Crystals Definition and 142 Threads

what does coordination no in crystal structures really mean? i know it's no of nearest neighbors but has it significantly to do with bonding of electrons. actually my doubt is that - I read Be can't show coordination no of 6 and is allowed to show only coordination no 4 due to lack of...

Hi I am doing my Masters by research in Photonic Crystals and I want to do a PhD later as I dream of an academic. I wanted to know to if the field of photonic crystals offers opportunities for growth in the future. Will this field be actively researched in the future? Thanks

Hey, this was the question could someone please help? "An aluminium single crystal alloy aircraft component is oriented such that a tensile stress is applied along a [102] direction. If slip in this material occurs on a (111) plane and in a [101] direction, compute the yield stress at which...

Hi Can you recommend me a simple to begin with book on Photoinc Crystals. I did my undergrad in Electronics Engineering and don't have any knowledge of photonics. Thanks

Does atom at the surface of a crystal have more or less energy than those in the bulk? And how does this relate to their Gibbs free energy?

I wish you a happy new year 2014 full of discoveries, surprises, changes, laughter, smiles, giggles and tenderness Is if possible to Study the phonon transport in photonic crystals.

Firstly, sorry if this doesn't go here please feel free to move it as I was a little confused where to put it. TL:DR Doing a project question interests me, "Why can photonic crystals be used to create a super lens?" Okay so I am doing an undergraduate project for my honours year that I...

I noticed that using the Laue equations reflections from some of the planes in the fcc and bcc crystal are not allowed. Now using the (maybe too naive?) Bragg model we can always find Bragg peaks whichever plane we hit with waves. So is the Bragg model too simple for these planes? And what is it...

My book considers waves in crystals. Especially it develops the idea of acoustical and optical branches of the waves. From what I can see these are different ways the dispersion of our phonon may look like. It is developed when the crystal contains more than one atom per unit cell, but I am not...

The chemical formula, BaB2O4, doesn't correspond with the image I see. Barium is green, boron is pink and oxygen is red. Wiki Barium borate No clue about crystals but willing to learn the basics.

Are phonons in crystals standing waves or traveling waves?

What would be the structure of the crystal if rc/ra=1? hexagonal closed packed or anything else? What would be the structure of the crystal if rc/ra< .23 ? What would be the structure of the crystal if rc/ra>1 ?

I have got confused about electron effective mass in crystals. Which of the definitions below are correct? 1) When an electron is in a crystal with periodic potential, it behaves such as a free electron with effective mass m^* 2) when an external force is applied on the electron in a...

Hello. I am about to show how heat is transferred through crystals i. e metals I know that it should be about conduction, and that the single quantum oscillators start vibrating in higher modes, due to the extra energy. Now is the question: HOW exactly is the energy trasnferred...

Hi! I study semiconductors and I am confused with the bonding picture for semiconductor crystals. For example, it is said that in Si crystal one can find covalent bonds. In the most books this bonds are shown like that: 2D crystal structure where lines between atoms are a covalent bonds, each...

I am in the process of building a piezoelectric device to harvest sound with a frequency generator at one side of a plastic/glass tube which sends out a low frequency which is then picked up by a piezo disk which send the energy to an led which demonstrates hoe sound can be converted to...

I'm looking at a glass "recipe" that heats the raw ingredients to melt at 1550C. This seems to present a problem in that the raw ingredients include: Al2O3: melting point = 2072 C MgO: melting point = 2852 C And even SiO2 (the primary ingredient) has a melting point (range) of...

If you look at liquid crystals in things like moodrings and LCthermometers then you will notice that they can change color when heated. Now I have looked on the internet and found that it has to do with the The cholesteric (or chiral nematic) liquid crystal phase, where they align with each...

I was just looking over a general list of antiferromagnetic crystals and couldn't help but notice that half the list were fluoride or chloride compounds which are often corrosive or otherwise problematic from a handling point of view (eg FeF2). This may seem a stupid question, but, are these two...

Just wondering - What factor decides whether a solid takes up a crystalline structure or an amorphous structure? And if it takes a crystalline structure , what decides if it will be cubic, tetragonal, hexagonal , trigonal, monoclinic or triclinic?

does anybody know the upper limit of the bcc and fcc metals like Fe, Cu, Ag? According to the fact that the planes with high (hkl) indices have small interplanar spacing d_hkl, the smallest spacing would be present. what is that? atomic diameter of a specifc metal?

Classical Time Crystals Alfred Shapere and Frank Wilczek We consider the possibility that classical dynamical systems display motion in their lowest energy state, forming a time analogue of crystalline spatial order. Challenges facing that idea are identified and overcome. We display...

Sorry if this is a dumb or noob question, but I have some FeCl3•6H2O crystals, and I want a 0.5M solution. How do I do it?

Hello Forum, a lattice is a set of points. We can place a basis at each set of points. The basis can be one atom or a group of atoms. I thought that a translation of the basis would produce the whole crystal... How is a basis different from the unit cell? Are they the same thing...

Hello forum, I have a question about photonic crystals. From Wikipedia: "photons (behaving as waves) propagate through this structure - or not - depending on their wavelength. Wavelengths of light that are allowed to travel are known as modes, and groups of allowed modes form bands...

Why are most of the ionic crystals Diamagnetism ?? Ionic crystals are those crystals that are related to ionic bonds of atoms such as sodium chloride NACL

What about the claim that crystals can heal or change moods? Total B.S?

Alright my question is: why do single crystals properties vary with direction (anisotropic) when it is a perfect crystalline structure. I mean doesn't that mean that the atoms are ordered correctly so shouldn't that mean that at every direction its the same magnitude? I really need help because...

So my book has an equation describing the wavelengths of light that are diffracted by a chiral nematic liquid crystal in terms of the refractive index (n), the pitch of the helix (p), and the angle (θ) with respect to the surface. The equation is this - λ = np√((1-cos2θ)/n2) If this isn't...

Homework Statement why are there crystals formed when a hot saturated solution is allowed to cool? the solid has already dissolved into the solution, forming the solute, so when the solution is cooled, and the temp decreases. does this mean they dissolve out of the solution? (i know...

Hi all: I encountered a problem when studying the diffusivity of Li atoms in Si crystals. From the textbook, it is shown the diffusivity tensor in the cubic crystals (BCC FCC) is a diagonal matrix and the values along different directions are also the same (from the rotational symmetry), which...

What is origin of magnetism in dielectric crystals?

This one article mention such strange issue as monopole polarization in highly asymmetric crystals. (I did not read entire article). I always thought that polarization could be only dipolar because you need to get charge separation.How monopole thing could exist in a crystal?

EDIT: fixed TeX issues Hi, I'm learning about the correspondence in string theory between the geometry of Calabi-Yau manifolds and melting crystals. I care more about the math and know almost nothing about string theory, so navigating the literature littered with so much string theory jargon...

Hello PF, I came across a fact that, tungsten, molybdenum and chromium all have 6 valence electrons. Now,if one uses Molybdenum and Chromium instead of tungsten in photonic crystals for TPV(Thermo PhotoVoltaics) does it mean: 1. All are capable of releasing equal number of photons...

I was tasked to calculate the yield of CuSO4 by the reaction of H2SO4 and CUO. My equation says the it should get CUSO4 and H2O. But should we use CUSO4.5H2O for theoretical yield instead since it is a crystal that we are calculating - if so then I could not balance the equation... what...

:shy: By looking at the figures showing diffration of x-rays by crystals, it looks more like reflection.. Seems like I am studying reflection... So, where is the diffraction part??

why is it that in electron diffraction from cystals, theta i and theta r are not necessarily equal?

Hello everyone, It's said that the first Brilloin zone is the k-space where electrons are not diffracted. Electrons with k-vectors on the surface of BZ are diffracted. How can we understand in terms of electron particules the behavior of electrons associated waves when these waves...

　 Is the Energy Band of Wood vs Crystals similar? 　 As I understand it. In crystals the interaction of the atoms are more intimate.. meaning all the atoms in the crystals can influence one another which produced solid energy band. While in wood, the distance are further and hence the...

Homework Statement I'd like to work out what the largest sphere I could fit in the tetrahedral interstitial site of a cubic unit cell. Preferably I believe I need an expression in terms of the lattice constant a. Homework Equations The Attempt at a Solution The tetrahedral site...

I read the following paragraph about surface definition" "Each surface is specified by at least two pieces of information.Firstly, there are the Miller indices (hkl) of the plane that defines the orientation of the bulk cleavage. Secondly, there is the so-called shift - i.e. the displacement of...

I have heard that Quartz crystals are able to store data and information in vast amounts. Is this possible and if so does it work?

Hello. I am interested in making homemade LEDs in the manner described here: http://www.popsci.com/diy/article/2010-02/gray-matter-light-mystery Could this work with silicon carbide sandpaper instead of the crystal form? If so, would I want to go for a lower grit to improve the chances of...

Should it grow indefinitely ?(assuming you have a permanently super-saturated solution) Or does it stop growing when it reaches a certain mass or something ? If so why ? Also, has anyone had success in growing huge sugar/sucrose crystals (if yes, then would you please post up some...

Homework Statement This is the worksheet: http://webcache.googleusercontent.com/search?q=cache:9jyqtuswY1AJ:www.chemmybear.com/groves/apch13_imfans.doc+ap+chem+pasadena+imf%27s&cd=1&hl=en&ct=clnk&gl=us&client=firefox-a Homework Equations None, as far as I know The Attempt at a...

hi all- having a strange (perhaps expected?) problem inserting a BBO into the optical path of a TiSaph fs laser. the issue is that i can achieve strong SHG output, but only with *severe* spatial distortion of the pulse shape. has anyone had experience/encountered this issue in an...

Hello I am currently researching on crystals and how their growth rate is affected by magnetic fields for my upcoming lab. Most of the information is based on labs but I quite don't understand what they speak of. So I was wondering if anyone here has any nice reading material on crystals and...

We learn in solid state physics that crystals cannot exist in one or two dimensions. The main enemy of low-dimensional crystals is the acoustic phonon (Goldstone mode). Due to its small energy in the long wavelength limit, it contributes signifiantly to the fluctuation of the atomic position...

I work as a machinest and Mill mostly aluminum. I was wondering if the billets are Aluminum its crystalline form? Or just lots of Aluminum atoms held together by Metallic bond? thank you. Attached is a photo of Aluminum Block.