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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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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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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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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Are the HKL planes for a primitive unit cell identical to that of the conventional unit cell?

Is there a general relation between hkl planes in primitive vs. conventional unit cells? For example, is (111) identical for both? To illustrate, let's say you took the planar packing density for (111)...
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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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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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Struvite Crystals: How does it 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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$P 4_{2} 22$ 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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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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How to get the coordinates of β12 borophene and χ3 borophene?

Can someone tell me how to draw the β12 borophen and χ3 borophene in Materials Studio or any other software? I've just started my project work, and I'm a beginner in this field. I have searched for ...
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Finding the atomic packing factor (APF) of Sodium Chloride and other FCC ionic compounds

For a piece of coursework I am doing, I need to calculate the atomic packing factor of some ionic compounds. I have had no formal teaching in this area, so what I know comes from information I have ...
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How is ECR (Electron Counting Rule) done in a structure?

I've been told how to apply the ECR to GaAs{001}(2×4) in my lectures but it makes no sense to me and I don't seem to be able to find any other sources that explain this. (This is a further question on ...
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Are diamonds as chemically inert as glass? [closed]

Every beaker that I have seen in a lab is made of glass. Glass, as I understand, is made of SiO2, or silicon dioxide, which has a crystalline structure that is similar to diamond. This property causes ...
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Why is the ionic radius of hydride so large?

The order of ionic radii for halides and hydride is apparently as follows: $$\ce{F-} < \ce{Cl-} < \ce{Br-} < \ce{H-} < \ce{I-}$$ Why is the hydride ion so large, even larger than bromide ...
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Is the lattice point in ZnO crystal structure occupied by the molecule ZnO or the ion O^2-/Zn^2+?

I learnt that ZnO has a hexagonal crystal system. I was expecting that cations or anions would occupy the lattice points in hcp while voids would be occupied by anions or cations respectively. But ...
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What is meant by "basis" in "... its basis in particles leads to a material comprising crystallites or grains tightly bound together, ..."?

I am currently studying Ultrasonic transducers – Materials and design for sensors, actuators and medical applications by Kentaro Nakamura. In chapter 1.2.1 Ferroelectricity, the author says the ...
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What would oxygen or nitrogen snow look like?

I was watching a video of what would happen if the earth got kicked out of the solar system and at one point it was mentioned that oxygen and nitrogen snow would form. So would such snow be any ...
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Can a crystal structure of a substance appear or disappear?

I read somewhere before that some substances no longer crystallize naturally in some specific structures, although it do that readily before. Instead, new structures that never happen before become ...
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If a good choice of a unit cell should be the one of most symmetry ,then why keep body centered tetragonal if face centered cubic exists?

For any lattice a good choice of a unit cell is the one that is the most symmetric. Now if every lattice made by a body centered tetragonal unit cell can be made by a face centered cubic unit cell ,...
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Conventional unit cell for a hexagonal crystal system

The figure shows a unit cell of a hexagonal crystal system. Drawn in bold, is the unit cell. The lightly shaded one is a unit cell as well and has a six fold symmetry along an axis, hence is more ...
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Interplanar distance given Miller indice of the planes

Say we've a cubic crystal of unity edge length. A set of planes in such a crystal is specified by their miller indice as $(3 2 0)$. One of these planes then has intercepts on the axes as $(2 ,3 ,\...
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Trouble understanding interplanar spacing using miller indices

We know that two parallel planes have the same Miller indices, this implies that we can have an infinite number of parallel planes close to one another all of which have the same Miller indices. But ...
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How to differentiate hydrous and anhydrous compound? [closed]

For an experiment, my teacher gave me containers of hydrates and their corresponding anhydrous compounds, but I have a feeling that for one of the compounds she switched the hydrate and anhydrous ...
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If stirring negatively affects crystal purity, why is it so?

My Intellectual Expectations Intuitively, I would expect strong stirring to improve crystal purity during the process of crystalization. My rationale is that strong stirring would increase contact ...
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302 views

Is iron(iii) hydroxide equivalent to hydrated iron(iii) oxide? [duplicate]

Are the chemicals $\ce{Fe(OH)3}$ and $\ce{Fe2O3⋅3H2O}$ equivalent? They are both network solids and have the same empirical formula but I know that doesn't always mean they are structurally the same.
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Change of ionic packing upon crystals are pressurized

When rock salt crystal is pressurized, its FCC structure changes to BCC structure whereby coordination ratio changes from 6:6 to 8:8. At the same time packing efficiency of the crystal decreases from ...
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How do I find miller indices for a plane whose intercepts are fractions of the lattice constant?

[I'm talking with respect to cubic lattices alone.] For instance, if a plane has $x,y,z$ intercepts $a/2,a/2,a/2$ (where $a$ is the lattice constant) the miller index would be $[2\space2\space2]$. The ...

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