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. H

    I How to index single crystal Bragg peaks

    I am able to find methods on how to index Bragg peaks for powder diffraction, and was wondering if the method is the same for single cubic crystals of NaCl? I have tried and cannot get the expected sequence of allowed reflections for cubic lattices (h^2 + k^2 + l^2= 3, 4, 8, 11, 12, 16, 19...
  2. Sasho Andonov

    Piezoelectric effect -- How long does a stressed crystal produce a DC voltage?

    I need help regarding piezolectric effect... If I add DC voltage to piezoelectric crystal it will change its dimension (length) and vice versa: if I put pressure on piezoelectric crystal it willl produce DC voltage on its surfaces... But I am wondering how long this voltage will last? If I keep...
  3. Jay Macarus

    I Calculate the distance between two cleaved crystals

    Hey guys, can't seem to make sense of this question from phys. It goes.. "A crystalline solid consists of atoms stacked up in a repeating lattice structure. Consider a crystal as shown in Figure a. The atoms reside at the corners of cubes of side L = 0.200 nm. One piece of evidence for the...
  4. Leggit9

    What is the equation for calculating crystal length using index of refraction?

    Hey, The question sounds like this: I have 100 fs 400 nm pulse passing through the CaF2 crystal. After passing, it gets twice wider (200 ps). What is the length of the crystal? Can anyone share the equation which would help me to calculate this? Thank you in advance!
  5. Petr Matas

    I Can We Cool a Macroscopic Crystal to 1 nK?

    Is it theoretically possible to cool a macroscopic crystal (for example NaCl 1×1×1 cm) to an extremely low temperature, like 1 nK? Will it retain its microscopic structure? Why? Does it have anything to do with zero point energy (I mean something like the lowest energy level of a quantum...
  6. C

    Laser Crystals -- effects of crystal size

    Say that I have a neodymium doped yttrium aluminum Garnet (Nd:YAG) laser crystal rod. If I'm using this crystal in a laser, will the size of the crystal affect any characteristics of the laser itself. That is, will a laser containing a 4-by-7 mm Nd:YAG rod operate differently than a laser...
  7. C

    Does the size of a crystal used for a laser affect lifetime?

    I would imagine that it doesn't. I'm really sure how to rationalize this. If emission is a decay process, I don't think the rate constant would change with concentration, and likewise crystal size. Any spectroscopist out there?
  8. patrickmoloney

    Magnetic Moment of a crystal

    Homework Statement Find the magnetic moment of a crystal when placed (i) in a weak field at high temperature (ii) in a strong field at low temperature Homework Equations This is the last part of a question which I feel I have solved correctly up until this point. The mean magnetic moment I...
  9. C

    B What are the potential uses of time crystals?

    I have stumbled upon an interesting article in wikipedia: https://en.wikipedia.org/wiki/Time_crystal While i somewhat understand the concept, i was unable to find applications or at least repercussions of said crystals. I am not of QP background, so even if its obvious, could someone be kind...
  10. Q

    I Birefringent walk off question

    Hi, I am having trouble wrapping my head around a simple (I think?) question about birefringent walkoff: If the crystal is oriented at some angle such that walkoff is nonzero between e and o beams (in a nonlinear conversion process, for example), it seems to me that reflecting the light...
  11. P

    B Do Quartz Crystals in Ancient Structures Emit Energy?

    we have heard that pyramids, old temples are made from hard stones containing quartz crystals. Is they radiate any kind of energy so that we get a pleasant feeling?
  12. N

    The Crystal Mill: Explore Windows 10 Welcome Image

    This picture appeared on the welcome page when windows10 was powering up this am . I found this further information : http://unusualplaces.org/the-crystal-mill/
  13. Mind----Blown

    I Miller indices for hexagonal crystal systems

    Hi everyone, to find the draw the direction for a given miller index say, [1234] we first convert this miller index consisting of 4 indices into one containing 3 indices. To do so, we have a set of formulae prescribed in almost every book. Sadly I haven't been able to come across a single book...
  14. M

    Impact of crystal defects on band diagram.?

    I was studying about Crystal defects in crystals and came to know that it has huge effect on band diagram.I don't know about their specific impact on band diagram.So what are major impacts of crystal defects on band diagram.?
  15. frostysh

    Crystal frames problem, what actually asking?

    Homework Statement The problem from Sterway, Jewett book. The Attempt at a Solution The answer in the book is something like 0,141 nm, as I remembered but I cannot achieve such answer coz' I cannot understand what actually asking, d is looks like a distance between two centers of the...
  16. P

    I Can we consider strained crystals as periodic crystals in theory and practice?

    Are a strained crystal still crystal? How to prove it? Are the unit cells of the strained crystal still the periodic elementary building blocks of the transformed crystal? Does the transformed crystal own the same volume as that of the perfect crystal? Can we treat the strained crystal as the...
  17. I

    Crystal lattices and structure in solid state physics

    For the crystal lattices and structure Question picture is uploaded. Question.jpg My attempted answer is uploaded by a picture. My attempted ans. 1.jpg My attempted ans. 2.jpgThere is any mistake?
  18. V

    Fourier transform of periodic potential in crystal lattice

    Homework Statement Homework Equations I'm not sure. The Attempt at a Solution I started on (i) -- this is where I've gotten so far. I am asked to compute the Fourier transform of a periodic potential, ##V(x)=\beta \cos(\frac{2\pi x}{a})## such that...
  19. A

    A Crystal Channeling: Explained

    Can someone explain this paragraph especially the bold part in simpler language: "If it is not in a major crystal direction or plane ("random direction", Fig. 2), it is much more likely to undergo large-angle scattering and hence its final mean penetration depth is likely to be shorter." full...
  20. A

    Why Does X-Ray Scatter at Angle 2dsinθ?

    This question is as dumb and simple as it can be: Why is the path difference 2dsinθ? Or better said: Why x-ray scatters like in the image? (Couldn't there be another scattering angle for both atoms other than θ?)
  21. L

    How Does Changing Load Capacitance Values Affect Crystal Oscillator Performance?

    How does the load capacitance affect the Crystal. For example, IC manufacturers recommend a Crystal and also load capacitance, like 25MHZ, 16pF. What happens if I choose a xtal with load cap of 10pF 25MHz? I am talking about changing the load caps recommended by IC manufacturer, not the ones in...
  22. G

    I Predicting new crystal structures

    Hello, Sorry if this is a rather basic question, but my memories of solid-state chemistry are a bit rusty. Basically I'm trying to predict new crystal structures. I understand the crystallographic aspects quite well and know that at given external temperature and pressure the most stable...
  23. hsdrop

    Help understanding recent work on "Space-Time Crystal" and TTSB please

    I was reading this interesting article at Wikipedia about recent work by Nobel laureate and professor at MIT Frank Wilczek in 2012: https://en.wikipedia.org/wiki/Space-time_crystal It sounds like some scientists are close to actually making some of these crystals: Could you please explain to...
  24. B

    [PoM] Electrons Fermi level in a crystal

    Homework Statement The conduction band of a hypothetical crystal of one-dimensional Cesium reticular with step a=300 pm (1 atom per cell) is characterized by the ε dispersion law ##\epsilon (k) = V_0 + \frac{\hbar^2}{m_e}(\frac{1}{2}k^2 - \frac{a}{3\pi}|k|^3## where ##V_0 = -4 eV##, is set so...
  25. E

    Material Science -- using materials without specifying crystal directions

    Why in most practical applications, most materials properties are given without specifying crystal directions. Are they trying to say all materials are isotropic?
  26. qnach

    I Could XY crystal be a special case of X2YZ crystal?

    There are some types of crystals we call them XY type (i.e. NaCl) or X2YZ type? Could XY type be a special case of X2YZ type by assigning Y=Z?
  27. Robert Sanchez

    B Exploring the Paradoxical Properties of Samarium Hexaboride

    I'm no physicist, but I found this material to be interesting. Samarium Hexaboride is a crystal that exhibits conductive properties at room temperature and insulating properties when cooled to below minus 223 degrees Celsius. A layman's article...
  28. qnach

    Nearest neighbour, nnn....etc. of an atom in a crystal

    There are some software can provide visualization of crystal or protein structure, i.e. VESTA. I want to know how many atoms is the nearest neightbour (and their distance), and the next nearest neighbour...etc of a particular atom. Is there any software (or perhaps some data book?) can do this?
  29. qnach

    I Crystal Structure Database (Pb0.5Sn0.5)Te

    I would like to find the crystal structure of (Pb0.5Sn0.5)Te I was told it is similar to NaCl basically an XY crystal I think it is called Space Group: 225 I would like to know the first, second, third ...layer of atoms closest to a X atom...and perhaps their distance... I found...
  30. N

    Calculating Energy Levels in a Ni2+ Ion Crystal

    Hello, I am stuck at the beginning of an exercise because I have some trouble to understand how are the energy level in this problem : In a crystal we have Ni2+ ions that we consider independent and they are submitted to an axial symmetry potential. Each ion acts as a free spin S=1. We have the...
  31. S

    Crystal Optics -- Learning resources wanted....

    What are some good resources : books, websites, etc to understand crystal optics? I am a graduate student and I want to start with the basics.
  32. B

    [PoM] Cohesive energy in an argon crystal

    Hey guys! I come back to solve a new problem with your help! 1. Homework Statement Use the Lennard-Jones function: $$ V(R)=4\epsilon[(\frac{\sigma}{R})^{12}- (\frac{\sigma}{R})^6] $$ like as a adiabatic potential energy model in function of separetion R between cople of argon nuclei. With ##...
  33. F

    I Laser Beam through Calcite crystal = Photon Entanglement?

    If I shine a laser beam through a calcite crystal, the beam is split in two, as shown below. Are the photons in the split beams in an entangled state?
  34. D

    I What is a "Space-Time Crystal"?

    I know what the definition is, but the concept it's conjuring for me seems in my experience of learning about these things, to indicate that I'm missing the point completely. What does it mean for something to be oscillating when it's in a ground state? I was under the impression that such a...
  35. G

    A Limiting factors in Diamond Anvil Cells

    Hello, I'm trying to better understand the limiting factors in Diamond Anvil Cells that limit the achievable pressure to around 7 or 8 Mbar at the moment, despite not being a specialist. For example, is there a special reason other than the tiny size of the crystal sample used in DACs for why...
  36. P

    I Photonic crystal switch- directional couplers

    Im supposed to make model to demonstrate all-optical switching using a nonlinear effects of photonic crystals. And I will be using a directional coupler for this purpose. However I am having trouble in understanding the theory and concepts related to coupling / coupling length / use of...
  37. G

    I Space Group Duplicates: Is it Possible for Monoatomic Crystals?

    Hello, I was building some test crystal structures with VESTA software and I noticed when generating the POSCAR output files to be read by VASP that for a simple monoatomic basis such as in elemental silicon crystals some distinct space groups produce the same exact POSCAR files (i.e. same...
  38. smak64

    I Piezoelectric crystal energy restoration

    Let's say that I deform some piezoelectric tile and the energy(Fs here) is stored in form of some stress energy and some electrical energy(distribution of the centres of charges looking as a capacitor). Now I remove the force and then remove the electrical energy somehow so by the inverse piezo...
  39. M

    Crystal leaving patterns of the electromagnetic spectrum?

    I was bored today so I took this diamond shaped crystal made of glas and simply put in infront of the light emitting from the sun. What I noticed was a lot of lines on the wall that were strangely colored, just like the electromagnetic spectrum. One end was blue, then progressively went to red...
  40. D

    A Basic questions on crystal lattice: k-vectors and Brillouin

    Hi all, I’m brushing up my skills on solid state physics and I have a few questions about crystal lattices: 1. What’s the spacing between allowed kx, ky, and kz states for a lattice of dimensions La x Lb x Lc? My attempt: The spacing is kx, ky, and kz: k_x = \frac{2\pi}{L_a}, \qquad k_y =...
  41. nmbr28albert

    I Does the ionic background of a crystal affect the index?

    In a crystal, the index of refraction is always calculated in the Lorentz oscillator model by examining the electronic response to an incident field and assuming a stationary nucleus. Is there however, any contribution to the index from the ionic nuclei in the background? I assume since I've...
  42. F

    Distinct modes of oscillation in a 3D crystal lattice

    Homework Statement Silicon crystalises in a cubic structure whose lattice is face-centred, with a basis [000],[1/4,1/4,1/4]. How many optic/acoustic modes are to be found in the phonon dispersion diagram for silicon. How many distinct branches would you expect along the [100] direction...
  43. F

    A Crystal field when inversion is absent

    I find in many textbooks that when expanding the crystal field in spherical harmonics, those terms of odd ranks do not appear in the expansion even if the crystal lacks an inversion centre such as the tetrahedral crystal field. Why is that? and when one should include spherical harmonics of odd...
  44. coolsalena

    I How does pH affect crystal growth?

    Hi! The crystal that I am growing is Mohr's salt. though i have already optimized the parameters (pH), i would like to know the reason why pH affects it's growth. pH 1: no crystals formed pH 2: crystals formed Thanks!
  45. S

    I What factors influence the crystal structure of metals?

    What determines the crystal structure taken by metals? For example Sr has FCC and Ba BCC. The packing fraction is greater for FCC. However, due apparently to coordination number and number of "next nearest" neighbors, BCC is favored in the case of Barium despite its lower packing fraction...
  46. Z

    A Can't crystal of simple lattice be antiferromagnetic?

    Is it correct that a crystall of simple lattice (lattice with primitive cells each having only one atom) cannot be antiferromagnetic? In other words, the antiparallelism must occur between atoms within each primitive cell. Thanks.
  47. Z

    A Does a type I superconductor have to be single crystal?

    Does a type I superconductor has to be single crystal? If not, is there any change in its Tc when it becomes polycrystal? Thanks.
  48. Elena14

    Are the properties of a crystal and its unit cell same?

    1) My teacher said that to analyze the properties of entire crystalline solid, we just need to analyze the properties of a unit cell, which is the smallest repeating unit of a crystalline solid. 2) But crystalline solids are known to be anisotropic, i.e. they have different properties in...
  49. B

    Preferred Crystal Structure of Steel (BCC vs FCC)

    What are the reasons behind the different microstructures of steel at different temperatures? I don't understand why steel at high temperatures (austenite phase) would favor an FCC crystal structure while steel at lower temperature (ferrite) would favor a BCC crystal structure.
  50. F

    B Quark Seeding: Info & Possibilities

    Hi. I'm wondering if anyone has any info on "quark seeding" like: Is it possible to dope the crystal lattice of a solid material by replacing electrons with quarks ?
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