Crystals Definition and 132 Threads

  1. S

    Begineers' books on Photonic Stuctures/ Crystals

    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
  2. A

    Atom Energy in Crystals: Gibbs Free Energy

    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?
  3. A

    Can Phonon Transport in Photonic Crystals Unlock New Discoveries?

    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.
  4. A

    Missing Reflections in FCC/BCC Crystals: Bragg Model Inadequate?

    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...
  5. A

    What Are Acoustical and Optical Branches in Crystal Waves?

    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...
  6. C

    Barium Borate- beta BBO crystals (what am I looking at?)

    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.
  7. H

    Phonons in Crystals: Standing or Traveling Waves?

    Are phonons in crystals standing waves or traveling waves?
  8. E

    Crystal Structure: rc/ra = 1, <.23, >1

    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 ?
  9. H

    Understanding Electron Effective Mass in Crystals

    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...
  10. R

    How do conduction-band electrons affect heat transfer in conductors?

    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...
  11. 1

    Bonds in Semiconductor crystals

    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...
  12. N

    Types of Piezoelectric Crystals to Harvest Sound

    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...
  13. G

    Why do high-melt-point crystals melt so low in molten glass?

    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...
  14. C

    Thermochromatic liquid crystals, how do they change color?

    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...
  15. A

    Antiferromagnetic crystals with F and Cl

    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...
  16. J

    Understanding the Factors Behind Solid Crystal Structures

    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?
  17. W

    Upper limit of Miller indices of BCC and FCC crystals?

    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?
  18. B

    Can Classical Dynamics Lead to Time Crystals?

    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...
  19. R

    How do I turn FeCl3•6H2O crystals into 0.5M solution?

    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?
  20. F

    Crystals: difference between basis and unit cell

    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...
  21. F

    Spontaneous emission in photonic crystals

    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...
  22. N

    Why are most of the ionic crystals Diamagnetism

    [SIZE="4"][FONT="Tahoma"]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
  23. N

    Crystals and Mood: Debunking the Healing Powers Myth

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

    Isotropic crystals & anisotropic crystals

    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...
  25. M

    Chiral nematic liquid crystals - describing light diffraction

    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...
  26. C

    Why are there crystals formed when a hot saturated solution is allowed

    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...
  27. M

    How Do Molecular Magnetic Moments Cause Magnetism in Dielectric Crystals?

    What is origin of magnetism in dielectric crystals?
  28. S

    Monopolar polarization of 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?
  29. M

    Quiver path algebra and F-term relations in melting crystals

    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...
  30. W

    Valence electrons and Photonic crystals

    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...
  31. M

    Calculating Yield of CuSO4 Crystals from Reaction of H2SO4 and CUO

    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...
  32. S

    Diffraction of x-rays by crystals

    :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??
  33. B

    Electron diffraction from crystals

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

    Electrons diffraction in crystals

    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...
  35. R

    Is the Energy Band of Wood vs Crystals similar?

      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...
  36. B

    Crystals- filling a tetrahedral site.

    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...
  37. Useful nucleus

    Surface definition in crystals question

    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...
  38. K

    Can Quartz Crystals Really Store Unlimited Data for an Unlimited Time?

    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?
  39. E

    How big should sugar crystals get?

    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...
  40. K

    Chemistry Determining Intermolecular Forces - Ionic Crystals and Network Solids?

    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...
  41. S

    Practical question- anyone w. experience w. BBO crystals?

    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...
  42. W

    The effect of a magnetic field on the growth rate of crystals

    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...
  43. J

    Are blocks (billets) of metal crystals?

    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.
  44. L

    Dr. Emoto's : the structural formation of ice crystals

    Hello every one I hope I'm in the right place to ask this question :) well , have you heared about Dr. Emoto's ? http://www.is-masaru-emoto-for-real.com/" my friend were in US last year , and she was joining some one who provides her by these info. when she told me , it was my 1st...
  45. S

    Piezoelectric Crystals: Constant Pressure & Electric Field

    If a constant pressure is kept on a piezoelectric crystal, will it continue to generate an electric field?
  46. L

    Why is the wavelength in a crystal assumed to be the same as outside?

    I read an introductory text about diffraction of X-rays in crystals and I am not sure why the wavelength in the crystal is assumed to be identical to the wavelength outside the crystal. I think that the speed of electromagnetic waves can depend on the type of matter, so wavelenghts can be...
  47. P

    Monocrystals vs. Crystals: Understanding the Difference

    Can I say that monocrystals, polycrystals,crystalline ... are types of crystals? What is the difference between monocrystal and crystal? I don't see any difference in definition?! In statistical mechanics for example if you say crystal you don't mean crystalline. Thanks for your answer
  48. B

    MATLAB Solving Photonic Crystal Resonance Frequency with Matlab

    Hi, I research on photonic crystals.I want to compute resonance frequency for single cylinder scattering. I use the below expression : J'(nkr)H(kr)-J(nkr)H'(kr)=0 J:bessel and H:hankel function. but I can't achieve correct result by write program in Matlab for computing that. Can you help me ?
  49. H

    How Do You Calculate the Formula for Hydrated MgSO4 Using Experimental Data?

    Homework Statement "Use your experimental data to calculate the formula for hydrated MgSO4" Homework Equations i used 2.25g x 1 mole/141.46 = 0.016 moles The Attempt at a Solution i'm not sure how to calculate the formula. how do i do that? is there a different equation involved...
  50. T

    Tight binding in cubic crystals

    \phiHi all, I would like to make band structure calculations with tight binding method and I start reading about this method from Ashcroft - Mermin, Chapter 10: The Tight Binding Method and try to solve the problems at the and of the chapter. In problem 2 a. As a consequence of cubic...
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