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. mathgirlie

    Rotating an elastic tensor from 100 to 711 axis

    I have the elastic tensor for a material where C11 aligns with the 100 axis , C22 aligns with the 010 axis and C33 aligns with the 001 axis. I want to rotate it so the the new axis are for a configuration with an axis along 711. How do I come up with the rotation matrix to do this?
  2. gggnano

    I Negative energy when a laser goes through lithium niobate crystal?

    A screenshot from a book which describes it: So I am trying to picture this one: 1. A laser is "pumped" through a cylinder made from lithium niobate which is placed at 90 degrees, perpendicularly...so that the laser passes through the body of the cylinder (and not through the 2 round ends)...
  3. A

    A The main charge carrier in the ionic crystal is polaron or conduction?

    Suppose I have a perfect crystal(e.g.TiO2-Rutile, band gap=3ev), under UV light, there should photoconductivity, according to the condensed matter theory, some of these excited conduction band electrons would form small polarons, I am wondering how many percent of the free conduction band...
  4. mishima

    Finding Piezoelectric Crystal Frequency for Coherer experiment?

    Hi there, I've been fascinated by using simple coherers to pick up the electromagnetic signal from a spark (in imitation of early radio experiments, for high school education). I am using a push button ignitor (piezoelectric crystal) attached to a simple dipole antenna for the transmitter. When...
  5. P

    Intensity of central maxima of crystal diffraction

    When the crystal above is illuminated with light of intensity ##I_0##, what is the intensity at the central maximum? (The picture shown above is a 4 x 4 unit cell of the crystal) The answer is ##(\frac {5} {16} )^2 I_0##. Why? Apparently, Electric field is proportional to the transparent area...
  6. davenn

    Visit to The National Gem and Crystal Expo, Windsor, NSW, Australia

    my first youtube video will do better next time ... was an awesome day with a wonderful selection of rocks, minerals fossils etc
  7. A

    B Understanding Crystal Structures: Energy Considerations

    This questions is hovering on my mind from a long time. Why would something which does not have life would want to be in such a beautiful neighborhood, while the world is so much disordered. What causes them to be in that regular array and how they choose which crystal structure is suitable for...
  8. Helena Wells

    A Crystal structures and number of bonds of each atom

    Is there a general rule for a crystal structure how many bonds each atom in the crystal lattice will make ?For example Si has a face centered cubic structure so it makes 4 bonds regardless of the fact Si has 4 valence electrons?
  9. amjad-sh

    I Van Laue Formulation: X-ray Diffraction from Crystal Structure

    When we shine an X-ray beam on a crystal, according to Van Laue formulation, for a sharp intensity peak to be observed on the screen there is a specific direction ##\mathbf{\hat{n}}## , in which for all the X-rays with wavelength ##\lambda## and wavevector...
  10. J

    Coupling of resonant modes in a 1D Photonic Crystal

    In 1D Photonic crystals, a defect can be introduced to create a defect/resonance mode and enable transmission. At first considerations, the thickness of the single defect layer determines the transmission frequency. Moreover, if it is a half-wavelength layer it will enable a resonance condition...
  11. S

    Harmonic Crystal and Bogoliubov trasformation

    I thought about writing $$a_q'|0'> =0$$ then develop the U operator in series, after I don't know how to proceed
  12. E

    Voltage developed across a cooled crystal

    Here I disagreed with my professor's solution, so I'd like to check with you guys. Each B4+ ion in a perovskite ABO3 structure is displaced by ##0.2 \mathring{A}## parallel to the ##c##-axis w.r.t. the centroid of the unit cell, after the cubic-tetragonal phase transition below the Curie...
  13. Mathew Murdock

    Number of atoms - Crystal Struture

    Do I do it right guys? The relative amount of low-coordinated atoms is The number of atoms at 8 corners: n_corner=8 1/8=1. The number of atoms at 12 edges: n_edge=12 (n-2)/4=3n-6. The number of atoms at 6 surfaces: n_surface=6 (n^2-4n)/2=3n^2-12n. The relative amount of low-coordinated atoms is...
  14. E

    Polarisation through a chiral nematic crystal

    If light passes into a birefringent material with constant fast and slow directions, ##\hat{x}## and ##\hat{y}##, that are oriented the same way at any point in the crystal, then the electric field is$$\vec{E}(z,t) = E_0\hat{x}\cos{(\theta_0)}e^{i\omega(t - \frac{n_x}{c}z)} +...
  15. E

    B Notation for indexing a crystal direction

    Given a crystal basis ##\{\vec{a}, \vec{b}, \vec{c} \}##, the two lattice vectors ##\vec{r}_1 = u_1 \vec{a} + u_2 \vec{b} + u_3 \vec{c}## and ##\vec{r}_2 = 2u_1\vec{a} + 2u_2 \vec{b} + 2u_3 \vec{c}## both obviously point in the same direction whilst ##\vec{r}_2## is twice as long as...
  16. Viona

    B Which Cleanroom ISO Class is suitable for Liquid Crystal research?

    I was wondering which cleanroom ISO class is suitable for liquid crystal research?
  17. tanaygupta2000

    Electrons impinging on a crystal

    Since the crystal spacing is given to be 0.4 nm, so d = 0.4 nm = 4e-10 m in Bragg's law formula For θ = 90° & n = 1, I got λ = 2d = 8e-10 m Using this value in De-broglie wavelength, I got p = h/λ = 8.28e-25 Now kinetic energy of the electrons is given by E = p^2/2m Using value of p, I am...
  18. R

    Force field suitable for studying silica crystal

    I need some advice and help please -Is There a two body force field suitable to study silica crystal or alpha quartz crystal? it's okay to gives Approximate results. - Is the BKS force field suitable for silica crystal? - If there are other simple terms of force field for studying the silica...
  19. K

    Polarization of light -- Determine the thickness of the crystal

    I don't even know where to start with this problem. What kind of slit makes linearly polarized light circularly polarized? The correct answer is d = lambda/(4(n1 - n2)) = 856nm. But how do I get there? Thanks in beforehand!
  20. E

    Battery to support Polymer Dispersed Liquid Crystal (PDLC) Film

    We are incorporating a PDLC layer into a product being developed by us and it requires almost constant activation to remain transparent. The PDLC draws 0.557 Watts of power per hour at 60VAC. The goal is to get a battery/power source (of any type even proprietary) to last the upwards of 26,000...
  21. V

    Solid State Textbook on crystal field theory and degeneracy breaking

    In particular I would like to have a resource for the relation between group theory, crystal field symmetries and breaking of degeneracies of orbitals. I've taken a graduate condensed matter course and graduate quantum mechanics courses. I have some basic knowledge of group theory but can learn...
  22. Philip Koeck

    A What is the mean inner potential in an ideal crystal of finite size?

    In a hypothetical, electrically neutral, ideal crystal, where all unit cells are identical, even the ones at the surface: What would the average value of the electrostatic potential be compared to that of the vacuum outside the crystal? Would it be the same or more positive? As a simple example...
  23. D

    Crystal oscillator not working

    I bought a raltron crystal oscillator. I connected it to a programmable frequency divider. It is supposed to cause a diode to blink on and off. The crystal oscillator has a rated frequency of 100 megahertz. The programmable frequency divider can divide a frequency by up to 2,147,483,648. Diode...
  24. T

    Crystal with two different melting points

    It turns out that the solid form is the same for the two situations but the liquid is two different isomers depending on external conditions during melting. https://physicstoday.scitation.org/do/10.1063/PT.6.1.20190606a/full/
  25. X

    A Question about crystal structure of long chain fatty acids (XRD)

    Hello, we are studying potato periderm before/after digestion and dewaxing and native vs wounded. One of the techniques is XRD, hence my user name. Among other things we are trying to use XRD to determine the arrangement of fatty acids, esters, and other long-chain aliphatics that are present...
  26. S

    How can I successfully grow high-quality KDP crystals?

    I've been trying to grow a KDP (potassium dihydrogen phosphate) crystal, but I'm having trouble growing anything. I've been adding potassium phosphate fertilizer to distilled water in a bottle I cleaned out and heating it to dissolve the chemicals, but so far haven't gotten much results. It's...
  27. T

    Reciprocal lattice for FCC and diffraction peaks

    My issue is more with the steps to approach rather than the calculations. I was just wondering if someone could confirm my approach to be correct. As it asking for the reciprocal lattice of an FCC I assume this would mean I need to use the points on the BCC to calculate the geometrical...
  28. Mark Palmer

    Electrical Troubleshooting Crystal Radio: Tips for Building and Improving Reception

    If anybody here has any experience with building a crystal radio, I would appreciate a response. My grandson and I are doing radio projects. This involves basic crystal build using a coil, diode, and resistor. The system is grounded and uses an antenna with no external power and a high...
  29. D

    Can you build an FM transmitter with a crystal oscillator

    Can you build a fm transmitter with A crystal oscillator? I already have a 100 megahertz crystal oscillator. I can't find instructions on how to do That on the internet.
  30. Edge5

    I Opal Crystals on Mars: Implications for Geochemical Conditions

    People found silica opals exist on the planet Mars, what does this imply about geochemical conditions on Mars?
  31. R

    Reversing the Faraday effect to get an induced current

    Hi all! I was thinking if it is possible to revert the Faraday effect. If I have a magnetic field, it interacts with EM wave (light) by changing its polarisation. Can I got a variable magnetic field interacting with polarised light so that I can get induced current in a coil? I can understand...
  32. steroidjunkie

    Powder sample crystal is analyzed using Debye-Scherrer method....

    Homework Statement Powder sample of monoatomic cubic lattice crystal is analyzed using Debye-Scherrer method. Primitive vetors of direct lattice are: a1 = (a, 0, 0), a2 = (0, a, 0) i a3 = (0, 0, a). Wavelength of x-ray radiation is 1 Å. a) Find primitive vectors of reciprocal lattice. b) Find...
  33. fluidistic

    I Understanding L&L's argument, constant current in a crystal

    I'm trying to go through chapter III of the vol.8 of Landau and Lifshitz series. (Fortunately the book is uploaded to the archive.org, I guess it is in the public domain.) At page 87 ( << Archive.org link deleted by the Mentors because of copyright violation >> ), they speak about the Joule...
  34. J

    A Lattice parameter difference: PBE vs PBE-D3 functional

    Hi guys! Does anyone know why the lattice parameters of a crystal calculated with PBE-D3 functional are lower than those calculated with PBE? Thanks in advance! :)
  35. J

    Experimental procedure for growing piezoelectric crystals

    At school I and a handful of other kids are devising an experiment to send up to ISS to test it over a period of 30 days next year. (Yep, we're quite fortunate to have this opportunity!) We've chosen to grow piezoelectric crystals using (super)saturated solution of the piezoelectric crystal...
  36. J

    Growing piezoelectric crystals experiment

    Homework Statement I'm not sure if this is a forum for these kinds of things. But anyways, at school I and a handful of other kids are devising an experiment to send up to ISS to test it over a period of 30 days next year. (Yep, we're quite fortunate to have this opportunity!) We've chosen to...
  37. C

    Bragg diffraction form an “inclined” crystal plane

    Homework Statement In picture, first-order reflection from the reflection planes shown occurs when an x-ray beam of wavelength ##0.260 nm## makes an angle ##\theta=63.8°## with the top face of the crystal. What is the unit cell size ##a_0##? Homework Equations Bragg law $$d=\frac{ n...
  38. S

    Schools PhD in Liquid Crystal Physics (or Engineering)

    Dear Forum member, I want to pursue research in Liquid Crystal Physics / Engineering, are you aware of any laboratories or university departments actively researching in this field in Canada or Germany? I will be very if you are aware of active groups and share their names. Thanks
  39. patrykh18

    Energy of a crystal in thermal equilibrium

    Homework Statement In a monatomic crystalline solid each atom can occupy either a regular lattice site or an interstitial site. The energy of an atom at an interstitial site exceeds the energy of an atom at a lattice site by an amount ε. Assume that the number of interstitial sites equals the...
  40. A

    Piezoelectric crystal and air pressure

    Will air pressure induce a voltage of a piezoelectric crystal or does it need to be mechanically compressed? My guess is that it would depend on the permeability of the crystal
  41. W

    I Phonons and Crystal Momentum: Conservation and Quantization

    Hi all, I have a few questions. Thanks in advance! Phonons: Can phonons be thought of as a quantised wave of sound, in the same manner photons being a quantised light wave? Also, can they be taken as particles of sound in the same way that photons can be particles of light? Crystal momentum...
  42. H

    A Help with determination of crystal orientation

    Dear all, Hi, I am looking for a non-destructive method of determining the crystal orientation of a smaller-than-50x50x50 μm single crystal, mounted on a quartz substrate. I've considered several x-ray methods like Laue method, or microfocused XRD, but there are some experimental difficulty...
  43. S

    A Size of nuclei wave function in a crystal

    I need to know what is the typical extention of the (spatial) wavefunction of an atomic nucleus in a crystal, in particular I am interested to the case of a Germanium cristal. Please together with the actual number of the size of the nuclei wavefunctions, let me know the references (articles or...
  44. B

    The crystal structure for Ba2TiO explained with symmetries

    Hello! I would love to get help on this particular question that I find extremely difficult to answer. -"Bariumtitanate can under a certain set of conditions crystallize in the given structure. With the help of the compounds symmetries, explain how it is possible for it to achieve such a...
  45. Clara Chung

    Question about a cubic crystal and its parameters

    Homework Statement Homework EquationsThe Attempt at a Solution So i got the answer by finding the diagonal of the square and then find the radius of A. ([(2x0.17)2 ]x2 )1/2 = 2a + 2x0.17 And find out a= 0.14 nm , however the answer is 0.124nm, please help
  46. J

    How Can Crystal Symmetry Affect Conductivity Tensor Components?

    Hello guys! I have to solve a problem about crystal symmetry, but I am very lost, so I wonder if anyone could guide me. The problem is the following: Using semiclassical transport theory the conductivity tensor can be defined as: σ(k)=e^2·t·v_a(k)·v_b(k) Where e is the electron charge, t...
  47. T

    Tuning Fork Crystal question

    I would like to understand the reason that tuning fork crystals have the negative parabolic temperature coefficient shape. Is it the material, the crystal cut or how its mounted. What is the physics behind that. Thank you
  48. fluidistic

    I Is there a crystal angular momentum?

    I've learned that in a crystal, the crystal momentum is conserved. When one considers the electrons as Bloch waves, they have a momentum that doesn't commute with the Hamiltonian and they have well definite energies, hence they cannot have a well definite momentum, because there is no basis in...
  49. W

    Advice on making a liquid crystal screen (shutter)

    I need to make my own smart film for some experiments. I've read enough articles on it to know the required components, how they are mixed and applied. I have a 1:1 mixture of liquid crystal and UV curable resin and glass bead spacers that I need to apply between two ITO PETs and UV cure to...
  50. G

    Find ##2\theta## Values from Rotated Crystal and Intensity

    Homework Statement Consider the crystal in the attached image (https://ibb.co/ftMrBH) (a triangular lattice of white atoms with a triangular basis of grey atoms attached to them at angles of 0, 60 and 120. From a previous problem the fractional coordinates of the atoms in the basis are (0,0)...