Chemistry Stack Exchange
Chemistry Stack Exchange

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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Why does pyrite form cubic crystals?

Pyrite ($\ce{FeS2}$) forms cubic crystals, like these ones: I know that the crystal structure is primitive cubic, but I don’t see how cubic structure on the molecular level translates to cubic structure on much larger scales. If you are given some…
math_lover
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What do the six polymorphs of chocolate look like?

Today I learnt that chocolate tempering works by controlling the temperature to ensure the crystals set to one (type V) of the six polymorphs. What do these polymorphs actually look like? By that I mean: what is the crystal structure? Also, what…
spraff
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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 colours. I am interested in its typical crystaline…
ben
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How is knowing about the symmetry of a crystal useful

I am studying the space groups and know that we use them to talk about crystal symmetry, I would like to know what material properties may be produced or predicted from knowing the symmetry or lack thereof in a crystal system of a material?
chilliBeanDream
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Why can a face-centered cubic lattice not be redrawn as a body-centered tetragonal lattice?

A base-centered cubic lattice can be redrawn as a primitive tetragonal lattice, therefore we do not include it in the list of Bravais lattices. Why is it then that a face-centered cubic lattice cannot be redrawn as a body-centered tetragonal…
waterlemon
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Possible to grow optical calcite?

I notice that most optical calcite for sale seems to be from natural (mined) sources. Also, I know in World War 2, mining optical calcite was a strategic objective. Is there some reason why high-grade optical calcite cannot be lab grown?
Shaka Boom
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What's up with SiO₂ being tetrahedral?

If silicon dioxide tends to form a crystal lattice with four $\ce{O}$'s around a central $\ce{Si}$, why isn't the molecular formula $\ce{SiO4}$ then? I'm confused why it's unique in that its molecular formula doesn't match up with its geometry.
reflexiv
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What does the Sm5Ge4 orthorhombic structure look like?

I see tons of papers referencing this structure but none show what it looks like.
user17338
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R32 Space Group (Crystallography)

Why R32 Space Group is so named? I mean, if R stands for Rhombohedral and 3 for Threefold Axis, what 2 stands for? I don't see any Twofold Axis in the cell: http://img.chem.ucl.ac.uk/sgp/large/155az1.htm EDIT: What does it means 1/2, 2/3 and 1/6 on…
user135755
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Crystal Lattice Defects

Why do defects in crystal lattices of various molecules and compound occur ? Is it due to the continuous contact or it arises due to impurities and human error during the formation?
Rajesh
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Miller indices. What determines the appropriate axis?

So, first of all, what's up with this "plane" I see two planes! The basis of my question is that to determine miller indices the plane cannot lie on your origin, so you have to make a translation. If I move my origin to the right then I get the…
DLV
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In the lattice model, what's a nearest neighbor?

I was reviewing my grad Thermodynamics textbook to go over a concept that I never learned well: the Lattice model. One set of equations1 has: \begin{align} zN_1 &= 2N_{11} + N_{12}\\ zN_2 &= 2N_{22} + N_{12}\\ \end{align} where $z$ is the…
Nat
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Calculating vacancies in crystal structure

I have this question on a practice exam. I'm not quite sure how to find the number of vacancies when replacing atoms. Question: The stable oxide for lithium is $\ce{Li2O}$. How many oxygen vacancies in $\ce{SiO2}$ will be created if 100 Si atoms…
holi4683
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How to predict if hydrogen atoms could be placed in the interstials of a lattice

Palladium hydride is an example of a hydride which contains H atoms in palladium's crystal lattice (which is fcc). I would like to know if it's possible to predict if another hydride, $\ce{NbH_{x}}$ could exhibit the same behavior. I know that in an…
Isaiah G.
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How does the atomic structure of crystals determines its shapes?

for example, table salt has an a cubic structure in the atomic level, and they are often cube like in the visible level. I don't see any reason that the atomic crystal structure should reflect the crystal's shape. Can someone explain this to me.
CognisMantis
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