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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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2answers
47k views

How are the number of tetrahedral voids twice the number of octahedral voids in a CCP structure?

How are the number of tetrahedral voids twice the number of octahedral voids in a CCP structure? Is there some kind of mathematical proof for it? Is there some way I can understand this intuitively? ...
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1answer
948 views

How to formally calculate the surface density of layered materials such as graphene?

Typically density is defined in units of mass per volume. In the case of graphene it is mass per area, i.e. surface density. What would be the correct way to calculate the surface density (mass per ...
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1answer
552 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
581 views

Charge density is the amount of charge per unit volume but what is charge?

I was studying about x ray crystallography and my book says that charge density is measured in electrons per nano-meter cubed and this means that charge is the amount of electrons. But i am not sure ...
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1answer
49 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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What does β stand for in β-potassium zirconate?

What do the Greek letters (α, β, γ...) convey when they are prefixed to a crystalline substance? For example: β-potassium zirconate
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2answers
749 views

Is there a difference between Close Cubic Packing and Face Centered Packing?

I see some places use close cubic packing (ccp) and face centered packing (fcp) interchangeably. Are they the same thing? Does one provide more information than the other?
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Why the atomic (metallic) radius of gallium is less than that of aluminium?

It is a well known fact that on moving down the group of p-block elements, the atomic radius is expected to increase. However, gallium is an exception. The atomic radius i.e., the metallic radius of ...
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1answer
52 views

Spinel or salt?

In reaction of $\ce{Al2O3}$ with $\ce{NaOH}$, we get product written as "$\ce{NaAlO2}$", "$\ce{Na2Al2O4}$" or just "$\ce{Na2O.Al2O3}$". My question is what's the real structure of this compound? ...
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39 views

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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1answer
752 views

Finding the nearest neighbour, from an atom within a crystal

Is there any software can give me the information of nearest neighbour, nest nearest neighbour,....(and their distance) from an atom within a crystal (described by a .cif file)? Perhaps some ...
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1answer
123 views

Validation of _atom_site_frac_*: Range outside of [0,1)?

I have the following cif file ...
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1answer
807 views

Is Changing between Allotropic forms a Physical or Chemical Process?

When a substance changes its alloptropic form, is this considered a physical change or a chemical change? Right now, I am thinking that it would depend on what the change was. For example, if ...
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1answer
282 views

Hydrogen bonding in solid bicarbonates

Why is there two different kinds of hydrogen bonding in solid bicarbonates $\ce{NaHCO3}$ and $\ce{KHCO3}$? In both cases we consider anions of each for hydrogen bonding . The anions involved in ...
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0answers
407 views

Osazone crystal structures

What is the reason behind the formation of different shapes of crystals for different osazones? Like glucose osazone- needle shaped, maltose osazone- sunflower shaped, lactose osazone - powderpuff ...
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0answers
498 views

Distance between two atoms that lie along a body diagonal

It is given that two atoms lie along the body diagonal of a unit cell (crystalline solid). The length of such cubic cell is $a=\mathrm{0.336\,nm}$. My book says that we should take the coordinates of ...
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1answer
2k views

Why does oxalic acid have exactly two water molecules of crystallization?

Why does oxalic acid have exactly two water molecules of crystallization? In other words, in the formula $\ce{C2H2O4\cdot2H2O}$, why is the number before the $\ce{H2O}$ exactly $2$? I tried to see ...
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1answer
5k views

Coordination numbers and radius ratio

According to the image above (source), for a radius-ratio between 0.732 and 1, the coordination number is 8. However, for a radius-ratio of 1, the coordination is 12. This is the same for the boundary ...
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2answers
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Second Peak in X-Ray Diffraction Pattern of bcc Metal

By Bragg’s law, $$2d\sin\theta=n\lambda$$ and $$d=\frac{a}{\sqrt{h^2+k^2+l^2}}$$ Combining the two gives: $$\sin\theta=\frac{n\lambda\sqrt{h^2+k^2+l^2}}{2a}$$ By the reflection rule for bcc, there ...
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1answer
3k views

What is crystallographic equivalence?

I’ve learnt that in crystallography, there are many crystallographic directions that are “equivalent.” For example, in a cubic crystal system, the [011] and [110] and [101] directions are “...
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1answer
858 views

Calculating the ionic polarizability from the Clausius-Mossoti relation

The concentration of atoms in a crystal is $N_d = \pu{2.24e28 m-3}$, and the relative dielectric constant is $\varepsilon_{r} = 5.62$. The crystal has a refractive index of $n = 1.5$. Using the ...
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2answers
688 views

Cubic crystals anisotropy

My textbook states "Cubic crystals contain four three-fold axes, converting the ellipsoid to a sphere." What indeed is the ellipsoid and sphere in the lattice? I know the meaning of three fold ...
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1answer
425 views

Primitive cells and their variations

Is there any intuitive way(without involving higher maths) to explain possible variations in seven primitive types of (unit)cells? I would like explanation in context of why end centred is possible ...
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1answer
244 views

Fixed cell parameters, TINKER

I am using TINKER package to calculate the external reorganization energy for pentacene crystal. But I have problems with that - I've generated .xyz file of 5 molecules with VESTA and I need to ...
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1answer
314 views

Why impurities of the solute are not separated in the process of crystallization?

In evaporation the impurities of the solute are separated with it but in case of crystallization only pure crystals are formed and the impurities of solute remains dissolved in it.why?why does it ...
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Interstitial Sites in unit cell

I wanted to calculate how many interstitial sites (tetrahedral and octahedral) are present in a simple unit cell and their location and radius. I am guessing they are at the center of unit cell and at ...
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1answer
152 views

Why does the barium ion in barium titanate move in its tetragonal crystal structure?

Barium titanate is known in the materials science world to be a great dielectric. This is known to be because the $\ce{Ba^2+}$ ion sits off center in the middle of the tetragonal crystal structure. ...
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0answers
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Are there processes to standardize the shape of a crystal during crystallization?

I am trying to standardize the shape of europium dibenzoylmethide triethylammonium (EuD4TEA) during its crystallization process. I'm a mechanical engineering student and am not too familiar on the ...
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1answer
3k views

Why alkali metals have bcc structure?

It is well known that metals are typically, well, metallic and usually favor the most dense packing, like hcp or fcc cells. This may be easily rationalized as dense packing of metal ions in a sea of ...
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5answers
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CuSO4.5H2O >> CuSO4 + 5H2O : chemical or physical reaction?

In a textbook it says it's a chemical reaction which involves breaking bonds. But I don't think so since I think water molecules are just trapped in the crystal. What's the right answer and why ?
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1answer
50 views

Is perovskite symmetric under exchange of A and B atoms?

A perovskite is any crystal with the general formula $\ce{ABX3}$ where if the $\ce{B}$ atoms form a cube, an $\ce{A}$ atom sits in its center and the $\ce{X}$ atoms sit between neighboring $\ce{B}$ ...
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1answer
150 views

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 ...
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1answer
12k views

Chemical structure of SiO2 vs CO2 [duplicate]

why does SiO2 form a crystal structure while CO2 forms a linear one? Would it be possible to make a CO2 crystal or SiO2 gas in a lab or is there something preventing that from happening. Thanks
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1answer
841 views

Which elements exhibit allotropy?

I was just reading this article about allotropes which relates allotropy with some specific elements and also this wiki article. Also some other articles some of which relate allotropy with catenation ...
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39 views

Physical reason for the ideal lattice approximation

Why can we approximate a lattice as being infinite when we describe it as an ideal crystal? Is there any physical reason or is it just because the number of ions (/atoms) is so huge that we can treat ...
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0answers
88 views

In powder x rd, if the crystals are randomly oriented ,why then do we get Debye rings and not random patterns?

In powder x-ray diffraction ,as I have learnt the sample is multi-crystalline.So if x-ray is diffracted through these randomly oriented crystal grains, aren't we supposed to get a random pattern?
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429 views

Is the plane close packed?

Is the (200) plane of fcc crystal structure(the plane parallel to the face of unit cell and passing through the body centre of it) a close packed plane? A close packed palne is a plane where the ...
4
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1answer
836 views

Is (high) pressure required to form (quartz) crystals?

I've been reading a lot of sources about the hydrothermal synthesis of quartz using autoclaves. I want to try doing this myself, but before I can I need to know the minimum pressure required. If you ...
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1answer
291 views

Alternative to Hanging Drop Crystallization

Forgive my ignorance if I am way off, but I was having a look at the crystallization of a number of different substances (e.g. proteins) through the hanging drop vapour diffusion method. The examples ...
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0answers
278 views

Understanding three-dimensional structure of common salt

I started reading through The Feynman Lectures and came across this diagram. What do the numbers next to the nodes in the diagram represent? It's not explained in the text. All that is mentioned is: "...
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1answer
916 views

Coordination number of carbon in methyllithium tetramer

According to J. D. Lee's Concise Inorganic Chemistry, the coordination number of carbon in $\ce{Li4(CH3)4}$ is $7$. But the structure of the tetramer is Doesn't carbon have coordination number $6$ ...
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0answers
386 views

Edge length unit cells ionic crystals

In ionic crystals there are mainly 3 types of structures: Face-centered cubic and octahedral interstices; face-centered cubic with tetrahedral interstices; and body-centered cubic. My question is how ...
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1answer
55 views

Is it feasible to make dendritic crystals at home?

I've become interested in the forms of dendritic metal crystals from an aesthetic perspective, and I'm interested in whether it is feasible (from a cost, safety, resources) perspective to create metal ...
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0answers
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19F MAS NMR chemical shift tensor and the crystal structure

$\ce{^{19}F}$ MAS NMR is measured on fluorine-doped $\ce{TiO2}$. $\ce{F}$ is to substitute $\ce{O}$ and the crystal structure is anatase, which has a tetragonal crystal system with a space group $\ce{...
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How to make sense of the crystal systems names

I cannot fix the names and structures of the seven crystal systems in my head. There's a thousand books explaining their geometry and it's totally fine and understandable, no problem. But what do the ...
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1answer
566 views

Slips System of BCC

We have been taught that there are 48 slip Systems in BCC. I need the miller indices of each slip plane and direction. Out of 48 I got miller indices of 12 systems of $\{110\}\ \left<111\right>$...
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1answer
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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 ...
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0answers
601 views

Why are certain reflections forbidden in body centered cubic and face centered cubic structures?

I know that for body centered cubic structures the allowed reflections only happen if h+k+l is even and reflections are forbidden is h+k+l is odd, and for basic face centered cubic structures (...
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53 views

If I have an alloy of two materials, will I have a chemical reaction between the two materials

I have always been told that an alloy is a mixture without chemical interference between the materials, but if I look at highly doped silicon (doped with Aluminum via ion implantation and then lattice ...
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3answers
1k views

Does crystalline glass exist?

As far as I know, glass is a non-crystalline amorphous solid. Does glass exist in crystalline forms? Or is it the definition of glass that it's non-crystalline, in which case my question is based off ...