The tag has no wiki summary.

learn more… | top users | synonyms

12
votes
1answer
425 views

What are some predictions from string theory that say some crystalline materials “will end up in one of many lowest-energy ground states?”

I am referring to this recent "news feature" by Zeeya Merali from Nature magazine www.nature.com/uidfinder/10.1038/478302a. Here is the specific quote: "To make matters worse, some of the testable ...
9
votes
3answers
145 views

Are synthetically-produced diamonds as hard as natural diamonds?

I was having a discussion with my friend about the intrinsic worthlessness of diamonds (DeBeers and whatnot) and how synthetic diamonds haven't caught on, again because of the marketing/propoganda ...
7
votes
2answers
1k views

Why does ice have a lower density than water?

Can someone explain me why is ice lighter than water? As I know, all solids are usually heavier than the liquids (correct me if I am wrong).
6
votes
2answers
100 views

Is it possible to have annealing without creep?

Annealing can repair a material by allowing atoms to find the minimum energy state; since solids have a surface tension this process will allow cracks to fuse and reverse fatigue. However, annealing ...
5
votes
7answers
866 views

Entropy and Crystal Growth

I was reading about growing single crystals and I'm a little confused about this - In most crystal growing processes, a "seed crystal" is used, and the rest of the material crystallizes on the seed ...
5
votes
1answer
2k views

Transparency of materials

Is transparency of material has something to do with inter- or intra-molecular bonding? E.g. both graphite and diamond are carbon, but graphite is opaque and diamond transparent.
5
votes
0answers
314 views

Does positronium have a stable crystalline phase?

This is a long shot, but while the 100YSS conference is going on at Houston, i haven't been able to get a grip on myself and think in other, more mundane and short-term rewards as normal people do. ...
4
votes
2answers
2k views

How does the process of freezing water remove salt?

How does freezing water to make ice remove whatever salts were in the water to begin with?
4
votes
1answer
86 views

Topological Insulators: is HgX a special case?

I got confused by reading this article: Francois Virot, Roland Hayn, Manuel Richter, and Jeroen van den Brink. “Engineering topological surface-states: HgS, HgSe and HgTe.” arXiv preprint ...
4
votes
2answers
236 views

Why do some things crystallize? (And others don't, for that matter.)

Ice, for example, will form a crystal when frozen under certain circumstances. Why is this the case for ice? While on the subject of water crystallization, why do snowflakes usually form in base 6 ...
4
votes
1answer
290 views

Born-Oppenheimer Approximation equivalent to Tensor-product ?

If you have a wave function $\Psi$ of a system consisting of an electron and the vibrational modes of the crystal, THEN we represent the wavefunction $\Psi%$ to be in the Hilbert Space formed by the ...
4
votes
1answer
139 views

Anisotropic refractive index with isotropic components?

In relation to my question here I wanted to make sure that my physical argument was not flawed. Anisotropic properties, (especially refractive index) is characteristic of a well-ordered solid ...
4
votes
0answers
28 views

What groups of symmetry are most suited for filling uniformely a spherical 3D space, whilst possessing the lowest possible surface-to-volume ratio?

I am looking for the closest known approximate solution to Kelvin foams problem that would obey a spherical symmetry. One alternative way of formulating it: I am looking for an equivalent of ...
4
votes
1answer
243 views

What is crystal field anisotropy or effect ? It forces the magnetic moment to point in particular local direction..

Can you give a basic explanation of what is crystal field anisotropy ? What is the reason to arise ? In spin ice it forces the dipoles to point in the local 111 direction. For partially filled rare ...
3
votes
1answer
286 views

The 2011 Nobel Prize in Chemistry

As far as I understand a new pattern of crystal growth has been found experimentally. How does it relate to the known 2D and 3D nucleation and growth of crystals? The dominating theory of crystal ...
3
votes
4answers
126 views

Molecule vs Crystal

Feynman mentions in his lectures: ...the concept of a molecule of a substance is only approximate and exists only for a certain class of substances. It is clear in the case of water that the ...
3
votes
1answer
439 views

Nature of tetragonal distortion in Jahn-Teller effect

I am wondering: If I have a regular octahedron as my starting point, oriented along the x-y-z axis, and now Jahn-Teller suggest I elongate or compress along the $z$-axis, what happens along the other ...
3
votes
1answer
689 views

How to write the Fröhlich Hamiltonian in one dimension?

I am currently working on a (functional) analysis problem refining Pekar's Ansatz (or adiabatic approximation, as it is called in his beautiful 1961 manuscript "Research in Electron Theory of ...
3
votes
1answer
1k views

Where are the ice rings in X-ray crystallography located?

I threw this image of one of my protein crystal's diffraction pattern (not the greatest) on a poster, and was wondering where (what reciprocal dimension) the ice rings are located as it might be a ...
3
votes
1answer
58 views

Difference in chemical potential in supersaturated solutions

I have been more or less struggeling to understand an equation that is apparently used in almost all books covering crystals in any way. Basically every book that I have found explains the following: ...
3
votes
1answer
134 views

What determines Phonon - Phonon collisions?

I was in Solid State Physics lecture yesterday and we BRIEFLY went over what causes phonons to collide with one another. Things such as crystal imperfections, boundaries, Temperature, but I was ...
3
votes
1answer
138 views

Difference between Wigner crystal state and fractional quantum Hall (FQH) state

Wigner crystal and FQH effect are both due to strong electron-electron interaction under magnetic field. As we know, Landau's symmetry-breaking cannot be used to describe FQH state. But can it be used ...
3
votes
1answer
180 views

Algorithm for identifying planes in a Bravais Lattice

I have a lattice with Lattice Vectors $(\vec{t}_1,\vec{t}_2,\vec{t}_3)$ which are NOT orthogonal in general. How can I identify the atoms/unit cells that belong to a plane - that is normal to a given ...
3
votes
1answer
337 views

Bragg condition for transmission: Why is the full diffracted angle Two times Theta? Or isn't it?

On a Bragg reflection with incomming angle Theta the total diffraction angle of the incomming wave is 2*Theta, of course. But I have Bragg transmission with electrons on a graphite crystal ...
3
votes
2answers
638 views

Madelung constant list (for surfaces as well)

Searching for this on google proved to be quite tedious, but I reckon that someone working with crystals a lot might know this off the top of his head: Is there a good source that lists the Madelung ...
3
votes
1answer
106 views

How strong is electron degeneracy pressure?

I'm trying to get some specific numbers for electron degeneracy that I can understand, using a concrete example. Take for example this portion of carbon crystal: Exactly how much energy would be ...
3
votes
1answer
104 views

Do indirect optical transitions “cool” the material a little?

So I'm reading in Ashcroft and Mermin about indirect optical transitions: So, a photon comes in, and it only excites the electron across the indirect band gap if a phonon with the appropriate wave ...
3
votes
2answers
743 views

Crystal visualization software for visualizing lattice with reciprocal vectors drawn in same image [closed]

I'm looking for a free crystal visualization program, preferably for Linux, that can visualize the common lattice structures in 3D interactively (rotatable with mouse) and draw in the same picture the ...
3
votes
0answers
146 views

Origin of Laue equations?

The Bragg condition (by Bragg in 1913) can be derived by the Laue equations that is making use of the Miller indices and all the latice/crystal stuff (so basically it's bringing Bragg's law to more ...
3
votes
0answers
33 views

Are there any electro-optic crystals that are also pyroelectric but not birefringent?

As the title says, a crystal that is electr-optic and pyroelectric can it be non-birefrigent?
3
votes
0answers
116 views

Bandgap Spacing in Photonic Crystals

I am doing some self-study on photonics and have encountered the following question: We know that amorphous electronic crystals such as amorphous silicon have a bandgap. Can amorphous photonic ...
3
votes
0answers
214 views

Does a thermally expanding torus experience internal stress?

I'm trying to learn continuum mechanics and thermo-mechanics. As we know, heating an object increases the mean atomic distance $a_0$ of the atoms in a rigid body. Let's assume it is a linear elastic ...
2
votes
2answers
3k views

How to make a single crystal silicon wafer?

How can I make a single crystal silicon wafer? What are the tools needed? What is the most diffcult part? Can I make it at home or at school lab? I am now interested on Czochralski process where you ...
2
votes
1answer
80 views

How to homegrow large, momocrystalline water ice crystals

This is a follow up to this question:Can one get clear ice crystals from a dirty suspension?. How could one grow a large - meaning visible with the naked eye - water ice crstal with common household ...
2
votes
3answers
1k views

What is the difference between lattice vectors and basis vectors?

Google has not been very useful in this regard. It seems no one has clearly defined terms and Kittel has too little on this.
2
votes
1answer
523 views

Derivation of Bloch's theorem

I'm having a problem following a derivation of Bloch's theorem, looking at a one dimensional lattice with $N$ nodes and spacing a, we impose periodic boundary conditions, meaning that the ...
2
votes
1answer
57 views

Experimental Evidence of Random Tiling Limit Shapes

In the area of random tilings, there are many results that fall under the term "Arctic Circle Theorems." This roughly means that if one chooses a tiling of a specific region uniformly at random, then ...
2
votes
1answer
202 views

Regarding Bravais lattices

There is 'End-Centered' Orthorhombic lattice . Why this type is not in 'Cubic' lattice ? On which basis did Bravais propose his theory ?
2
votes
1answer
96 views

Is this 2D structure triclinic?

The only rotation axis obvious to me is rotation by 360 degrees, the identity. Vertical mirror planes I've been dicing and cutting it through several planes and I still see none. Yet, the structure ...
2
votes
2answers
187 views

I can't figure out crystal planes with negative intercepts

As seen above, I don't follow how you figure out those planes. It seems they're not using the origin labeled. I'm not really sure I understand spatially what's going on in the left figure so let's ...
2
votes
1answer
74 views

Estimate the difference between two sets of atoms

I've been working on amorphous structures derived from a crystalline one (using MD) containing $N$ atoms. I want to prove that these structures are different and to quantify their "differentness". One ...
2
votes
3answers
184 views

What are local electrons in a crystal?

I am reading Pekar's "Research in Electron Theory of Crystals" and I came across a passage I find a bit unclear: The theory developed below takes into account the dielectric polarization of a an ...
2
votes
0answers
20 views

How can one reasonably theoretically model polycrystalline materials?

Many techniques are taught in advanced solid state courses but they are almost all derived for perfectly crystalline materials. For example, band structure really only appears theoretically when you ...
2
votes
0answers
88 views

Lattice theory in mathematics and physics

I have undertaken a project examining lattice model and trying to construct algorithm that could work on all lattice (in physical sense, or crystal structure). I notice there is a branch in ...
2
votes
0answers
65 views

The boundary between polycrystalline and crystalline

My current understanding of solid crystalline-like materials (please correct me if I'm wrong!) is that it is a continuum in terms of crystallinity, from amorphous (basically no periodicity) to single ...
2
votes
0answers
45 views

How does a snowflake “know” to form symmetrically? [duplicate]

Possible Duplicate: Why are snowflakes symmetrical? Under ideal situations, a snowflake forms into near perfect hexagonal symmetry. How? For instance, when a water molecule moves towards ...
2
votes
0answers
118 views

Crystal momentum and the vector potential

I noticed that the Aharonov–Bohm effect describes a phase factor given by $e^{\frac{i}{\hbar}\int_{\partial\gamma}q A_\mu dx^\mu}$. I also recognize that electrons in a periodic potential gain a phase ...
2
votes
0answers
150 views

Discrete sum over an exponential with imaginary argument, considering only every second lattice site?

Let's say I sum an exponential function $e^{\imath \left(k-k^{\prime}\right) x_{i}}$ over a chain system where every member of the chain is of the same type, e.g., A-A-A-...-A-A (total of N sites) ...
1
vote
2answers
166 views

Why is the crystallography restriction obeyed?

The crystallography restriction states that any 2-dimensional lattice can have rotational symmetry of degree 1, 2, 3, 4 or 6 - and that's it. A simple proof of I've heard of this is: the magnitude of ...
1
vote
1answer
42 views

What does (001) Silicon mean?

If someone gives me a thin film of Si, and they tell me it's (001) Si, does that mean that the (001) planes of Si are the ones making up the surface of the film?