Questions tagged [crystal-structure]

In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid.

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Are there tools or algorithms to detect organic molecules from 3D crystal structures?

The task I'm thinking of is to detect entire molecules from structures, such as in a crystallographic information file (CIF) or from the XYZ file generated in a molecular dynamics simulation. ...
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What is the structure of hydrated beryllium chloride [closed]

Is there water of crystallization or does water act as ligand? Also Be2+ is smaller than Li 2+ then why Li2+ has only 2 water molecules as ligands
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Number of bridge oxygen atoms in a silicate mineral

Total number of oxygen atom(s) which act(s) as bridge between any two silicon atoms in a mineral with composition $\ce{MM’Si3O_x}$ $(\ce{M}$ is the divalent metal ion and $\ce{M’}$ is the tetravalent ...
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Where can I find data for ionic radii? [duplicate]

Where can I find data for the ionic radius of various ions? I am looking specifically at yttrium ions, zirconium ions, niobium ions, molybdenum ions, chlorine ions, hafnium ions, tantalum ions, and ...
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Data for Madelung Constants

Where can I find data for the Madelung constants for various ionic compounds? Specifically, I am looking at silicon tetrachloride, yttrium (III) chloride, zirconium (IV) oxynitrate hydrate, niobium (V)...
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How do other elements fit into a diamond's carbon lattice (e.g. nitrogen in yellow diamonds)

Traditional pure-carbon diamonds have a simple structure (tetrahedral, if I'm not mistaken). But common types of diamonds have other elements within them. For example, yellow diamond has nitrogen in ...
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How is the cubic d-spacing formula derived from the Miller indices of a standard plane? [duplicate]

I just had a question about deriving the cubic structure d spacing formula. Just trying to work through the logic so I understand it better. If I start with the standard plane: • The plane ...
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Two atoms exist in the same coordinate position in the lattice?

I am trying to simulate the properties of FeF3(H2O)3, so I download its crystal structure file from Crystallography Open Database, but it seems that in the lattice, ...
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In calculating the radius ratio in a tetrahedral site in an FCC lattice, why do we take tetrahedral void in the middle of the body diagonal line? [closed]

When calculating the ratio of cation / the ratio of anion in a Tetrahedral system in an FCC lattice, why do we take the void to be in the center instead of it being √3a/4 from the corner.
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Why does density decrease when pressure is increased on an NaCl type lattice?

I was told that the effect of pressure on an NaCl type structure would make the atoms come closer and therefore change the type to CsCl type making Z (no of atoms per unit cell) go down, hence density ...
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Why is there a difference in crystal shapes of sodium chloride (NaCl) and potassium chloride (KCl)?

According to Sodium chloride and Potassium chloride: Sodium chloride (NaCl) crystallizes, among various other shapes, into octahedron and tetragonal pyramid shapes which are absent in potassium ...
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How to find the standard deviations of lattice parameters after Rietveld refinement with GSASII?

I am trying to learn how to use GSASII. It is different from GSAS/EXPGUI, so I feel hard to find some information from GSASII interface. I want to find what are the values for the standard deviations ...
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Radius ratio of capped octahedral coordination (CN=7)

I was asked to work out the Radius ratio of capped octahedral coordination when CN = 7. How to define a capped octahedral? Is there any restrictions on the lengths of the edges or the distances of the ...
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Why aren't ionic crystals stronger than diamond?

If ionic bonds are stronger than covalent bonds, then why aren't ionic crystals stronger than diamond, which is bonded by covalent bonds? Diamond has tetrahedral structure with carbons forming ...
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Why does Samarium have such a large c-axis lattice constant? (>26 Å) Are there significantly larger lattice constants of the elements?

Figure 1.2 on page 12 of The Structure of Rare-earth Metal Surfaces linked below shows a repeating stack of hexagonal layers arranged as A B A B C B C A C... and several sources give the c-axis ...
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Restoring potential of atoms in a solid

Above $\pu{0 K}$ the atoms in a solid are vibrating. However, what kind of potential restores each atom in the starting position? Consider the crystal lattice of NaCl. The potential energy of a $\ce{...
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Distribution of molecules in a crystal

If I dissolve 0.999 mol NaCl and 0.001 mol citric acid in water and then evaporate the water, will the citric acid be uniformly distributed in the resulting crystals? I found this post which suggest ...
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Given a CIF (crystallographic interchange format) file (and thus cartesian atomic coordinates), how can you find the bonds between atoms?

Applications like Vesta show bonds when viewing a CIF file; how could one algorithmically find all bond pairs? Here is an example CIF file: ...
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How exactly are unit cells arranged in a crystal? [closed]

Does a certain type of compound only contain a single type of unit cell (eg.bcc,fcc,etc) or different type of units cells combine to form a crystal of any compound?
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How do I crystallize Sodium Acetate w/o a crystal? [duplicate]

I made some sodium acetate. Definitely not pure or anything close. But I just did it as a quick experiment. Just some vinegar and baking powder. When I search how to make $\ce{NaOAc}$ crystals, people ...
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Why use diamond-like carbon instead of diamond?

Diamond-like carbon is an amorphous form of carbon, made of many small crystallites, mixing up the polytypes of diamond (most commonly the cubic lattice diamond, but also its lonsdaleite polytype with ...
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For a given packing (hcp, fcc, bcc), which ions occupy the corners and which occupy the faces or centers?

I recently came across the packing of atoms in unit cells. I wanted to know if there was a way to tell where the atoms in the unit cell are just by knowing the compound and its packing (hcp, fcc, etc.)...
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Lysozyme crystals versus NaCl

If someone has some experience with lysozyme crystals I would be interested in knowing whether any of the images below seem likely to be lysozyme. Solutions were made with powdered lysozyme ($\pu{50 ...
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Determine anion radius in FCC cell

The edge length of an FCC cell is $\pu{508 pm}$. If radius of cation is $\pu{110 pm}$, the radius of anion is? My approach: $$(2R_{\text{cation}}+2R_{\text{anion}})^2=2a^2$$ Which on simplification ...
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Height of FCC arrangement

I have read that height of HCP arrangement is given by $\mathrm{4r\sqrt{\frac23}}$ as distance between consecutive layers is $\mathrm{2r\sqrt{\frac23}}$(in both FCC and HCP). If that is the case, then ...
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stoichiometric crystal

I wonder if there is something like a "stoichiometric crystal"? In other words: Is it possible to have a crystal that is non-stoichiometric? I'm not interested in crystal defects but don't ...
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Why does fcc lithium melt with increased pressure?

According to the phase diagram of lithium given here, the fcc phase formed at moderately high pressure melts at decreasing temperature upon adding more pressure, an effect better known with the ...
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Is this the first report that acetonitrile & propionitrile crystals create highly polar nano surfaces? How does one detect or quantify such surfaces?

Phys.org's Titan-in-a-glass experiments hint at mineral makeup of Saturn moon says: Titan, Saturn's largest moon, is a natural laboratory to study the origins of life. Like Earth, Titan has a dense ...
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How many 4th nearest neighbours are there in an hcp lattice?

My teacher told us that there are 18 4th nearest neighbors in an hcp lattice, at a distance of √3a . I have only been able to identify 12. Can you help me find all the 4th nearest neighbors?
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What does “Average Width” mean in crystallography?

Mathematician G. Polya noted (the solution for Problem 8, Axes of a Cube) in his book How to Solve it: ... there are three kinds of axes: (1) 4 axes, each through two opposite vertices ... (2) 6 axes,...
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What is the difference between structure and morphology in polymer blends?

When talking about polymer blends there is a difference between its structure and morphology, but I am not sure what it is. These two terms are used interchangeably in materials I use to study, but I ...
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Radius ratio of octahedral interstitial site in BCC lithium

Problem Determine the minimum radius of an atom that will just fit into (a) the tetrahedral interstitial site in FCC nickel and (b) the octahedral interstitial site in BCC lithium. Solution (a) For ...
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How to understand the chemical formula of Prussian blue complex w.r.t its crystal structure?

Note: Just to be clear, I do not refer to "complex molecules" (i.e. "complex" as "complicated"), but to actual complexes. I am trying to understand the structure of ...
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How many bonds does oxygen really make in minerals?

I'm studying some metallurgy things and interested in iron oxides. The simple 2-D representation of a mineral like hematite shows $\ce{O=Fe-O-Fe=O}$. But the crystal structure seems to show each ...
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HCP and hexagonal primitive cell [duplicate]

There are 14 types of Bravais lattices one of them is hexagonal which is just present as primitive cell ie the basis are at its corners , now when I read about hexagonal closed packing I came to know ...
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2 votes
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Whats the difference between unit cell and motif?

The definition in my material is that motif and unit cells are both a repeating unit, but whereas motif is with respect to 2D lattice the unit cell is with respect to 3D lattice. But I can't find ...
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2 votes
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Converting a CIF file to a .com or .gjf file

I would like to perform DFT calculations and extract atom coordinates for calculations in Gaussian. I am using Mercury and have been able to isolate the atoms that I am interested in simulating. ...
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Why are there exactly 5 types of two-dimensional lattices, and what distinguishes them?

In the book Chemistry: The Central Science, they introduced the following 5 types of two-dimensional lattices: The book said that the blue square represents the unit cell, the black dots are lattice ...
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What is the crystal structure of ammonium hydrogen sulfate? It's beautifully birefringent

I make art using a microscope and camera. I have heated ammonium sulphate that decomposes to ammonium hydrogen sulfate, melts, and then recrystalises to produce exceptionally beautiful birefiringent ...
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What is the maximum number of water molecules that has been recorded till date to present as water of crystallization in a compound?

Context: I was casually looking through some old questions when I found this question. The OP wanted a compound that has all the hydrates ranging from monohydrate to decahydrate. I found chromium(III) ...
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Why is the disordered CuAu structure more stable at high temperatures?

I know that the disordered CuAu structure is based around FCC whereas the ordered CuAu structure is tetragonal. Why would the FCC structure be more stable at high temperatures? For context, I was ...
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4 votes
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Getting an “index” of 7 for a set of powder diffraction data

I tried to index powder diffractogram from the following problem: A metal (of density $\pu{0.862 g cm^-3})$ gives the following powder X-ray diffraction data $(\lambda = \pu{1.5418 Å}).$ $$2\theta \...
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4 votes
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Struvite crystals: how do they form?

I'm in general chemistry, and I was wondering how ionic species crystallize and form the shapes they do, specifically in regard to the struvite precipitate $\ce{MgNH_4PO_4. 6H_2O}$. Deconstructing the ...
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Find the Linear Packing factor of FCC [-1 -2 1]

I have been trying to figure out this question, and essentially if I assume that the only atoms that the vector touches are the starting and ending atoms, then I get 0.58. I am trying to find a more ...
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7 votes
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$P 4_{2} 22$ tetragonal group choice of origin for symmetry of special projections

I was looking at the description of the tetragonal group $$P 4_{2} 2 2$$ (No 93 in the International Tables of Crystallography) and there is one aspect that I do not understand. Namely, what is the ...
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octahedral interstitial sites located entirely within a full hexagonal HCP unit cell at a height of $c/4$ up from the bottom of the unit cell

I have been trying to visualize and find the number of them for a while, through the image attached. I can't tell whether the c/4 part includes the octahedral site or not...how should I go about ...
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2 votes
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On the exact definitions of Frenkel and Schottky defects

The wiki page on vacancy defects says; It is also known as a Schottky defect, although in ionic crystals the concepts are not identical. As far as I'm aware, they're the same. Furthermore, the wiki ...
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Height of CCP Lattice

Are the height of the Cubic Close packing Lattice and the cubic Hexagonal Close Packing the same? My understanding says that these unit cells are formed by different arrangement of atoms, ABC for CCP ...
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Interatomic spacing vs electric conductivity

I have a theory which may be wrong but I will write it down.If 2 elements at the same group (in solids)have the same crystal structure then the one with the biggest interatomic spacing has better ...
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Miller Indices of Goldnanoparticles from Turkevich and Frens method

I need the miller indices of gold nanoparticles that were synthesized after the route of Turkevich and Frens. I during my research I found a lot of publications, but it looks like no one measured it ...
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