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. D

    High symmetry directions in a two-dimensional oblique crystal

    What are the high symmetry directions for a two-dimensional oblique crystal? Please provide a figure of the corresponding Brillouin zone with high symmetry points labelled.
  2. C

    Should you hear static on a crystal radio?

    Hi, I'm hoping I'm in the right section, I wasn't quite sure. For a couple of days I've been trying with no success to make a crystal radio. To save me the trouble of having to build my own components, I decided to build a tuned circuit that should resonate at a radio frequency (and insert...
  3. D

    Quartz Crystal Microbalance equilibrium

    Hi guys, I am a new user of QCM and I am having trouble reaching equilibrium. I have isolated the chamber from air flows and vibrations, the crystals are clean and all the other removable parts have been cleaned as well. The real problem is that sometimes I have managed to reach equilibrium...
  4. B

    Crystal Radios - Understanding The Tuning Mechanism

    Hello, I bought an electronics kit for my 12 year old brother (and perhaps a little for myself too...) for building a crystal radio. I would like to understand what's going on when I tune the radio, so that I can explain it to him. It's a simple setup, where changing the position of a...
  5. EternusVia

    What is the significance of crystal momentum?

    Hello, Could someone please explain crystal momentum in understandable terms? Thanks, EV
  6. A

    Crystal Lattice of Spin-1 Particles: Chemical Potential?

    Homework Statement A crystal lattice consists of a spin 1 particle at each lattice point. Spin 1 particles can have z-components of magnetic moment that take on the values +μZ, 0, and -μZ. In an external magnetic field B, each spin can have an energy U = -μZB, so the possible energies are...
  7. T

    Stainless steel crystal structure

    Hi, I'm looking for a simple s.s crystal unit cell structure and can't find it anywhere. I understand that stainless steel is a very general word and takes many forms and has many different types, but isn't there a standard type that people use in the industry and ususlay talk about when they...
  8. L

    Is the Salt Crystal Lamp Really Effective as an Air Purifier?

    So my dad got this Salt Crystal Lamp for a wedding gift that supposedly freshens the air naturally, and I need some help explaining to him why this doesn't actually work. It says on the box: "This lamp is scientifically proven to work like an air purifier. When lit, it can emit negative ions...
  9. K

    Atomic Energy States in a Crystal: Einstein's Relation

    Does atoms in a crystal have energy states like electronic states? it is according to Einstein relation for harmonic oscillator.E=nhw
  10. K

    Number of modes for a 2d crystal

    Hi, I have problems with the following: Number of modes for a 2d crystal with one atom per primittive unit cell. 1. Number of discrete vibrational modes? Should there be 2N of them? That is what I come up with if I think of one transverse and one longitudinal mode for each k. But I am...
  11. K

    Understanding Rest Mass of an Electron in a Crystal

    Hi all. we know that the rest is the mass of an object within a coordinate system which has zero velocity, but how does it exist for an electron inside a crystal, which we call rest mass of electron, how electron exist with zero velocity.or we mean by zero velocity of electron with respect to...
  12. Choisai

    SLMS: Liquid crystal vs Digital micromirror devices

    Hi there! I'm interested in Spatial Light Modulators for my project and I was hoping you (whoever you are) could help me. I try to explain everything as compact as possible but it's still quite a story. Sorry for that! For spatial modulation of light, a 'spatial light modulator' is needed...
  13. A

    Predicting Crystal Shapes: Wulfs Theorem

    Is it possible to predict, at least in theory, which shape a crystal of some combination of atoms would have. If so, what are the principles for such a calculation. I have seen a theorem in classical thermodynamics called wulfs theorem about the equilibrium shape of crystals. Does this explain...
  14. A

    Surface energy simple cubic crystal

    I want to calculate the surface energy for the (001) plane in a simple cubic lattice. My idea is this: When I cleave a simple cubic crystal I create 2 surfaces each sharing an amount of broken bonds. I want to find the amount of broken bonds per area, because I can associate an energy with...
  15. C

    Crystal Structure vector question

    Homework Statement Identify the [221] vector? A B C D E Homework Equations The Attempt at a Solution I reduce [221] to [1 1 0.5].BUT after getting the wrong answer, the feed back is as follows "Feedback: [221]: has a 0.5 component along the x-axis...
  16. U

    Designing a crystal decanter cleaning apparatus

    I need to create a machine that'll help me clean out my crystal decanters. Brown rice and soap work great, just shake and viola...however some decanters need a bit more shaking, or 'spinning' of the rice and soap than I can provide so I've devised a plan with a box fan motor that would create a...
  17. U

    Interference of Xrays from a salt crystal

    Hello, In my textbook(Serway), Constructive interference of two rays hitting the first and the second planes , respectively, of a crystal lattice is derived as 2dsin(Θ)=mλ , where Θ is the angle shown in the picture. My question is: shouldn't the equation be 2dsin(Θ) = (m+1/2 )λ instead...
  18. A

    What is the unit cell and coordinates for wurtzite crystal structure?

    As far as I understand wurtzite is the name given to the crystal structure defined by the stacking sequence ABABABAB.. However, I am having a hard time understanding what the unit cell is of wurtzite. From what I know the unit cell is the smallest repetitive unit and in it you specify the...
  19. A

    Understanding the Unit Cell of Wurtzite Crystal Structure: A Brief Overview

    My teacher wrote down something to day which I wish I had written down myself. It was about the crystal structure of wurtzite, which is an ABABABAB stacking of hexagonal lattices. What he wrote was two different specifications of the unit cell of wurtzite depending on which groups of elements in...
  20. A

    Crystal Directions: Finding Basis Vectors

    I found the following picture of the Wurtzite and Zincblende structure as viewed from a specific direction. I could do with some help on which basis vectors are chosen for either the [1 1 1] or [0 0 0 1]. Now I am pretty sure that the last one refers to a basis where we have three vectors...
  21. artfullounger

    Crystal structure/lattice resources (with examples)?

    Hello PF :D So, I am an (engineering) undergraduate working on an independent study project, which for me is doing some computational work for a lecturer's research. Specifically, I am using the Abinit package to calculate the elastic properties of some metalloids. To create the input file I...
  22. H

    Relation between crystal momentum of the electron and other momentums

    As far as I know, F_ {ext} = d (\hbar k)/dt = d p_{electron} / dt + d P_{crystal} /dt. could one say that \hbar k = P_{electron} + P_{crystal}?
  23. M

    Crystal Field Theory: Exploring Octahedral Complexes & Their Bonding

    I have recently been learning CTF and energy differences and orbital splitting is starting to make sense to me a bit more. I have not seen any definitive answers yet so any help would be great. In CTF, octahedral complexes are most common and there are 5 d orbitals that participate. Whether it...
  24. R

    If a crystal has distinguishable sites

    compare the number of microstates for crystals consisting of a mixture of A atoms and B atoms if the crystals have 4, 8 and 16 distinguishable sites the question is ambiguous in that it simply states crystals, so I am assuming its the same as given examples and is 2 crystals AAAA and BBBB...
  25. H

    How about the energy of crystal in a direct transition?

    When a photon is absorbed by an electron through a direct transition in a crystal, the crystal momentum of electron would not approximately change. Therefore momentum change of electron would neutralize momentum change of crystal. In other words, the crystal would gain momentum as well as...
  26. H

    Isotropic crystal and energy band

    Since all the directions are equivalent in an isotropic crystal, can we deduce that the energy band is exactly spherical?
  27. S

    Vibrational modes of quartz crystal

    I have a problem about the vibrational modes of a quarts crystal Two vibrational modes are induced simultaneously in a quartz crystal at MHz frequencies via a transducer hooked up to two signal generators it appears as if a third average frequency is also generated but only becomes...
  28. H

    Electron collision and periodic crystal

    Ashcroft & Mermin, Solid State Physics, page 315: "According to the Bloch theory, an electron in a perfectly periodic arrays of ions experiences no collision at all". But how about the electron at the border of Brillouin zone? How does diffraction take place there?
  29. A

    Fourier component crystal potential - physical significance

    I have done several exercises concering periodic potentials in crystal. Especially I did one, where I had to show that the Fourier component of the shortest reciprocal lattice vector (call this vector a) in the z-direction was zero. Now solving the problem was just about writing up the right...
  30. G

    Why does a BBO crystal create entangled photons?

    Hi, If we pump a beta barium borate (BBO) crystal, we get one circle of vertically polarized photons ##\left|V\right\rangle## and an intersecting circle of horizontally polarized ones ##\left|H\right\rangle##: http://quantum.ustc.edu.cn/old/img/image002.gif At the intersection points of the...
  31. T

    Brillouin Zones, Phonons, Energy Propagation through a Crystal

    Hello, I am having quite a bit of trouble really grasping Brillouin Zones and their relation to phonons, energy propagation, etc. I've got a few questions, and there will probably be a number of misconceptions, but I figure they'll clarify what I exactly don't understand. I think a lot of the...
  32. B

    Polarisation of photons exiting a birefringent crystal

    Homework Statement The problem is taken from A Modern Approach to Quantum Mechanics by Townsend, and is stated as follows: The answer given in the back of the book is 0.12, though I have not managed to get this result. Homework Equations Classically, light traveling through a crystal...
  33. 7

    Complex problem from crystallography - rotating the crystal

    The problem statement: What I have managed to do: This problem seems a bit tricky at first because it is talking about rotating a crystal while also changing the voltage - changing two variables at the same time makes no sense to me. This is why I assumed that while we change the voltage...
  34. 7

    What happens when we rotate crystal while shooting electrons at it?

    I know that if we shoot narrow beam of electrons at the crystal (we don't change the angle) we will get a diffraction of electrons according to the brag's law. Therefore we get minimums and maximums on the screen around the crystal. Until now we have been dealing with problems where...
  35. S

    Light - stopped or trapped inside a crystal?

    Light -- stopped or trapped inside a crystal? In the below experiment: http://www.extremetech.com/extreme/162289-light-stopped-completely-for-a-minute-inside-a-crystal-the-basis-of-quantum-memory Opaque crystal of yttrium silicate doped with praseodymium1. Is light stopped or trapped (i.e...
  36. 6

    Understanding my crystal oscillator

    I have an obsolete, proprietary crystal oscillator. It is a 200MHz, 10 pin, SMT component. The number on the unit is 200N1. I cannot find another C.O. like it in size, number of pins or footprint. What I don't understand is 9 of the pins are grounded. Only one pin is used and it obviously puts...
  37. 7

    Gravitational redshift inside a crystal - Pound-Rebeka experiment

    Homework Statement Some atoms emit X-rays at transition from excited to ground state. Energy of an excited state of the atom ##\scriptsize^{57}_{26}\textrm{Fe}## is ##\scriptsize14.4keV## larger than than the energy of it's ground state. The mass of the atom is...
  38. M

    Can the crystal particle expand?

    Homework Statement With increasing the temperature, can the crystal particle expand? Actually, what really happen to the structure when increase the temperature? Why its look bigger size compare to actual size. Does it mean the crystal of particle expand? or something happen to the...
  39. SSGD

    Crystal Structure of Metals at Absolute Zero, Waves

    I have been trying to find information on the crystal structure or phase of solid elemental metals at temperatures close to absolute zero, but I can only find information on there ambient structures. Does anyone know of any sources that would have thermodynamic tables for solid metals at low...
  40. Nemo's

    Distance between 2 atoms in a crystal

    Homework Statement Given a crystal (cube) with regularly arranged atoms (Total 27 atoms) The mass of each atom is 3.5*10^-25. The density of the crystal is 9.2*10^3 What is the shortest distance between the centres of two adjacent atoms? Homework Equations density = mass / volume The...
  41. D

    Which crystal dissolves in only hot water and recrystalize on cooling

    Dear all! Somebody, please tell me which crystal is soluble in hot water but not in cold water. I am looking for some crystalline chemicals which are strong enough to bind something like glass beads. As I mentioned, it should be highly soluble in hot water (or change into liquid on high...
  42. F

    Crystal Osc 30MHz Design or Purchase

    Hello experts…i am new in the RF field and i need some help… So i have a double balanced mixer (ZAD-6+ of Mini Circuits) that need +7dBm Local OsC power and 30MHz Loca.osc frequency. At the time i use signal generator for l.o How can i make a crystal oscillator with these parameters? Can...
  43. S

    Crystal Thickness for particular phase difference

    1. Hey, the question I believe should be fairly simple to solve but it's been a while since I've looked over such content. There are two light waves that enter a crytstal at the same time, one linearly polarised parallel to the optic axis and one perpendicular to the optic axis, they have...
  44. M

    What is the Correct Crystal Lattice Structure?

    what is this answer choices: a. Primitive cubic with an octahedral hole b. Body centered cubic with an octahedral hole c. Face centered cubic with an octahedral hole d. None of the above e. Not enough information to determine We didn't talk about this in class, and this was a question...
  45. M

    Young's Modulus of a single crystal specimen?

    Does a single crystal specimen have a smaller Young's Modulus than a polycrystalline specimen? I think a single crystal would have a lower elastic mudolus since it has less grain boundaries and probably less dislocations than a polycrystalline specimen. I'd appreciate any ideas thanks
  46. 1

    Scattering of Neutrons from 2d Crystal Lattice

    Homework Statement A two-dimensional rectangular crystal has a unit cell with sides a 6.28Å and b 3.14Å. A beam of monochromatic neutrons of wavelength 5.0 Å is used to examine the crystal. Using either the Laue condition for diffraction or Bragg's Law, determine whether it would be...
  47. K

    Transmission phase of finite 1D photonic crystal

    I use transfer matrix method. I try to plot the phase Φ(ω) versus frequency ω graph in the vicinity of a band gap. The transmission coefficient t(ω) is t(ω) = |t(ω)|*exp(i*Φ(ω)) from which I get the transmission phase Φ(ω) = atan(t_imaginary(ω)/t_real(ω)). Since I assume that -pi/2 ≦ Φ ≦...
  48. Z

    Understanding the Six Degrees of Freedom in Crystal Structures

    It seems to me that there should only be three degrees of freedom for each atom in a crystal, one for each direction of vibration; but apparently there are six? Can someone explain? Thanks.
  49. L

    Piezo Crystal Load vs. Current Values Explained

    I am working on a project. could you please help me in piezo crystal. I just want to know the load vs current values. on what load the respective value of piezo crystal??
  50. heycoa

    Solid State Physics | ionic crystal bonding | Born & Meyer equation

    Homework Statement 1) Find the expression for the equilibrium interatomic distance as a function of A, n, and α 2) Determine the expression for the binding energy at equilibrium. 3) Calculate the constant n for NaCl, using the data from the Table 1.2 of Omar book and the fact that the...
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