Questions tagged [crystallography]
For questions concerning crystalline structures and their properties.
105
questions
0
votes
1answer
38 views
Cation-anion radius ratio of manganese difluoride
How to determine the cation-anion radius ratio for $\ce{MnF2}?$
I tried to calculate the $r_\mathrm{c}/r_\mathrm{a}$ ratio using the relationships:
$$2r_\mathrm{c} = c$$
and
$$(2r_\mathrm{c} + 4r_\...
1
vote
1answer
87 views
Does a unit cell have to contain a whole number of atoms?
I was given this problem recently to compute the number of ions in a unit cell of ferrous oxide $\ce{FeO}$. The data given was:
Side length $a = \pu{5 Å}$
Density $d = \pu{4 g/cc}$
Using the ...
0
votes
1answer
26 views
PdPS interlayer distance [closed]
PdPS is being considered as a layered material but when I look at its crystal structure it does not look like that. Fo example I could not figure out its interlayer distance. Does anyone familiar with ...
0
votes
1answer
61 views
HCP unit cell c-axis
Today I was asked to show that the perpendicular height, $H,$ of a regular tetrahedron is related to the length of a side, $L,$ of the tetrahedron, by $H = \sqrt{(2/3)} \cdot L$. I did this no problem....
1
vote
0answers
25 views
Why are colloidal dispersions stable? [closed]
Smaller particles in a colloidal dispersion are less stable than larger ones due to their higher surface to volume ratio.
Therefore Ostwald ripening occurs, a process which promotes growth of larger ...
1
vote
2answers
74 views
What happens to the crystal structure of ice as it gets colder and colder [duplicate]
Not sure if this belongs on Chemistry or Physics stackexcahnge.
As water freezes into ice, it turns into a solid, and expands as it forms a crystal structure. But what happens to this crystal ...
1
vote
0answers
49 views
Data-processing pipeline for protein x-ray crystallography: uncertain of terminology and order of procedures [closed]
Background: I am trying to get an overview of the data-processing pipeline for solving protein structures by x-ray crystallography, and in a very simple way understand what mathematical procedures are ...
3
votes
2answers
129 views
Importance of zinc blende and wurzite crystal structures for semiconductors?
I am currently studying the textbook Physics of Photonics Devices, Second Edition, by Shun Lien Chuang. In a section discussing the basic concepts of semiconductor band and bonding diagrams, the ...
5
votes
1answer
108 views
How do the three Miller indices (hkl) denote planes orthogonal to the reciprocal lattice vector?
The Wikipedia page for Miller indices defines Miller indices as follows:
There are two equivalent ways to define the meaning of the Miller indices: via a point in the reciprocal lattice, or as the ...
4
votes
1answer
95 views
Miller Indices and the case of a cubic crystal
My textbook, Solid-State Physics, Fluidics, and Analytical Techniques in Micro- and Nanotechnology, by Madou, presents the following image and explanation in a section on x-ray diffraction and Laue ...
2
votes
1answer
414 views
Do we really have technology with the resolution to distinguish between layers of single atoms of materials?
My textbook, Solid-State Physics, Fluidics, and Analytical Techniques in Micro- and Nanotechnology, by Madou, says the following:
X-ray analysis reveals the symmetries of crystals (lattice type), ...
3
votes
1answer
79 views
Interstitial defects in crystals: “high energy configurations”?
In the Wikipedia article on crystallographic defects, a type of point defect known as an interstitial defect is described as follows:
Interstitial defects are atoms that occupy a site in the ...
4
votes
1answer
226 views
Structure of crystalline boron trioxide
I recently came across the statement
The structure of crystalline $\ce{B2O3}$ consists of $\ce{BO4}$ tetrahedra, two sets of which form two types of interconnected spiral chains, three $\ce{B-O}$ ...
1
vote
1answer
77 views
Why Frenkel defect does not impact the density of the solid?
The following text is from Chemistry Part I - Textbook for Class XII (NCERT), chapter "The Solid State", page 23, topic "1.9 Imperfections in Solids", sub topic "1.9.1 Types of Point Defects - (iii) ...
2
votes
0answers
63 views
Substitute Sr with Mg in MgO
Could someone please help me with the following question.
Due to the perspective of voids in the MgO structure, what is the maximal amount of Sr that can substitute with Mg.
And why is it unlikely ...
0
votes
1answer
52 views
What do X-ray diffraction and NMR tell about the Proteins? [closed]
I have gone through a simple idea that proteins have different conformations; it is a dynamic system. Moreover, whenever we do ensemble experiments, so we get an average picture. There are some ...
1
vote
1answer
45 views
What is a material more easily cut than shattered? [closed]
I'm currently developing a sci-fi concept for animation which partially involves a typical "the earth has been overrun by XYZ" scenario.
One of the ideas for XYZ we're thinking of is a species of ...
0
votes
0answers
40 views
Visualization of all hcp voids
There are 12 tetrahedral voids and 6 octahedral voids in hcp unit cell but I can't find any image that can show all tetrahedral voids and all octahedral voids in hcp unit cell (the common picture in ...
2
votes
0answers
83 views
How to counter crust formation when crystallizing NaCl on the liquid-air interface?
Saturated sodium chloride solutions are evaporated at elevated temperature. The aim of evaporation is to produce hollow pyramid salt crystals. Temperatures used range from 65°C to 85°C. With 80°C ...
1
vote
1answer
80 views
How strong are molecular bonds in layman's terms?
Suppose you had a single sheet of graphite the size of an A4 page. What would it feel like to handle it?
Would your fingers instantly tear through it as you tried to grasp it?
Could you punch your ...
3
votes
0answers
52 views
Sources for files for testing a thermal ellipsoid (ORTEP) program
I am trying to reimplement the functionality of the classical program ORTEP for producing thermal ellipsoid plots of a crystal/molecule in a modern computer language. Unfortunately, I am having ...
1
vote
0answers
50 views
Pncn space group diagram
I'm trying to make a diagram of the Pncn space group.
Firstly, I know that this space group belongs to the orthorhombic system and derives from the point group (2/m 2/m 2/m).
Therefore, although the ...
0
votes
1answer
88 views
Symmetry Space Group Diagram
I am doing an introductory course to Crystallography and I have found in the following web page: http://pd.chem.ucl.ac.uk/pdnn/symm3/sgmonoc.htm a guide for the elaboration of the diagrams of the ...
14
votes
2answers
1k views
How were x-ray diffraction patterns deciphered before computers?
I know the general idea behind x-ray crystallography is to take a high quality crystal and place it in the path of an x-ray beam. Areas of high electron density will diffract the beam and lead to ...
1
vote
1answer
50 views
Are there examples of crystals with random but static mixtures of two unit cell configurations?
The image in this question turned out to probably be wrong, but it still makes me wonder. Are there examples of crystals where the atoms within a unit cell can have two (or more) different ...
2
votes
0answers
74 views
Crystallographic terminology associated with the honeycomb structure
I'm trying to quickly learn basic crystallographic principles in 2D under pressure (it's me whose under pressure, not the lattice) so I'm checking many sources to find those that "speak to me" the ...
1
vote
0answers
584 views
Calculating distance between adjacent planes (hkl) in a simple cubic crystal
My textbook says the following in a section on Miller indices:
Adjacent planes $(hkl)$ in a simple cubic crystal are spaced a distance $d_{hkl}$ from each other, with $d_{hkl}$ given by:
$$d_{...
2
votes
1answer
76 views
Miller indices: How does one translates the orientation to the origin of the unit cell?
In a section discussing Miller indices, my textbook says the following:
The rules for determining the Miller indices of a direction or an orientation in a crystal are as follows: translate the ...
1
vote
1answer
134 views
How do I view a DSN6 file as text?
I am trying to isolate certain pieces of information within a dsn6 file. Specifically, I want to find the electron density around two atoms within a protein. I want to then run a python code to ...
3
votes
1answer
153 views
Space groups: Herman-Maugin notation, diagrams and Wyckoff positions
I am currently taking an Introduction to Crystallography course. After studying and understanding the punctual symmetry groups (2mm, 4/m 2/m 2/m, 32,...), the flat groups and the diverse elements of ...
0
votes
2answers
98 views
How can I find the smaller symmetric structure from big crystal unit cell?
I have Pyrope (Mg3Al2(SiO4)3) crystal structure, downloaded from materialsproject:
https://materialsproject.org/materials/mp-6073/#
It appeared as triclinic cell, but if you download CIF file and ...
2
votes
1answer
45 views
Why is the order of reflection simplified to n = 1?
My professor told us that for the sake of simplicity, we will assume that the order of reflection for Braggs' Law is always equal to 1 but failed to explain why. Is it because d(h,k,l) for materials ...
1
vote
0answers
39 views
How do blue shifts in Raman spectra indicate a co-crystalline compound?
The short conference paper The Acetylene-Butane Co-Crystal: A Potentially Abundant Molecular Mineral on Titan (mentioned in EurekaAlert's 'Bathtub rings' around Titan's lakes might be made of alien ...
0
votes
1answer
388 views
What kind of isomerism does Ni(PPh3)2Cl2 have and what is their IUPAC name? [duplicate]
I know that there are 2 isomers that $\ce{Ni(PPh3)2Cl2}$ have and they exist in equilibrium. I am tempted to name them cis- and trans- but it does not sound right.
1
vote
2answers
78 views
Why is Libethenite (Cu2(OH)PO4) color green?
It is not a complex compound and the copper atom is not oxidized so I'm wondering how does its color change. The book mentioned that at favorable conditions, adding water in Copper phosphate, which is ...
2
votes
0answers
99 views
Understanding lattice matching of graphene on silver (111) crystal surface and meaning of the √3 x √3 lattice?
Figure 1 in Ivor Lončarić and Vito Despoja, Phys. Rev. B 90, 075414 Benchmarking van der Waals functionals with noncontact RPA calculations on graphene-Ag(111) (available in Researchgate) shows a ...
1
vote
0answers
416 views
Silver (111) surface structure, and is bulk structure body-center or face-center cubic?
I'd like to understand the atomic arrangement is on a silver (111) surface.
Step 1 would be to find out the bulk crystal structure.
Wikipedia lists silver as face-center cubic (fcc) here and here ...
0
votes
2answers
2k views
Relation between size of ion and hydration energy [closed]
Suppose I take 1 tablespoon of an ionic crystal and put it in excess water. We know that shall the hydration energy of the crystal be more than the lattice energy, the crystal will separate in ions ...
3
votes
0answers
45 views
What is “detwinning” as a 2D crystallography technique?
The Phys.org article Iron selenide revealed as 'garden-variety iron-based superconductor' is quoted below. Normally I would hesitate to quote so much but in this case it all seems germane.
Question: ...
3
votes
1answer
332 views
Space group diagram
If you give me the name of a certain space group, for example, the P222 (orthorhombic system). How could I construct the following diagram?
Image source: http://img.chem.ucl.ac.uk/sgp/large/sgp.htm
...
14
votes
2answers
3k views
Are there any crystals that are theoretically possible, but haven't yet been made?
Are there any crystals (that exist at standard temperature and pressure) that are theoretically possible, but haven't yet been made?
For example, the predicted requirements for temperature, pressure, ...
0
votes
0answers
80 views
Explanation of metallic crystal structures using orbitals and electron configuration
There has to be a direct relation between metallic crystal structure formation and electrons in orbitals. For instance, we know that Fe2+ forms body centered cubic or bcc structure with the ...
6
votes
1answer
239 views
Are electronic descalers a scam?
It seems there are some electronic kits sold around nowadays by major retailers (e.g., Home Depot and Amazon) claimed to remove built-up scale from water pipes.
But, do they actually work? If so, ...
4
votes
2answers
865 views
Sulfuric acid symmetry point group
On the following page: https://cccbdb.nist.gov/pglist.asp It appears that the point symmetry group of sulphuric acid is $C_2$. I know that $C_2$ means that there is an axis of symmetry of order 2 (180 ...
6
votes
0answers
58 views
Effect of spontaneous transmutation of atom in crystal
What happens to a compound when one of its atoms changes via spontaneous nuclear reaction to an atom with very different bonding? For example, beryllium-7 turns into lithium-7 with a half-life of 53 ...
1
vote
1answer
57 views
Lattice type from image
What type of 2D lattice is depicted in the image shown below? Is it possible to determine without knowing the length of the unit vectors and the angles in between them? I'm confused because it ...
12
votes
4answers
1k views
What is the smallest molar volume?
I wondered how small a volume a mole of material could occupy, so I started with carbon, which would need 12 grams. That's 60 carats, and there happens to be a famous 60 carat diamond.
If my density/...
5
votes
1answer
148 views
Testing for asbestos using readily available chemicals and tools?
Given that it is difficult to determine who is telling the truth in the recent claim that J&J covered up finding asbestos in their powder, is there any chemical test that we can perform on our own ...
2
votes
0answers
58 views
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/...
3
votes
0answers
153 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 ...
