What is Crystal: Definition and 427 Discussions

A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macroscopic single crystals are usually identifiable by their geometrical shape, consisting of flat faces with specific, characteristic orientations. The scientific study of crystals and crystal formation is known as crystallography. The process of crystal formation via mechanisms of crystal growth is called crystallization or solidification.
The word crystal derives from the Ancient Greek word κρύσταλλος (krustallos), meaning both "ice" and "rock crystal", from κρύος (kruos), "icy cold, frost".Examples of large crystals include snowflakes, diamonds, and table salt. Most inorganic solids are not crystals but polycrystals, i.e. many microscopic crystals fused together into a single solid. Examples of polycrystals include most metals, rocks, ceramics, and ice. A third category of solids is amorphous solids, where the atoms have no periodic structure whatsoever. Examples of amorphous solids include glass, wax, and many plastics.
Despite the name, lead crystal, crystal glass, and related products are not crystals, but rather types of glass, i.e. amorphous solids.
Crystals are often used in pseudoscientific practices such as crystal therapy, and, along with gemstones, are sometimes associated with spellwork in Wiccan beliefs and related religious movements.

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  1. V

    Uniaxial crystal D direction

    Homework Statement Here you will calculate the direction of energy flow in a uniaxial crystal. The crystal has dielectric constant \varepsilon in the x and y directions and \varepsilon_z in the z direction. (a) Assume the wavevector makes an angle \theta relative the z-axis of the...
  2. J

    Couple light into photonic crystal fiber

    I have one hollow core fiber, the core is around 20um, Numerical Aperture is 0.03. The spot size of Ti:Sapphire laser is around 2~2.5mm. So I used focal length 50mm. But only very few power can be achieved (6uw). I wonder the reason. Could someone please give me some suggestions?
  3. A

    Deriving the Relationship of Cubic Crystal Structure

    How can one derive the relationship for a cubic crystal: d= \frac{a}{\sqrt{h^2 + k^2 + l^2}} It is shown here. This is probably trivial but I am having trouble proving it as the Miller indices are reciprocals but the reciprocal is not distributive. This isn't for homework by the way - I...
  4. P

    Optic axis of a calcite crystal

    What is an optic axis of a calcite crystal ?
  5. I

    Do you have to use a Beta-barium borate crystal in order to entangle photons?

    im just curious and i just want to know, do you need a Beta-barium borate crystal to entangle photons? are there any alternatives? can you use sodium chloride crystals as a possible option? what makes a Beta-barium borate so special and different from any other crystals? please provide good info...
  6. P

    How to dehydrate a solid crystal?

    How to dehydrate a solid crystal? I have a solid crystal with structural channels in it which are filled with water molecules. The size of each channel is 2.5 to 5 angstrom and a water molecule is 2.7 angstrom on its longest side. What is the best way to dehydrate it? I have tried heating it...
  7. L

    CSCL Crystal Structure - Confused by Clarity?

    Hello, I'm really confused by something. Cscl is simple cubic. But how it this possible? With the cl in the middle it looks like a bcc structure. Also howcome when you have 2 caesium its bcc and not simple cubic? its the same structure yet it changes to bcc. Is it because they are both atoms...
  8. A

    Why different crystal phases have different colours?

    Like quinacridones or HgS and HgS \gamma. I don't understand how crystal phase can act on the resonace of the electrons...Please reference! Thank!
  9. A

    How we see things, relating to Crystal field theory.

    Sorry this is largely chemistry based, but delves into electron theory. I'm a little confused about how the colour of transition metal compounds arises. I understand that say for [Cu(H2O)6]2+, you have an octahedral arrangement around the central atom, and the specific positioning of these...
  10. D

    Understanding HCP Crystal Structure: Confusion with Coordinates of Center Atom

    Considering only the 4 lower-right atoms (one unit cell), I'm somewhat confused as to why the coordinates for the center atom (b) is (1/3, 2/3, 1/2) with respect to (a1, a2, c). c is pretty self explanatory, but I don't quite get the other 2. I think one of my main confusions is where the...
  11. A

    Crystal field splitting energy

    In this diagram I can't figure out what that barycentre part of the diagram means. The first section of the diagram represents the energy of the d orbitals before the ligands come into the picture and the 3rd section represents the energy of the d orbitals after the 6 ligands have arranged in...
  12. F

    Crystal diffraction using Bragg's Law

    Homework Statement You wish to study a material with a cubic crystal structure with three orthogonal sides of length a = 0.3nm. What is the longest possible wavelength of the X-ray source you could use to reveal the (211) Bragg peak of the crystal? Homework Equations nλ =...
  13. H

    Cohesive energy of covalent crystal

    Homework Statement The potential Energy per atom in a covalent crystal with interatomic spacing r may be written φ(r) =2ε [A (σ/r)^12 -B (σ/r)^ 6 ] Derive expressions for the equilibrium interatomic spacing and the cohesive energy of the crystal. Homework Equations Again the problem is...
  14. K

    What is the breaking point of quartz crystal

    So how many pounds does it take for quartz to break into several diffrent peices?
  15. D

    Where can I buy a bbo doubling crystal for my lab's femtosecond laser?

    My lab needs to purchase a new bbo doubling crystal for our femtosecond laser. I have been looking around but cannot find any. Our old one is from Thor Labs but they discontinued making them. Does anyone know a company that sells them?
  16. L

    Crystal Emission: Understanding Fundamental and Harmonic Frequencies"

    Say I have a 25MHz Crystal that's connected to a Microprocessor/Microcontroller or spread spectrum clock generator. Does the crystal emit Electromagnetic radiation at its fundamental frequency or it's harmonic frequencies? I keep hearing - " I see a peak at ~50MHz, it must be the 2nd harmonic...
  17. J

    Cohesive Energy of Atoms in a Crystal

    Homework Statement I would like to know what the cohesive energy of the crystal is. Homework Equations The Attempt at a Solution Is it the energy required to break the atoms free from a crystal (ie into free atoms with no potential)? So would it be the minimum energy of a...
  18. Useful nucleus

    What are the crystallographically equivalent sites in a crystal unit cell?

    Given a crystal structure and the cell edges (a,b,c) , angles (alpha, beta, gamma) and the fractional coordinates of all atoms in the unit cell. Also given an arbitrary unoccupied site P by fractional coordinates (s1,s2,s3). How can I determine all the sites that are crystallographically...
  19. S

    Ques. on high symm points of a crystal

    Hi! I'm new to these forums. To get right to it, My head'z been spinning wondering .. Is there a high symmetry point in a crystal about which *all* point operations can be re-centered? I can show this for a simple lattice. Does anyone know if this is true for any complex crystal as...
  20. R

    Miller Indexing crystal structures

    Hello, I have a TEM diffraction pattern of an unknown compound. I have obtained the camera constant and hence measured the lattice constants. Unfortunately I was unable to do EDX analysis of the area and have ~10 possible elements present. So I need to index the miller indices to obtain the...
  21. 1

    Crystal spacing of a solid surface, Bragg's law

    Homework Statement In a particular Low Energy Electron Diffraction (LEED) study of a solid surface, electrons at 45 eV were diffracted at \phi = 53 degrees. Calculate the crystal spacing d. Homework Equations n\lambda=2dsin(\phi) \lambda = hc/E wavelength = c/v E = vh(n + 1/2) Note here v...
  22. M

    How Do You Measure the Frequencies of Natural Crystals?

    If I am correct, crystal frequencies depend on the size, shape/cut, and purity of a crystal(?) How can you measure (what instrumentation) the frequency/ies of a natural crystal (other than just quartz)?
  23. E

    How to balance chem.eq. with crystal water?

    Homework Statement 10 g Fe and x ml H2SO4 forms y gFeSO4*7H2O Write a balanced chemical equation for the reaction, and determine the coeffisients y and x. The H2SO4 is 1 M. Homework Equations n=V*c n=m/Fm The Attempt at a Solution First thing I was trying to set up the chemical...
  24. P

    Dynamics of electron in crystal lattice

    I'm not sure what is the correct equation for motion of electron in a crystal lattice under the influence of magnetic force. On may easily proof that for electric force the following equation holds (the proof might be found in http://ajp.aapt.org/resource/1/ajpias/v54/i2/p177_s1" ): \hbar...
  25. S

    How crystal + electricity works together

    hey everyone I am new to the site an new to physics ( bare with me if I am not as smart as some ) , =) ok, i have this friend who is world widly known for his work, but cut this short, he uses electricity an crystal an can do some out of the ordinary stuff with this he has been in numerous...
  26. Z

    Is it important that I use crystal sugar from the same source in my experiment?

    Is it at all possible for the crystal sugar from one package to be qualitatively different from crystal sugar from another package (brand, etc.)? In other words, if I need sucrose for an experiment, could it affect the results if I use crystal sugar from different packages or of different...
  27. G

    Colour of complex compounds and crystal field theory

    Hi It is know that the colour exhibited by coordinate compound is because of d-d electron transitions. These d-d transition lead to absorption of photons of a paticular frequence. AND when a electron become exited due to absorption of photon it should radiate electromagnetic wave of frequency...
  28. G

    Do more energetic orbitals have wider bands in crystals?

    Let's consider we have a crystal and we search the energy relation of the bands as function of the reciprocal lattice vectors. We would do that theoretical by applying the Tight-binding method. Let's consider that each band is associated with some kind of orbital ( for instance, 3d orbitals). Is...
  29. W

    How to determine band structure (E(k)) of a one dimensional crystal?

    Hi! I'm new to the physics forum but I've read a little bit and I'm impressed with the knowledge a lot of people have here. I've tried searching for any topic on my question without any luck. My question is simply what the algorithm is to determine the band structure for a one dimensional...
  30. P

    Building Crystal Oscillator for Highest Amp Output Underwater

    I am trying to build something but I’m too stupid to understand this stuff so I need some help. Basically I am trying to create a system that will produce a constant sine wave, frequency of somewhere between 420 – 440 hertz under water with the greatest amount of amp output possible. I...
  31. M

    Powder pattern calculation from single crystal data

    Powder pattern calculation from single crystal data Hi Kindly, I want to know what the theoretical base of X-ray powder diffraction pattern calculation from single crystal data? and is the obtained pattern same as experimental powder pattern and if not same what the cause of difference? Thanks
  32. L

    Why the crystal momentum k in 2D band structure is defined on a torus?

    Hi, Could someone help to explain that why for the 2 D system, like 2 dimensional electronic gas, the crystal momentum k in 2D band structure is defined on a torus? Thanks a lot.:)
  33. C

    Spin-1 particle in uniaxial crystal field

    Homework Statement H = -D(S^z)^2 for cases D>0, D<0, where D<0 should remove the degeneracy in the ground state.Homework Equations H = -D(S^z)^2 = -D\hbar^2 (1 0 0; 0 0 0; 0 0 1) (`;' separates rows) det(H-1E)= 0, or by inspection... The Attempt at a Solution I get, for D>0, E_1 = -D...
  34. Z

    How is the microscopic crystal structure visible?

    I just noticed that it's often taken for granted that a macroscopic crystal has a similar geometric structure as in the atomic scale. What is the physical explanation for this (assuming it is true)?
  35. F

    Why are there only seven crystal systems and not 11

    I mean, the system is clearly related to seeing if the sides are of equal length and if the angles equal 90 degrees. If we first exclude the hexagonal, we have three sides and three angles each of which could be either equal/90degree. That gives us 3^2 = 9 possibilities. Then looking at the...
  36. Useful nucleus

    X-ray diffraction for 2-D crystal

    Is it possible to perform x-ray diffraction for 2-D crystal like Graphene? If poossible how does the bragg interference criteria look like here?
  37. M

    Unit cell dimensions of crystal structure

    Hello all, I already have the answer to my question, but what I would like to know is why. My question is: why in the question below is the plane 111 used to find ao and not another plane? An ordered compound of NiAl has a cubic structure with one formula unit/cell. One Al atom at...
  38. mbrmbrg

    Semiconductor: Cz Crystal Growth

    Homework Statement A Czochralski growth process is begun by inserting 1000 moles of pure silicon and 0.01 mole of pure arsenic in a crucible. For this boule, the maximum permissible doping concentration is 1018 cm-3. What fraction (X) of the boule is usable? (k=0.3) Homework Equations...
  39. D

    Monopole crystal radio antenna length

    Good Morning Can anyone help me understand why, apparently the physical length of a monopole end feed wire for a crystal set need to be ½ the wave length of the desired signal. The reason I ask is, that I understood that, if you have a variable coil in series with the antenna, the...
  40. A

    Crystal Visualization for Intro Class: Cheap and Easy Tutorials

    I'm TAing an introductory class, and of course Miller indices and unit cells versus primitive cells and all that crystallographic stuff is a big first week. It's tough for some students to wrap their heads around all the 3-D symmetries, and *really* tough for me to draw all those structures on...
  41. Z

    Name the crystal spinel from the image.

    Hello, I appreciate your help in naming the structure of the molecular structure which image is attached. The answer should include the molecular formula and crystal structure characteristics. Considering the distribution of atoms within the cell and that the caption below states the atomic...
  42. D

    Calculating Density of NaCl Crystal

    Homework Statement Calculate the density of crystalline NaCl, given that NaCl has a face-centred cubic lattice with a dimension a = 5.64A. Homework Equations 1/8 Cl ion at each corner, 1/2 Cl ion on each face. 1 whole Na in the center, 1/4 Na ion along each edge. The Attempt at a...
  43. M

    Can a Single Crystal Cover 700MHz to 3.2GHz for Frequency Variation?

    I am attempting to construct a device that will vary frequency between MHz and 3200MHz. Does anyone know of a fairly inexpensive crystal that will allow me to use all frequencies in this range? Thanks ~Matt
  44. P

    Does Work Hardening Create Smaller Crystal Grains?

    This might be more of a simple engineering question, but does work hardening (cold worked) of say a metal create smaller, more numerous crystal grains (and thus, more grain boundaries)? or does it just create dislocations in the crystal?
  45. H

    Transmission Electron Microscopy - Crystal Structure

    Hi I have a tutorial problem involving determining the ideal methods for identifying material properties of a layered semiconductor structure. The problem states to use either scanning or transmission electron microscopy. THe structure consists of several monolayers (around 5nm) of AlGaAs...
  46. P

    Elementary crystal cell or the whole crystal?

    Is fullerene C_{60} elementary crystal cell or the whole crystal? I do not clearly understand it fom the context? Why is considered most perfect point symmetry form?
  47. Z

    Elastic Modulus of an Anisotropic Crystal

    If I am given that mica has a modulus of 52GPa parallel to the c-axis and 179 GPa perpendicular to the c-axis, how do I figure out the elastic modulus of a polycrystalline mica where grains are oriented randomly?
  48. D

    Calculating Atom/Cell Volume in Simple Cubic Crystal

    What is the volume of atom/volume of cell?
  49. Z

    Properties of a Single Crystal

    Homework Statement In a mock exam I was asked for Q. Two properties associated with a single crystal. Homework Equations The Attempt at a Solution For one answer I gave that they are hard. I think another answer might have been something to do with crystal...
  50. R

    MD simulation of crystal oriented along 110, 111 planes

    Dear friends, I am doing a Molecular dynamics simulations of a crystal. For this the initial configuration is FCC (face centered cubic) lattice. My problem is that I have to study the system for different orientations of the crystal i.e. (100) plane, (110) plane and (111) planes. For (100), the...
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