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 ...
William R. Ebenezer's user avatar
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 ...
Ivan Neretin's user avatar
  • 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 ...
A.K.'s user avatar
  • 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 ...
Jon Custer's user avatar
  • 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 ...
Berry Holmes's user avatar
  • 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 ...
paracetamol's user avatar
  • 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 ...
Mitchell's user avatar
  • 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 ...
orthocresol's user avatar
  • 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 ...
DrMoishe Pippik's user avatar
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 ...
Nilay Ghosh's user avatar
  • 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 ...
Jon Custer's user avatar
  • 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....
khaverim's user avatar
  • 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 ...
Linear Christmas's user avatar
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 ...
Ivan Neretin's user avatar
  • 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),...
Jon Custer's user avatar
  • 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,(...
Oscar Lanzi's user avatar
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 ...
Ivan Neretin's user avatar
  • 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 ...
Jay Chudasama's user avatar
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 ...
Gimelist's user avatar
  • 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 ...
ankit7540's user avatar
  • 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 ...
Divyansh Jain's user avatar
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 ...
Ivan Neretin's user avatar
  • 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 ...
voffch's user avatar
  • 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 ...
andselisk's user avatar
  • 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 ...
Buttonwood's user avatar
  • 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+][...
Jan's user avatar
  • 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 ...
Karsten's user avatar
  • 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, ...
Buttonwood's user avatar
  • 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 ...
andselisk's user avatar
  • 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 ...
Desai's user avatar
  • 451

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