Superconductors The Chemist’s Perspective

transcript

SuperconductorsThe Chemist’s Perspective

Randolph Miller

Superconductors

• Introduction• History• Common Types– Ferropnictides– Cuprates– Organics

• Applications

What is a superconductor?

http://mikejory.blogspot.com/2010/12/superconductor.htmlhttp://supermanlogo.org/

http://www.berkshirefinearts.com/05-07-2010_launching-125th-season-of-boston-pops.htm

What is a superconductor?

Pin(electrical) Pout(electrical)

Normal metal

Pout(non-electrical)

Normal metal: Pout(electrical) < Pin(electrical)

Superconductor: Pout(electrical) = Pin(electrical)

Why do metals have resistance?

http://cnx.org/content/m22750/1.3/

•The crystal lattice has vibrations.•These vibrations scatter the electrons.•Higher temperature = more vibration = more scattering

How is a superconductor different?

http://webs.mn.catholic.edu.au/physics/emery/hsc_ideas_implementation.htm

•The first electron distorts the lattice•The distortion attracts a second electron•The lattice is returned to normal after a pair of electrons go by

http://en.wikipedia.org/wiki/John_Ambrose_Fleming http://en.wikipedia.org/wiki/James_Dewar

Resistance goes down linearly with temperature.James Dewar and John Fleming predicted that any pure metal would have zero resistance at absolute zero, but Dewar later changed his mind.

http://en.wikipedia.org/wiki/Walther_Nernst

Walther Nernst stated that absolute zero is unattainable.

http://en.wikipedia.org/wiki/William_Thomson,_1st_Baron_Kelvin

Lord Kelvin predicted that electrons would stop completely at absolute zero, causing infinite resistance, but he also believed that absolute zero was unattainable.

http://th.physik.uni-frankfurt.de/~jr/gif/phys/onnes.jpg

•H. Kamerlingh Onnes was first to liquify helium and was using the extreme cold to study metals. •Temperatures below 123 K are called cryogenic temperatures.•As the temperature of mercury went down, the resistance went down linearly until 4.2 K.•From 4.2 K lower, the resistance was 0.•TC is the critical temperature, maximum temperature it’s superconducting.•Onnes won the Nobel Prize in Physics in 1913.

http://hoffman.physics.harvard.edu/materials/SCintro.php

Ferropnictides: LaFeAsO

http://jolisfukyu.tokai-sc.jaea.go.jp/fukyu/mirai-en/2009/12_3.html http://www.natureasia.com/asia-materials/highlight.php?id=290

•Ferro means iron•Pnictogen means from Nitrogen’s group (Group 15 in IUPAC notation)•Ferropnictide layer is the superconducting layer•Some of the O atoms are replaced with F•In this example, As is the pnictogen•FeAs layer is –•LaO is +

Ferropnictide: overhead view

(Ren 9)

Re = rare earth metal: Sm, Nd, Pr, Ce, La (same as lanthanoids)Pr stands for praseodymium, Ce is Cerium

Ferropnictides: comparing Re elements

(Ren 9)

These compounds have the same structure, but very different Tc.

Ferropnictides: bond angle

(Ishida 9)

•The vertical line is at 109.4°, the regular tetrahedral angle.•The light green sphere is Fe, the 4 orange spheres are As.

Ferropnictide: LaOFeP

http://pubs.acs.org/doi/full/10.1021/ja063355c

•Alternating stack of layers•Layered structure allows researchers to try different carrier densities•Impurity doping in the LaO layer transfers carriers to the FeP layer

Doping

“Chemical substitution results in (i) the doping of carriers into the system, by introducing heterovalent ions, and (ii) deformation of the crystal structures, caused by the ionic radius mismatch of the guest elements. F- and K-substitution and O-deficiency are considered to play both roles, namely, to supply electron/hole carriers and to suppress the crystal structural transition occurring in the parent compounds.” (Miyaza 11)

1. Chemical substitution dopes carriers into the system, by introducing heterovalent ions

2. Chemical substitution deforms the crystal structures, caused by ionic radius mismatch

•Substituting F for O does both

•Band: mobile electronic state within a solid, electron is free to move within the atomic lattice•Hole: empty electronic state in a band, a traveling vacancy in a band

Ferropnictide: SmFeAsO1-xFx

http://www.nanotech-now.com/news.cgi?story_id=31632

•Formula specifies some O atoms are replaced with F atoms

Doping: CeFeAsO1-xFx

(Lynn 9)

•SC stands for superconducting•Like many ferropnitictides, has a minimum doping level to be superconducting.

Doping: (Ba1−xKx)Fe2As2

(Rotter 3)

Ferropnictide: SmFeAsO0.85F0.15

(Yi 10)

Only superconducting at low pressure.

Magnetic Field Dependence

(Karpinski 23)

TC is reduced by an external magnetic field.

Ferropnictide synthesis

•Explosion can result in contamination with arsenide compounds. •This is the HP (high pressure) technique.

http://iopscience.iop.org/1367-2630/11/4/045002/fulltext

LnAs can react with moisture, making arsine!!!

http://en.wikipedia.org/wiki/File:Arsine-3D-vdW.png

Cuprates

(Jin 400)

•Cuprates have two alternating types of layers or blocks.•Charge reservoir layer can be rock salt, perovskite, or fluorite substructure.•The CuO2 plane is the “infinite layer.”“The role of the charge reservoir block is to generate and inject charge carriers into the [CuO2] plane.” (Jin 400)

Cuprate: Hg-1223

(Jin 404)

Cu-12(n-1) homologous series

(Jin 405)

Ca is the spacer layer, BaO is the interfacial layer

Cuprates: Doping

•Apical means axial (or not coplanar)•CuO layer is superconducting•Apical oxygen is connection between superconducting layer and charge reservoir•Doping means substituting Cl- for O2-

(Liu 24)

Sr2CuO2+dCl2-y

Cuprates: Magnetic Fields

•SCCO stands for Sm2-xCexCuO4-d

•TC goes down with increasing magnetic fields

(Kawakami 017001-2)

Cuprate: YBCO

http://www.fhi-berlin.mpg.de/~hermann/Balsac/BalsacPictures/YBaCuO.gif

•YBa2Cu3O7 was first superconducting cuprate discovered•Cu4O4 layer is superconducting layer•Cuprate means compound has Cu2-(cupric) anions•Yttrium is the spacer layer.•"The fundamental building block of the copper oxide superconductors is a Cu4O4 square plaquette." Hinkov

http://en.wikipedia.org/wiki/File:Ybco002.svg

Cuprate: BSCCO http://commons.wikimedia.org/wiki/File:BSCCO-2212.gif

http://hoffman.physics.harvard.edu/materials/CuprateIntro.php

•BSCCO is pronounced bisco•Bi2Sr2Ca2Cu3O10

•The CuO2 layer is the superconducting plane

Cuprate synthesis

•1.825g or 0.005M Y(NO3)3.5H2O•2.614g or 0.010M Ba(NO3)2

•3.624g or 0.015M Cu(NO3)2.3H2O

Common method:

1. Grind all three ingredients2. Heat with a slow flow of oxygen at 350°C for an hour3. Cook at 950°C for a few hours4. Cool down5. Grind into powder6. Crush into pellets with 12 tons of force7. Heat up to 950°C again with a slow flow of oxygen (sintering)8. Cool at 50°C per hour past 690°C. (tetragonal-orthorhombic phase transition)

Sintering: making an object from powder by heating it below its melting point until its particles adhere to each other.

Organicshttp://www.riken.go.jp/r-world/info/release/press/2008/080623/detail.html

(bis(ethylenedithio)tetrathiafulvalene)

http://www.lcsim.univ-rennes1.fr/thematiques/Ouahab/ouahab_index.htm

BEDT-TTF

Organics: BEDT-TTF

“For example, the BEDT-TTF molecule is roughly flat, so that it can be packed in a variety of arrangements in a solid, and it is surrounded by voluminous molecular orbitals; to create electronic bands, it is merely necessary to stack the BEDT-TTF molecules next to each other, so that the molecular orbitals can overlap. Crudely one might say that this enables the electrons to transfer from molecule to molecule.”

(Singleton and Mielke 3)

•To get the molecules to stack up, they are usually put in a “charge transfer salt.”•The BEDT-TTF donates an electron to the other molecule, becoming the donor or cation.•The other molecule receives the electron and becomes the anion.•This makes the layers bond, similar to ionic bonding.

Organics: BEDT-TTF

•The BEDT-TTF molecules line up flatly against each other while the I atoms line up in planes above and below in the charge-transfer salt β-(BEDT-TTF)2I3.•The β means the arrangement of molecules.

Organics: BEDT-TTF

•The BEDT-TTF molecules line up flatly against each other in pairs while the Cu(NCS)2 groups line up at the ends in Κ-(BEDT-TTF)2Cu(NCS)2.•Each pair is called a dimer.

Organics: Lateral Interactions

(Misaki 2)

Lateral interactions in ladder like array of sulfur atoms cause it to form 2-D conducting sheets.

(Misaki 15)

•A schematic drawing of overlaps between the donor molecules in λ-(ET-PDT)4PF6(cn); bars and broken lines denote the donor molecules projected along the long molecular axis and relatively large intra- and interstack interactions, respectively.•cn stands for 1-chloronaphthalene

(Wang et al. 2270)

•Stereogram of packing structure of β-(ET)2I3

•Dashed lines show short intermolecular contacts

(Wang et al. 2270)

•Stereogram of packing structure of α-(ET)2I3

•Dashed lines show short intermolecular contacts

(Schlueter 268)

•Packing diagram shows layers.•Lines show S to S bonds shorter than Van der Waals radius of 3.60Å•Molecule shown is β”-(ET)2SF5CH2CF2SO3

Organics: Other Donor Molecules

(Kobayashi and Cui 5267)

Donor molecules for organic superconductors come in many sizes but not shapes:They’re all flat!

Organics: BEDT-TTF

•Salts of BEDT-TTF•Note that the I3 salt has a structural phase transition at about 0.6 kbar.)•“Decreasing the unit cell size, either by using a shorter anion or by increasing the pressure, reduces TC”•Should be (ET)2AuI2

κ-(BEDT-TTF)2Cu[N(CN)2]Cl

SC only above roughly 200 bars

Organics: Doping, T, and P

•Molecule is λ-(BETS)2GaBrxCl4-x.•TC goes down with increasing pressure.•TC is affected by Br content, ideal at x=0.8•Above x=0.8, not a SC at ambient pressure.

Organic: Synthesis

•Steps are at ambient pressure.•Most steps are ambient temperature.•One step at low temperature

Organic: Synthesis

(Takimiya 1123)

1. a) BuLi, Se, CSe2 , THF2. b) NCS(CH2)2CO2Me3. c) 1,3-diselenole-2-selone, P(OMe)3, C6H6

4. d) CsOH-H2O5. e) ClCH2I6. f) NaI, 2-butanone

•Several steps have <100% yield

Levitation

•A magnet can levitate, above, below, or to the side of a superconductor

(Saito 3)

Application: Maglevs

•Maglevs are magnetically levitated trains•Shown is a MLX01 maglev test train capable of achieving 361 mph, the current record

http://www.n-sharyo.co.jp/business/tetsudo_e/pages/maglev.htm

Application: Maglevs

http://www.dvorak.org/blog/2007/06/01/superconducting-mystery-solved/

Shown is a maglev vehicle at the end of a track. Notice the electronmagnets visible underneath each side of the track.

Application: SQUIDSQUID is Superconducting Quantum Interference Device

•SQUIDs are based on the principle that superconductors block magnetic fields•Extremely sensitive detector of magnetic fields

http://www.learner.org/courses/physics/unit/text.html?unit=8&secNum=5

Application: MEG•MEG stands for magnetoencephalography•Many SQUIDs (122 in example shown) are used to measure brain activity

http://www.lanl.gov/quarterly/q_spring03/meg_helmet_measurements.shtmlhttp://www.hbci.com/~wenonah/hudson/index.html

Application: MEG

http://www.unitn.it/en/cimec/10906/magnetoencephalography-labhttp://www.kumc.edu/hoglund/posters/brooks.html

http://en.wikipedia.org/wiki/Magnetoencephalography

It takes 50,000 neurons firing to make a detectable signal.

Application: MRI

http://www.fightmesotheliomacancer.com/mri.html

http://www.conectus.org/technology.html

MRI stands for Magnetic Resonance ImagingMRI is the biggest market for superconductors

Application: particle acceleration

http://indiavisions.wordpress.com/2008/09/10/lhc-tunnel-the-path-of-proton-beam/

The LHC has a tube 27km in circumference, with superconducting magnets the whole way to speed up charged particles to relativistic speeds.

1200 tonnes of NbTi superconducting cable at 1.9 K to make up to 8.3 T field

Application: Detectors

•ATLAS detector in the LHC has 8 magnets, each with 100 tonnes of superconductor•Measures energy and momentum of charged particles•Stores 1.6 GJ

http://cdsweb.cern.ch/record/910381

Application: Gravity Probe B

http://www.resonancepub.com/gravity.htm

•These are parts from Gravity Probe B. •Gravity Probe B studied gravity from Earth orbit.•Blue sphere is coated with a superconductor.•The blue sphere rotates and acts as a gyroscope. •SQUID detectors monitor the blue gyroscope.

Application: Motors

•Electric motors with superconductors are more energy efficient, lighter, smaller, and a quieter. •Shown is the first 36.5MW electric motor made from high temperature superconductor (HTS) and the equivalent made with copper.•That's 49,000 horsepower. •It might be used for propulsion of Navy ships. •It would make Navy ships more fuel efficient and free up valuable space.

http://www.amsc.com/products/motorsgenerators/shipPropulsion.html

http://www.superconductorweek.com/free-content-photo-gallery

Application: Power Transmission

•Shown are superconducting YBCO cables compared with the copper cables they replace.•The superconducting cables carry 150 times as much electricity as same sized copper.•They carry up to 574 MW. •This is Holbrook, Long Island.•It’s been operating since April 22, 2008.

http://www.amsc.com/products/htswire/LIPAHTSCableProjectBrief.html http://www.superconductorweek.com/free-content-photo-gallery

Application: Plasma containment

http://blogs.knoxnews.com/munger/2010/01/fields_for_fusion.htmlhttp://homepages.spa.umn.edu/~llrw/a1001/tokamak.html

•Hot plasma has to be contained by a magnetic field.•Shown is a Tokamak type fusion reactor.

Superconductors

•Chemistry•Physics•Quantum Mechanics

Randolph Miller

Questions?

Superconductors The Chemist’s Perspective

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