32
votes
Accepted
Contribution of Tetrahedral and Octahedral voids in HCP
I cannot find anywhere..
Couldn't find? You can figure it out on your own, with me, right now.
Disclaimer: By "hexagonal unit cell" I assume you mean hexagonal prism, which comprises of 3 primitive ...
- 2,825
29
votes
How can brass still be made even though the crystal structures of zinc and copper are not the same?
The $\ce{Cu-Zn}$ phase diagram is, to put it mildly, complicated.
(source)
See that wide area denoted $\alpha\rm (Cu)$? Now, when we add a little amount of one metal into the crystal lattice of ...
- 30.9k
21
votes
Accepted
What makes Gorilla Glass more durable with each generation?
Are there other ways of "chemical strengthening" besides cationic exchange that can be utilized to strengthen the glass, keeping it flexible and less fragile at the same time?
In a word: No.
To ...
- 12.3k
20
votes
Accepted
Why are there only 7 types of unit cells and 14 types of Bravais lattices?
All quotes will be from Solid State Physics by Ashcroft and Mermin.
Bravais Lattice:
A fundamental concept in the description of any crystalline solid is that of the Bravais lattice, which ...
- 8,205
18
votes
How to calculate the height of an hcp lattice?
To calculate the height of a unit cell, consider a tetrahedral void in an hexagonal closed packing arrangement. It can be imagined as a 3 solid spheres touching each other and at the center-point, you ...
- 4,084
17
votes
Accepted
Will a solid object lose or gain atoms on standing over time (without being acted upon by external influences)?
Short answer: Yes they do.
Firstly, you need to arrive at a proper definition for an "object". Why you ask? Because it would otherwise present philosophical problems which become apparent when we ...
- 18.5k
16
votes
How are the number of tetrahedral voids twice the number of octahedral voids in a CCP structure?
To be precise, if in a close packed structure (ccp or fcc) there are $n$ atoms or ions then the number of octahedral voids and tetrahedral voids will be $n$ and $2n$ respectively.
For example, there ...
- 1,108
16
votes
Accepted
For a given packing (hcp, fcc, bcc), which ions occupy the corners and which occupy the faces or centers?
The actual answer is that it doesn't matter. For many of the 1:1 solid-state structures, either the cations or the anions may be considered to be at the vertices (i.e. corners) of the unit cell. By ...
- 70.8k
14
votes
How can brass still be made even though the crystal structures of zinc and copper are not the same?
While molten, copper and zinc (and tin) are miscible. As the alloy cools and crystalizes, the metals do indeed separate, forming grain boundaries. These inclusions "pin" slippage between ...
- 29.6k
13
votes
What does β stand for in β-potassium zirconate?
They signify one polymorph (the beta polymorph) of barium zirconate.
Allotropy is the property of some chemical elements or compounds to exist in two or more different forms in the same physical state ...
- 24.8k
11
votes
Accepted
Yellow color of NaCl
An F-center (or any color center) is a point defect in the material that generates localized electronic states. When these states are in the band gap, they will result in strong peaks in optical ...
- 8,205
11
votes
Accepted
Why are X-rays used in crystallography?
There are a few reasons, but the most direct answer is that the wavelength of X-ray photons is on the order of the distance between atomic nuclei in solids, e.g. ~ 4 ångströms (bonds are roughly 1.5-2....
- 3,564
11
votes
What is "chemical pressure"?
External and internal pressure
To study the effect of pressure on properties of a solid, is equivalently to learn how changes in volume transform physical parameters. For external pressure at ...
- 6,981
10
votes
Accepted
Materials with solid volume greater than liquid volume
There is a bunch of such materials; among the elemental compounds, they include silicon, gallium, germanium, and bismuth. As for the properties... well, it just so happens that their crystal structure ...
- 30.9k
10
votes
Why are p-type solar cells more prone to degradation in space than the n-type ones?
The space radiation environment is a quite complex subject. Generally speaking one needs to be careful about just where in space you are concerned about - near earth orbit (within the Van Allen Belts),...
- 8,205
10
votes
Calculate the third and fourth nearest neighbours in bcc
You can think of the body centered cubic lattice as two simple cubic lattice, one with points at coordinates $(ma,na,pa)$ where $m,n,p$ are integers, the other with points at $((m+(1/2))a,(n+(1/2))a,(...
- 51k
10
votes
Accepted
Calculate the third and fourth nearest neighbours in bcc
With $\sqrt3\over2$ being that close to $1$, BCC packing is better not looked at in terms of coordination spheres. But if you insist...
Say you are sitting in the center of a cell. Then:
Your first ...
- 30.9k
9
votes
Distance between successive tetrahedral voids in FCC
As shown in figure, if we divide a FCC unit cell into 8 small cubes, then each small cube has 1 Tetrahedral void at its own body centre.
Thus, there are total 8 Tetrahedral voids in one unit cell.
It ...
9
votes
Accepted
How can diamond have a fixed refractive index?
Your textbook is wrong. Some crystalline solids are optically anisotropic. Many crystalline solids are indeed optically isotropic in nature. In solids like this the light beam experiences the same ...
- 5,174
9
votes
What does β stand for in β-potassium zirconate?
Some inorganic crystals show the property of structural polymorphism where two or more crystal polymorphs exist. These polymorphs may differ either by position of metal ion or ligand (or other ion ...
- 1,562
9
votes
Accepted
What is the reason for isotropy in amorphous solids?
Assume that the spheres in the drawing are atoms.
In the second picture atoms are not orderly arranged. No matter where you go in crystal of a amorphous solid, the disarrangement will be same. Since ...
- 206
9
votes
Accepted
Why we don't talk about unit cells in hcp/fcc structures?
We do not remain silent about the unit cells in this context. The hexagonal close packed structure is called so because it has hexagonal unit cell, and the other one is called fcc precisely because ...
- 30.9k
9
votes
How do I know crystal structures from formula?
I'll just point out the direction in which you could look for an answer.
In general case, it should be almost impossible to determine the crystal structure by looking at the chemical composition of a ...
- 753
9
votes
Calculating the strength of an ionic bond that contains poly-atomic ions
With enough effort, Born–Haber cycle can be extended to polyatomic ionic solids, however it's practically never done in practice due to the lack of experimental data or because it's impossible to ...
- 37.3k
9
votes
Accepted
Software for generating a lattice from a unit cell for molecular crystals?
In addition to the presentations about CCDC Mercury and Vesta by @andselisk here and later mine about Avogadro could be extended. As described earlier, Avogadro's capability to read .cif files about ...
- 27.7k
9
votes
Accepted
Why does Xenon Hexafluoride exist as [XeF5+][F-] and not [XeF5+][XeF2-] in the solid state
First and most obviously, if something in solid state forms ions by shuffling atoms around, the end result must yield the same ratio of atoms. Take for example $\ce{PF5}$: this exists as $\ce{[PF4+][...
- 66.9k
9
votes
Why are there exactly 5 types of two-dimensional lattices, and what distinguishes them?
First, about the black lines. I think they are helpful for the hexagonal and the rhombic lattice. For the hexagonal system, it shows you the hexagons. One hexagon contains exactly the same space as ...
- 37.8k
8
votes
Accepted
What are some materials that expand a lot proportionally to heat?
You are looking for thermal expansion and its coefficient. Of course such tables, and diagrams exist
(source)
as it is of relevance in daily live. Thermometers based on liquid mercury, or alcohol, ...
- 27.7k
8
votes
Accepted
Structure of crystalline boron trioxide
This statement is relevant for the initially [incorrectly] determined structure of $\ce{B2O3}$ by Berger [1, 2] who used powder x-ray diffraction data.
You can still access the structure and visualize ...
- 37.3k
8
votes
Why is sea salt coarse?
The method of production of sea salt usually involves bulk evaporation of seawater. This allows the salt to crystallise and due to it's bigger size it is sold without much processing. On the other ...
- 451
Only top scored, non community-wiki answers of a minimum length are eligible