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For questions concerning crystalline structures and their properties.

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Reading Stereographs

On an old paper, I found an interesting representation of some symmetry operations: stereographs. Online I found a set of symmetry operations and related stereographs (see: http://newton.ex.ac.uk/...
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80 views

X-ray structure analysis mirrored coordinates?

How to ensure, that X-ray crystallography structure analysis was done right to provide correct, non-mirrored atomic coordinates? Example: Following Wikipedia image, is generated from data taken from ...
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0answers
21 views

Why the Pmcm group space is replaced by Pmma?

I had an exercice with a "Pmcm" cristal structure, I tried to do it and it was incoherent. I realized that this space group doesn't really exist : we need to change the base vector to have a Pmma ...
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What it the point group of bilayer MoS2?

When I see the structure of bilayer MoS2, its point group is 6/mmm by Materials Project. https://materialsproject.org/materials/mp-1018809/# Yon can download and see the structure from cif file. Can ...
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36 views

How to get ionic radii for coordination number = 12?

I am studying ABX3 perovskites, and I would like to calculate Goldschmidt tolerance factors for them. The A sites in these materials have a coordination number = 12. The Shennon's paper (R. D. ...
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1answer
43 views

What is the Crystal System of MoS2?

I'm confused about the crystal system of MoS2. In the case of the monolayer MoS2, it has 3-fold rotation symmetry when viewed from the top of its unit cell (c-axis). Even in the case of bulk (AB ...
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1answer
52 views

What about Miller Indices of planes passing through origin?

For Miller Indices of planes if we encounter a case where the plane passes through the origin then I have heard that the only remedy can be arrived by shifting the origin to a different point.However ...
5
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1answer
78 views

What is the diagram of the roto-inversion of $\bar 6$?

Using the standard way of representation: Here we have a rotation followed by an inversion (technically called 'rotational inversion'). So as to represent it, what I have done is: 1) Both rotation ...
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1answer
76 views

Solubility curve for sodium tetraborate in water

What is the solubility curve for sodium tetraborate decahydrate ($\ce{Na2[B4O5(OH)4]·8H2O}$), otherwise known as borax, in water ($\ce{H2O}$)? Additionally, what is the solubility of the ...
3
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1answer
64 views

Does a molecule need to be placed symmetrically in the unit cell?

I was watching an OCW by MIT (3.091X) on solid state. My previous notion of lattice point and unit cell got shattered after this example. Where are the unit cell and lattice points in this picture? ...
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49 views

Types of unit cells of solid state

$\ce{NaCl}$ forms FCC unit cell but not BCC though $\ce{Na}$ atoms occupy body centre as well as edge centre. Why?
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Rietveld (FullProf) general background function

I was reading through Eric Mittemeijer's book 'Modern Diffraction Methods' when I found the following statement in the Rietveld chapter by Robert Dinnebier. It is common practice to use orthogonal ...
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1answer
184 views

Length of NaH bond from the edge length of unit cell

If the edge length of $\ce{NaH}$ unit cell is $\pu{488 pm}$, what is the length in $\pu{pm}$ of an $\ce{NaH}$ bond? The answer is $\pu{244 pm}$, I thought that $d = 2 \sqrt{2}\times r$ , do you not ...
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1answer
33 views

Is there a piece of software that can help me see the (hkl) planes in a crystal lattice?

I am doing research with calcium carbonate structures. I need a way in which I can familiarize myself with the lattice structure of calcium carbonate polymorphs, especially calcite. I really struggle ...
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0answers
28 views

Rietveld refinement “fronting” of peak signal

I was trying to refine a crystal structure using Rietveld refinement yesterday. The crystal structure is already known for a related compound and the powder pattern seems to show a phase pure compound....
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2answers
733 views

Calculate the third and fourth nearest neighbours in bcc

My textbook has given data for third and fourth nearest neighbours to be 12 and 8 with distances $\sqrt{2}a$ and $\frac{\sqrt{11}a}{2}$. I have been able to calculate for the first and second ...
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1answer
59 views

Why lattice constant (unit cell) is always a parallelepiped?

Wikipedia defines lattice constant as physical dimension of unit cells in a crystal lattice. Unit cell is defined as: The unit cell is defined as the smallest repeating unit having the full ...
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55 views

How to find out which plane in a cubic structure has the highest density?

For a cubic structure (namely FCC, BCC, or simple cubic) we can always draw a plane and predict the plane which has highest density of atoms. Is there any rule of thumb to arrive at such a plane? How ...
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47 views

Incomplete definition of the unit cell of a lattice

All of the books/online sources that I have found cite the following definition of the unit cell of a lattice : The unit cell is defined as the smallest repeating unit having the full symmetry of ...
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0answers
203 views

Body centered cubic lattice vs Primitive cubic unit cell

I was reading about Bravias lattices(cubic crystal system) when got confused about an article in my book. Please refer to Counting body center as lattice point when basis consists of 2 atoms. The ...
2
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1answer
44 views

Crystal structure database search for space groups

I'm usually using databases like the Springer Materials site or the free Crystallography Open Database to get crystal structure data. But none of these offers the possibility to search for all entries ...
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1answer
18 views

Electrochemical manufacturing of small metal components

Metal crystals easily can be grown via electrochemical pathways. Copper is a great example of this. I recently had an idea of growing those crystals in controlled ways (i.e.: surrounding the electrode ...
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Why different shapes of crystals are formed despite having cubic unit cell? [duplicate]

For instance, diamond has a cubic unit cell inspite of that it forms octahedron crystal.
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25 views

Single Crystalline Thin Films is detect by GIXRD? [closed]

I understand epitaxal thin film, have lattice match with substrate. But what about those films that doesnt match but have only one XRD peak? Is this proof of single crystale thin film?
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1answer
279 views

How to dock aggregated structures comprised of “elementary” protein units like LEGO pieces?

There are proteins with intrinsic symmetries. For example: I was wondering how to use transformations such as: rotations, translation, replications to construct possible structures using 2 types of ...
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724 views

How to make pyramid-shaped NaCl salt crystals

I'm attempting to make sea salt pyramids like the one below. I understand this needs to be evaporated at a reasonable speed to stop the crystals forming a cube, as the when formed quickly, the edges ...
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Finding the percent void of the crystalline structure of NaCl [closed]

Find the percent of void in the crystal structure of $\ce{NaCl}$. I am trying to calculate the percent void of the packing structure of $\ce{NaCl}$. Let's denote radius of anion as $r$, radius of ...
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28 views

What system of nomenclature can I use to indicate the positions of specific kinds of atoms of a surface reconstruction?

I was reading a journal based on SiC reconstructions, and they seem to mention that every dangling bond in the $(1\times 1)$ unreconstructed Si face or the $(0001)$ direction bonds up with a Si adatom ...
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41 views

Computational determination of unique adosrption sites

I'm not sure it's a chemistry question or physics question or math question. Since I'm active on this site, maybe someone here can point me in the right direction. I'm trying to enumerate all the ...
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0answers
63 views

What is the crystal structure for a crystal where the ratio of the squares of the angle peaks is 0.825?

I followed this and it gives an example of how to identify a crystal structure using XRD data. I have an unknown alkali halide where two peaks were found at $2\theta =25.66$ and $2\theta = 28.3$. I ...
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43 views

What can be concluded from two different values for the interplanar distance between planes of atoms in an X-Ray diffraction experiment?

I analyzed an unknown Alkali Halide crystal using x-rays from a copper source. I need to find the d-spacing for this crystal, i.e. the interplanar distance between planes of atoms. I found my $K_\...
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2answers
3k views

How do I calculate lattice points per unit volume? [duplicate]

My professor was explaining simple cubic, body centered cubic, and face centered cubic lattices and I didn't quite understand the calculations below: Simple Cubic: $8 \cdot 1/8 = 1$ lattice point per ...
10
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1answer
534 views

Miller Indices: How to deal with some weird(-ish) cases?

I've recently been doing a spot of self-learning (Crystallography), and some of the examples provided in the Wikipedia article for Miller Indices have stumped me. I can't for the world figure out how ...
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2answers
910 views

Why is crystallography still used in some cases for small molecule structure determination?

I was wondering for some time why in some cases x-ray crystallography and not NMR is used for structure determination of small molecules? Does crystallization maybe require a smaller amount of the ...
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0answers
71 views

Physical meaning of thermal parameters dimension (Ų)

In single-crystal x-ray crystallography both isotropic and anisotropic displacement parameters $U_{ij}$ of thermal ellipsoids have dimension of square angstrom ($Å^2$) as follows from the definition ...
4
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0answers
558 views

Can a solid be both crystalline and amorphous? [closed]

The first line in the Wikipedia article for "Glass" reads: Glass is a non-crystalline amorphous solid that is often transparent and has widespread practical, technological, and decorative usage in, ...
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1answer
339 views

Crystallization in a solution of 2 or more solutes

This is a very basic question I found myself wondering. For simplicity's sake, we'll say it is a super saturated aqueous solution of an equivalent measure of sugar and salt. As the solution cools and ...
5
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1answer
179 views

Use of geometry index for the determination of coordination environment

Geometry index $\tau$ is supposed to resolve proper geometry for coordination numbers (C.N.) 4 and 5 based on its extreme values ($0$ or $1$). There is also a web app Geom which handles both cases for ...
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1answer
2k views

Number of atoms per unit cell

I don't understand the concept of unit cell and the number of atoms per unit cell in a cubic lattice also the calculations for the number of atoms. For example in the $\ce{fcc}$ lattice, number of ...
5
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1answer
148 views

Assigning absolute configuration when determining crystal structure isn't possible

When natural products are isolated, their structures are often determined by x-ray crystallography which gives a complete picture of the atom coordinates, the relative and the absolute stereochemical ...
10
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1answer
187 views

Is the 'central Tin atom' in crystalline tin oxide really offset like this?

Is the position of the central Tin atom as shown in the first figure ($\ce{SnO2}$) drawn offset towards the oxygen to the right for a reason? The oxygen also seems to reciprocate and move towards the ...
8
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1answer
507 views

How many crystal forms of HCl have been identified - where to find the unit cells/lattice constants?

This blog about stomach acid shows this image of the "zig-zag" form of crystalline HCl (see also Wikipedia where it looks (to me) like five four HCl's per unit cell), but links to this cubic crystal ...
3
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1answer
121 views

crystallinity of seed crystals

Does the crystallinity of seed crystals affect the final crystal structure? and is it different depending on the crystallized material?
4
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1answer
232 views

Structure of lead(II,IV) oxide

I need help sorting out the molecular structure of tri-lead tetroxide, aka lead(II,IV) oxide $\ce{Pb3O4}$. This data sheet shows this image: The Wikipedia's lead (II,IV) oxide's link to a Jmol ...
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0answers
602 views

What is the symmetry of the cuboctahedron (FCC metal)?

The background to this is that I've recently given a tutorial wherein we had to go through the determination of point groups for atoms in various lattices (BCC, FCC/CCP and HCP). BCC and HCP, I have ...
2
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1answer
348 views

Bravais Crystal Lattices and Voids

What is the difference between Hexagonal Close Packing (HCP) structures and the hexagonal crystal Bravais lattice? I've looked up some sites but can't seem to understand them. It would help if you ...
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1answer
43 views

How the crystal structure varying for the same compound?

i have synthesized the crystal Cyclohexylammonium acetate. Structure of this compound was already solved and it s under centro symmetric space group I2/a. But when i took single crystal analysis it ...
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Could XY crystal be a special case of X2YZ crystal?

There are some types of crystals we call them XY type (i.e. NaCl) or X2YZ type? Could XY type be a special case of X2YZ type by assigning Y=Z?
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64 views

Equivalent Wyckoff position in different groups

I am not a chemist, I am a physicist, so please bare with me if what I am asking is rather obvious. If I have two symmetry groups ($P4/mmm$ and $P\!-\!1$), is there a way to find their respective ...
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1answer
196 views

Why are snowflakes shaped as they are?

(It was the Winterbash icon that got me thinking on this.) Snow flakes take on a variety of intricate shapes, but what processes are responsible for this? (Got the image off of Wikipedia) I mean, ...