is largely historical information, with a narrow focus on transition metal salts, metals and intermetallics. If this stuff is still state-of-the-art CSP in 2011, we should find a recent review to prove the original 1930s-1950s papers are worth including.

Phys. Chem. Chem. Phys. (2010) 12 (30) was a special issue on "solid state and cluster structure prediction". There should be plenty of up-to-date summaries of the field present in those articles.

I propose Crystal structure#Prediction of structure be shortened and most of the content moved to Crystal structure prediction. A sentence or two should be written about molecular CSP, as it's just as important as predicting the structure of metals and other simple inorganic network structures. Predicting and understanding polymorphism, particularly in pharmaceuticals, is a very important application of molecular CSP. I suspect its importance dwarves that of the stuff mentioned here at the moment.

Ben (talk) 09:42, 8 April 2011 (UTC)

## Intensive vs. extensive variables wrong again

In the polymorphs section, someone edited my previous change (noted above) to state that both pressure and temperature are extensive variables. They are actually intensive, as they are independent of the scale of the system.

Proof: from the ideal gas law we know that PV = nRT. The # of moles (n) is extensive (scales with amount of material), and so is the volume (V). If we scale the entire system by a factor of two, the # of moles doubles and so must the volume. The pressure (P) and temperature (T) will remain constant, and are therefore intensive properties. I think this point gets lost on many physical chemistry students.

See intensive and extensive properties for the correct definition. Both pressure and temperature are correctly classified as intensive there.

Original sentence: "According to Gibbs' rules of phase equilibria, these unique crystalline phases will be dependent on extensive variables such as pressure and temperature."

New sentence: "According to Gibbs' rules of phase equilibria, these unique crystalline phases will be dependent on intensive variables such as pressure and temperature."

Jthechemist (talk) 23:57, 20 August 2011 (UTC)

## Principal axis

Principal axis (crystallography) redirects here, but isn't defined in the article. Ratzd'mishukribo (talk) 18:57, 30 March 2012 (UTC)

I now redirected Principal axis (crystallography) to the appropriate subsection. Ratzd'mishukribo (talk) 20:23, 10 September 2012 (UTC)

## Asymmetric unit

I think that this article should also discuss the asymmetric unit so that we can make Asymmetric unit redirect here. Bmdubs (talk) 06:13, 9 July 2012 (UTC)

## Merger with Crystallography?

The two terms are closely related and the subject matter and content are overlapping and redundant. This article is now much better, but ideally I would prefer to have the information under "Crystallography" particularly as 2014 is going to be the International Year of Crystallography (http://www.iycr2014.org/). A redirect would be OK, but I feel it would be best if people see a good Wikipedia article with that term, as this now is. Martino3 (talk) 18:01, 30 December 2013 (UTC)

## Monoclinic

The definiton of angles of the monoclinic system seem to be different from other sources. --Uvainio (talk) 12:32, 5 May 2016 (UTC)